[cairo] Adding Noise To A Picture
ldo at geek-central.gen.nz
Tue Nov 17 20:59:34 PST 2015
On Sat, 28 Mar 2015 11:27:31 +1300, I wrote:
> It’s easy enough to generate a bunch of random pixel values, to make
> an image of pure noise. Adding noice to an existing image is another
> matter. Ideally what you want is exclusive-or operation between the
> bits of the noise pixels and the image pixels.
I figured out the right way to do this: fill a pattern surface with the
full-strength noise, then mask that into the destination image (using
cairo_mask or cairo_mask_surface) with the alpha channel of the mask
controlling the relative proportion of the noise, from 0 for a
noise-free image to 1 for total noise.
> The script is here
> and you can see the output here
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