How to remove whitespace from an image in OpenCV?

Question

I have the following image which has text and a lot of white space underneath the text. I would like to crop the white space such that it looks like the second image.

Answer 1

Opencv reads the image as a numpy array and it's much simpler to use numpy directly (scikit-image does the same). One possible way of doing it is to read the image as grayscale or convert to it and do the row-wise and column-wise operations as shown in the code snippet below. This will remove the columns and rows when all pixels are of pixel_value (white in this case).

def crop_image(filename, pixel_value=255):
    gray = cv2.imread(filename, cv2.IMREAD_GRAYSCALE)
    crop_rows = gray[~np.all(gray == pixel_value, axis=1), :]
    cropped_image = crop_rows[:, ~np.all(crop_rows == pixel_value, axis=0)]
    return cropped_image

and the output: