app.py

import cv2
from PIL import Image
import numpy as np
import time
import math
import gradio as gr

def find_signature_bounding_boxes(image):
    # Start measuring time
    start_time = time.time()

    if image is None:
        raise ValueError("Could not open or find the image")

    # Binarize the image using Otsu's thresholding method
    gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
    # Threshold the image using Otsu's method
    _, binary_image = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY_INV + cv2.THRESH_OTSU)

    # Find connected components
    num_labels, labels, stats, centroids = cv2.connectedComponentsWithStats(binary_image, connectivity=8, ltype=cv2.CV_32S)

    # Calculate median area of components
    areas = stats[1:, cv2.CC_STAT_AREA]  # Exclude background
    median_area = np.median(areas)
    print('median_area: ' + str(median_area))
    median_character_width = int(math.sqrt(median_area))
    print('median_character_width: ' + str(median_character_width))

    # Define area thresholds
    min_area_threshold = median_area * 4
    max_area_threshold = median_area * 50

    # Filter components based on area thresholds
    possible_signatures = []
    for i in range(1, num_labels):  # Exclude background
        area = stats[i, cv2.CC_STAT_AREA]
        if min_area_threshold < area < max_area_threshold:
            left = stats[i, cv2.CC_STAT_LEFT]
            top = stats[i, cv2.CC_STAT_TOP]
            width = stats[i, cv2.CC_STAT_WIDTH]
            height = stats[i, cv2.CC_STAT_HEIGHT]
            print('Found candidate with area: ' + str(area))
            #filter horizontal lines
            if height < median_character_width * 5 and width > median_character_width*30:
              print('   -> candidate is horizontal line with width, height: ' + str(width) + ',' + str(height))
              continue
            #filter vertical lines
            if width < median_character_width * 5 and height > median_character_width*30:
              print('   -> candidate is vertical line with width, height: ' + str(width) + ',' + str(height))
              continue
            #filter on a ratio of black pixels (logos for example have a higher ratio)for now guestimate is 0.3
            roi = binary_image[top:top+height, left:left+width]
            num_black_pixels = cv2.countNonZero(roi) # Calculate the number of black pixels in the ROI
            total_pixels = width * height # Calculate the total number of pixels in the ROI
            ratio = num_black_pixels / total_pixels # Calculate and return the ratio of black pixels
            print('   -> candidate has black pixel ratio: ' + str(ratio))
            if ratio > 0.30:
              print('   -> candidate has too high black pixel ratio: ' )
              continue
            possible_signatures.append((left, top, width, height))

    print('Nr of signatures found before merging: ' + str(len(possible_signatures)))
    possible_signatures = merge_nearby_rectangles(possible_signatures, nearness=median_character_width*4)

    # End measuring time
    end_time = time.time()
    print(f"Function took {end_time - start_time:.2f} seconds to process the image.")
    info = f"Detection took {end_time - start_time:.2f} seconds. "

    return possible_signatures, info

def merge_nearby_rectangles(rectangles, nearness):
    def is_near(rect1, rect2):
        left1, top1, width1, height1 = rect1
        left2, top2, width2, height2 = rect2
        right1, bottom1 = left1 + width1, top1 + height1
        right2, bottom2 = left2 + width2, top2 + height2
        return not (right1 < left2 - nearness or left1 > right2 + nearness or
                    bottom1 < top2 - nearness or top1 > bottom2 + nearness)

    def merge(rect1, rect2):
        left1, top1, width1, height1 = rect1
        left2, top2, width2, height2 = rect2
        right1, bottom1 = left1 + width1, top1 + height1
        right2, bottom2 = left2 + width2, top2 + height2
        min_left = min(left1, left2)
        min_top = min(top1, top2)
        max_right = max(right1, right2)
        max_bottom = max(bottom1, bottom2)
        return (min_left, min_top, max_right - min_left, max_bottom - min_top)

    merged = []
    while rectangles:
        current = rectangles.pop(0)
        has_merged = False

        for i, other in enumerate(merged):
            if is_near(current, other):
                merged[i] = merge(current, other)
                has_merged = True
                break

        if not has_merged:
            for i in range(len(rectangles) - 1, -1, -1):
                if is_near(current, rectangles[i]):
                    current = merge(current, rectangles.pop(i))

        if not has_merged:
            merged.append(current)

    return merged


def run_detection(input_image):

    # inputimage is PIL as RGB
    image = np.asarray(input_image.convert("RGB"))

    # Find bounding boxes of possible signatures on the document
    signatures, info = find_signature_bounding_boxes(image)
    print('Nr of signatures found: ' + str(len(signatures)))
    # Draw bounding boxes on the image
    for (x, y, w, h) in signatures:
        cv2.rectangle(image, (x, y), (x+w, y+h), (0, 255, 0), 2)
    image_with_box = Image.fromarray(cv2.cvtColor(image, cv2.COLOR_BGR2RGB))
    
    info = info + 'Nr of signatures found: ' + str(len(signatures))
    return image_with_box, info

if __name__ == "__main__":
    
    visit_badge = '<a href="https://visitorbadge.io/status?path=https%3A%2F%2Fhuggingface.co%2Fspaces%2Fto-be%2Fsignature_detection_opencv"><img src="https://api.visitorbadge.io/api/combined?path=https%3A%2F%2Fhuggingface.co%2Fspaces%2Fto-be%2Fsignature_detection_opencv&label=%20&countColor=%23263759" /></a>'

    css = """
            #mkd {
                height: 500px; 
                overflow: auto; 
                border: 1px solid #ccc; 
            }
            """
    block = gr.Blocks(css=css).queue()
    with block:
        gr.Markdown("<h1><center>Signature detection with OpenCV<h1><center>")
        gr.Markdown("<h3><center>See my <a href='https://towardsdatascience.com/machine-learning-is-not-all-you-need-a-case-study-on-signature-detection-9551f2e5d0e7'>article</a> for more details.<h3><center>")
        gr.Markdown("<h3><center>Serves as an example where deep learning is not needed.<h3><center>")

        with gr.Row():
            with gr.Column():
                input_image = gr.Image(source='upload', type="pil")
                run_button = gr.Button(label="Run")
                info = gr.Textbox(label="Info")
                

            with gr.Column():
                gallery = gr.outputs.Image(type="pil").style(full_width=True, full_height=True)

        run_button.click(fn=run_detection, inputs=[
                        input_image], outputs=[gallery, info])
        gr.Examples(
          [["Sample1.jpg"],["Sample2.jpg"],["Sample3.jpg"],["Sample4.jpg"],["Sample5.jpg"]],
          inputs = [input_image],
          outputs = [gallery, info],
          fn=run_detection,
          cache_examples=True,
          label='Try these examples:'
        )
        gr.HTML(visit_badge)
    block.launch(share=False, show_api=False, show_error=True)