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

Question

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) .

Answer 1

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]

Answer 2

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))

Answer 3

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