Hacker News Reader

Comment by ssp | Hacker News Reader

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...

View on HN

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.

Reply on news.ycombinator.com