Adding feature to remove annotations

src/database/db_manager.py

@@ -706,6 +706,25 @@ class DatabaseManager:
         finally:
             conn.close()
 
+    def delete_annotation(self, annotation_id: int) -> bool:
+        """
+        Delete a manual annotation by ID.
+
+        Args:
+            annotation_id: ID of the annotation to delete
+
+        Returns:
+            True if an annotation was deleted, False otherwise.
+        """
+        conn = self.get_connection()
+        try:
+            cursor = conn.cursor()
+            cursor.execute("DELETE FROM annotations WHERE id = ?", (annotation_id,))
+            conn.commit()
+            return cursor.rowcount > 0
+        finally:
+            conn.close()
+
     # ==================== Object Class Operations ====================
 
     def get_object_classes(self) -> List[Dict]:

src/gui/tabs/annotation_tab.py

@@ -38,6 +38,9 @@ class AnnotationTab(QWidget):
         self.current_image = None
         self.current_image_path = None
         self.current_image_id = None
+        self.current_annotations = []
+        # IDs of annotations currently selected on the canvas (multi-select)
+        self.selected_annotation_ids = []
 
         self._setup_ui()
 
@@ -61,6 +64,8 @@ class AnnotationTab(QWidget):
         self.annotation_canvas = AnnotationCanvasWidget()
         self.annotation_canvas.zoom_changed.connect(self._on_zoom_changed)
         self.annotation_canvas.annotation_drawn.connect(self._on_annotation_drawn)
+        # Selection of existing polylines (when tool is not in drawing mode)
+        self.annotation_canvas.annotation_selected.connect(self._on_annotation_selected)
         canvas_layout.addWidget(self.annotation_canvas)
 
         canvas_group.setLayout(canvas_layout)
@@ -80,24 +85,35 @@ class AnnotationTab(QWidget):
 
         # Annotation tools section
         self.annotation_tools = AnnotationToolsWidget(self.db_manager)
-        self.annotation_tools.pen_enabled_changed.connect(
+        self.annotation_tools.polyline_enabled_changed.connect(
-            self.annotation_canvas.set_pen_enabled
+            self.annotation_canvas.set_polyline_enabled
         )
-        self.annotation_tools.pen_color_changed.connect(
+        self.annotation_tools.polyline_pen_color_changed.connect(
-            self.annotation_canvas.set_pen_color
+            self.annotation_canvas.set_polyline_pen_color
         )
-        self.annotation_tools.pen_width_changed.connect(
+        self.annotation_tools.polyline_pen_width_changed.connect(
-            self.annotation_canvas.set_pen_width
+            self.annotation_canvas.set_polyline_pen_width
         )
+        # Show / hide bounding boxes
+        self.annotation_tools.show_bboxes_changed.connect(
+            self.annotation_canvas.set_show_bboxes
+        )
+        # RDP simplification controls
+        self.annotation_tools.simplify_on_finish_changed.connect(
+            self._on_simplify_on_finish_changed
+        )
+        self.annotation_tools.simplify_epsilon_changed.connect(
+            self._on_simplify_epsilon_changed
+        )
+        # Class selection and class-color changes
         self.annotation_tools.class_selected.connect(self._on_class_selected)
+        self.annotation_tools.class_color_changed.connect(self._on_class_color_changed)
         self.annotation_tools.clear_annotations_requested.connect(
             self._on_clear_annotations
         )
-        self.annotation_tools.process_annotations_requested.connect(
+        # Delete selected annotation on canvas
-            self._on_process_annotations
+        self.annotation_tools.delete_selected_annotation_requested.connect(
-        )
+            self._on_delete_selected_annotation
-        self.annotation_tools.show_annotations_requested.connect(
-            self._on_show_annotations
         )
         self.right_splitter.addWidget(self.annotation_tools)
 
@@ -180,6 +196,9 @@ class AnnotationTab(QWidget):
             # Display image using the AnnotationCanvasWidget
             self.annotation_canvas.load_image(self.current_image)
 
+            # Load and display any existing annotations for this image
+            self._load_annotations_for_current_image()
+
             # Update info label
             self._update_image_info()
 
@@ -217,7 +236,22 @@ class AnnotationTab(QWidget):
         self._update_image_info()
 
     def _on_annotation_drawn(self, points: list):
-        """Handle when an annotation stroke is drawn."""
+        """
+        Handle when an annotation stroke is drawn.
+
+        Saves the new annotation directly to the database and refreshes the
+        on-canvas display of annotations for the current image.
+        """
+        # Ensure we have an image loaded and in the DB
+        if not self.current_image or not self.current_image_id:
+            logger.warning("Annotation drawn but no image loaded")
+            QMessageBox.warning(
+                self,
+                "No Image",
+                "Please load an image before drawing annotations.",
+            )
+            return
+
         current_class = self.annotation_tools.get_current_class()
 
         if not current_class:
@@ -229,153 +263,260 @@ class AnnotationTab(QWidget):
             )
             return
 
-        logger.info(
+        if not points:
-            f"Annotation drawn with {len(points)} points for class: {current_class['class_name']}"
+            logger.warning("Annotation drawn with no points, ignoring")
-        )
+            return
-        # Future: Save annotation to database or export
 
-    def _on_class_selected(self, class_data: dict):
+        # points are [(x_norm, y_norm), ...]
-        """Handle when an object class is selected."""
+        xs = [p[0] for p in points]
-        logger.debug(f"Object class selected: {class_data['class_name']}")
+        ys = [p[1] for p in points]
+        x_min, x_max = min(xs), max(xs)
+        y_min, y_max = min(ys), max(ys)
+
+        # Store segmentation mask in [y_norm, x_norm] format to match DB
+        db_polyline = [[float(y), float(x)] for (x, y) in points]
+
+        try:
+            annotation_id = self.db_manager.add_annotation(
+                image_id=self.current_image_id,
+                class_id=current_class["id"],
+                bbox=(x_min, y_min, x_max, y_max),
+                annotator="manual",
+                segmentation_mask=db_polyline,
+                verified=False,
+            )
+
+            logger.info(
+                f"Saved annotation (ID: {annotation_id}) for class "
+                f"'{current_class['class_name']}' "
+                f"Bounding box: ({x_min:.3f}, {y_min:.3f}) to ({x_max:.3f}, {y_max:.3f})\n"
+                f"with {len(points)} polyline points"
+            )
+
+            # Reload annotations from DB and redraw (respecting current class filter)
+            self._load_annotations_for_current_image()
+
+        except Exception as e:
+            logger.error(f"Failed to save annotation: {e}")
+            QMessageBox.critical(self, "Error", f"Failed to save annotation:\n{str(e)}")
+
+    def _on_annotation_selected(self, annotation_ids):
+        """
+        Handle selection of existing annotations on the canvas.
+
+        Args:
+            annotation_ids: List of selected annotation IDs, or None/empty if cleared.
+        """
+        if not annotation_ids:
+            self.selected_annotation_ids = []
+            self.annotation_tools.set_has_selected_annotation(False)
+            logger.debug("Annotation selection cleared on canvas")
+            return
+
+        # Normalize to a unique, sorted list of integer IDs
+        ids = sorted({int(aid) for aid in annotation_ids if isinstance(aid, int)})
+        self.selected_annotation_ids = ids
+        self.annotation_tools.set_has_selected_annotation(bool(ids))
+        logger.debug(f"Annotations selected on canvas: IDs={ids}")
+
+    def _on_simplify_on_finish_changed(self, enabled: bool):
+        """Update canvas simplify-on-finish flag from tools widget."""
+        self.annotation_canvas.simplify_on_finish = enabled
+        logger.debug(f"Annotation simplification on finish set to {enabled}")
+
+    def _on_simplify_epsilon_changed(self, epsilon: float):
+        """Update canvas RDP epsilon from tools widget."""
+        self.annotation_canvas.simplify_epsilon = float(epsilon)
+        logger.debug(f"Annotation simplification epsilon set to {epsilon}")
+
+    def _on_class_color_changed(self):
+        """
+        Handle changes to the selected object's class color.
+
+        When the user updates a class color in the tools widget, reload the
+        annotations for the current image so that all polylines are redrawn
+        using the updated per-class colors.
+        """
+        if not self.current_image_id:
+            return
+
+        logger.debug(
+            f"Class color changed; reloading annotations for image ID {self.current_image_id}"
+        )
+        self._load_annotations_for_current_image()
+
+    def _on_class_selected(self, class_data):
+        """
+        Handle when an object class is selected or cleared.
+
+        When a specific class is selected, only annotations of that class are drawn.
+        When the selection is cleared ("-- Select Class --"), all annotations are shown.
+        """
+        if class_data:
+            logger.debug(f"Object class selected: {class_data['class_name']}")
+        else:
+            logger.debug(
+                'No class selected ("-- Select Class --"), showing all annotations'
+            )
+
+        # Changing the class filter invalidates any previous selection
+        self.selected_annotation_ids = []
+        self.annotation_tools.set_has_selected_annotation(False)
+
+        # Whenever the selection changes, update which annotations are visible
+        self._redraw_annotations_for_current_filter()
 
     def _on_clear_annotations(self):
         """Handle clearing all annotations."""
         self.annotation_canvas.clear_annotations()
+        # Clear in-memory state and selection, but keep DB entries unchanged
+        self.current_annotations = []
+        self.selected_annotation_ids = []
+        self.annotation_tools.set_has_selected_annotation(False)
         logger.info("Cleared all annotations")
 
