Compares images based on pixel modifications between original file (jpg,png) and converted an resized jpg from that original. Fixed RGBA problem when saving to JPEG with PIL.

compare_images.py

import io
from PIL import Image
import numpy as np


def countDiff(img1, img2):
    s = 0

    if img1.size != img2.size or img1.getbands() != img2.getbands():
        return -1

    for band_index, band in enumerate(img1.getbands()):
        m1 = np.array([p[band_index] for p in img1.getdata()]).reshape(*img1.size)
        m2 = np.array([p[band_index] for p in img2.getdata()]).reshape(*img2.size)
        s += np.sum(np.abs(m1 - m2))

    return s


def compare(im1, im2):
    img1 = Image.open(im1)
    img2 = Image.open(im2)
    
    if img1.size != img2.size:
        img2 = img2.resize(img1.size, resample=Image.BILINEAR)
        
    if img1.format == "PNG":
        print(img1.format)
        print("Converting " + img1.format + " image to RGB")
        buff = io.BytesIO()
        
        if img1.mode == "RGBA":
            img1.load() # required for img1.split()

            rgb = Image.new("RGB", img1.size, (255, 255, 255))
            print("Modo de la nueva imagen creada: " + rgb.mode)
            print(rgb.mode)
            rgb.paste(img1, mask=img1.split()[3]) # 3 is the alpha channel
            rgb.save(buff, 'JPEG', quality=80)
            
            # put back everything to original variable img1
            img1 = Image.open(buff) # load into Image
            print("Buffered image mode: " + img1.mode)
            print("Image should be now JPEG in memory, result: "+ img1.format)
        else:
            img1.convert("RGB")
    
    print("Waiting result for countDiff()")
    return countDiff(img1, img2)

'''
Most of the code gotten from StakOverflow, but had to tweak few things and used io.BytesIO to avoid writting to files.

compare("original_image.png", "converted_and_resized_image.jpg")
Returns:
    PNG
    Converting PNG image to RGB
    Waiting result for countDiff()

    36423731

compare("original_image_modified.png", "converted_and_resized_image.jpg")
Returns:
    PNG
    Converting PNG image to RGB
    Modo de la nueva imagen creada: RGB
    RGB
    Buffered image mode: RGB
    Image should be now JPEG in memory, result: JPEG
    Waiting result for countDiff()

    39863802

This means, that because the value for original_image is lower than original_image_modified, the converted_and_resized_image is much more than the original_image than the original_modified_image, which is totally TRUE
'''