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POColor to transparency - programmatically
 

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  1. POColor to transparency - programmatically
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    <p>you might know the "Color to transparency" effect of professional image editing programs like Photoshop. How is this effect done? I want to add some transparency to my images programmatically with Python (and for testing PIL, because I can check with generated images). This effect is going to be used for some fractal things, so here's my current code: </p> <pre><code>i = "i.png" o = "o.png" key = (0, 0, 0, 255) from PIL import Image as I _i = I.open(i) _ii = _i.load() _o = I.new("RGBA", _i.size) _oo = _o.load() for x in range(0, _i.size[0]): for y in range(0, _i.size[1]): col = list(_ii[x, y]) for i in range(0, 4): col[i] = abs(col[i] - key[i]) _oo[x, y] = tuple(col) _o.save(o) </code></pre> <p>I thought of subtracting the both colors, but i end up with black images (loses all alpha). Another thought was to double the original color and check if the key is lower, like reverse-mixing the two colors.</p> <p>So, do you have any ideas?</p> <p><strong>EDIT</strong></p> <p><img src="https://i.stack.imgur.com/RQTAF.png" alt="Example of &quot;Color to transparency&quot;"></p> <p>This effect was done with GIMP using it's "Color to transparency" function. I selected #FFF to be transparent and GIMP somehow made white to transparent, without ignoring the color of the pixel at first. This is, what I actually want to do, make a color in an image transparent, like in the image. </p> <p>(I added a black background to the second image, so you know it's transparent. The original image was just like the first one, white background, slightly green surrounding, black center)</p>
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    1. COCheck out this wikipedia article: http://en.wikipedia.org/wiki/Transparency_%28graphic%29#Compositing_calculations
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    2. COI read this article several times but I actually don't get it. Might be, because I'm pretty tired after coding night... Could you help me along this?
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