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  • #1

    LC vs QM

    I was trying to render 2 white cups (other colors ended up ok) in a studio environment with light cache but I couldn't make them stand out from the background and floor (I tried lowering the environment light too), it all looked so white. I changed the secondary GI to QM and it did a wonderful job. I want to know how it would be possible to get the same kind of render with light cache? It seemed impossible to me

    Here are my 2 pics, one with QM and one with LC and I'm also posting the visoption files.

    thanks, I would appreciate if anyone could tell me as to why I can't get a similar result.

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  • #2
    Re: LC vs QM

    Well, first off LC is much brighter than QMC because of 2 reasons... 1) more bounces are calculated as opposed to just 3 which is the default for qmc. 2) LC doesn't separate bounces, so it calculates the first bounce as well. The fix for this is to, when using LC, decrease the secondary bounce multiplier (to about .8 will do). That will make those shadow details not as flat.

    The second thing is that the default sample size is too big (IMHO) for a good LC solution. A smaller sample size will lead to better details. The default is .02 and I bring that down to .01 or even .005

    In general QMC is a far more accurate calculation the IM or LC. That only means that its a little easier to get good results from it, but this goes along with longer render times. The right tweeks of LC or IM will yield results that are comparable to QMC, but not nearly as time intensive.
    Damien Alomar<br />Generally Cool Dude

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    • #3
      Re: LC vs QM

      Hi damien, I tried lowering the multiplier to .8 and I had much better results. And I also read this website http://www.spot3d.com/vray/help/150R...s_lightmap.htm and saw this:

      "Do not apply perfectly white or very close to white materials to a majority of the objects in the scene, as this will cause excessive render times. This is because the amount of reflected light in the scene will decrease very gradually and the light cache will have to trace longer paths. Also avoid materials that have one of their RGB components set to maximum (255) or above."

      I tried changing the color from a 255 255 255 white to something very similar and it yielded much better results too.

      I'm still trying to get the hang of vray!

      thanks

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      • #4
        Re: LC vs QM

        Oh btw, what do you think a good render time would be to render that kind of image? It is taking me about 5-10 mins to render those, lol.

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        • #5
          Re: LC vs QM

          This is what the 2 cups look like after I took your advice :P

          thanks a lot much much better results now It took 9 m and 59 secs to render though lol

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          • #6
            Re: LC vs QM

            Yea, spot3d is a great site...if it weren't for that I'd would be in the dark about allot of V-Ray..

            Anyway, that image should really not be taking any more then 1-2 min at max. There aren't very complex interactions going on, so you don't need settings that are overkill. I've attached two images and the visopts that go with each. The first was done with my standard defaults that I use. That image came out @ 11-12 sec. The second one was done with what I would consider good quality for this type of scene. Again, only about 53 sec. This was also done with a 4 year old, non multitreaded, cheap laptop...so its not like I've done these on a screamer either. Enjoy

            EDIT: Those cups are available in the V-Ray for Rhino Training Scenes.
            Damien Alomar<br />Generally Cool Dude

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            • #7
              Re: LC vs QM

              Thanks for the visoptions Damien, I'll check them out. They seem pretty nice and very fast renders.

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              • #8
                Re: LC vs QM

                Hi again, both visoptions failed to load Is it a version issue or something?

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                • #9
                  Re: LC vs QM

                  I'm using some decent quality options for this render and I can still see sort of an ugly shadow... Any ideas of why this happens?

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                  • #10
                    Re: LC vs QM

                    It may be a version issue because I do have an internal build...but I haven't run into those issues before...weird.

                    As far as the shadows its best to decrease the sample size for Light Cache (thats one of the common elements from the two images that I posted before). The default is .02, which is too big. Either .01 or .005 is better and should get rid of that.
                    Damien Alomar<br />Generally Cool Dude

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                    • #11
                      Re: LC vs QM

                      Originally posted by cnicog
                      I'm using some decent quality options for this render and I can still see sort of an ugly shadow... Any ideas of why this happens?
                      If you use IM, than try more IM subdivs or smooth the calculation by more (interpolation) samples. Or you use IM+DE.
                      www.simulacrum.de - visualization for designer and architects

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