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Am 08.11.2017 um 23:40 schrieb cbpypov:
> clipka <ano### [at] anonymous org> wrote:
>>
>> Actually POV-Ray chooses to not use chroma subsampling in JPEG output.
>>
>
> Interesting! Why that?
To allow for the highest quality possible. Note that even if you set
quality to 100%, chroma subsampling would cause loss of information.
> However, if I change the window size of the viewer, causing the images to be
> scaled internally (by whatever method), something interesting happens: the
> undithered and the +th images do not change at all, while for the Bayer
> dithering the concentric rings increase drastically at specific window sizes, --
> even beyond the undithered images! It seems to be a characteristic of this
> dithering when scaled. And the same has obviously happend when I played back an
> MPEG rendered using the +thB4-images.
That's indeed an unsurprising characteristic of pattern-based dithering
(such as Bayer dithering), and is related to the Moiree effect. (Plus,
even if the resiting application is smart enough to avoid Moiree-like
effects, it may also be dumb enough to simply re-introduce colour banding.)
It /can/ also happen with diffusion-based dithering (such as
Floyd-Steinberg), though it is less likely. For an algorithm to be
really safe from such issues it has to be based on random noise.
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