Pil Change Color Channel Intensity

I want to make a color picker, which recolors a png texture while preserving transparency in python3. I only want the brighter parts of the image to be recolored, but also keep the

Solution 1:

I dreamt up an approach for this:

• Extract and save the Alpha/transparency channel
• Convert the image, minus Alpha, to HSV colourspace and save the V (lightness)
• Get a new Hue (and possibly Saturation) from your Colour Picker
• Synthesize a new Hue channel, and a new Saturation channel of 255 (fully saturated)
• Merge the new Hue, Saturation and original V (lightness) to a 3 channel HSV image
• Convert the HSV image back to RGB space
• Merge the original Alpha channel back in

That looks like this:

#!/usr/local/bin/python3import numpy as np
from PIL import Image

# Open and ensure it is RGB, not palettised
img = Image.open("keyshape.png").convert('RGBA')

# Save the Alpha channel to re-apply at the end
A = img.getchannel('A')

# Convert to HSV and save the V (Lightness) channel
V = img.convert('RGB').convert('HSV').getchannel('V')

# Synthesize new Hue and Saturation channels using values from colour picker
colpickerH, colpickerS = 10, 255
newH=Image.new('L',img.size,(colpickerH))
newS=Image.new('L',img.size,(colpickerS))

# Recombine original V channel plus 2 synthetic ones to a 3 channel HSV image
HSV = Image.merge('HSV', (newH, newS, V))

# Add original Alpha layer back in
R,G,B = HSV.convert('RGB').split()
RGBA = Image.merge('RGBA',(R,G,B,A))

RGBA.save('result.png')

With colpickerH=10 you get this (try putting Hue=10here):

With colpickerH=120 you get this (try putting Hue=120here):

---

Just for fun, you can do it exactly the same without writing any Python, just at the command line with ImageMagick which is installed on most Linux distros and available for macOS and Windows:

# Split into Hue, Saturation, Lightness and Alpha channels
convert keyshape.png -colorspace hsl -separate ch-%d.png

# Make a new solid Hue channel filled with 40, a new solid Saturation channel filled with 255, take the original V channel (and darken it a little), convert from HSL to RGB, copy the Alpha channel from the original image
convert -size 73x320 xc:gray40 xc:white \( ch-2.png -evaluate multiply 0.5 \) -set colorspace HSL -combine -colorspace RGB ch-3.png -compose copyalpha -composite result.png

Yes, I could do it as a one-liner, but it would be harder to read.