Need a little Help: Why are these renderings so blotchy?

[steelers05]

This is a problem that I have had a few times and seems to occur mostly when I am trying to use a lot of white in the scene, they come up with blotchy spots everywhere and I am not sure how to fix it. At first I thought it was the HDRI image that I was using as the light source, but I tried many different HDRI's and they all produced different results but they all had some blotchiness to it. Then I completely deactivated the GI and environement and only used lights from the scene and I still got blotchiness all over the place (see the first image). Why is this so? Can anyone tell me how to fix it? because there is a lot of times where I want to do a simple rendering to just show massing with white or where I want to do product renderings on a white canvas like the one you see in the second image. If anyone can chime in on this, it is truely appreciated, because I am out of ideas. Thank you in advance.

[thomthom]

Re: Need a little Help: Why are these renderings so blotchy?

Have you tried setting DMC/QMC Sampler Adaptive Amount to 0.85?

[Jackson_cg]

Re: Need a little Help: Why are these renderings so blotchy?

Whe I use homemade (i.e. created in Photoshop and hence technically innaccurate) HDRIs I overcome the blotchiness by increasing the IM samples (see below, trying to push the forums back to full size LOL). I really should have increased the HSph. Subdivs proportionally, but I wanted to do a quick test without long render times. I should mess around with Sample Adaptive Amount a bit more!

[dalomar_cg]

Re: Need a little Help: Why are these renderings so blotchy?

Increasing the Samples blurs the GI solution, which in most situations is not desirable. If you look very closely at the 3rd solution, there are several places where the solution is to blurry and details are lost. I could also put a test together that exhibits that more that even more.

Most likely this is a Adaptive Amount issue and setting it at .85 should help. Also, there's a lot of light emitting geometry in the first image Steelers05 posted. Its generally not a very good idea to light models only with light emitting geometry since its not sampled as effectively and reliably as standard lights are.

[Jackson_cg]

Re: Need a little Help: Why are these renderings so blotchy?

Damien and/or Thom,

Would it be possible to explain a little about what the DMC Adaptive Amount actually does? Looking through my custom visopts I found most are set at 0.85 by default, but some vary. Why is 0.85 an optimum figure? Is it an optimum figure for most render setups? I ran 3 test renders on a very simple white model, black background lit with an HDRI with DMC AA at 0.4, 0.85 & 1, but didn't see much difference other than a slightly longer render time for the lower figures.

Thanks in advance,
Jackson

[steelers05]

Re: Need a little Help: Why are these renderings so blotchy?

Thanks for the suggestions guys. I tried changing the adaptive amount but that really did not do much of anythinng. There any other ideas on how to possibly fix this?

[dalomar_cg]

Re: Need a little Help: Why are these renderings so blotchy?

Another long explanation...hold on tight...

In order to achieve some of the speed that V-Ray does, there are two concepts that V-Ray uses to prevent samples from being taken where they will be of no practical use. Those concepts are Importance Sampling and Early Termination (also called Adaptive Sampling). Importance sampling simply means that values that have more potential to influence the final result of the scene will receive more samples. Practically, this means that brighter areas of a scene will be sampled more than darker areas.

Early Termination is the idea that if two values are similar to each other then they can do with fewer samples. There are two parts to implementing this concept...First is at what point to I want to even start comparing two values as being similar(how adaptive do I want to be), and second is once I'm adaptive how close do I want those samples to be. These are controlled by Adaptive Amount and Noise Threshold, respectively.

An adaptive amount of 1 will opens up the proverbial flood gates in terms of what values are to be considered for being similar. Since now any value will considered as possibly being similar every value will have to rely on the noise threshold for whether it gets more samples or not. At typical noise thresholds, there wind up being a number of places where some will slip through even when they haven't been sampled enough. In most cases lowering the noise threshold will help overcome this, but this really slows things down.

The idea is still to have the adaptive amount as high as possible without introducing artifacts because that is what's going to allow things to be speedy. Through a number of tests .85 has been determined as a "goldie locks" kind of value...high enough to be quick, yet low enough to prevent unnecessary artifacts. Although I tend to always recommend that number, if you have a brighter scene you probably won't see as many (or any) artifacts from a higher adaptive amount.

