[Pixman] [PATCH 7/7] utils.c: Increase acceptable deviation to 0.0064 in pixel_checker_t
spitzak at gmail.com
Wed Mar 6 19:01:58 PST 2013
Søren Sandmann wrote:
> However, unless using 16 bpp for the internal buffers is really a
> performance win, there doesn't seem to be any benefits to doing it this
> way over just dithering the final image. And I definitely want to see
> convincing numbers before believing that 16 bpp for internal buffers is
> a performance benefit.
No, you are confusing dithering with just adding enough noise to hide
dithering artifacts. And that is a *lot* of noise. Imagine if the
destination is 1-bit and you wanted to show a grayscale image on it: it
would turn into black and white blotches, and I think enough noise to
hide the edges of those blotches would result in no image visible at all!
Dithering involves adding the pattern to the source, such that a pixel
of 5.5 is much more likely to end up >= 6 than a pixel of 5.0, and thus
on average will be brighter. If both of these are converted to 5.0
before the pattern is added then both will end up the same level.
Error diffusion will result in the highest quality result, such as
really silky smooth gradients. However it is a pain to implement on the
GPU so most schemes add patterns.
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