在具有透明背景的单色PNG图像上更改/覆盖颜色？

Question

What I would like to be able to do is dynamically change a solid single-colored png to another color simply by inputting the desired color code without losing the transparent background. The implementations I've seen tend to be a bit sloppy, so I was wondering if anyone can give me advice on how they would implement it.

I'd be most comfortable with a PHP solution but Python works too, hell I'll even take a good canvas solution. Any advice/examples regarding this would be very much appreciated, thanks guys.

Answer 1

Ordinarily I like to work in the RGB color space, but this is a case where HLS works very well. The conversion in Python is simple, by replacing the H and S and leaving L the same.

import colorsys
from PIL import Image

def recolor(im, r, g, b):
    h, l, s = colorsys.rgb_to_hls(r/255.0, g/255.0, b/255.0)
    result = im.copy()
    pix = result.load()
    for y in range(result.size[1]):
        for x in range(result.size[0]):
            r2, g2, b2, a = pix[x, y]
            h2, l2, s2 = colorsys.rgb_to_hls(r2/255.0, g2/255.0, b2/255.0)
            r3, g3, b3 = colorsys.hls_to_rgb(h, l2, s)
            pix[x, y] = (int(r3*255.99), int(g3*255.99), int(b3*255.99), a)
    return result

recolor(im_flag, 255, 0, 0).save(r'c:\temped_flag.png')