In this dataset, the images and annotations are organized as follows: Images: Located in a directory (PNG/JPG format).
Annotations: JSON files containing polygon-based segmentation masks. Each JSON file corresponds to an image and contains polygon annotations with coordinate points defining object boundaries.

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Segmentation Mask Annotation Format

Each annotation file contains polygon shapes in the following JSON structure: 
{
  "version": "4.5.6",
  "shapes": [
    {
      "label": "QSBD",
      "points": [
        [64, 10],
        [64, 15],
        [67, 15],
        [68, 14],
        [68, 10]
      ],
      "shape_type": "polygon"
    }
  ],
  "imagePath": "example_image.png"
}
Example annotation structure: 
{
  "label": "QSBD",
  "points": [
    [64, 42], [68, 43], [69, 41], [71, 40], [75, 40],
    [77, 38], [77, 36], [78, 33], [76, 30], [71, 29],
    [70, 27], [68, 26], [64, 26], [64, 29]
  ],
  "shape_type": "polygon"
}
label: Represents the object class (e.g., “QSBD”).
points: Array of [x, y] coordinates defining the polygon boundary.
shape_type: Type of annotation (“polygon” for segmentation masks).
imagePath: Corresponding image filename.

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Conversion Process

The conversion script performs the following steps:
  • Load Each JSON File:
    The script reads each JSON annotation file to extract polygon coordinates.
  • Extract Polygon Points:
    For each shape, it extracts the array of [x, y] coordinate points.
  • Calculate Bounding Box:
    The script converts polygon coordinates to bounding boxes by finding the minimum and maximum x,y values:
min_x = minimum x-coordinate from all points
max_x = maximum x-coordinate from all points  
min_y = minimum y-coordinate from all points
max_y = maximum y-coordinate from all points

col_x = min_x (left edge)
row_y = min_y (top edge)
width = max_x - min_x
height = max_y - min_y
  • Generate the CSV File:
    The CSV is generated with the following columns:
filename: The image file name.
col_x: The x‑coordinate (column) of the top‑left corner.
row_y: The y‑coordinate (row) of the top‑left corner.
width: Bounding box width (pixels).
height: Bounding box height (pixels).
label: The object label (e.g., “QSBD”).

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Python Conversion Script

import json
import csv
import os
from pathlib import Path
from typing import List, Tuple, Dict, Any

def extract_polygon_points(shape: Dict[str, Any]) -> List[Tuple[int, int]]:
    """Extract polygon points from a shape annotation."""
    if 'points' not in shape:
        return []
    
    points = []
    for point in shape['points']:
        if len(point) >= 2:
            x, y = int(point[0]), int(point[1])
            points.append((x, y))
    
    return points

def polygon_to_bbox(points: List[Tuple[int, int]]) -> Tuple[int, int, int, int]:
    """Convert polygon points to bounding box coordinates."""
    if not points:
        return (0, 0, 0, 0)
    
    x_coords = [point[0] for point in points]
    y_coords = [point[1] for point in points]
    
    min_x = min(x_coords)
    max_x = max(x_coords)
    min_y = min(y_coords)
    max_y = max(y_coords)
    
    col_x = min_x
    row_y = min_y
    width = max_x - min_x
    height = max_y - min_y
    
    return (col_x, row_y, width, height)

def process_json_file(json_path: Path) -> List[Dict[str, Any]]:
    """Process a JSON annotation file and extract bounding boxes."""
    try:
        with open(json_path, 'r', encoding='utf-8') as f:
            data = json.load(f)
    except (json.JSONDecodeError, FileNotFoundError) as e:
        print(f"Error reading {json_path}: {e}")
        return []
    
    if 'shapes' not in data:
        print(f"No 'shapes' key found in {json_path}")
        return []
    
    # Get the corresponding image filename
    image_filename = data.get('imagePath', json_path.stem + '.png')
    
    bboxes = []
    for shape in data['shapes']:
        if shape.get('shape_type') != 'polygon':
            continue
            
        label = shape.get('label', 'unknown')
        points = extract_polygon_points(shape)
        
        if not points:
            continue
            
        col_x, row_y, width, height = polygon_to_bbox(points)
        
        # Skip invalid bounding boxes (zero width or height)
        if width <= 0 or height <= 0:
            continue
            
        bbox_info = {
            'filename': image_filename,
            'col_x': col_x,
            'row_y': row_y,
            'width': width,
            'height': height,
            'label': label
        }
        bboxes.append(bbox_info)
    
    return bboxes

# Paths to your folders
annotations_folder = "annotations"
output_csv = "segmentation_annotations.csv"

# Process all JSON files and convert to CSV
all_bboxes = []
json_files = list(Path(annotations_folder).glob('*.json'))

for json_file in json_files:
    print(f"Processing: {json_file.name}")
    bboxes = process_json_file(json_file)
    all_bboxes.extend(bboxes)
    print(f"  Found {len(bboxes)} bounding boxes")

# Write to CSV
fieldnames = ['filename', 'col_x', 'row_y', 'width', 'height', 'label']

with open(output_csv, 'w', newline='', encoding='utf-8') as csvfile:
    writer = csv.DictWriter(csvfile, fieldnames=fieldnames)
    writer.writeheader()
    writer.writerows(all_bboxes)

print(f"Conversion complete! Output saved to: {output_csv}")
print(f"Total bounding boxes: {len(all_bboxes)}")

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Script Explanation

  • Input Processing:
    The script iterates over all .json files in the annotations folder and extracts polygon shapes from each file.
  • Polygon Extraction:
    For each polygon shape, the script extracts the coordinate points and validates the data structure.
  • Bounding Box Calculation:
    The polygon coordinates are converted to bounding boxes by finding the minimum and maximum x,y values to determine the rectangular bounds.
  • CSV Output:
    The CSV file is written with each bounding box as a row containing the image filename, top-left coordinates, dimensions, and object label.
Example CSV Output
After running the script, the CSV output will look similar to this:
filenamecol_xrow_ywidthheightlabel
example.png641045QSBD
example.png64261417QSBD
example.png65681324QSBD
filename: Name of the image file.
col_x & row_y: Top‑left pixel coordinates of the bounding box.
width & height: Width and height of the bounding box in pixels.
label: Object label from the segmentation mask.

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Usage

  1. Place your JSON annotation files in the annotations folder
  2. Run the conversion script: python convert_segmentation.py
  3. The output CSV file segmentation_annotations.csv will be generated
  4. Import this CSV file into Visual Layer for object detection tasks
The converted bounding boxes provide approximate rectangular bounds for the original polygon segmentation masks, making them compatible with Visual Layer’s object annotation format.