-    def _on_process_annotations(self):
+    def _on_delete_selected_annotation(self):
-        """Process annotations and save to database."""
+        """Handle deleting the currently selected annotation(s) (if any)."""
-        # Check if we have an image loaded
+        if not self.selected_annotation_ids:
-        if not self.current_image or not self.current_image_id:
+            QMessageBox.information(
-            QMessageBox.warning(
-                self, "No Image", "Please load an image before processing annotations."
-            )
-            return
-
-        # Get current class
-        current_class = self.annotation_tools.get_current_class()
-        if not current_class:
-            QMessageBox.warning(
                 self,
-                "No Class Selected",
+                "No Selection",
-                "Please select an object class before processing annotations.",
+                "No annotation is currently selected.",
             )
             return
 
-        # Compute annotation parameters asbounding boxes and polylines from annotations
+        count = len(self.selected_annotation_ids)
-        parameters = self.annotation_canvas.get_annotation_parameters()
+        if count == 1:
-        if not parameters:
+            question = "Are you sure you want to delete the selected annotation?"
-            QMessageBox.warning(
+            title = "Delete Annotation"
-                self,
+        else:
-                "No Annotations",
+            question = (
-                "Please draw some annotations before processing.",
+                f"Are you sure you want to delete the {count} selected annotations?"
             )
-            return
+            title = "Delete Annotations"
 
-        # polyline = self.annotation_canvas.get_annotation_polyline()
-
-        for param in parameters:
-            bounds = param["bbox"]
-            polyline = param["polyline"]
-
-            try:
-                # Save annotation to database
-                annotation_id = self.db_manager.add_annotation(
-                    image_id=self.current_image_id,
-                    class_id=current_class["id"],
-                    bbox=bounds,
-                    annotator="manual",
-                    segmentation_mask=polyline,
-                    verified=False,
-                )
-
-                logger.info(
-                    f"Saved annotation (ID: {annotation_id}) for class '{current_class['class_name']}' "
-                    f"Bounding box: ({bounds[0]:.3f}, {bounds[1]:.3f}) to ({bounds[2]:.3f}, {bounds[3]:.3f})\n"
-                    f"with {len(polyline)} polyline points"
-                )
-
-                # QMessageBox.information(
-                #     self,
-                #     "Success",
-                #     f"Annotation saved successfully!\n\n"
-                #     f"Class: {current_class['class_name']}\n"
-                #     f"Bounding box: ({bounds[0]:.3f}, {bounds[1]:.3f}) to ({bounds[2]:.3f}, {bounds[3]:.3f})\n"
-                #     f"Polyline points: {len(polyline)}",
-                # )
-
-            except Exception as e:
-                logger.error(f"Failed to save annotation: {e}")
-                QMessageBox.critical(
-                    self, "Error", f"Failed to save annotation:\n{str(e)}"
-                )
-
-        # Optionally clear annotations after saving
         reply = QMessageBox.question(
             self,
-            "Clear Annotations",
+            title,
-            "Do you want to clear the annotations to start a new one?",
+            question,
             QMessageBox.Yes | QMessageBox.No,
-            QMessageBox.Yes,
+            QMessageBox.No,
         )
+        if reply != QMessageBox.Yes:
+            return
 
-        if reply == QMessageBox.Yes:
+        failed_ids = []
-            self.annotation_canvas.clear_annotations()
+        try:
-            logger.info("Cleared annotations after saving")
+            for ann_id in self.selected_annotation_ids:
+                try:
+                    deleted = self.db_manager.delete_annotation(ann_id)
+                    if not deleted:
+                        failed_ids.append(ann_id)
+                except Exception as e:
+                    logger.error(f"Failed to delete annotation ID {ann_id}: {e}")
+                    failed_ids.append(ann_id)
 
-    def _on_show_annotations(self):
+            if failed_ids:
-        """Load and display saved annotations from database."""
+                QMessageBox.warning(
-        # Check if we have an image loaded
+                    self,
-        if not self.current_image or not self.current_image_id:
+                    "Partial Failure",
-            QMessageBox.warning(
+                    "Some annotations could not be deleted:\n"
-                self, "No Image", "Please load an image to view its annotations."
+                    + ", ".join(str(a) for a in failed_ids),
+                )
+            else:
+                logger.info(
+                    f"Deleted {count} annotation(s): "
+                    + ", ".join(str(a) for a in self.selected_annotation_ids)
+                )
+
+            # Clear selection and reload annotations for the current image from DB
+            self.selected_annotation_ids = []
+            self.annotation_tools.set_has_selected_annotation(False)
+            self._load_annotations_for_current_image()
+
+        except Exception as e:
+            logger.error(f"Failed to delete annotations: {e}")
+            QMessageBox.critical(
+                self,
+                "Error",
+                f"Failed to delete annotations:\n{str(e)}",
             )
+
+    def _load_annotations_for_current_image(self):
+        """
+        Load all annotations for the current image from the database and
+        redraw them on the canvas, honoring the currently selected class
+        filter (if any).
+        """
+        if not self.current_image_id:
+            self.current_annotations = []
+            self.annotation_canvas.clear_annotations()
+            self.selected_annotation_ids = []
+            self.annotation_tools.set_has_selected_annotation(False)
             return
 
         try:
-            # Clear current annotations
+            self.current_annotations = self.db_manager.get_annotations_for_image(
-            self.annotation_canvas.clear_annotations()
-
-            # Retrieve annotations from database
-            annotations = self.db_manager.get_annotations_for_image(
                 self.current_image_id
             )
-
+            # New annotations loaded; reset any selection
-            if not annotations:
+            self.selected_annotation_ids = []
-                QMessageBox.information(
+            self.annotation_tools.set_has_selected_annotation(False)
-                    self, "No Annotations", "No saved annotations found for this image."
+            self._redraw_annotations_for_current_filter()
-                )
-                return
-
-            # Draw each annotation's polyline
-            drawn_count = 0
-            for ann in annotations:
-                if ann.get("segmentation_mask"):
-                    polyline = ann["segmentation_mask"]
-                    color = ann.get("class_color", "#FF0000")
-
-                    # Draw the polyline
-                    self.annotation_canvas.draw_saved_polyline(polyline, color, width=3)
-                    self.annotation_canvas.draw_saved_bbox(
-                        [ann["x_min"], ann["y_min"], ann["x_max"], ann["y_max"]],
-                        color,
-                        width=3,
-                    )
-                    drawn_count += 1
-
-            logger.info(f"Displayed {drawn_count} saved annotations from database")
-
-            QMessageBox.information(
-                self,
-                "Annotations Loaded",
-                f"Successfully loaded and displayed {drawn_count} annotation(s).",
-            )
-
         except Exception as e:
-            logger.error(f"Failed to load annotations: {e}")
+            logger.error(
-            QMessageBox.critical(
+                f"Failed to load annotations for image {self.current_image_id}: {e}"
-                self, "Error", f"Failed to load annotations:\n{str(e)}"
             )
+            QMessageBox.critical(
+                self,
+                "Error",
+                f"Failed to load annotations for this image:\n{str(e)}",
+            )
+
+    def _redraw_annotations_for_current_filter(self):
+        """
+        Redraw annotations for the current image, optionally filtered by the
+        currently selected object class.
+        """
+        # Clear current on-canvas annotations but keep the image
+        self.annotation_canvas.clear_annotations()
+
+        if not self.current_annotations:
+            return
+
+        current_class = self.annotation_tools.get_current_class()
+        selected_class_id = current_class["id"] if current_class else None
+
+        drawn_count = 0
+        for ann in self.current_annotations:
+            # Filter by class if one is selected
+            if (
+                selected_class_id is not None
+                and ann.get("class_id") != selected_class_id
+            ):
+                continue
+
+            if ann.get("segmentation_mask"):
+                polyline = ann["segmentation_mask"]
+                color = ann.get("class_color", "#FF0000")
+
+                self.annotation_canvas.draw_saved_polyline(
+                    polyline,
+                    color,
+                    width=3,
+                    annotation_id=ann["id"],
+                )
+                self.annotation_canvas.draw_saved_bbox(
+                    [ann["x_min"], ann["y_min"], ann["x_max"], ann["y_max"]],
+                    color,
+                    width=3,
+                )
+                drawn_count += 1
+
+        logger.info(
+            f"Displayed {drawn_count} annotation(s) for current image with "
+            f"{'no class filter' if selected_class_id is None else f'class_id={selected_class_id}'}"
+        )
 
     def _restore_state(self):
         """Restore splitter positions from settings."""

