read image byte by byte doesn't work python

December 10, 2021

I have this function that writes image to a file byte by byte:

(The function stores in the first 2 bytes the amount of the rows in the image, the next 2 bytes it stores the amount of columns in the image and then in every byte the pixels rows by rows.)

import cv2
import numpy as np
from matplotlib.image import imread

def write_pic(pic_name):
    pic = imread(pic_name)
    height = pic.shape[0]
    width = pic.shape[1]

    with open("Resources/out.bin", "wb") as outfile:
        outfile.write(height.to_bytes(2, byteorder='big'))
        outfile.write(width.to_bytes(2, byteorder='big'))
        for x in pic:
            outfile.write(x.tobytes())

Then I have this function that reads an image byte by byte:

def read_pic(pic_name):
    with open(pic_name, "rb") as f:
        rows = int.from_bytes(f.read(2), byteorder='big')
        columns = int.from_bytes(f.read(2), byteorder='big')
        mat_pic = np.empty([rows, columns])
        print(rows)
        print(columns)
        while byte := f.read(1):
            for i in range(rows):
                for j in range(columns):
                    mat_pic[i][j] = int.from_bytes(byte, byteorder='big')
            if i == 287 and j == 511:
                break;

    cv2.imshow("The picture", mat_pic)
    cv2.waitKey(0)

But when I show the image, it shows white picture, anyone knows why?
Also, I could not figure out why this while loop while byte := f.read(1): looped infinite times so I added this line

if i == 287 and j == 511: break;

I run this with these lines:

write_pic("Resources/pic.jpg")
read_pic("Resources/out.bin")

>Solution :

If that’s a JPEG, then you’re probably getting an X by Y by 3 array, one for each color component. You need to handle that.

Why do you write the height and width big-endian? That’s not natural any more. Almost all systems you encounter today are little-endian.

This works:

import cv2
import numpy as np
from matplotlib.image import imread

def write_pic(pic_name):
    pic = cv2.imread(pic_name)
    print(pic.shape)
    height = pic.shape[0]
    width = pic.shape[1]

    with open("out.bin", "wb") as outfile:
        outfile.write(height.to_bytes(2, byteorder='big'))
        outfile.write(width.to_bytes(2, byteorder='big'))
        pic.tofile( outfile )

def read_pic(pic_name):
    with open(pic_name, "rb") as f:
        rows = int.from_bytes(f.read(2), byteorder='big')
        columns = int.from_bytes(f.read(2), byteorder='big')
        mat_pic = np.fromfile( f, dtype=np.uint8 ).reshape( (rows, columns, 3) )

    cv2.imshow("The picture", mat_pic)
    cv2.waitKey(0)

write_pic( 'walk.jpg' )
read_pic( 'out.bin' )