image_preprocessing.py

import numpy as np
from skimage import color, restoration


def rm_white_frame(img):
    """Crops the image to remove outer white fram

    Args:
        img (RGB Image): 

    Returns:
        RGB Image: cropped image
    """
    # create a negative (to invert the white frame into black, to fill with 0)
    img = 1 - img

    h, w, d = img.shape
    #left limit
    for i in range(w):
        if np.sum(img[:, i, :]) > 0:
            break
    #right limit
    for j in range(w - 1, 0, -1):
        if np.sum(img[:, j, :]) > 0:
            break

    #top limit
    for k in range(h):
        if np.sum(img[k, :, :]) > 0:
            break
    #bottom limit
    for l in range(h - 1, 0, -1):
        if np.sum(img[l, :, :]) > 0:
            break

    cropped = img[k:l + 1, i:j + 1, :].copy()
    #back to normal
    cropped = 1 - cropped

    return cropped


def preprocess(img):
    """Applies preprocessing steps to images

    Converts to grayscale, removes white frame, and applies nl means denoising

    Args:
        img (RGBA img): 

    Returns:
        Gray Image: processed gray image
    """
    img = color.rgba2rgb(img)
    img = rm_white_frame(img)
    img = color.rgb2gray(img)
    img = restoration.denoise_nl_means(img)
    return img