Sonntag, 13. Dezember 2009

QMC optimized | Oversampling, Rule of Thumb

So we know that we can achieve clean results with sufficient samplecount and scenes with high contrasting illumination values need more samples.
Sometimes rendertimes can get out of hand so how can we optimize the renderspeed by maintaining the same or even enhanced quality?

Make use of Oversampling if you have GI portals and/ or illuminated objects within the scene!

You can get away with fewer samples and still have less noise. Be aware though that oversampling can also be a speedhit if wrong settings are applied! There are a couple of oversampling options available in the rendersettings as well as in the material settings.
A little explanation is due here:
Oversampling sends out additional rays but the smart thing about it is that these rays will be ignored if they don't target towards an illuminated object (or gi portal). This results in a cleaner pic.
There are three different kinds of oversampling available:

The first one is accessed through the rendersettings, the other two modes are are assigned per material. Again, you can only take advantage of oversampling by having either gi portals or luminant objects in your scene.


click to enlarge
Material-> Illumination -> Sampling Mode
If it is set to oversampling the oversampling value from the rendersettings menu will be applied. The other two modes will overwrite whatever is set in the rendersettings even if the oversampling in the rendesettings is set to none! The last mode Per-Pixel QMC Sampling is redundant when using QMC GI as I gathered.
Let's take a look first at the oversampling enabled by the rendersettings. The strength can be picked either from the presets dropdown menu or entered in numerically. The ratio describes the amount of rays in relation to the samplecount. A useful rule of thumb would be:

Multiply the samplecount with the ratio. That resulting value would be the samplecount you'd have to use to achieve approximately the same quality without oversampling.

There is a specific ratio for every scenario that works best. So this time we keep the quality "constant" (using the rule of thumb) and look which samplecount/ oversampling ratio setting was the fastest to render.
We later come back to the oversampling enabled by the material settings and see how that works for the different lighting scenarios. My renderqueue is stuffed - ROCK'N'ROLL!!
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6 Kommentare:

  1. Anonym15. Dezember 2009 um 05:21

    This blog is great, thanks for taking the time.

    Subjects I would appreciate more coverage of in the future are efficent ways of creating advanced scenes without standard lights and fake speculars. Instead, using just luminous materials and standard reflection to create real speculars. Is this even possible in AR3?

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  2. nutriman15. Dezember 2009 um 13:12

    Thanks alot, much appreciated!
    It might take me a while to get to materials but that's definitely interesting, too.
    If you say "fake speculars" than that is actually a double negation because it's the speculars themselves that are the fake as they fake the reflection of lightsources. But because they are very fast to render and still can give nice results they are still being used.
    I avoid speculars on highly reflective to semi-glossy materials but use them for materials that are between a very diffuse reflection and just receiving colorbleeding.
    But if you light your scene with luminous materials only there will be no speculars anyway. So the glossiness can only be described by the amount of diffuse reflection only and yes that's definetely possible but can take forever to render..

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  3. Anonym17. Dezember 2009 um 03:10

    Ok. The reason I was hoping to use reflection to make highlights was because I always find that the mats I make get too plastic speculars, even though I change to blinnshading. But that´s probably me not knowing enough about material creation :)

    Another thing, although the gifs are great, it would be nice to have single pictures so one can compare them in their own tempo.

    Anyhow, keep them posts coming, always nice to learn more about rendering :)

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  4. nutriman17. Dezember 2009 um 16:17

    Thanks again,
    I'm not so happy with the gifs either.
    Actually I wanted to have quicktimes so that you could use scrubbing as a slider to compare but that unfortunately doesn't work with the blog.
    I wanted the pictures to overlay for better comparison if I seperate them it's going to be harder I think. But I could generally slow them down or speed up, let me know what you think.

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  5. Anonym18. Dezember 2009 um 04:30

    Well, I always open pictures in a new firefox-tab, so maybe you could have them automatically open in a new tab when one click on them? Cause then you can make comparisons with out a prob.

    Or maybe have both gif and stills :)

    Gif-speed is fine. Although I sometimes probably want them a bit slower, that would probably just be annoying in the end :)

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  6. nutriman18. Dezember 2009 um 05:38

    There are some resources on the web showing how to embed a quicktime. Let me see if that works here, that would be perfect!

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