Caustics quality

[Thomas An._cg]

Caustics quality

I had to try PPT and see how it goes. It seems that speed-wise it is comparable to Maxwell. This image took 35 hours and still has some noise to resolve, so if left to go up to 60 it would be quite good ...


Now, I want to see if I can use 15000 photons (as Wouter suggested) and replicate this PPT image in 1.5 hour (instread of 35)

The only problem I have with Vray so far is that we can do tests with low parameters to get a feel of the illumination, but then even after bumping up the parameters to high quality and wait for an hour we may still end up finding out that the image still has blotches and then have to start over again.

[flipside]

Caustics quality

Once you're used to it, you won't have that problem in 99% of the cases. Only with caustics like here, you can have problems. But normal GI renders, you know after a while what will produce good/bad results. Especially product renders require almost the same settings everytime.

For example I always use QMC AA at 1/4. Then for glossy reflections I always use 20 to 30 subdivs. While test rendering, I set noise th in qmc sampler rollout to 0.5. When I want a good render I set it to 0.002 and I know for sure my glossies will be noise free. Same for GI quality, this varies of course with arch viz interiors vs product renders.

You can always do a region render of a problematic region with your supposed-to-be-good-settings and see if it's good enough. If it is, just do the full render. I use the region render (renderinwindow) all the time for testing.

[flipside]

Caustics quality

Oh, I used 12500 for caustics, not 15000, small mistake

[Thomas An._cg]

Caustics quality

Thanks Wouter

Good idea about the region render, didn't think of that. Will definately put it to good use.

Thanks about the photons tip too. I did try 15000 earlier today but for some reason the memory usage exploded to almost 1.5 Gb and windows started paging the drive a lot, so I stopped it. I think somewhere I show an option in the photon settings that clamps the maximum photons and prevents this sort of thing from happening... will have to give it a closer look.

About the settings, I guess you are right ... once experience sets in it should be easier, but I do plan to use more reflective caustics in my scenes so I want to learn them quite well.

[flipside]

Caustics quality

These ware my caustics settings:
I used these caustics settings:
max photons=60
max density=0.01
multiplier=1
search distance=0.75

Max desnity controls ram usage a bit, the higher the smaller the caustics map.

Region render doesn't work to speed up photon mapped caustics, because the photon map is created for the whole scene always, unlike IR map or LC for example.

I would suggest using GI caustics and satisfy with less detail For scenes like this of course photon mapped caustics. One problem when using photon mapped caustics is that 'affect shadows' option for refractive materials is auto disabled, so no light will pass trough refractive objects, all this will have to be calculated by the photon mapped caustics.

[Thomas An._cg]

Caustics quality

Wouter,

Thank you once again

You are a great help here and you also help indirectly via your tutorials on your website. I appreciate it !

[Thomas An._cg]

Caustics quality

Wouter,

I have a question about the blurry reflections on the coins...

in my tests, it seems the only thing that affects the quality of the coin blurry reflections is the material editor under Reflection-->Subdiv.
However, when I bump the material subDiv higher (about subDiv=35) the render times go up exponensially. Is this the only way to improve blurry reflections.
(I have been playing with the QMC sampler, but it doesn't seem to affect that aspect)

[flipside]

Caustics quality

Ok, first of all, this scene seems to be a very difficult case. As you can see in my image and even better in your ppt example, there is something going on on the coins surfaces.


The left of that coin is smooth glossy reflection. But the right is not. I think this is because of the very strong small light, which creates problems for the QMC sampler.

I also can't get rid of this noise.

But usually you indeed control blurry reflection quality by the subdivs in the material, or with the QMC sampler settings. To be able to use the QMC sampler to the max, you should use QMC AA, then you notice the effect best. QMC AA is also faster than adapt subdiv AA if your scene has lots of glossies, area shadows, DOF, etc... Actually I always use QMC AA at min/max=1/4. I never change it!

Then you control the AA, glossies, DOF, MB, Area shadows, ... with the QMC sampler settings, together with material settings of course. The QMC sampler is a global quality control, while the subdivs on materials, or dof subdivs etc are controls for the quality of these individual effects.