Going back to the concept of Importance Sampling, I suspect that Adaptive Amount also somehow controls how "unimportant" dark areas are, and therefore how undersampled those dark areas will be. Through a lot of tests, the biggest culprit of undersampling with a high Adaptive Amount are the darker areas of the scene. I don't know if this is a natural byproduct of how things work or something is specifically changed. However, I have not found any documentation that supports this. Also, AFAIK there isn't a setting that controls the Importance of a given value.

HTH

[Jackson_cg]

Re: Need a little Help: Why are these renderings so blotchy?

Thanks yet again Damien for such a detailed and yet clear explanation. I really wish that the VfSU manual explained every parameter as well as you do on these forums! I might make it a little mission of mine to collect all your descriptions and re-post them in one thread, I'm sure it would benefit everyone and save you some time answering questions like mine! lol

[thomthom]

Re: Need a little Help: Why are these renderings so blotchy?

Thanks yet again Damien for such a detailed and yet clear explanation. I really wish that the VfSU manual explained every parameter as well as you do on these forums! I might make it a little mission of mine to collect all your descriptions and re-post them in one thread, I'm sure it would benefit everyone and save you some time answering questions like mine! lol

Yea, collecting these answers is a good idea. I've been thinking that myself.

[dalomar_cg]

Re: Need a little Help: Why are these renderings so blotchy?

Well there are several reasons why they're not in the manual, with the first one being that I didn't have all of the knowledge I currently do when the manual was translated. Secondly, putting these into a book isn't as easy as just putting them in there. There has to be a flow and continuity to the ideas...right now you guys say "what about this specific thing" and I answer it...much simpler than trying to give things a logical and discernible order. Thirdly, the book itself wasn't aimed at advanced users worrying about the intricacies of how V-Ray works. You guys will read these responses, but a user who just picked up V-Ray would be utterly baffled by these responses and they would be practically useless to them.

As always I suggest taking a look at Spot3d.com ...It has all the information on every individual setting, and although you don't get the connection between settings, knowing what they do is more than half the battle.

Although an "Advanced" manual would be great, its also a ton of work to put it together. As it stands these responses typically take me a while to write and they are more often then not just the tip of the iceberg. I would like to write it, but I'm doing way to much on a day to day basis to take it on. As side project it would have more of a possibility of working out I guess.

[karamouza]

Re: Need a little Help: Why are these renderings so blotchy?

Vray's control panel is way too complicated and even a slight difference in a value (say from 1.50 to 1.75) is capable of changing the result dramatically. The whole procedure reminds me the (good ?) old days back in the early '90s when almost no program had a real GUI panel.
Now I'm an architect and not a programmer and nowdays we are used in a much more simple approach, that's why we use sketchup in the first place
I like the renders produced with vray which is a very powerfull tool and you guys do a tremendously good work, but I find myself wasting precious time fiddling with lots of abstract numbers (honestly now, "HDRI with DMC AA at 0.4, 0.85 & 1" ?) and settings and waiting for results based on trial and error, instead of working after all.
IMHO the whole Vray control panel needs to be redesigned from scratch and everything has to be replaced with scrolling bars (Artlantis style). And a preview window SHOULD be there too! Otherwise I could use Kerkythea which btw it is still free...
I KNOW that this post does not belong here, but you have to understand that I get a little bit more frustrated every time I search for an answer to my problem and I get solution which to me is so abstract. I have to comprehend something so, next time I will avoid doing the same mistake.
As for steelers05, nice job man, I particularly like your wall mounted lights result and your trees. I would love to know how you did those.

[Jackson_cg]

Re: Need a little Help: Why are these renderings so blotchy?

I've got say that as an architect myself (and also having a very unprogrammer-like brain) after a few years of using Vue (which has a pretty good slider-based GUI with lots of previews) as well as the Maxwell SU plug-in I actually didn't mind V-Ray's complex and parameter based UI simply because most of the bundled visopts produce excellent results with no or little tweaking.

