Irradiance Map Min/Max settings question

[TONKA201]

I understand that these setting have a connection to the clarity and gainyness of an image so...my question is do higher negative numbers mean a cleaner image?

example:
would min -4 max -3 be a cleaner image than min -1 max 0?

what are some other settings that can clean an image of grain/noise?

thanks in advance for any clarity to this question.

Scott

[dalomar_cg]

Re: Irradiance Map Min/Max settings question

Well, there are several comments to make about your question. The first being that there are several types of noise in V-ray. Noise, pertains to artifacts due to inaccurate or insufficient calculations. That means that each different type of calculation will produces a different type of noise. What I'm getting at is that the noise from Irradiance Mapping is rarely described as being "grainy" but more often said to be "splotchy". So if you'd describe the things that you don't want to see as splotchy, then thats probably an IR issue. But if they are grainy, then chances are it comes down to some sort of qmc or brute force sampling issue.

So back to IR. The way IR adaptively samples an image is by processing it at varying resolutions. What this means is that and Max Rate (or Min) of 0 will sample the image at the resolution that it will be rendered. Negative values will sample at resolutions lower then the image, with each step down (from 0 to -1 or from -1 to -2) being half of the resolution that was before it. Positive values will sample at resolutions higher then the image, with each step up being double the resolution. In most cases, having positive values for IR aren't very efficient, so 0 is the maximum I typically set things at.

The Max Rate is always going to set your quality because its the most refined the calculation will be. The Min rate will determine how many different levels will be sampled. As you can guess, the more levels that are set, the more adaptive the IR calculation will be. And for the most part this holds true, but there are issues with having too many levels, most of them being that either an area will have too few samples or that in search for samples during reconstruction of the IR map, samples will be taken from areas they shouldn't. So the general rule of thumb is to have between 3 and 5 sampling levels, or prepasses. So for a max rate of 0, 3 prepasses would be a min rate of -2 (0,-1,and -2) and 5 prepasses would be a min rate of -4 (0,-1,-2,-3,and -4). Keep in mind that the number of prepasses don't dictate the quality, because I could have 3 prepasses with a min/max rate of -1,1 and -7,-5...a max rate of 1 isn't the same as a max rate of -5

The other place where you can tweek IR is through the H.Subdivisions. This is going to determine the quality of each individual sample with lower values being faster, but noisier, and larger values being slower, but more accurate. I've found that sometimes there are allot more artifacts due to wrong/insufficient IR min/max rates as well as the reconstruction of the IR samples. So where others have used H.Subdivisions to smooth out those artifacts, if you have your min/max rate set up right then you can probably afford to skimp on those a little more. The exception to this is interiors, as they will typically need more subdivisions then an exterior or studio scene will.

[TONKA201]

Re: Irradiance Map Min/Max settings question

Thank you very much for this very good description. This is a very big help. I will play with the settings and see what I come up with.

Scott