Splotches

[Devin Johnston]

Hey Everyone I've got a little problem here, my rendering is coming out with these splotches on it. In the past I've seen similar results when there is coplanar geometry present but that is not the case this time. This model was created in ArchiCAD and exported as a 3DS file. Image 1 was rendered with low settings:

 

IR-Map: Default settings (Low)

QMC: 8 Subdivs

 

Image 2 was rendered with high settings:

 

IR-Map: Default settings (high)

QMC: 24 Subdivs

 

As I increase the settings to higher levels the splotches get smaller and more concentrated but never go away. I'm not sure where to go from here, any help is appreciated.

[Tommy L]

What are your interp samples and your HSph. subdivs in the Irr map parameters?

Try doing everything from default. Im sure its a sampling issue, whats your lighting setup?

[Devin Johnston]

Interp. samples: 20

HSph. subdivs: 50

 

For lighting I'm using a GI Environment (skylight) overide with the multiplier set to 1.4, I've also got a Vray Light set to sphere with a multiplier of 100 and a radius of 400'

[Brian Smith]

As I increase the settings to higher levels the splotches get smaller and more concentrated but never go away. I'm not sure where to go from here, any help is appreciated.

 

This is always what happens. The higher the resolution of your irradiance map (which doubles in size every time you increase the min/max rate), the more detail you place in your map. If you render a 640x480 image with a high preset, your max rate value is 0. A value of 0 means your irradiance map matches the resolution of your image. If you drop down to a low preset, your max rate value is -2, which means your irradiance map is 1/4th the size of your render output, i.e. 180x120. If you take an image that small and blow it up to 640x480, you're naturally going to get a blurred, undetailed image. So with the low preset, the result looks like a smoother image but it doesnt have the detail.

 

If you want to get the splotches to go away, simply increase the interpolation steps. You could increase hsph subdivs to improve sample quality so that the variation in the noise isnt so drastic, but you'll get much more bang for the buck increasing interpolation. I would personally never use more than 50 on hsph subdivs, though 90% of the time I use 20 and increase interpolation samples.

[FlytE]

how many sampling subdivisions has your light got?

[rivoli]

as pointed out, the problem it's not a bad geometry one but a irr map one. increasing your max rate will surely help (decreasing the normal threshold might help as well), as will turning detail enhancement on.

even though I wouldn't use irr map at all for a scene with such small details all over the building's facade, qmc will give you perfectly crisp details and no splotches at all.

[Devin Johnston]

Rivoli, your right about the QMC when I use it as both my primary and secondary engine it removes the splotches, now there is quite a bit of noise though.

[rivoli]

one thing you might want to try is qmc as primary method and light cache for secondary bounces, it should be faster than qmc/qmc.

 

as long as noise goes, try switching to adaptive qmc antialiasing (if you're not using it already), uncheck "use qmc sampler thresh" and decrease it to something like 0,005 (default it's 0,01). then try raising the max subdivisions a couple of steps at a time (like from 4 to 6 then 8). if you can't see anything going better after some point, it means you have to further lower the threshold (the two are linked, if the threshold is set too high, this will prevent vray from taking more samples even if you set the max subdivisions to 100). you can try turning the antialiasing filter off altogether.

[Devin Johnston]

That's much better thank you, I guess it's just going to take some time to figure out all of these settings.

[rivoli]

I guess it's just going to take some time to figure out all of these settings.

 

lol, I know what you mean.

 

another thing you may want to try as noise comes into play, it's to set the "adaptive amount" in the rQMC sampler to 1,0. this way vray will be as adaptive as possible and it might save some time.

 

of course qmc/light cache will be slower than irr map/light cache, and if in your final image those facades ends up to be mainly glass (which you can totally exclude from gi, and casting or receiving shadows), then you're probably better off with irr map render times wise.

anyway, I tend to use qmc all the time, to me it looks much much better than anything you can get out of an irr map. but this is just me.

[Brian Smith]

Rivoli, your right about the QMC when I use it as both my primary and secondary engine it removes the splotches, now there is quite a bit of noise though.

 

to get rid of the noise when you use qmc gi, increase the subdivs and decrease the qmc noise threshold....if you have 100% importance sampling (i.e. adaptive amount=1.0), then one does no good without the other. you will definitely be able to get more detail to show up than with irmap but to get rid of the noise you will probably have very long render times