Replace image pixel color on condition in Python

Question

I have an RGBA image where I have to find if any pixel has red value < 150 and to replace such pixels to black. I am using following code for this:

import nu         


        

Answer 1

For one channel image, we can do as follow

out_val = 0
gray = cv2.imread("colour.png",0)

gray[gray<value] = out_val

Answer 2

Use np.where with the mask of comparison against the threshold -

img = np.asarray(img)
imgarr = np.where(img[...,[0]]<150,(0,0,0,255),img)

We are using img[...,[0]] to keep the number of dims as needed for broadcasted assignment with np.where. So, another way would be to use img[...,0,None]<150 to get the mask that keeps dims.