Why the automatic change in pixel value in python?

问题

I am extracting frames from video with the help of VideoCapture. Extracted the first frame converted the frame into an image with the help of PIL. Printed the previous pixel value at position (1,1) Printed the pixel value at position(1,1) of the newly created image Can anyone explain why?

Function to extract frames

import cv2

from PIL import Image

def FrameCapture(path):

# Path to video file
    vidObj = cv2.VideoCapture(path)
    fourcc = cv2.VideoWriter_fourcc(*'mp4v')
    width = cv2.CAP_PROP_FRAME_WIDTH
    height = cv2.CAP_PROP_FRAME_HEIGHT
    fps = cv2.CAP_PROP_FPS
    out = cv2.VideoWriter("D:\Funny 3 second video.mp4", fourcc, fps, (width, height))

    cnt = int(0)

    while 1:

        # vidObj object calls read
        # function extract frames

        success, arrayframe = vidObj.read()
        if success == 0:
            break



        if cnt == 0:
            #IF FIRST FRAME SAVE IT

            sp = Image.fromarray(arrayframe)
            sp.save("D:\sp2.jpg")
            fp = "D:\sp2.jpg"
            im = Image.open(fp, mode='r')
            im = im.convert('RGB')
            print("Old Value:  ",arrayframe[1][1])
            print("New Value:  ",im.getpixel((1, 1)))

        out.write(arrayframe)

        cnt += 1

    vidObj.release()
    out.release()
    cv2.destroyAllWindows()

# Driver Code
if __name__ == '__main__':
    # Calling the function

    FrameCapture("D:\Funny 2 second video.mp4")

Output

Old Value:   [94 95 90]
New Value:   (94, 95, 89)

回答1:

The answer is very simple. You saved your data in a lossy format, namely JPEG, and it lost data.

Use a lossless format like PNG if every bit is important to you.

来源：https://stackoverflow.com/questions/52640023/why-the-automatic-change-in-pixel-value-in-python