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Comment by Geee | Hacker News Reader

I wonder if GPU hardware does it right or wrong on texture rendering. Someone care to test?

GPU hardware runs software designed for it, so in the end if it doesn't work properly it's not the hardware that's at fault.

Texture sampling is still performed with specialized hardware. It does bilinear or trilinear sampling, which would be "wrong" by the original article's definition.

Yes, but I think the GPU designers did the right thing here by not injecting "magic" gamma-correction functionality into the texture sampler. There are many operations done on textures before they become pixel colors, plus they are often used to store non-image information (positions, normals, CT densities) where gamma correction would be incorrect.If you care about correct tone-mapping (most games probably don't), you can correct your textures beforehand.

Oh, I agree entirely. I just called it "wrong" in response to Geee's original question. Should have clarified.

Basically all newer hardware has the ability to convert from sRGB to linear RGB during texture sampling, and back again during ROP. See these OpenGL extensions:

http://www.opengl.org/registry/specs/EXT/texture_sRGB.txt

http://www.opengl.org/registry/specs/ARB/framebuffer_sRGB.tx...

Is the sRGB-to-linear transformation actually done in the GPU's texturing hardware? nVidia's PTX ISA at least doesn't expose any sRGB-specific sampling opcodes.

The conversion should take place before filtering, so it has to be in the texturing hardware. There is no need for sRGB specific sampling opcodes because sRGB is considered a property of the texture, not of the way you sample it.

Yeah, but PTX doesn't give texture or sampler values an sRGB mode either. Are you sure the driver doesn't just convert the texture when glTex(Sub)Image* is called?

I would be very surprised. I do know that both Intel and ATI chips support it in texture hardware.

See this, for example:

http://www.x.org/docs/AMD/R5xx_Acceleration_v1.5.pdf

Bit 21 of TXFORMAT0:

    GAMMA 21 none Optionally remove gamma from texture before passing to
              shader. Only apply to 8bit or less components.
           POSSIBLE VALUES:
                 00 - Disable gamma removal
                 01 - Enable gamma removal

There is also support for re-applying gamma before storing to a color buffer.

Pinch scaling on the iPad turned all the examples in the article to pink and green garbage, so maybe someone at Apple needs to take a look at that.

Might be worth trying to use the CATiledLayer stuff and the CoreImage scaling to generate 'live' scaling. That might work better than whatever Safari, UIKit and the GPU presently do.

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