Geek asks and answers

Colorize an image while maintaining transparency with PIL?

Ok, here is the situation:

I want to use the Python image library for the "theme", for example:

Theme color: swatch showing tint color"#33B5E5"

IN: http://mupload.nl/img/olpiyj9is.png OUT:http://mupload.nl/img/fiaoq6gk5.png

I got the result using these commands with ImageMagick:

convert image.png -colorspace gray image.png
mogrify -fill "#33b5e5" -tint 100 image.png
Explanation:


The image is first converted to black and white, and then it is thematic.

I want to get the same result with the Python image library. But it seems that I have some problems associated with this, because:

  • Unable to handle transparency
  • The background (transparency in the main image) also has a theme.

I am trying to use this script:

import Image
import ImageEnhance

def image_overlay(src, color="#FFFFFF", alpha=0.5):
    overlay = Image.new(src.mode, src.size, color)
    bw_src = ImageEnhance.Color(src).enhance(0.0)
    return Image.blend(bw_src, overlay, alpha)

img = Image.open("image.png")
image_overlay(img, "#33b5e5", 0.5)

You can see that I did not convert it to shades of gray in the first place, because it also did not work with transparency.

, , : $

, .

+5
2

. Python 3/pillow PIL .

4. , . PIL , , , , , , , PIL .

, , , , . , , , . , Image.point() .

from PIL import Image
from PIL.ImageColor import getcolor, getrgb
from PIL.ImageOps import grayscale

def image_tint(src, tint='#ffffff'):
    if Image.isStringType(src):  # file path?
        src = Image.open(src)
    if src.mode not in ['RGB', 'RGBA']:
        raise TypeError('Unsupported source image mode: {}'.format(src.mode))
    src.load()

    tr, tg, tb = getrgb(tint)
    tl = getcolor(tint, "L")  # tint color overall luminosity
    if not tl: tl = 1  # avoid division by zero
    tl = float(tl)  # compute luminosity preserving tint factors
    sr, sg, sb = map(lambda tv: tv/tl, (tr, tg, tb))  # per component adjustments

    # create look-up tables to map luminosity to adjusted tint
    # (using floating-point math only to compute table)
    luts = (map(lambda lr: int(lr*sr + 0.5), range(256)) +
            map(lambda lg: int(lg*sg + 0.5), range(256)) +
            map(lambda lb: int(lb*sb + 0.5), range(256)))
    l = grayscale(src)  # 8-bit luminosity version of whole image
    if Image.getmodebands(src.mode) < 4:
        merge_args = (src.mode, (l, l, l))  # for RGB verion of grayscale
    else:  # include copy of src image alpha layer
        a = Image.new("L", src.size)
        a.putdata(src.getdata(3))
        merge_args = (src.mode, (l, l, l, a))  # for RGBA verion of grayscale
        luts += range(256)  # for 1:1 mapping of copied alpha values

    return Image.merge(*merge_args).point(luts)

if __name__ == '__main__':
    import os

    input_image_path = 'image1.png'
    print 'tinting "{}"'.format(input_image_path)

    root, ext = os.path.splitext(input_image_path)
    result_image_path = root+'_result'+ext

    print 'creating "{}"'.format(result_image_path)
    result = image_tint(input_image_path, '#33b5e5')
    if os.path.exists(result_image_path):  # delete any previous result file
        os.remove(result_image_path)
    result.save(result_image_path)  # file name extension determines format

    print 'done'

, . -, - , .

sample input and output images showing results of image with and without alpha

+8

. :

  • -, Image.split()
  • ImageOps.colorize
  • -

:

import Image
import ImageOps

def tint_image(src, color="#FFFFFF"):
    src.load()
    r, g, b, alpha = src.split()
    gray = ImageOps.grayscale(src)
    result = ImageOps.colorize(gray, (0, 0, 0, 0), color) 
    result.putalpha(alpha)
    return result

img = Image.open("image.png")
tinted = tint_image(img, "#33b5e5")
+3

More articles:


All Articles