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Re: [Public WebGL] Gamma correction and texImage2D/texSubImage2D
On 2010-09-07 04:53, Mark Callow wrote:
On 07/09/2010 02:23, Gregg Tavares (wrk) wrote:
...
WebGL already specifies that if the incoming format is a lossless
8bit format (ie, an 8bit png) that the bits in the file must be
passed straight through, no conversion. There are conformance tests
for this. This is to support getting non-image data into WebGL.
Why should losslessly compressed files be treated differently than
lossy compressed files? Just because they are more likely to be used
for non-image data does not seem like sufficient reason. There are a
lot of PNG images out on the web. People creating PNG files for, e.g.
normal maps, can easily write a gAMA chunk indicating the gamma value
is 1.0.
What would it mean if we said that jpeg or some other lossy format has
to pass the values through "untouched"? What precision and which IDCT
algorithm should be used to consider the pixels "untouched"? Two
conforming jpeg decoders can produce different data, the requirement for
conformance is that the PSNR of the decoded image and the original is
small enough iirc.
Avoiding that issue is the reason it only applies to lossless images.
That limitation is btw mostly to keep browsers from doing premultiply
alpha + un-premultiply alpha before uploading the data to gl, color
space was not considered when it was added.
//Tim
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