src/gui/widgets/annotation_canvas_widget.py

@@ -1,9 +1,10 @@
 """
 Annotation canvas widget for drawing annotations on images.
-Supports pen tool with color selection for manual annotation.
+Currently supports polyline drawing tool with color selection for manual annotation.
 """
 
 import numpy as np
+import math
 
 from PySide6.QtWidgets import QWidget, QVBoxLayout, QLabel, QScrollArea
 from PySide6.QtGui import (
@@ -19,25 +20,102 @@ from PySide6.QtGui import (
 from PySide6.QtCore import Qt, QEvent, Signal, QPoint
 from typing import Any, Dict, List, Optional, Tuple
 
-from scipy.ndimage import binary_dilation, label, binary_fill_holes, find_objects
-from skimage.measure import find_contours
-
 from src.utils.image import Image, ImageLoadError
 from src.utils.logger import get_logger
 
-# For debugging visualization
-import pylab as plt
-
 logger = get_logger(__name__)
 
 
+def perpendicular_distance(
+    point: Tuple[float, float],
+    start: Tuple[float, float],
+    end: Tuple[float, float],
+) -> float:
+    """Perpendicular distance from `point` to the line defined by `start`->`end`."""
+    (x, y), (x1, y1), (x2, y2) = point, start, end
+    dx = x2 - x1
+    dy = y2 - y1
+    if dx == 0.0 and dy == 0.0:
+        return math.hypot(x - x1, y - y1)
+    num = abs(dy * x - dx * y + x2 * y1 - y2 * x1)
+    den = math.hypot(dx, dy)
+    return num / den
+
+
+def rdp(points: List[Tuple[float, float]], epsilon: float) -> List[Tuple[float, float]]:
+    """
+    Recursive Ramer-Douglas-Peucker (RDP) polyline simplification.
+
+    Args:
+        points: List of (x, y) points.
+        epsilon: Maximum allowed perpendicular distance in pixels.
+
+    Returns:
+        Simplified list of (x, y) points including first and last.
+    """
+    if len(points) <= 2:
+        return list(points)
+
+    start = points[0]
+    end = points[-1]
+    max_dist = -1.0
+    index = -1
+
+    for i in range(1, len(points) - 1):
+        d = perpendicular_distance(points[i], start, end)
+        if d > max_dist:
+            max_dist = d
+            index = i
+
+    if max_dist > epsilon:
+        # Recursive split
+        left = rdp(points[: index + 1], epsilon)
+        right = rdp(points[index:], epsilon)
+        # Concatenate but avoid duplicate at split point
+        return left[:-1] + right
+
+    # Keep only start and end
+    return [start, end]
+
+
+def simplify_polyline(
+    points: List[Tuple[float, float]], epsilon: float
+) -> List[Tuple[float, float]]:
+    """
+    Simplify a polyline with RDP while preserving closure semantics.
+
+    If the polyline is closed (first == last), the duplicate last point is removed
+    before simplification and then re-added after simplification.
+    """
+    if not points:
+        return []
+
+    pts = [(float(x), float(y)) for x, y in points]
+    closed = False
+
+    if len(pts) >= 2 and pts[0] == pts[-1]:
+        closed = True
+        pts = pts[:-1]  # remove duplicate last for simplification
+
+    if len(pts) <= 2:
+        simplified = list(pts)
+    else:
+        simplified = rdp(pts, epsilon)
+
+    if closed and simplified:
+        if simplified[0] != simplified[-1]:
+            simplified.append(simplified[0])
+
+    return simplified
+
+
 class AnnotationCanvasWidget(QWidget):
     """
-    Widget for displaying images and drawing annotations with pen tool.
+    Widget for displaying images and drawing annotations with zoom and drawing tools.
 
     Features:
     - Display images with zoom functionality
-    - Pen tool for drawing annotations
+    - Polyline tool for drawing annotations
     - Configurable pen color and width
     - Mouse-based drawing interface
     - Zoom in/out with mouse wheel and keyboard
@@ -49,6 +127,9 @@ class AnnotationCanvasWidget(QWidget):
 
     zoom_changed = Signal(float)
     annotation_drawn = Signal(list)  # List of (x, y) points in normalized coordinates
+    # Emitted when the user selects an existing polyline on the canvas.
+    # Carries the associated annotation_id (int) or None if selection is cleared
+    annotation_selected = Signal(object)
 
     def __init__(self, parent=None):
         """Initialize the annotation canvas widget."""
@@ -63,13 +144,33 @@ class AnnotationCanvasWidget(QWidget):
         self.zoom_step = 0.1
         self.zoom_wheel_step = 0.15
 
-        # Drawing state
+        # Drawing / interaction state
         self.is_drawing = False
-        self.pen_enabled = False
+        self.polyline_enabled = False
-        self.pen_color = QColor(255, 0, 0, 128)  # Default red with 50% alpha
+        self.polyline_pen_color = QColor(255, 0, 0, 128)  # Default red with 50% alpha
-        self.pen_width = 3
+        self.polyline_pen_width = 3
-        self.current_stroke = []  # Points in current stroke
+        self.show_bboxes: bool = True  # Control visibility of bounding boxes
-        self.all_strokes = []  # All completed strokes
+
+        # Current stroke and stored polylines (in image coordinates, pixel units)
+        self.current_stroke: List[Tuple[float, float]] = []
+        self.polylines: List[List[Tuple[float, float]]] = []
+        self.stroke_meta: List[Dict[str, Any]] = []  # per-polyline style (color, width)
+        # Optional DB annotation_id for each stored polyline (None for temporary / unsaved)
+        self.polyline_annotation_ids: List[Optional[int]] = []
+        # Indices in self.polylines of the currently selected polylines (multi-select)
+        self.selected_polyline_indices: List[int] = []
+
+        # Stored bounding boxes in normalized coordinates (x_min, y_min, x_max, y_max)
+        self.bboxes: List[List[float]] = []
+        self.bbox_meta: List[Dict[str, Any]] = []  # per-bbox style (color, width)
+
+        # Legacy collection of strokes in normalized coordinates (kept for API compatibility)
+        self.all_strokes: List[dict] = []
+
+        # RDP simplification parameters (in pixels)
+        self.simplify_on_finish: bool = True
+        self.simplify_epsilon: float = 2.0
+        self.sample_threshold: float = 2.0  # minimum movement to sample a new point
 
         self._setup_ui()
 
@@ -128,6 +229,12 @@ class AnnotationCanvasWidget(QWidget):
         """Clear all drawn annotations."""
         self.all_strokes = []
         self.current_stroke = []
+        self.polylines = []
+        self.stroke_meta = []
+        self.polyline_annotation_ids = []
+        self.selected_polyline_indices = []
+        self.bboxes = []
+        self.bbox_meta = []
         self.is_drawing = False
         if self.annotation_pixmap:
             self.annotation_pixmap.fill(Qt.transparent)
@@ -218,21 +325,21 @@ class AnnotationCanvasWidget(QWidget):
         """Update display after drawing."""
         self._apply_zoom()
 
-    def set_pen_enabled(self, enabled: bool):
+    def set_polyline_enabled(self, enabled: bool):
-        """Enable or disable pen tool."""
+        """Enable or disable polyline tool."""
-        self.pen_enabled = enabled
+        self.polyline_enabled = enabled
         if enabled:
             self.canvas_label.setCursor(Qt.CrossCursor)
         else:
             self.canvas_label.setCursor(Qt.ArrowCursor)
 
