HDR textures

[JPulham]

When modelling game environments for HDR game play.. what textures need to be in HDR format?
I know EnvMaps need to be.
Does the Lightmap need to be (probably yes ) and does the diffuse map need to be? (I might be able to get away with LDR diffuse).

[jingquan]

Anything luminance like flood lights and glow in the dark stickers during the night. Most often it's used for the sky, outdoors during the day. I think if I'm to use HDR textures for my indoors design, I'll use it on shiny metallic objects.

The rest of the textures will probably be taken care by the envmap.

[omaremad]

The important format is the framebuffer one, unless your texture will have pixels varying over a big dynamic range, you can just ramp up the light emmited from an object mathematically(just the colour output) rather than loading textures. if the texture has allot of variety in its light emmitance then you will need hdr textures.

The rgbe format may interest you in this case,since its easy to decode in the shader 3 inst cost and can be stored in a tga loadable by irrlicht(alpha channel has the brightness, using logs you can create brightness from the rgb and alpha of around 0 -20000) rgb ratio stays the same as normal so the rgbe format will artefact if you say display a very red colour with very small blue and green.

some people just use an extra ldr glow map and multiply by a brightness factor, but rgbe is cheap enough now.

[JPulham]

I was thinking of using the fake HDR found here:
http://www.ogre3d.org/wiki/index.php/Faking_HDR
This uses RGBe in the alpha channel. Basically I wanted to know which textures should be encoded this way.

once I've encoded them.. can I just expose them (exponential exposure) for LDR use? it should work...

[omaremad]

You still need bloom/tonemaps to actually see the hdr, encoding normal float values in a shader to rgbe and back allows you to store 0-22000 values in a texture which supports 0-255.

My last post was highlighting a big diffrence between a HDR framebuffer and a HDR texture, which one do you want(or both)?

[fmx]

wouldn't framebuffer operations to fake it be more computationally expensive than using HDR values directly?

[JPulham]

basically my game offers HDR/LDR options. All surfaces use a shader (directional radiosity and shadowmapping). The shader can then use either HDR textures and render to a 'fake' HDR target, which is used in combo with a bloom shader, or the LDR equivilent uses LDR textures and no bloom.

[omaremad]

You sound like your on the right path JPullham. Diffuse shouldnt emit light(only modulate the reflacted light) so it can be ldr in the hdr version, glow maps can be used for emmitance(can be ldr or hdr depending on the math you do in shader).

wouldn't framebuffer operations to fake it be more computationally expensive than using HDR values directly?

Well there a few things:
hdr values take more vram
hdr values are bigger and hence take longer to load<-not only at start up but during each texture read
Limited filtering modes
Antialiasing problems

all of these depend on the hdr format.

ALU power is always getting faster at a pace than memory speed, so 3 shader instructions are now faster than a large memroy read.