How to change all the black pixels to white (OpenCV)?

user_14085528 0
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I am new to OpenCV and I do not understand how to traverse and change all the pixels of black with colour code exact RGB(0,0,0) to white colour RGB(255,255,255). Is there any function or way to check all the pixel and if RGB(0,0,0) the make it to RGB(255,255,255).

rgb opencv colors python
3 Answers

Assuming that your image is represented as a numpy array of shape (height, width, channels) (what cv2.imread returns), you can do:

height, width, _ = img.shape

for i in range(height):
    for j in range(width):
        # img[i, j] is the RGB pixel at position (i, j)
        # check if it's [0, 0, 0] and replace with [255, 255, 255] if so
        if img[i, j].sum() == 0:
            img[i, j] = [255, 255, 255]

A faster, mask-based approach looks like this:

# get (i, j) positions of all RGB pixels that are black (i.e. [0, 0, 0])
black_pixels = np.where(
    (img[:, :, 0] == 0) & 
    (img[:, :, 1] == 0) & 
    (img[:, :, 2] == 0)
)

# set those pixels to white
img[black_pixels] = [255, 255, 255]
user_31424720

Subtract 255 from each Pixel and get the positive values only

For grayscale and black and white images

sub_array = 255*np.ones(28, dtype = int) img_Invert = np.abs(np.subtract(img,sub_array))

user_185148320 
cv.rectangle(img,(0,0),(img.shape[1],img.shape[0],(255,255,255),thickness=-1)
cv.imshow('img',img)
user_174760620
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