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Re: [Public WebGL] Gamma correction and texImage2D/texSubImage2D



 On 07/09/2010 17:40, Tim Johansson wrote:
>  On 2010-09-07 04:53, Mark Callow wrote:
>>
>> 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.
>
My concern is the failure to apply the gAMA or other color space
metadata to PNG files while doing so for files using jpeg compression.
This can lead to the same image looking very obviously different
depending on whether  it is loaded from a JPEG or a PNG.

I agree that passing values "untouched" is meaningless in terms of JPEG
but that is no reason to ignore the PNG spec. and treat PNG files
incorrectly.

Regards

    -Mark

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