tight_dewarp.py

import cv2
import numpy as np
import matplotlib.pyplot as plt
import sys
from pygam import LinearGAM

def uncurve_text(input_path, output_path, n_splines = 5):
    # Load image, grayscale it, Otsu's threshold
    image = cv2.imread(input_path)
    gray = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
    thresh = cv2.threshold(gray, 0, 255, cv2.THRESH_BINARY + cv2.THRESH_OTSU)[1]
    
    # Dilation & Erosion to fill holes inside the letters
    kernel = np.ones((3, 3), np.uint8)
    thresh = cv2.erode(thresh, kernel, iterations=1)
    thresh = cv2.dilate(thresh, kernel, iterations=1)
    
    black_pixels = np.column_stack(np.where(thresh == 0))
    leftmost_x, rightmost_x = np.min(black_pixels[:, 1]), np.max(black_pixels[:, 1])
    X = black_pixels[:, 1].reshape(-1, 1)
    y = thresh.shape[0] - black_pixels[:, 0]
    
    gam = LinearGAM(n_splines = n_splines)
    gam.fit(X, y)
    
    # Create the offset necessary to un-curve the text
    y_hat = gam.predict(np.linspace(leftmost_x, rightmost_x, num = rightmost_x - leftmost_x + 1))
    
    # Plot the image with text curve overlay
    plt.imshow(image[:,:,::-1])
    plt.plot(np.linspace(leftmost_x, rightmost_x, num = rightmost_x - leftmost_x + 1), (thresh.shape[0] - y_hat), color='red')
    plt.axis('off')
    plt.subplots_adjust(bottom = 0, left = 0, right = 1, top = 1)
    plt.show()

    # Roll each column to align the text
    for i in range(leftmost_x, rightmost_x + 1):
        image[:, i, 0] = np.roll(image[:, i, 0], round(y_hat[i - leftmost_x] - thresh.shape[0]/2))
        image[:, i, 1] = np.roll(image[:, i, 1], round(y_hat[i - leftmost_x] - thresh.shape[0]/2))
        image[:, i, 2] = np.roll(image[:, i, 2], round(y_hat[i - leftmost_x] - thresh.shape[0]/2))

    # Plot the final image
    plt.imshow(image[:,:,::-1])
    plt.axis('off')
    plt.subplots_adjust(bottom = 0, left = 0, right = 1, top = 1)
    plt.show()
    
    # Save image to desired directory
    cv2.imwrite(output_path, image)

if __name__ == "__main__":
    
    input_path = sys.argv[1]
    output_path = sys.argv[2]
    uncurve_text(input_path, output_path)