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Re: [css-images] Gamma errors in image downscaling

From: Simon Sapin <simon.sapin@exyr.org>
Date: Sun, 09 Nov 2014 21:26:13 +0000
Message-ID: <545FDBF5.9090705@exyr.org>
To: www-style@w3.org
On 09/11/14 19:15, Lea Verou wrote:
> A colleague brought this [1] to my attention, which seems to demonstrate
> an image scaling bug in pretty much every browser I tried the testcase
> [2] on. Furthermore, the results across UAs are inconsistent, which
> might indicate a standardization opportunity. I, myself, have noticed
> similar errors when scaling down certain patterns in the past, so
> stumbling on these issues is not that rare.
> Applying different values to the image-rendering property seems to
> affect the results, but no value produces a correctly downscaled image
> (including the various properietary values…).
> Shouldn’t image-rendering: crisp-edges fix this? Is there any spec
> violation here at all, or is that part of image scaling undefined? Any
> thoughts?
> [1]: http://www.4p8.com/eric.brasseur/gamma.html
> [2]: http://www.4p8.com/eric.brasseur/gamma_dalai_lama.html

On my machine at least, it gets even more “interesting” when playing 
with the zoom level.

Chromium seems to have a fast scaling algorithm to show something as 
fast as possible when the zoom level changes, and then (about one second 
later on this laptop) replaces the image with another one, presumably 
one scaled with an algorithm that takes more time but gives better 
results on non-pathological cases.

Simon Sapin
Received on Sunday, 9 November 2014 21:26:38 UTC

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