Can someone please explain to me how the texture compression feature works?

hlln334

This is one of those things where I'm Googling for over 2 hours and can't find a simple explanation.

The "medium" compression and the "high" compression.  These get values (in mb). Suppose we have 512mb for medium, and 1024mb for high. What, in the simplest possible explanation, does that mean?

The explanation I read online is that if the texture size is greater than the "medium" (512mb), then it gets compressed, up to the "high" size.

This explanation makes literally no sense to me. And this is all I've been able to find from Googling, both here and in the forums. So in an attempt to phrase my question as concicesly and easily as possible, I'd like to offer a hypothetical.

Suppose there are three textures: one is 300mb, another gets loaded at 800mb, and finally, a third gets loaded at 1200mb ~1.2gb

If the texture compression settings are set to medium for 512 and high for 1024, then what, specifically, happens to these three textures?

Chuckdozer

First of all, the 512 and 1024 you mention are not indications of file size... they are the image resolution in pixels. The texture compression helps to conserve memory when rendering by reducing the size of certain textures. I'm sure there are others who can explain this much better than I can, but I really don't think the compression feature would ever increase the size of a texture for a render.

Also, if you have a single texture map that comes out to 300, 800, or 1200mb then something is horribly wrong somewhere....

Richard Haseltine

Anything under the Medium size, in pixels, is passed to Iray uncompressed

Anything equal to or over the Medium value in size but under the High value is passed to Iray with Medium compression.

Anything with a size equal to or greater than the High value is passed with High compression.

The compression techniques are not lossless, so there's some loss of image quality when they are applied - but of course if the textures are too large you will run out of GPU memory (assuming your scene woudl otherwsie fit) so there's a trade-off - if you know that an element is going to be a small aprt of the final render you can replace the textures with smaller textures (below the threshold for compression) and perhaps lower RAM use sufficiently to allow the use of larger textures without compression for nearer items. It's a quality/speed balancing act.

SnowSultan

I asked this a while back as well, but Richard gave a much clearer answer this time.  :)   So basically if we want our textures to have no compression at all, we should set the medium to 4100 or so and the high to something like 8100? That way, 4096 textures, the largest ones we normally use, will be passed on to Iray with no compression?

Chuckdozer

SnowSultan said:

I asked this a while back as well, but Richard gave a much clearer answer this time.  :)   So basically if we want our textures to have no compression at all, we should set the medium to 4100 or so and the high to something like 8100? That way, 4096 textures, the largest ones we normally use, will be passed on to Iray with no compression?

Can't texture compression be turned off?

Richard Haseltine

Chuckdozer said:

SnowSultan said:

I asked this a while back as well, but Richard gave a much clearer answer this time.  :)   So basically if we want our textures to have no compression at all, we should set the medium to 4100 or so and the high to something like 8100? That way, 4096 textures, the largest ones we normally use, will be passed on to Iray with no compression?

Can't texture compression be turned off?

Not as far as I know.

Chuckdozer

Setting both the Medium and High threshold values to 16384 on my system effectively turns off all Iray texture compression.

hlln334

SnowSultan said:

I asked this a while back as well, but Richard gave a much clearer answer this time.  :)   So basically if we want our textures to have no compression at all, we should set the medium to 4100 or so and the high to something like 8100? That way, 4096 textures, the largest ones we normally use, will be passed on to Iray with no compression?

Yes, this was the exact explanation I was hoping to receive. A warm and heartfelt thank you to Richard for absolutely clearing up this topic. I completely understand now, thank you!