It's worth bearing in mind that the render in the first post of this topic is a very unusual type, brightly lit, black background with very bright materials. For more common daylit renders V-Ray rarely runs into such problems IMO.

As much as I myself have criticised how much is left out of the V-Ray manual, it does cover the most important parameters (especially min and max rates in Irradiance Map) and a quick read gave me just enough understanding to produce renders as good as any other render program out there in a fraction of the time. The fact that V-Ray could render out a daylit interior at 1400px wide in under 30 minutes compared to Vue which would run overnight to produce inferior results (or Maxwell taking 3 weeks on a single image!) the time spent experimenting with a few parameters was easily paid for by getting out batches of renders overnight rather than telling my boss "it'll be finished rendering sometime next week" and leaving a big note on that machine saying "DO NOT TOUCH- RENDERING!".

As a biased renderer V-Ray will always have a fairly complex interface (Kerkythea also has many obsure unintuitive settings which take some mastering), but the good news is that Damien has revealed that V-Ray's GUI is in for a fairly major overhaul with the next version, I for one am really looking forward to seeing it.

[dalomar_cg]

Re: Need a little Help: Why are these renderings so blotchy?

Karamouza,

Most people completely agree with you...so we're changing it with the next version. There will be a tiered interface where you can choose how much of all that stuff you actually see. A basic one with just a few sliders and significantly fewer choices. An intermediate one with a few more exposed and a few more choices. An an advanced one which would be exactly the same as what you'd see now.

For now if you want things really easy I'd say go 1 of two ways...the first would be to use the visopt settings that ship with VfS as a basis for any settings that look complicated. The second would be to switch to a progressive mode which is a "set it and forget it" thing (similar to maxwell or fry) and you won't have to worry about any sort of settings with that (but it does take a lot of time). If you want to do things that way its just a few quick adjustments an you'll be on your way.

[thomthom]

Re: Need a little Help: Why are these renderings so blotchy?

That's very interesting to hear.
I was having a conversation this week with some of the architects at work where we talked about how most render applications had a UI that was very technical and exposing all the knobs and levers and that they wished they instead had a more simplified and more intuitive way to use them.

It'd certainly be a very good selling argument if the UI is simplified. In my experience with architects they want to use and create 3D render apps for visualisation, but really do not want to spend alot of time to learn all the technical workings of it.

[steelers05]

Re: Need a little Help: Why are these renderings so blotchy?

I have to say that I still am looking for some sort of solution to this problem, but I am having more success when I start to apply real materials; the splotches pretty much dissappear but that does mean that I dont want to resolve the white issue, because U can create a lot of good renderings with all white scenes or massing studies in white that look very clean and professional. I tried some of the suggestion but had little success. I wonder, and dalomar you may know, if the problem is the way SU handles v-ray and geometries... it reminds me of a previous thread talking about how hard it is to get caustics working in SU compared to 3DS max. Now i have not worked with vray for max yet, but it seems that v-ray works cleaner and more predicatable within max. I could be wrong and I am not trying to bash vray for SU because it is by far my favorite app, but it just seems that max can accomplish the same things as SU can, but a little better and if you ran a rendering that had the exact same settings in both apps that it would turn out a little more realistic in max.

As for the interface, i like the idea of being able to have more or less options but I would be very dissappointed to see a simpler interface with less options for a rendering. There are a lot of architects that do not want to have learn as much for a rendering app but illustrators still want that extra bit that gives them more control and realism. I think more literature or video tutorials could really help, but I understand how much hard work is going into everything. To be honest though you asgvis guys may want to think about this, but I would pay for video tutorials and I am sure many people would too. They would really help if you guys could find the time to create them. I do know that a v-ray book was coming out that was written for i believe max, but helped explain practically every switch and characteristic of vray and it is practically the same for SU. Can anyone tell me if the english verion of it is out yet? because I really want to get my hands on it. But thanks for all response guys.

Karamouza: Thanks. I am still working on a final image of this, but when I am done I will explain any questions anyone may have. Keep your eye on the gallery, I hope to be done someitme soon.