Script to find vertical lines in the middle of the image and convert location to a distance on sensor from center

find_vertical_lines.py

import sys
import os
from PIL import Image, ImageDraw


def find_vertical_lines_by_gradient(image_path, gradient_threshold=10, min_width=1, max_width=7):
    """
    Find vertical lines by detecting strong contrast changes in the middle row, scanning from center to left.
    Returns a list of center X positions for each detected line.
    min_width and max_width now refer to the actual pixel width of the detected line.
    """
    img = Image.open(image_path).convert('L')  # Convert to grayscale
    width, height = img.size
    middle_row = height // 2
    pixels = img.load()

    # Get the pixel values for the middle row
    row = [pixels[x, middle_row] for x in range(width)]

    # Compute the gradient (difference between neighbors)
    center = width // 2
    x = center
    edge_positions = []
    while x > 0:
        diff = abs(row[x] - row[x-1])
        if diff >= gradient_threshold:
            edge_positions.append(x)
        x -= 1

    # Group close edges as a single line, using actual pixel width
    edge_positions.sort()
    lines = []
    group = []
    for pos in edge_positions:
        if not group:
            group = [pos]
        elif pos - group[-1] <= max_width:
            group.append(pos)
        else:
            group_width = group[-1] - group[0] + 1
            if min_width <= group_width <= max_width:
                center_x = (group[0] + group[-1]) / 2
                lines.append(center_x)
            group = [pos]
    # Handle last group
    if group:
        group_width = group[-1] - group[0] + 1
        if min_width <= group_width <= max_width:
            center_x = (group[0] + group[-1]) / 2
            lines.append(center_x)
    return lines


def main():
    if len(sys.argv) < 2:
        print("Usage: python find_vertical_lines.py <image1.png> [image2.png ...]")
        return
    image_paths = sys.argv[1:]
    DEBUG_IMAGE = True  # Set to False to disable debug image output
    sensor_width_px = 5496
    sensor_width_mm = 35.9
    sensor_middle_mm = sensor_width_mm / 2
    px_to_mm = sensor_width_mm / sensor_width_px
    results = {}
    max_lines = 0
    for image_path in image_paths:
        lines = find_vertical_lines_by_gradient(image_path)
        lines_mm = [sensor_middle_mm - (center_x * px_to_mm) for center_x in lines]
        lines_mm.sort()
        base = os.path.splitext(os.path.basename(image_path))[0]
        results[base] = lines_mm
        if len(lines_mm) > max_lines:
            max_lines = len(lines_mm)
        if DEBUG_IMAGE:
            orig_img = Image.open(image_path).convert('RGB')
            width, height = orig_img.size
            debug_img = orig_img.copy()
            draw = ImageDraw.Draw(debug_img)
            for center_x in lines:
                x = int(round(center_x))
                draw.line([(x, 0), (x, height - 1)], fill=(255, 0, 0), width=1)
            debug_img.save(f"{base}_lines.png")
            print(f"Debug image with detected lines saved as {base}_lines.png")
    # Write tab-separated CSV
    bases = list(results.keys())
    with open("lines_output.tsv", "w") as f:
        f.write("\t".join(bases) + "\n")
        for i in range(max_lines):
            row = []
            for base in bases:
                if i < len(results[base]):
                    row.append(f"{results[base][i]:.2f}")
                else:
                    row.append("")
            f.write("\t".join(row) + "\n")
    print("Tab-separated results written to lines_output.tsv")

if __name__ == "__main__":
    main()