-    def set_pen_color(self, color: QColor):
+    def set_polyline_pen_color(self, color: QColor):
-        """Set pen color."""
+        """Set polyline pen color."""
-        self.pen_color = color
+        self.polyline_pen_color = color
 
-    def set_pen_width(self, width: int):
+    def set_polyline_pen_width(self, width: int):
-        """Set pen width."""
+        """Set polyline pen width."""
-        self.pen_width = max(1, width)
+        self.polyline_pen_width = max(1, width)
 
     def get_zoom_percentage(self) -> int:
         """Get current zoom level as percentage."""
@@ -291,6 +398,41 @@ class AnnotationCanvasWidget(QWidget):
             return (int(x), int(y))
         return None
 
+    def _find_polyline_at(
+        self, img_x: float, img_y: float, threshold_px: float = 5.0
+    ) -> Optional[int]:
+        """
+        Find index of polyline whose geometry is within threshold_px of (img_x, img_y).
+        Returns the index in self.polylines, or None if none is close enough.
+        """
+        best_index: Optional[int] = None
+        best_dist: float = float("inf")
+
+        for idx, polyline in enumerate(self.polylines):
+            if len(polyline) < 2:
+                continue
+
+            # Quick bounding-box check to skip obviously distant polylines
+            xs = [p[0] for p in polyline]
+            ys = [p[1] for p in polyline]
+            if img_x < min(xs) - threshold_px or img_x > max(xs) + threshold_px:
+                continue
+            if img_y < min(ys) - threshold_px or img_y > max(ys) + threshold_px:
+                continue
+
+            # Precise distance to all segments
+            for (x1, y1), (x2, y2) in zip(polyline[:-1], polyline[1:]):
+                d = perpendicular_distance(
+                    (img_x, img_y), (float(x1), float(y1)), (float(x2), float(y2))
+                )
+                if d < best_dist:
+                    best_dist = d
+                    best_index = idx
+
+        if best_index is not None and best_dist <= threshold_px:
+            return best_index
+        return None
+
     def _image_to_normalized_coords(self, x: int, y: int) -> Tuple[float, float]:
         """Convert image coordinates to normalized coordinates (0-1)."""
         if self.original_pixmap is None:
@@ -300,26 +442,156 @@ class AnnotationCanvasWidget(QWidget):
         norm_y = y / self.original_pixmap.height()
         return (norm_x, norm_y)
 
+    def _add_polyline(
+        self,
+        img_points: List[Tuple[float, float]],
+        color: QColor,
+        width: int,
+        annotation_id: Optional[int] = None,
+    ):
+        """Store a polyline in image coordinates and redraw annotations."""
+        if not img_points or len(img_points) < 2:
+            return
+
+        # Ensure all points are tuples of floats
+        normalized_points = [(float(x), float(y)) for x, y in img_points]
+        self.polylines.append(normalized_points)
+        self.stroke_meta.append({"color": QColor(color), "width": int(width)})
+        self.polyline_annotation_ids.append(annotation_id)
+
+        self._redraw_annotations()
+
+    def _redraw_annotations(self):
+        """Redraw all stored polylines and (optionally) bounding boxes onto the annotation pixmap."""
+        if self.annotation_pixmap is None:
+            return
+
+        # Clear existing overlay
+        self.annotation_pixmap.fill(Qt.transparent)
+
+        painter = QPainter(self.annotation_pixmap)
+
+        # Draw polylines
+        for idx, (polyline, meta) in enumerate(zip(self.polylines, self.stroke_meta)):
+            pen_color: QColor = meta.get("color", self.polyline_pen_color)
+            width: int = meta.get("width", self.polyline_pen_width)
+
+            if idx in self.selected_polyline_indices:
+                # Highlight selected polylines in a distinct color / width
+                highlight_color = QColor(255, 255, 0, 200)  # yellow, semi-opaque
+                pen = QPen(
+                    highlight_color,
+                    width + 1,
+                    Qt.SolidLine,
+                    Qt.RoundCap,
+                    Qt.RoundJoin,
+                )
+            else:
+                pen = QPen(
+                    pen_color,
+                    width,
+                    Qt.SolidLine,
+                    Qt.RoundCap,
+                    Qt.RoundJoin,
+                )
+
+            painter.setPen(pen)
+            for (x1, y1), (x2, y2) in zip(polyline[:-1], polyline[1:]):
+                painter.drawLine(int(x1), int(y1), int(x2), int(y2))
+
+        # Draw bounding boxes (dashed) if enabled
+        if self.show_bboxes and self.original_pixmap is not None and self.bboxes:
+            img_width = float(self.original_pixmap.width())
+            img_height = float(self.original_pixmap.height())
+
+            for bbox, meta in zip(self.bboxes, self.bbox_meta):
+                if len(bbox) != 4:
+                    continue
+
+                x_min_norm, y_min_norm, x_max_norm, y_max_norm = bbox
+                x_min = int(x_min_norm * img_width)
+                y_min = int(y_min_norm * img_height)
+                x_max = int(x_max_norm * img_width)
+                y_max = int(y_max_norm * img_height)
+
+                rect_width = x_max - x_min
+                rect_height = y_max - y_min
+
+                pen_color: QColor = meta.get("color", QColor(255, 0, 0, 128))
+                width: int = meta.get("width", self.polyline_pen_width)
+                pen = QPen(
+                    pen_color,
+                    width,
+                    Qt.DashLine,
+                    Qt.SquareCap,
+                    Qt.MiterJoin,
+                )
+                painter.setPen(pen)
+                painter.drawRect(x_min, y_min, rect_width, rect_height)
+
+        painter.end()
+
+        self._update_display()
+
     def mousePressEvent(self, event: QMouseEvent):
-        """Handle mouse press events for drawing."""
+        """Handle mouse press events for drawing and selecting polylines."""
-        if not self.pen_enabled or self.annotation_pixmap is None:
+        if self.annotation_pixmap is None:
             super().mousePressEvent(event)
             return
 
-        if event.button() == Qt.LeftButton:
+        # Map click to image coordinates
-            # Get accurate position using global coordinates
+        label_pos = self.canvas_label.mapFromGlobal(event.globalPos())
-            label_pos = self.canvas_label.mapFromGlobal(event.globalPos())
+        img_coords = self._canvas_to_image_coords(label_pos)
-            img_coords = self._canvas_to_image_coords(label_pos)
 
+        # Left button + drawing tool enabled -> start a new stroke
+        if event.button() == Qt.LeftButton and self.polyline_enabled:
             if img_coords:
                 self.is_drawing = True
-                self.current_stroke = [img_coords]
+                self.current_stroke = [(float(img_coords[0]), float(img_coords[1]))]
+            return
+
+        # Left button + drawing tool disabled -> attempt selection of existing polyline
+        if event.button() == Qt.LeftButton and not self.polyline_enabled:
+            if img_coords:
+                idx = self._find_polyline_at(float(img_coords[0]), float(img_coords[1]))
+                if idx is not None:
+                    if event.modifiers() & Qt.ShiftModifier:
+                        # Multi-select mode: add to current selection (if not already selected)
+                        if idx not in self.selected_polyline_indices:
+                            self.selected_polyline_indices.append(idx)
+                    else:
+                        # Single-select mode: replace current selection
+                        self.selected_polyline_indices = [idx]
+
+                    # Build list of selected annotation IDs (ignore None entries)
+                    selected_ids: List[int] = []
+                    for sel_idx in self.selected_polyline_indices:
+                        if 0 <= sel_idx < len(self.polyline_annotation_ids):
+                            ann_id = self.polyline_annotation_ids[sel_idx]
+                            if isinstance(ann_id, int):
+                                selected_ids.append(ann_id)
+
+                    if selected_ids:
+                        self.annotation_selected.emit(selected_ids)
+                    else:
+                        # No valid DB-backed annotations in selection
+                        self.annotation_selected.emit(None)
+                else:
+                    # Clicked on empty space -> clear selection
+                    self.selected_polyline_indices = []
+                    self.annotation_selected.emit(None)
+
+                self._redraw_annotations()
+            return
+
+        # Fallback for other buttons / cases
+        super().mousePressEvent(event)
 
     def mouseMoveEvent(self, event: QMouseEvent):
         """Handle mouse move events for drawing."""
         if (
             not self.is_drawing
-            or not self.pen_enabled
+            or not self.polyline_enabled
             or self.annotation_pixmap is None
         ):
             super().mouseMoveEvent(event)
@@ -330,18 +602,33 @@ class AnnotationCanvasWidget(QWidget):
         img_coords = self._canvas_to_image_coords(label_pos)
 
         if img_coords and len(self.current_stroke) > 0:
-            # Draw line from last point to current point
+            last_point = self.current_stroke[-1]
+            dx = img_coords[0] - last_point[0]
+            dy = img_coords[1] - last_point[1]
+
+            # Only sample a new point if we moved enough pixels
+            if math.hypot(dx, dy) < self.sample_threshold:
+                return
+
+            # Draw line from last point to current point for interactive feedback
             painter = QPainter(self.annotation_pixmap)
             pen = QPen(
-                self.pen_color, self.pen_width, Qt.SolidLine, Qt.RoundCap, Qt.RoundJoin
+                self.polyline_pen_color,
+                self.polyline_pen_width,
+                Qt.SolidLine,
+                Qt.RoundCap,
+                Qt.RoundJoin,
             )
             painter.setPen(pen)
-
+            painter.drawLine(
-            last_point = self.current_stroke[-1]
+                int(last_point[0]),
-            painter.drawLine(last_point[0], last_point[1], img_coords[0], img_coords[1])
+                int(last_point[1]),
+                int(img_coords[0]),
+                int(img_coords[1]),
+            )
             painter.end()
 
