Identify all values that are close to zero

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I have a numpy array and I am minusing a constant value from the array. I want the values to go negative if necessary (and not wrap around or floor to zero). I then need to extract all array values that are close to zero and produce a new array/image that is where where the values are close to zero.

I have tried to implement this but its hacky and I'm not sure if its correct. Can you achieve what I am trying to do above?

# roi is a numpy array/image in Cielab colour space
swatch_colour = (255, 10, 30) # Cielab colour space
swatch_roi = np.full((roi.shape[0], roi.shape[1], 3), swatch_colour, dtype='int8')
int_roi = roi.astype('int8')
diff = np.subtract(int_roi, swatch_roi)

thresh = diff.copy()
# Get all pixels whose Cielab colour is close to zero
thresh[np.abs(thresh) < (12,6,12)] = 0
# the remaining pixels are greater than/less than the above threshold
thresh[np.abs(thresh) > (0,0,0)] = 255

thresh = thresh.astype('uint8')
# convert from 3 channels to 1 channel
thresh = cv2.cvtColor(thresh, cv2.COLOR_BGR2GRAY)
# Invert the image so that the pixels that were close to zero are white
thresh = cv2.bitwise_not(thresh)