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Sep 24, 2017 - 10:14 PM  
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Global Illumination and the Blur effect

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Global Illumination and the Blur effect

Some findings findings about Realsoft's global illumination system by Mark Heuymans

I'm assuming that you read chapter 'Easy Global Illumination' in the Realsoft3d 4.5 manual.

I was astonished to find that post processing is a very important component in Realsoft's GI system. It offers increased control when working on GI scenes. The advice in the manual to use 'Raytrace + backup' and then 'Post process' with various adjustments is invaluable when you're experimenting! The backup file View_backup.r3i (on my system - don't remember if I configured that myself?) is then created and re-used.

One essential post effects is 'blur'. In the image below you can see why: no blur was applied here and the grain is obvious. Personally I kind of like the grain, but this image was rendered with Raycount1 = 64 (GI-shader) and took 7 1/2 hours on a Athlon 1800+ / 512 MB system. With lower GI sampling rates the grain would get more and more obtrusive. Let's see what the Blur effect can do to reduce the grain.

The unblurred image shows a lot of grain artifacts indeed, but also rich details at the edges of objects..

Generally, blurring masks small details like at the pillar edges; often it's better to use high Raycount values and apply less blur to preserve these details. But raytrace render times are quickly exploding. This is a simple scene without any materials... I tried to render it with procedural stone materials but that was taking just too long to be practical. In that case you just have to use a lower Raycount setting in the GI shader.

Below: Blur Level=4 and iterations=9. The artifacts have not completely disappeared but many details are preserved. Maybe the best compromize.

The image below used Blur level=7 and iterations=20. Yeah, the grain has gone but so are the fine details. The image appears a bit bland. In more real-life, textured and more complex scene it may not be necessary to use such an extreme blur: the artifacts are then less pronounced.

My preliminary conclusion: if render times allow it, use Raycount values as high as possible and try to find a good compromize between grain and detail blurring.

I worked a bit with other GI renderers like Brazil, Final Render and Virtualight and encountered similar issues. It's too early to say where Realsoft fits in but it's certainly extremely flexible. The GI effect is just one of many things that can be done with VSL.

The next investigation will be about reflections, refractions and GI. And caustics: I'll add water and let the light reflect on the walls. Hopefully a real tutorial will follow if it's worthwhile. I promise to use smaller images!

Have fun and mail me if you have comments.

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