How to remove seven low bits of a grayscale image using OpenCV

Question

I wrote a script to remove the seven least significant bits and only keep the MBS for each pixel of a gray-scale 8-bit image. To do this, I mask each pixel with 0b10000000, but am not getting the expected output.

import cv2
import numpy as np

imageSource = 'input.jpg'
original_img = cv2.imread(imageSource,cv2.COLOR_BGR2GRAY)
cv2.imshow( "original", original_img )
result = original_img & 0b10000000
cv2.imshow( "out", result )
cv2.imwrite('out.jpg',result)
cv2.waitKey(0)
cv2.destroyAllWindows()

Original image:

Output from my code:

Desired result:

Asked By: Kaihan

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Source

Answer 1

import cv2
import numpy as np

imageSource = 'input.png'
original_img = cv2.imread(imageSource, cv2.CV_LOAD_IMAGE_GRAYSCALE)
cv2.imshow("original", original_img)
result = original_img & 0b10000000
_, result = cv2.threshold(result, 1, 255, cv2.THRESH_BINARY)
cv2.imshow("out", result)
cv2.imwrite('out.jpg', result)
cv2.waitKey(0)
cv2.destroyAllWindows()

What you wanted is binary image(0, 255), so use the threshold function.

Answered By: Hao Li

Answer 2

So you basically want all values that are:

greater than 127 (128 = 0b1000000 to 255 = 0b11111111) to be 255,
lower or equal 127 (0 = 0b00000000 to 127 = 0b01111111) to be 0.

You can avoid the binary AND &, and simply use the threshold function:

_, result = cv2.threshold(result, 127, 255, cv2.THRESH_BINARY)

Answered By: Miki

How to remove seven low bits of a grayscale image using OpenCV

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