colormap.py

#!/usr/bin/env python

import cv2
import numpy as np

def make_custom_lut(src_img):
    """
    Given a color source image that is 256 pixels tall, this will extract the color
    values from the first pixel on each row of the image and use those pixels to 
    make a color LUT.

    Args:
        src_image (opencv image object)
    Returns:
        LUT (list) - array of BGR values
    """
    lut = np.zeros((256, 1, 3), dtype=np.uint8)

    blue_values = range(256)
    green_values = range(256)
    red_values = range(256)

    for row in range(0, 256):
        pixel = src_img[row, 0]
        blue_values[row] = pixel[0]
        green_values[row] = pixel[1]
        red_values[row] = pixel[2]
    #end for

    lut[:, 0, 0] = blue_values
    
    lut[:, 0, 1] = green_values

    lut[:, 0, 2] = red_values

    return lut
#end def


if __name__  == '__main__' :
    # first load an image to use as a color LUT
    lut_img = cv2.imread('customcolormap.png', cv2.IMREAD_COLOR)
    color_table = make_custom_lut(lut_img)

    # read in the image to be processed as a grayscale image
    img_gray = cv2.imread('img256x256.png', cv2.IMREAD_GRAYSCALE)
    
    # convert to a color image and apply the LUT
    img_temp = cv2.cvtColor(img_gray, cv2.COLOR_GRAY2BGR)
    img_color = cv2.LUT(img_temp, color_table)

    # save colorized image
    cv2.imwrite('colormapped.png', img_color)
#end if