GI cache alters render results

Started by sboerner, June 29, 2020, 01:18:10 am

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sboerner

I was having some trouble fine-tuning the render settings for this image and finally realized that I was getting different results, depending on whether or not I was using a GI cache.

These patches were rendered with the path tracer, same TG version, file, settings, etc., except one uses a cache file and the other doesn't. The dust clouds are V2 clouds.

Am I missing something? Never run across this before.

Dune

Did you make the cache of the whole size or just the crop? Likely a GI cache of the whole thing (for the crop render) will be different from an non-GI-cached crop. But I have had a slightly similar experience while having completed a 100% PT render, and needing an additional crop, with only a slight change. So I made a GI cache of the whole thing (thinking it would be the same as the 100% render) and rendered that crop. But the results were different as well.

sboerner

The cache was full-frame, not just the crop.

So, OK . . . the GI in the cached rendering was calculated from the full frame, while the GI in the non-cached rendering was calculated from the cropped area.  Hence the difference, and the cached rendering would be more accurate.

Dune

Yes, the no-GI cache version doesn't take the sky into account and lightens up the dark crop.

WAS

Isn't TG's crop just a fake kinda "Focus" crop unless you actually have the command line parameter to then not take into account outside the crop area? Like it's not physically rendering the area outside the crop, but it takes into account things coming from outside the crop unless that setting it set?

sboerner

QuoteIsn't TG's crop just a fake kinda "Focus" crop unless you actually have the command line parameter to then not take into account outside the crop area? Like it's not physically rendering the area outside the crop, but it takes into account things coming from outside the crop unless that setting it set?


Not sure, but I would guess not, based on the results I'm getting. Maybe when you're working from the GUI it sets that parameter as well.

And come to think of it, I have been bitten by this before. Maybe this time the lesson will stick. :P

Dune

I'm 99.9% sure it doesn't take (much) into account when doing a crop. I don't know if that's different in PT than standard rendering though, but I don't think so.

WAS

Quote from: Dune on June 30, 2020, 02:39:03 amI'm 99.9% sure it doesn't take (much) into account when doing a crop. I don't know if that's different in PT than standard rendering though, but I don't think so.

It should. Especially if you have your corp settings adjusted, it will to a higher degree.

Though I think I'm thinking of cropoutput which crops to the crop region without the padding of the original image resolution.

N-drju

I'm afraid this problem reaches deeper than you might think...

I have rendered out four crops for my contest entry and was terrified to see that upper left and upper right had a huge discrepancy between the cloud shading. I have literally ended up with having half of the cloud steel-dark and the other half creamy-white.

I have to confirm this finding yet before I report a bug as such, but I believe this is not the first time I have experienced something like that. I'm afraid GI cache processing might have been "damaged" somehow on the way...
"This year - a factory of semiconductors. Next year - a factory of whole conductors!"

Dune

I think v3 clouds are not cacheable.

N-drju

Quote from: Dune on July 01, 2020, 03:58:37 amI think v3 clouds are not cacheable.

I'd say they are, because after re-cropping, the cloud rendered fine. But it really was apples and oranges in the first go. :(
"This year - a factory of semiconductors. Next year - a factory of whole conductors!"

sboerner

Quote from: undefinedI'm afraid this problem reaches deeper than you might think...

I don't think so, N-drju. The results I was getting were completely attributable to human error. :-[


Quote from: undefinedI think v3 clouds are not cacheable.
True, unless it's changed in the last year or so. With path tracing, the GI cache applies only to the atmosphere and v2 clouds. The cache in turn influences lighting for v3 clouds and for sky influence on ground, on the fly, via path tracing.

WAS

When you crop, off camera rays are more approximated, which will of course impact cloud lighting. The cloud can be cached but the lighting it's receiving isn't.

Matt

I was looking at this issue a couple of weeks ago and made some improvements to the GI caching of atmosphere. I haven't applied the same improvement to Cloud V2 yet, but I will do if it's successful on the atmosphere.
Just because milk is white doesn't mean that clouds are made of milk.

Matt

Quote from: Dune on July 01, 2020, 03:58:37 amI think v3 clouds are not cacheable.

They are in Terragen 4.5.38 and above :)
Just because milk is white doesn't mean that clouds are made of milk.