-            self.current_stroke.append(img_coords)
+            self.current_stroke.append((float(img_coords[0]), float(img_coords[1])))
             self._update_display()
 
     def mouseReleaseEvent(self, event: QMouseEvent):
@@ -352,23 +639,44 @@ class AnnotationCanvasWidget(QWidget):
 
         self.is_drawing = False
 
-        if len(self.current_stroke) > 1:
+        if len(self.current_stroke) > 1 and self.original_pixmap is not None:
-            # Convert to normalized coordinates and save stroke
+            # Ensure the stroke is closed by connecting end -> start
-            normalized_stroke = [
+            raw_points = list(self.current_stroke)
-                self._image_to_normalized_coords(x, y) for x, y in self.current_stroke
+            if raw_points[0] != raw_points[-1]:
-            ]
+                raw_points.append(raw_points[0])
-            self.all_strokes.append(
-                {
-                    "points": normalized_stroke,
-                    "color": self.pen_color.name(),
-                    "alpha": self.pen_color.alpha(),
-                    "width": self.pen_width,
-                }
-            )
 
-            # Emit signal with normalized coordinates
+            # Optional RDP simplification (in image pixel space)
-            self.annotation_drawn.emit(normalized_stroke)
+            if self.simplify_on_finish:
-            logger.debug(f"Completed stroke with {len(normalized_stroke)} points")
+                simplified = simplify_polyline(raw_points, self.simplify_epsilon)
+            else:
+                simplified = raw_points
+
+            if len(simplified) >= 2:
+                # Store polyline and redraw all annotations
+                self._add_polyline(
+                    simplified, self.polyline_pen_color, self.polyline_pen_width
+                )
+
+                # Convert to normalized coordinates for metadata + signal
+                normalized_stroke = [
+                    self._image_to_normalized_coords(int(x), int(y))
+                    for (x, y) in simplified
+                ]
+                self.all_strokes.append(
+                    {
+                        "points": normalized_stroke,
+                        "color": self.polyline_pen_color.name(),
+                        "alpha": self.polyline_pen_color.alpha(),
+                        "width": self.polyline_pen_width,
+                    }
+                )
+
+                # Emit signal with normalized coordinates
+                self.annotation_drawn.emit(normalized_stroke)
+                logger.debug(
+                    f"Completed stroke with {len(simplified)} points "
+                    f"(normalized len={len(normalized_stroke)})"
+                )
 
         self.current_stroke = []
 
@@ -376,152 +684,61 @@ class AnnotationCanvasWidget(QWidget):
         """Get all drawn strokes with metadata."""
         return self.all_strokes
 
-    # def get_annotation_bounds(self) -> Optional[Tuple[float, float, float, float]]:
+    def get_annotation_parameters(self) -> Optional[List[Dict[str, Any]]]:
-    #     """
-    #     Compute bounding box that encompasses all annotation strokes.
-
-    #     Returns:
-    #         Tuple of (x_min, y_min, x_max, y_max) in normalized coordinates (0-1),
-    #         or None if no annotations exist.
-    #     """
-    #     if not self.all_strokes:
-    #         return None
-
-    #     # Find min/max across all strokes
-    #     all_x = []
-    #     all_y = []
-
-    #     for stroke in self.all_strokes:
-    #         for x, y in stroke["points"]:
-    #             all_x.append(x)
-    #             all_y.append(y)
-
-    #     if not all_x:
-    #         return None
-
-    #     x_min = min(all_x)
-    #     y_min = min(all_y)
-    #     x_max = max(all_x)
-    #     y_max = max(all_y)
-
-    #     return (x_min, y_min, x_max, y_max)
-
-    # def get_annotation_polyline(self) -> List[List[float]]:
-    #     """
-    #     Get polyline coordinates representing all annotation strokes.
-
-    #     Returns:
-    #         List of [x, y] coordinate pairs in normalized coordinates (0-1).
-    #     """
-    #     polyline = []
-
-    #     fig = plt.figure()
-    #     ax1 = fig.add_subplot(411)
-    #     ax2 = fig.add_subplot(412)
-    #     ax3 = fig.add_subplot(413)
-    #     ax4 = fig.add_subplot(414)
-
-    #     # Get np.arrays from  annotation_pixmap accoriding to the color of the stroke
-    #     qimage = self.annotation_pixmap.toImage()
-    #     arr = np.ndarray(
-    #         (qimage.height(), qimage.width(), 4),
-    #         buffer=qimage.constBits(),
-    #         strides=[qimage.bytesPerLine(), 4, 1],
-    #         dtype=np.uint8,
-    #     )
-    #     print(arr.shape, arr.dtype, arr.min(), arr.max())
-    #     arr = np.sum(arr, axis=2)
-    #     ax1.imshow(arr)
-
-    #     arr_bin = arr > 0
-    #     ax2.imshow(arr_bin)
-
-    #     arr_bin = binary_fill_holes(arr_bin)
-    #     ax3.imshow(arr_bin)
-
-    #     labels, _number_of_features = label(
-    #         arr_bin,
-    #     )
-
-    #     ax4.imshow(labels)
-
-    #     objects = find_objects(labels)
-    #     bounding_boxes = np.array(
-    #         [[obj[0].start, obj[0].stop, obj[1].start, obj[1].stop] for obj in objects]
-    #     ) / np.array([arr.shape[0], arr.shape[1]])
-
-    #     print(objects)
-    #     print(bounding_boxes)
-    #     print(np.array([arr.shape[0], arr.shape[1]]))
-
-    #     polylines = find_contours(arr_bin, 0.5)
-    #     for pl in polylines:
-    #         ax1.plot(pl[:, 1], pl[:, 0], "k")
-
-    #     print(arr.shape, arr.dtype, arr.min(), arr.max())
-
-    #     plt.show()
-
-    #     return polyline
-
-    def get_annotation_parameters(self) -> Dict[str, Any]:
         """
         Get all annotation parameters including bounding box and polyline.
 
         Returns:
-            Dictionary containing:
+            List of dictionaries, each containing:
-            - 'bbox': Bounding box coordinates (x_min, y_min, x_max, y_max)
+            - 'bbox': [x_min, y_min, x_max, y_max] in normalized image coordinates
-            - 'polyline': List of [x, y] coordinate pairs
+            - 'polyline': List of [y_norm, x_norm] points describing the polygon
         """
-
+        if self.original_pixmap is None or not self.polylines:
-        # Get np.arrays from  annotation_pixmap accoriding to the color of the stroke
-        qimage = self.annotation_pixmap.toImage()
-        arr = np.ndarray(
-            (qimage.height(), qimage.width(), 4),
-            buffer=qimage.constBits(),
-            strides=[qimage.bytesPerLine(), 4, 1],
-            dtype=np.uint8,
-        )
-        arr = np.sum(arr, axis=2)
-        arr_bin = arr > 0
-        arr_bin = binary_fill_holes(arr_bin)
-
-        labels, _number_of_features = label(
-            arr_bin,
-        )
-        if _number_of_features == 0:
             return None
 
-        objects = find_objects(labels)
+        img_width = float(self.original_pixmap.width())
-        w, h = arr.shape
+        img_height = float(self.original_pixmap.height())
-        bounding_boxes = [
-            [obj[0].start / w, obj[1].start / h, obj[0].stop / w, obj[1].stop / h]
-            for obj in objects
-        ]
 
