Need advice on Direct Computation rendering setup

[josiah]

I am resuming work on an old project, a character animation in which the camera and character both move.

I have spent considerable time trying to use an IR map in single mode, but I can't get rid of a few flickering GI artifacts around the character's mouth as it speaks. Here are my settings:

First diffuse bounce
Multiplier= 1.0
IR Map
Min/Max rates = -4, 1
Clr Thresh = 0.3
Nrm Thresh = 0.3
Dist thresh = 0.1
HSph Subdiv's= 80
Interp Samples= 60

Secondary bounce
Multiplier= 0.5
direct computation
Subdiv's= 10
Depth = 30

Single Frame mode

(I am using adaptive AA set at 0,3.)

I have decided to try direct computation on first and second bounce. However a HSph subdiv of 100 on the first and 10 on the second bounce, still does not give me near as good a solution as the Ir map (blotchy), and takes much, much longer to render. Do I need to raise the second bounce more, or should I keep raising the first? Can someone help me with what the best relationship between the two should be? Trial and error is eating up all my time!

Thanks!

[percydaman]

lower those interp samples alot. your kind of cancelling out yourself by having both them and hemishp samples high like that.

[losbellos]

min max rate is not well definied try -3/-1 or -3/0 (high settings) you better go with the presets. Also the high Interpolate samples unnecesarry. high, 40 is a max (it will already makes less deteail) wich is ok. Especially at high settings. Hsp80 is higher too but thats okay. (can decrease flicker problems)

You can also increase the resolution of the frames a bit, that might helps.
Much better than with go for DC. Youl have to wait... I dont know how long... (increasing the image resolution a bit, u might have luck that more rays will reach the mouth)

Secondary rays depth 30 is also just a slowdown, set it 3-5. As I experienced no difference after 5 with these settings.

Maybe you could tell more about the envoroment?

[josiah]

Thank you both very much for your replies! The environment is an outdoor area, lighting is by a HDR image only. The character has a pretty high polygon count, especially the face where this artifact appears.

If each prepass further refines the GI solution, wouldn't more prepasses help get rid of artifacts?

Thank you!

[tammo]

if the character is a highres mesh there is no way to stop the flickering.
it will always flicker at some areas like around the armpits, mouth, ears.

that doesnt matter if theres a lot of action going on with motionblur but if its a slow scene you can only go back to light-domes with shadow maps.

[losbellos]

yes, but the initial resolution also count quite some...
-4 mean your.res/(2^(|imap.min|) = your.res/(2^4)
so that will be quite lowres. But u can try the difference, put an object which have some detail, and try -4/-1 and then -3/-1 and -2/-1 you'll see there will be quite some dirrerence especially using hdri. (sensitive for the imap res, and Hsph) However this also increase rendertime. So if u render for PAL its oke to start with -3, but -4 is to low I think.

[Da_elf]

no one has pointed out that your dist thresh is way too low as well. put it to something like 0.3 thats the average i use

[josiah]

Thanks everyone! Very helpful! The mesh is very high resolution indeed. I have spent alot of time trying to get rid of this artifacting, but maybe it's not possible using an IR map. Direct computation with 85 first bounce and 20 on the second seems to produce no artifacts in a small 320 x 200 20 frame test animation and almost no blotches, but I can only produce a couple 800 x 600 frames per day this way. I think I'll probably have to compromise and fake the GI with a light dome.

Thanks for the tip Da_elf, I have always left the thresh set at 0.1. I will try it higher.

Thanks again everybody.