Irradiance and light cache test.

[bradon]

im doing a series of test to try to get better with vray.

I normally render with the IR + LC method. however the LC seems to be giving me some trouble so i try to turn it off and only render with the IR. asside from the image being slightly darker due to only one GI bounce I notice that the particular flickering issue I have is going away as well. however whats puzzling me is the render time increased. I would figure it would go down if i left out the second bounce. Is this normal and expected? render time went from 10 min using IR+LC to 15 min just using IR alone.

just did another quick test, and it looks like if i enable both the IR +LC but set the LC multiplier to something low like 0.2 the rendertime drops back down to 10 min. The contribution of the LC is low so i don't notice any flickering that i received from the LC before but trying to figure why having the LC enabled but multiplier low would speed up the render.

[snivlem]

The LC can store direct light which can speeds up scenes by a huge amount (especially with multiple lights). Maybe you had "Store direct light" ticked with the light cache? If not, then maybe someone else can answer!

[vlado]

Yep, this is normal; the light cache can speed up calculations for the irradiance map quite a bit, especially with many lights.

As for the flickering, there might be different reasons for it, depending on what it looks like. If the entire image is flashing, then it's probably due to insufficient light cache subdivs; if it is only around object edges and such, it might mean that the sample size is too big. If it is around direct shadows, then you may solve it by turning of the "store direct light" option.

Best regards,
Vlado

[bradon]

ok good to know. its too bad that if we use the LC we get a fast render but we also get a flicker and alot of ram usage ^^)

our LC flickering has been hard to pinpoint. it looks like its mostly in the fine details and cracks of objects. sometimes we see splotches on large flat areas where we are using a glossy material with a small amount of reflection in it. (the white interior of our fridge example has been brutal).

our settings for LC are
subdiv 2000
sample size .05
store direct light ON
world scale ON
adaptive sampleing ON

fixed filter
prefilter 25
size .5

some of these settings well they depend on our world scale so might be hard to take a look at without knowledge of our scene. well keep trying .. that tip about turning off GI refractive cuastics and to use affect shadows in clear materials seems to be helping... THANKS!

[bradon]

The LC can store direct light which can speeds up scenes by a huge amount (especially with multiple lights). Maybe you had "Store direct light" ticked with the light cache? If not, then maybe someone else can answer!

yes we are using store direct light options so that would explain it.