-        polylines = find_contours(arr_bin, 0.5)
+        params: List[Dict[str, Any]] = []
-        params = []
-        for i, pl in enumerate(polylines):
-            # pl is in [row, col] format from find_contours
-            # We need to normalize: row/height, col/width
-            # w = height (rows), h = width (cols) from line 510
-            normalized_polyline = (pl[::-1] / np.array([w, h])).tolist()
 
-            logger.debug(f"Polyline {i}: {len(pl)} points")
+        for idx, polyline in enumerate(self.polylines):
-            logger.debug(f"  w={w} (height), h={h} (width)")
+            if len(polyline) < 2:
-            logger.debug(f"  First 3 normalized points: {normalized_polyline[:3]}")
+                continue
+
+            xs = [p[0] for p in polyline]
+            ys = [p[1] for p in polyline]
+
+            x_min_norm = min(xs) / img_width
+            x_max_norm = max(xs) / img_width
+            y_min_norm = min(ys) / img_height
+            y_max_norm = max(ys) / img_height
+
+            # Store polyline as [y_norm, x_norm] to match DB convention and
+            # the expectations of draw_saved_polyline().
+            normalized_polyline = [
+                [y / img_height, x / img_width] for (x, y) in polyline
+            ]
+
+            logger.debug(
+                f"Polyline {idx}: {len(polyline)} points, "
+                f"bbox=({x_min_norm:.3f}, {y_min_norm:.3f})-({x_max_norm:.3f}, {y_max_norm:.3f})"
+            )
 
             params.append(
                 {
-                    "bbox": bounding_boxes[i],
+                    "bbox": [x_min_norm, y_min_norm, x_max_norm, y_max_norm],
                     "polyline": normalized_polyline,
                 }
             )
 
-        return params
+        return params or None
 
     def draw_saved_polyline(
-        self, polyline: List[List[float]], color: str, width: int = 3
+        self,
+        polyline: List[List[float]],
+        color: str,
+        width: int = 3,
+        annotation_id: Optional[int] = None,
     ):
         """
         Draw a polyline from database coordinates onto the annotation canvas.
@@ -548,36 +765,24 @@ class AnnotationCanvasWidget(QWidget):
         logger.debug(f"  Image size: {img_width}x{img_height}")
         logger.debug(f"  First 3 normalized points from DB: {polyline[:3]}")
 
-        img_coords = []
+        img_coords: List[Tuple[float, float]] = []
         for y_norm, x_norm in polyline:
-            x = int(x_norm * img_width)
+            x = float(x_norm * img_width)
-            y = int(y_norm * img_height)
+            y = float(y_norm * img_height)
             img_coords.append((x, y))
 
         logger.debug(f"  First 3 pixel coords: {img_coords[:3]}")
 
-        # Draw polyline on annotation pixmap
+        # Store and redraw using common pipeline
-        painter = QPainter(self.annotation_pixmap)
         pen_color = QColor(color)
         pen_color.setAlpha(128)  # Add semi-transparency
-        pen = QPen(pen_color, width, Qt.SolidLine, Qt.RoundCap, Qt.RoundJoin)
+        self._add_polyline(img_coords, pen_color, width, annotation_id=annotation_id)
-        painter.setPen(pen)
 
-        # Draw lines between consecutive points
+        # Store in all_strokes for consistency (uses normalized coordinates)
-        for i in range(len(img_coords) - 1):
-            x1, y1 = img_coords[i]
-            x2, y2 = img_coords[i + 1]
-            painter.drawLine(x1, y1, x2, y2)
-
-        painter.end()
-
-        # Store in all_strokes for consistency
         self.all_strokes.append(
             {"points": polyline, "color": color, "alpha": 128, "width": width}
         )
 
-        # Update display
-        self._update_display()
         logger.debug(
             f"Drew saved polyline with {len(polyline)} points in color {color}"
         )
@@ -587,7 +792,7 @@ class AnnotationCanvasWidget(QWidget):
         Draw a bounding box from database coordinates onto the annotation canvas.
 
         Args:
-            bbox: Bounding box as [y_min_norm, x_min_norm, y_max_norm, x_max_norm]
+            bbox: Bounding box as [x_min_norm, y_min_norm, x_max_norm, y_max_norm]
                   in normalized coordinates (0-1)
             color: Color hex string (e.g., '#FF0000')
             width: Line width in pixels
@@ -602,12 +807,11 @@ class AnnotationCanvasWidget(QWidget):
             )
             return
 
-        # Convert normalized coordinates to image coordinates
+        # Convert normalized coordinates to image coordinates (for logging/debug)
-        # bbox format: [y_min_norm, x_min_norm, y_max_norm, x_max_norm]
         img_width = self.original_pixmap.width()
         img_height = self.original_pixmap.height()
 
-        y_min_norm, x_min_norm, y_max_norm, x_max_norm = bbox
+        x_min_norm, y_min_norm, x_max_norm, y_max_norm = bbox
         x_min = int(x_min_norm * img_width)
         y_min = int(y_min_norm * img_height)
         x_max = int(x_max_norm * img_width)
@@ -617,29 +821,35 @@ class AnnotationCanvasWidget(QWidget):
         logger.debug(f"  Image size: {img_width}x{img_height}")
         logger.debug(f"  Pixel coords: ({x_min}, {y_min}) to ({x_max}, {y_max})")
 
-        # Draw bounding box on annotation pixmap
+        # Store bounding box (normalized) and its style; actual drawing happens
-        painter = QPainter(self.annotation_pixmap)
+        # in _redraw_annotations() together with all polylines.
         pen_color = QColor(color)
         pen_color.setAlpha(128)  # Add semi-transparency
-        pen = QPen(pen_color, width, Qt.SolidLine, Qt.SquareCap, Qt.MiterJoin)
+        self.bboxes.append(
-        painter.setPen(pen)
+            [float(x_min_norm), float(y_min_norm), float(x_max_norm), float(y_max_norm)]
-
+        )
-        # Draw rectangle
+        self.bbox_meta.append({"color": pen_color, "width": int(width)})
-        rect_width = x_max - x_min
-        rect_height = y_max - y_min
-        painter.drawRect(x_min, y_min, rect_width, rect_height)
-
-        painter.end()
 
         # Store in all_strokes for consistency
         self.all_strokes.append(
             {"bbox": bbox, "color": color, "alpha": 128, "width": width}
         )
 
-        # Update display
+        # Redraw overlay (polylines + all bounding boxes)
-        self._update_display()
+        self._redraw_annotations()
         logger.debug(f"Drew saved bounding box in color {color}")
 
+    def set_show_bboxes(self, show: bool):
+        """
+        Enable or disable drawing of bounding boxes.
+
+        Args:
+            show: If True, draw bounding boxes; if False, hide them.
+        """
+        self.show_bboxes = bool(show)
+        logger.debug(f"Set show_bboxes to {self.show_bboxes}")
+        self._redraw_annotations()
+
     def keyPressEvent(self, event: QKeyEvent):
         """Handle keyboard events for zooming."""
         if event.key() in (Qt.Key_Plus, Qt.Key_Equal):

src/gui/widgets/annotation_tools_widget.py

@@ -1,6 +1,6 @@
 """
 Annotation tools widget for controlling annotation parameters.
-Includes pen tool, color picker, class selection, and annotation management.
+Includes polyline tool, color picker, class selection, and annotation management.
 """
 
 from PySide6.QtWidgets import (
@@ -12,6 +12,8 @@ from PySide6.QtWidgets import (
     QPushButton,
     QComboBox,
     QSpinBox,
+    QDoubleSpinBox,
+    QCheckBox,
     QColorDialog,
     QInputDialog,
     QMessageBox,
@@ -31,28 +33,33 @@ class AnnotationToolsWidget(QWidget):
     Widget for annotation tool controls.
 
