Initial commit

skills/extracting-form-fields/scripts/convert_coordinates.py

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+#!/usr/bin/env python3
+"""
+Converts bounding box coordinates from image coordinates to PDF coordinates.
+
+This script takes a .scan.json file (with image coordinates) and converts all
+bounding boxes to PDF coordinates, producing a .form.json file.
+
+Image coordinates: Origin at top-left, Y increases downward
+PDF coordinates: Origin at bottom-left, Y increases upward
+
+Usage:
+    python convert_coordinates.py <scan.json> <pdf_file>
+"""
+
+import json
+import sys
+from pathlib import Path
+
+from PIL import Image
+from pypdf import PdfReader
+
+
+def image_to_pdf_coords(image_bbox, image_width, image_height, pdf_width, pdf_height):
+    """
+    Convert bounding box from image coordinates to PDF coordinates.
+
+    Args:
+        image_bbox: [x1, y1, x2, y2] in image coordinates (top-left origin)
+        image_width: Width of the image in pixels
+        image_height: Height of the image in pixels
+        pdf_width: Width of the PDF page in points
+        pdf_height: Height of the PDF page in points
+
+    Returns:
+        [x1, y1, x2, y2] in PDF coordinates (bottom-left origin)
+    """
+    x_scale = pdf_width / image_width
+    y_scale = pdf_height / image_height
+
+    # Convert X coordinates (simple scaling, same origin)
+    pdf_x1 = image_bbox[0] * x_scale
+    pdf_x2 = image_bbox[2] * x_scale
+
+    # Convert Y coordinates (flip vertical axis)
+    # Image: y1 is top, y2 is bottom (y1 < y2 in image coords)
+    # PDF: need to flip - what's at top of image is high Y in PDF
+    pdf_y1 = (image_height - image_bbox[3]) * y_scale  # Bottom in PDF (was bottom in image)
+    pdf_y2 = (image_height - image_bbox[1]) * y_scale  # Top in PDF (was top in image)
+
+    return [pdf_x1, pdf_y1, pdf_x2, pdf_y2]
+
+
+def get_image_dimensions(images_dir, page_number):
+    """Get dimensions of the PNG image for a specific page."""
+    image_path = Path(images_dir) / f"page_{page_number}.png"
+    if not image_path.exists():
+        raise FileNotFoundError(f"Image not found: {image_path}")
+
+    with Image.open(image_path) as img:
+        return img.width, img.height
+
+
+def convert_scan_to_form(scan_json_path, pdf_path, output_json_path):
+    """
+    Convert .scan.json (image coords) to .form.json (PDF coords).
+
+    Args:
+        scan_json_path: Path to input .scan.json file
+        pdf_path: Path to the PDF file
+        output_json_path: Path to output .form.json file
+    """
+    # Load scan data
+    with open(scan_json_path, 'r') as f:
+        fields = json.load(f)
+
+    # Get PDF dimensions
+    reader = PdfReader(pdf_path)
+
+    # Determine images directory (same directory as scan.json)
+    scan_path = Path(scan_json_path)
+    images_dir = scan_path.parent
+
+    if not images_dir.exists():
+        raise FileNotFoundError(
+            f"Images directory not found: {images_dir}\n"
+            f"Expected to find page images in {images_dir}"
+        )
+
+    # Convert each field
+    converted_fields = []
+
+    for field in fields:
+        page_num = field.get('page', 1)
+
+        # Get dimensions for this page
+        page = reader.pages[page_num - 1]  # Convert to 0-indexed
+        pdf_width = float(page.mediabox.width)
+        pdf_height = float(page.mediabox.height)
+        image_width, image_height = get_image_dimensions(images_dir, page_num)
+
+        # Create converted field
+        converted_field = field.copy()
+
+        # Convert main rect
+        if 'rect' in field:
+            converted_field['rect'] = image_to_pdf_coords(
+                field['rect'],
+                image_width, image_height,
+                pdf_width, pdf_height
+            )
+
+        # Convert label_rect if present
+        if 'label_rect' in field:
+            converted_field['label_rect'] = image_to_pdf_coords(
+                field['label_rect'],
+                image_width, image_height,
+                pdf_width, pdf_height
+            )
+
+        # Convert radio button options if present
+        if 'radio_options' in field:
+            converted_options = []
+            for option in field['radio_options']:
+                converted_option = option.copy()
+                if 'rect' in option:
+                    converted_option['rect'] = image_to_pdf_coords(
+                        option['rect'],
+                        image_width, image_height,
+                        pdf_width, pdf_height
+                    )
+                converted_options.append(converted_option)
+            converted_field['radio_options'] = converted_options
+
+        converted_fields.append(converted_field)
+
+    # Write output
+    with open(output_json_path, 'w') as f:
+        json.dump(converted_fields, f, indent=2)
+
+    print(f"Converted {len(converted_fields)} fields from image to PDF coordinates")
+    print(f"Input:  {scan_json_path}")
+    print(f"Output: {output_json_path}")
+
+    # Show an example conversion
+    if converted_fields:
+        print("\nExample conversion (first field):")
+        orig = fields[0]
+        conv = converted_fields[0]
+        print(f"  Field: {orig.get('field_id')}")
+        print(f"  Image rect: {orig.get('rect')}")
+        print(f"  PDF rect:   {conv.get('rect')}")
+
+
+if __name__ == "__main__":
+    if len(sys.argv) != 3:
+        print("Usage: convert_coordinates.py <scan.json> <pdf_file>")
+        print()
+        print("Example:")
+        print("  python convert_coordinates.py my_form.chatfield/my_form.scan.json my_form.pdf")
+        print()
+        print("Output filename is automatically computed by replacing .scan.json with .form.json")
+        sys.exit(1)
+
+    scan_json_path = sys.argv[1]
+    pdf_path = sys.argv[2]
+
+    # Compute output filename by replacing .scan.json with .form.json
+    scan_path = Path(scan_json_path)
+    if not scan_path.name.endswith('.scan.json'):
+        print(f"Error: Input file must end with .scan.json, got: {scan_path.name}", file=sys.stderr)
+        sys.exit(1)
+
+    output_json_path = str(scan_path.parent / scan_path.name.replace('.scan.json', '.form.json'))
+
+    try:
+        convert_scan_to_form(scan_json_path, pdf_path, output_json_path)
+    except Exception as e:
+        print(f"Error: {e}", file=sys.stderr)
+        sys.exit(1)