"Blotchy" GI Shadows

[rareseu]

i'm no gi expert but some of your settings are way too high, the accuracy should never be 100, if you can't get good results with 85% you're just wasting rendertime by kicking it up,
i think the blotches are there because there aren't enough stochastick rays, try these settings :

acc 85%
stochastic : 350
min 20
max 200

[georgedrakakis]

i think it's a matter of stoch samples, but i am looking for an answer to this issue too.

[knight42]

My accuracy is actually 90%, I misread the screen. I'll try upping the stochastic samples and see what that does, thanks.

[andrewillingworth]

Definately increase the Stocastic samples - to around 650 - The high the better, it is a matter balancing render time, but Sto needs to be a lot higher. Also look at the lumination of materials - bear in mind that unless you want a material to contribute to the GI in a scene then turn it off that helps the blotchy marks too.

[barcombpictures]

We are going to work backward here, because that is what makes the most sense.

Recompute: self explainitory.

Max. Resolution: This tells the GI engine what the maximum sampling rate should be for any given area. More samples, more accurate result, greater render time.

Min. Resolution: Tells the GI what the minimum sampling rate should be for any given area.

Here is how you should think of these 2: (set Accuracy to like 50%) If my scene has flat surfaces in it, how many samples should be taken of it before I get a good result (and i am not oversampling and wasting time)? This will be your Min. Resolution.
If my scene has intersecting or joining surfaces, how many samples should be taken of them before i get a good result? This will be your Max.

Stochastic Sampling: This one is a little tricky to understand and it took me some trial and error. It is the size of the radius around any given sample to be evaluated and changed. Weird right. I'm not sure exactly how it work but if you have a really low #, like 1, you'll get a ton of dots which vary wildly in shade, but as you increase the # the dots will get larger and start to even out over the area. If you make it too high though, you are just adding render time and not much else.

Diffuse Depth: Is the coolest and most central part of this engine. It tells the engine how many times a photon is bounced off a surface and can then be reused as a light source (which takes along with is the color of whatever it bounced off of, so as you increase it your scene will take on a more realistic overall hue). This is the thing that globally illuminates your scene. Usually a good # is 3, maybe 4; anything above 5 or 6 is just adding render time.

Prepass Size: Is unnecessary I think. Though it does cut your render time a little as you go toward 1/10, you are also sacrificing quality. All this thing really does it change the size of the GI preview when you are rendering.

Accuracy: (the reason why i starting backwards) This is like a dial for the Min and Max Resolution settings. This tells the GI engine how strictly it should follow the Max Resolution for any given area. Increasing the accuracy will make the GI calculate every surface using a sampling rate closer to the Max. Resolution sampling rate and less of the Min Resolution Sampling rate. 100% tell the GI to use only the Max Res. and 0% tells only to use the Min Res.

Strength: Is like a mixer, saying how much of the GI effect should be add to a regular render of the scene. (which is what the prepass is all about, GI renders the scene, then a regular render of the scene is done and then they are added together.)

*Save Solution: caches a version of the GI render pass in a seperate file within the project. if recompute is set to first time, then the next time you render youll be using the saved version. change recomp to always to fix this.

**I havent seen any difference in having Identical noise dist. checked or not.

[STRAT]

i'm no gi expert but some of your settings are way too high, the accuracy should never be 100, if you can't get good results with 85% you're just wasting rendertime by kicking it up,


not true. 100% is 100%. i used to render at 99 or 100% and got fantastic results. (still do if the job requires it). although as you say, it isn't the norm.

Knight - at a diffdepth of 3 and 90% accuracy that must have taken a fair amount of time to render. and yup, your blotches are a combination of low samples. Your diffdepth is a notch or 2 too high too, your lighting is flat, too high and washed.

perasonally i'd try -

strength - 100
accuracy - 70
prepass - 1/3
diffdepth - 1 (add a small touch of ambient infill if needed)
stoch - 750+
min - 50
max - 350+

for things like those gutterings which are extra blotchy i'd put a comping tag on the object and bump their gi accuracy up to 85% maybe.

you might also want to look at your area shad settings too to speed things up. try 50,5,50 as a starter.

[knight42]

Thanks, Strat, I was hoping you'd reply! ;)

I'll try with the settings you've given - the whole scene is taking nearly three hours to render at 800x600 right now.

I'm using just a Sky preset (At the Sea) for illumination - I haven't added any other lights, and I think that's contributing to the washed out look. I am using the Color post effect to up the Gamma to 1.2 too.

I'll post a render when it's done.

J.

[knight42]

Okay, this is what I ended up with - this took about an hour as opposed to three. In the end I put Comp tags on the fascia objects and excluded them from the GI, even with Sto up to 750 I was still getting blotchy shadows (there are still some dodgy areas even now).

The same objects in a new scene didn't suffer from the poor shadows so it's scene-related rather than modelling, which is what I was suspecting.

Linky (http://i20.photobucket.com/albums/b209/baldus885/House/Release0010.jpg).

[STRAT]

yeah, blotchiness is pure lack of samples. and it looks like it's your dark grey fascia objects which are the main offenders.

excluding and object from gi will only exclude it from recieving it, not casting it. you need to change the material properties too. i'd suggest letting it recieve and cast full gi, but up the gi accuracy in the comping tag.

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