     Features:
-    - Enable/disable pen tool
+    - Enable/disable polyline tool
-    - Color selection for pen
+    - Color selection for polyline pen
     - Object class selection
     - Add new object classes
     - Pen width control
     - Clear annotations
 
     Signals:
-        pen_enabled_changed: Emitted when pen tool is enabled/disabled (bool)
+        polyline_enabled_changed: Emitted when polyline tool is enabled/disabled (bool)
-        pen_color_changed: Emitted when pen color changes (QColor)
+        polyline_pen_color_changed: Emitted when polyline pen color changes (QColor)
-        pen_width_changed: Emitted when pen width changes (int)
+        polyline_pen_width_changed: Emitted when polyline pen width changes (int)
         class_selected: Emitted when object class is selected (dict)
         clear_annotations_requested: Emitted when clear button is pressed
     """
 
-    pen_enabled_changed = Signal(bool)
+    polyline_enabled_changed = Signal(bool)
-    pen_color_changed = Signal(QColor)
+    polyline_pen_color_changed = Signal(QColor)
-    pen_width_changed = Signal(int)
+    polyline_pen_width_changed = Signal(int)
+    simplify_on_finish_changed = Signal(bool)
+    simplify_epsilon_changed = Signal(float)
+    # Toggle visibility of bounding boxes on the canvas
+    show_bboxes_changed = Signal(bool)
     class_selected = Signal(dict)
+    class_color_changed = Signal()
     clear_annotations_requested = Signal()
-    process_annotations_requested = Signal()
+    # Request deletion of the currently selected annotation on the canvas
-    show_annotations_requested = Signal()
+    delete_selected_annotation_requested = Signal()
 
     def __init__(self, db_manager: DatabaseManager, parent=None):
         """
@@ -64,7 +71,7 @@ class AnnotationToolsWidget(QWidget):
         """
         super().__init__(parent)
         self.db_manager = db_manager
-        self.pen_enabled = False
+        self.polyline_enabled = False
         self.current_color = QColor(255, 0, 0, 128)  # Red with 50% alpha
         self.current_class = None
 
@@ -75,43 +82,51 @@ class AnnotationToolsWidget(QWidget):
         """Setup user interface."""
         layout = QVBoxLayout()
 
-        # Pen Tool Group
+        # Polyline Tool Group
-        pen_group = QGroupBox("Pen Tool")
+        polyline_group = QGroupBox("Polyline Tool")
-        pen_layout = QVBoxLayout()
+        polyline_layout = QVBoxLayout()
 
-        # Enable/Disable pen
+        # Enable/Disable polyline tool
         button_layout = QHBoxLayout()
-        self.pen_toggle_btn = QPushButton("Enable Pen")
+        self.polyline_toggle_btn = QPushButton("Start Drawing Polyline")
-        self.pen_toggle_btn.setCheckable(True)
+        self.polyline_toggle_btn.setCheckable(True)
-        self.pen_toggle_btn.clicked.connect(self._on_pen_toggle)
+        self.polyline_toggle_btn.clicked.connect(self._on_polyline_toggle)
-        button_layout.addWidget(self.pen_toggle_btn)
+        button_layout.addWidget(self.polyline_toggle_btn)
-        pen_layout.addLayout(button_layout)
+        polyline_layout.addLayout(button_layout)
 
-        # Pen width control
+        # Polyline pen width control
         width_layout = QHBoxLayout()
         width_layout.addWidget(QLabel("Pen Width:"))
-        self.pen_width_spin = QSpinBox()
+        self.polyline_pen_width_spin = QSpinBox()
-        self.pen_width_spin.setMinimum(1)
+        self.polyline_pen_width_spin.setMinimum(1)
-        self.pen_width_spin.setMaximum(20)
+        self.polyline_pen_width_spin.setMaximum(20)
-        self.pen_width_spin.setValue(3)
+        self.polyline_pen_width_spin.setValue(3)
-        self.pen_width_spin.valueChanged.connect(self._on_pen_width_changed)
+        self.polyline_pen_width_spin.valueChanged.connect(
-        width_layout.addWidget(self.pen_width_spin)
+            self._on_polyline_pen_width_changed
+        )
+        width_layout.addWidget(self.polyline_pen_width_spin)
         width_layout.addStretch()
-        pen_layout.addLayout(width_layout)
+        polyline_layout.addLayout(width_layout)
 
-        # Color selection
+        # Simplification controls (RDP)
-        color_layout = QHBoxLayout()
+        simplify_layout = QHBoxLayout()
-        color_layout.addWidget(QLabel("Color:"))
+        self.simplify_checkbox = QCheckBox("Simplify on finish")
-        self.color_btn = QPushButton()
+        self.simplify_checkbox.setChecked(True)
-        self.color_btn.setFixedSize(40, 30)
+        self.simplify_checkbox.stateChanged.connect(self._on_simplify_toggle)
-        self.color_btn.clicked.connect(self._on_color_picker)
+        simplify_layout.addWidget(self.simplify_checkbox)
-        self._update_color_button()
-        color_layout.addWidget(self.color_btn)
-        color_layout.addStretch()
-        pen_layout.addLayout(color_layout)
 
-        pen_group.setLayout(pen_layout)
+        simplify_layout.addWidget(QLabel("epsilon (px):"))
-        layout.addWidget(pen_group)
+        self.eps_spin = QDoubleSpinBox()
+        self.eps_spin.setRange(0.0, 1000.0)
+        self.eps_spin.setSingleStep(0.5)
+        self.eps_spin.setValue(2.0)
+        self.eps_spin.valueChanged.connect(self._on_eps_change)
+        simplify_layout.addWidget(self.eps_spin)
+        simplify_layout.addStretch()
+        polyline_layout.addLayout(simplify_layout)
+
+        polyline_group.setLayout(polyline_layout)
+        layout.addWidget(polyline_group)
 
         # Object Class Group
         class_group = QGroupBox("Object Class")
@@ -122,7 +137,7 @@ class AnnotationToolsWidget(QWidget):
         self.class_combo.currentIndexChanged.connect(self._on_class_selected)
         class_layout.addWidget(self.class_combo)
 
-        # Add class button
+        # Add / manage classes
         class_button_layout = QHBoxLayout()
         self.add_class_btn = QPushButton("Add New Class")
         self.add_class_btn.clicked.connect(self._on_add_class)
@@ -133,6 +148,17 @@ class AnnotationToolsWidget(QWidget):
         class_button_layout.addWidget(self.refresh_classes_btn)
         class_layout.addLayout(class_button_layout)
 
+        # Class color (associated with selected object class)
+        color_layout = QHBoxLayout()
+        color_layout.addWidget(QLabel("Class Color:"))
+        self.color_btn = QPushButton()
+        self.color_btn.setFixedSize(40, 30)
+        self.color_btn.clicked.connect(self._on_color_picker)
+        self._update_color_button()
+        color_layout.addWidget(self.color_btn)
+        color_layout.addStretch()
+        class_layout.addLayout(color_layout)
+
         # Selected class info
         self.class_info_label = QLabel("No class selected")
         self.class_info_label.setWordWrap(True)
@@ -148,24 +174,22 @@ class AnnotationToolsWidget(QWidget):
         actions_group = QGroupBox("Actions")
         actions_layout = QVBoxLayout()
 
-        self.process_btn = QPushButton("Process Annotations")
+        # Show / hide bounding boxes
-        self.process_btn.clicked.connect(self._on_process_annotations)
+        self.show_bboxes_checkbox = QCheckBox("Show bounding boxes")
-        self.process_btn.setStyleSheet(
+        self.show_bboxes_checkbox.setChecked(True)
-            "QPushButton { background-color: #2196F3; color: white; font-weight: bold; }"
+        self.show_bboxes_checkbox.stateChanged.connect(self._on_show_bboxes_toggle)
-        )
+        actions_layout.addWidget(self.show_bboxes_checkbox)
-        actions_layout.addWidget(self.process_btn)
-
-        self.show_btn = QPushButton("Show Saved Annotations")
-        self.show_btn.clicked.connect(self._on_show_annotations)
-        self.show_btn.setStyleSheet(
-            "QPushButton { background-color: #4CAF50; color: white; }"
-        )
-        actions_layout.addWidget(self.show_btn)
 
         self.clear_btn = QPushButton("Clear All Annotations")
         self.clear_btn.clicked.connect(self._on_clear_annotations)
         actions_layout.addWidget(self.clear_btn)
 
+        # Delete currently selected annotation (enabled when a selection exists)
+        self.delete_selected_btn = QPushButton("Delete Selected Annotation")
+        self.delete_selected_btn.clicked.connect(self._on_delete_selected_annotation)
+        self.delete_selected_btn.setEnabled(False)
+        actions_layout.addWidget(self.delete_selected_btn)
+
         actions_group.setLayout(actions_layout)
         layout.addWidget(actions_group)
 
@@ -193,7 +217,7 @@ class AnnotationToolsWidget(QWidget):
 
