red balloons

red_balloons.py

image_file = 'up.jpeg'
output_file = 'output.png'
image = plt.imread(image_file)/255

target_hue = 0.0

def falloff(hue_diff, intensity):
    return max(0,min(1,(np.exp(1 - intensity * hue_diff) - 1)))

for i in range(image.shape[0]):
    for j in range(image.shape[1]):
        # use HLS color space
        hls = list(colorsys.rgb_to_hls(*image[i,j]))
        # get hue difference (between 0 and 0.5)
        hue_diff = min(((hls[0] - target_hue) % 1), ((target_hue - hls[0]) % 1))
        # Reduce saturation using a falloff function based on the hue difference
        hls[2] *= falloff(hue_diff, intensity=20)
        image[i,j] = colorsys.hls_to_rgb(*hls)
plt.imsave('output.png', image)