Modifying the alpha value of multiple colours in an image?

Asked Dec 04 '18 at 23:56

Active Dec 04 '18 at 23:56

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I was wondering how to change the alpha value of an image (.png or .jpg), only for multiple colours? I have done a some looking around and found some solutions with the PIL module, and I found a partial solution here:

Python: PIL replace a single RGBA color (Code used from link provided)

import Image
import numpy
im = Image.open('test.png').convert('RGBA')
data = numpy.array(im)
r, g, b, a = data.T

colour_to_keep = (r == 255) & (b == 255) & (g == 255) 
data[..., :-1][colour_to_keep.T] = (255, 0, 0)
im2 = Image.fromarray(data)
im2.show()

But after playing around with it, I don't think that it will do what I am attempting to do. This code will replace all except one colour.

I am attempting to set only one "background colour" (in this case, green) of a very simple image to transparent (with alpha = 0).

Can anyone please point me in a direction of how to do this? Thank you!

asked Dec 04 '18 at 23:56

New to Programming

I have read your question several times but I cannot understand what you mean! Your title says you want too change multiple colours, then your question says you want to change only green pixels and you also mention transparency but I don't understand how that fits in. Do you want to make all green pixels transparent? Or something else? Please show a sensible starting image and a result image. – Mark Setchell Dec 06 '18 at 18:06
Hello? Anybody there? – Mark Setchell Dec 09 '18 at 18:30
Not sure how to paste images. Sorry for late reply! – New to Programming Dec 13 '18 at 20:18
@MarkSetchell I have an image with a green background. I am trying to edit the image file to make green pixels invisible. – New to Programming Dec 13 '18 at 20:19
@MarkSetchell again, sorry for the late reply :( – New to Programming Dec 13 '18 at 20:36

Modifying the alpha value of multiple colours in an image?

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