             # Clear and repopulate combo box
             self.class_combo.clear()
-            self.class_combo.addItem("-- Select Class --", None)
+            self.class_combo.addItem("-- Select Class / Show All --", None)
 
             for cls in classes:
                 self.class_combo.addItem(cls["class_name"], cls)
@@ -206,46 +230,115 @@ class AnnotationToolsWidget(QWidget):
                 self, "Error", f"Failed to load object classes:\n{str(e)}"
             )
 
-    def _on_pen_toggle(self, checked: bool):
+    def _on_polyline_toggle(self, checked: bool):
-        """Handle pen tool enable/disable."""
+        """Handle polyline tool enable/disable."""
-        self.pen_enabled = checked
+        self.polyline_enabled = checked
 
         if checked:
-            self.pen_toggle_btn.setText("Disable Pen")
+            self.polyline_toggle_btn.setText("Stop Drawing Polyline")
-            self.pen_toggle_btn.setStyleSheet(
+            self.polyline_toggle_btn.setStyleSheet(
                 "QPushButton { background-color: #4CAF50; }"
             )
         else:
-            self.pen_toggle_btn.setText("Enable Pen")
+            self.polyline_toggle_btn.setText("Start Drawing Polyline")
-            self.pen_toggle_btn.setStyleSheet("")
+            self.polyline_toggle_btn.setStyleSheet("")
 
-        self.pen_enabled_changed.emit(self.pen_enabled)
+        self.polyline_enabled_changed.emit(self.polyline_enabled)
-        logger.debug(f"Pen tool {'enabled' if checked else 'disabled'}")
+        logger.debug(f"Polyline tool {'enabled' if checked else 'disabled'}")
 
-    def _on_pen_width_changed(self, width: int):
+    def _on_polyline_pen_width_changed(self, width: int):
-        """Handle pen width changes."""
+        """Handle polyline pen width changes."""
-        self.pen_width_changed.emit(width)
+        self.polyline_pen_width_changed.emit(width)
-        logger.debug(f"Pen width changed to {width}")
+        logger.debug(f"Polyline pen width changed to {width}")
+
+    def _on_simplify_toggle(self, state: int):
+        """Handle simplify-on-finish checkbox toggle."""
+        enabled = bool(state)
+        self.simplify_on_finish_changed.emit(enabled)
+        logger.debug(f"Simplify on finish set to {enabled}")
+
+    def _on_eps_change(self, val: float):
+        """Handle epsilon (RDP tolerance) value changes."""
+        epsilon = float(val)
+        self.simplify_epsilon_changed.emit(epsilon)
+        logger.debug(f"Simplification epsilon changed to {epsilon}")
+
+    def _on_show_bboxes_toggle(self, state: int):
+        """Handle 'Show bounding boxes' checkbox toggle."""
+        show = bool(state)
+        self.show_bboxes_changed.emit(show)
+        logger.debug(f"Show bounding boxes set to {show}")
 
     def _on_color_picker(self):
-        """Open color picker dialog with alpha support."""
+        """Open color picker dialog and update the selected object's class color."""
+        if not self.current_class:
+            QMessageBox.warning(
+                self,
+                "No Class Selected",
+                "Please select an object class before changing its color.",
+            )
+            return
+
+        # Use current class color (without alpha) as the base
+        base_color = QColor(self.current_class.get("color", self.current_color.name()))
         color = QColorDialog.getColor(
-            self.current_color,
+            base_color,
             self,
-            "Select Pen Color",
+            "Select Class Color",
-            QColorDialog.ShowAlphaChannel,  # Enable alpha channel selection
+            QColorDialog.ShowAlphaChannel,  # Allow alpha in UI, but store RGB in DB
         )
 
-        if color.isValid():
+        if not color.isValid():
-            self.current_color = color
+            return
-            self._update_color_button()
+
-            self.pen_color_changed.emit(color)
+        # Normalize to opaque RGB for storage
-            logger.debug(
+        new_color = QColor(color)
-                f"Pen color changed to {color.name()} with alpha {color.alpha()}"
+        new_color.setAlpha(255)
+        hex_color = new_color.name()
+
+        try:
+            # Update in database
+            self.db_manager.update_object_class(
+                class_id=self.current_class["id"], color=hex_color
             )
+        except Exception as e:
+            logger.error(f"Failed to update class color in database: {e}")
+            QMessageBox.critical(
+                self,
+                "Error",
+                f"Failed to update class color in database:\n{str(e)}",
+            )
+            return
+
+        # Update local class data and combo box item data
+        self.current_class["color"] = hex_color
+        current_index = self.class_combo.currentIndex()
+        if current_index >= 0:
+            self.class_combo.setItemData(current_index, dict(self.current_class))
+
+        # Update info label text
+        info_text = f"Class: {self.current_class['class_name']}\nColor: {hex_color}"
+        if self.current_class.get("description"):
+            info_text += f"\nDescription: {self.current_class['description']}"
+        self.class_info_label.setText(info_text)
+
+        # Use semi-transparent version for polyline pen / button preview
+        class_color = QColor(hex_color)
+        class_color.setAlpha(128)
+        self.current_color = class_color
+        self._update_color_button()
+        self.polyline_pen_color_changed.emit(class_color)
+
+        logger.debug(
+            f"Updated class '{self.current_class['class_name']}' color to "
+            f"{hex_color} (polyline pen alpha={class_color.alpha()})"
+        )
+
+        # Notify listeners (e.g., AnnotationTab) so they can reload/redraw
+        self.class_color_changed.emit()
 
     def _on_class_selected(self, index: int):
-        """Handle object class selection."""
+        """Handle object class selection (including '-- Select Class --')."""
         class_data = self.class_combo.currentData()
 
         if class_data:
@@ -260,20 +353,23 @@ class AnnotationToolsWidget(QWidget):
 
             self.class_info_label.setText(info_text)
 
-            # Update pen color to match class color with semi-transparency
+            # Update polyline pen color to match class color with semi-transparency
             class_color = QColor(class_data["color"])
             if class_color.isValid():
                 # Add 50% alpha for semi-transparency
                 class_color.setAlpha(128)
                 self.current_color = class_color
                 self._update_color_button()
-                self.pen_color_changed.emit(class_color)
+                self.polyline_pen_color_changed.emit(class_color)
 
             self.class_selected.emit(class_data)
             logger.debug(f"Selected class: {class_data['class_name']}")
         else:
+            # "-- Select Class --" chosen: clear current class and show all annotations
             self.current_class = None
             self.class_info_label.setText("No class selected")
+            self.class_selected.emit(None)
+            logger.debug("Class selection cleared: showing annotations for all classes")
 
     def _on_add_class(self):
         """Handle adding a new object class."""
@@ -351,36 +447,32 @@ class AnnotationToolsWidget(QWidget):
             self.clear_annotations_requested.emit()
             logger.debug("Clear annotations requested")
 
-    def _on_process_annotations(self):
+    def _on_delete_selected_annotation(self):
-        """Handle process annotations button."""
+        """Handle delete selected annotation button."""
-        if not self.current_class:
+        self.delete_selected_annotation_requested.emit()
-            QMessageBox.warning(
+        logger.debug("Delete selected annotation requested")
-                self,
-                "No Class Selected",
-                "Please select an object class before processing annotations.",
-            )
-            return
 
-        self.process_annotations_requested.emit()
+    def set_has_selected_annotation(self, has_selection: bool):
-        logger.debug("Process annotations requested")
+        """
+        Enable/disable actions that require a selected annotation.
 
-    def _on_show_annotations(self):
+        Args:
-        """Handle show annotations button."""
+            has_selection: True if an annotation is currently selected on the canvas.
-        self.show_annotations_requested.emit()
+        """
-        logger.debug("Show annotations requested")
+        self.delete_selected_btn.setEnabled(bool(has_selection))
 
     def get_current_class(self) -> Optional[Dict]:
         """Get currently selected object class."""
         return self.current_class
 
-    def get_pen_color(self) -> QColor:
+    def get_polyline_pen_color(self) -> QColor:
-        """Get current pen color."""
+        """Get current polyline pen color."""
         return self.current_color
 
-    def get_pen_width(self) -> int:
+    def get_polyline_pen_width(self) -> int:
-        """Get current pen width."""
+        """Get current polyline pen width."""
-        return self.pen_width_spin.value()
+        return self.polyline_pen_width_spin.value()
 
-    def is_pen_enabled(self) -> bool:
+    def is_polyline_enabled(self) -> bool:
-        """Check if pen tool is enabled."""
+        """Check if polyline tool is enabled."""
-        return self.pen_enabled
+        return self.polyline_enabled