In the QMC sampler, lower noise th is higher quality. There is a global subdivs multiplier too, altough I prefer to do it locally, gives me more control. Note that the QMC sampler settings also affect IR map calculations! The only things that are not affected are lightcache, photon map and photon mapped caustics.

Good quality for glossies is smth between 20 and 30 subdivs, same for area lights altough this depends on the size of the light too. If you then set noise th=0.002, you get very smooth results. For test renders, simply set noise th= 0.2, and global subdivs multi to 0.3 or something. That will render very fast so you can check lighting or material colors etc... I also change the ir map min/max for test renders, just lower them both. The hsph is lowered for your test renders by the global subdivs multi=0.3, so you can leave this at a high value if you want.

The global subdivs multiplier is tricky. If you have 30 subs on a glossy material, and you use a global subdivs multiplier of 5, this doesn't mean that your material will now render with 5*30=150 subdivs. 30 subdivs actually means 30*30=900. So globally multiplying by 5 means 5*30*30=4500. If you want the same quality for your glossy, but with global subdivs at 1 again, you should set material subs to square root of 4500=67!!!

Keep this in mind, because 150 or 67 subdivs is a really big difference Same goes for hsph subdivs and all other subdivs values that are controlled by the QMC sampler.

[Thomas An._cg]

Caustics quality

Wouter,

Excellent info again Thank You.

The global subdivs multiplier is tricky. If you have 30 subs on a glossy material, and you use a global subdivs multiplier of 5, this doesn't mean that your material will now render with 5*30=150 subdivs. 30 subdivs actually means 30*30=900. So globally multiplying by 5 means 5*30*30=4500. If you want the same quality for your glossy, but with global subdivs at 1 again, you should set material subs to square root of 4500=67!!!

This is the culprit, I would not have guessed this is how it multiplies. Makes more sense now. Thank You !

[flipside]

Caustics quality

That's why I don't use it, I only use it to downgrade quality.

If for example you want all your glossy materials to look a bit better, you would increase the global subdivs value. But you don't want hsph subs to increase, so you have to calculate the new hsph subs value to get same quality here. Same for area shadows, DOF, MB, etc... I would like to see global subdivs multiplier for seperate things like area lights, reflection glossy, refraction glossy, etc... That would be the easiest way imo if you want to increase all you glossies, or all your area shadow subs, all at once without affecting all other settings.

[Thomas An._cg]

Caustics quality

Oh, I used 12500 for caustics, not 15000, small mistake

Wouter,

I have found that the time stamp does not include the caustic-map calculation phase. In my test a map having lights of 8000 photons costs me 1hour just for the photon calc phase... so ... when you said 1.5 hour of render then you only meant the IR+LC .... but with your settings a 12500 photons a scene would have taken over 2hours (maybe 3) just for the photons alone and the memory usage would be enormous (so your total time should have been well over 3hours unless you are on a renderfarm).

This makes me curious because in my first image (beginner's lack) in only 2hours the caustic was getting good by IR alone and without shooting photons. So I still wonder if the caustics tab does any good after all.

I will try to replicate the settings of that first image (if I can remember them ) (Now I wish we had EXIF data in the images)

[flipside]

Caustics quality

Hi Thomas,

That rendertime was all inclusive. I didn't use the frame stamp, I read it from the command line, or is this wrong too?

I use a dual xeon 2.8 system.

Your initial test looks decent, but not clean at all. The small caustics patters are good, but the big reflections are really noise (big blotchy noise) and these are the hardest to clear up.

I agree that IR map is good enough, I would never need such sharp caustics anyway. Maybe I'll do another test, a more balanced one between quality and speed. I did the 12500 photons test just to get maximum quality out of it.

[Thomas An._cg]

Caustics quality

Hi Thomas,

That rendertime was all inclusive. I didn't use the frame stamp, I read it from the command line, or is this wrong too?

Indeed the command line is the correct one. hmm now I am puzzled.

This means that i am doing something wrong when setting up the caustics tab because with only 8000 subdivs on the lights I get 1 hour of caustic map calculation and I think I used conservative caustic settings:

• MaxPhotons = 10
  Max Density = 0.03
  Multiplier = 1
  Search Dist = 1

Well, I will look into it some more.

Material and DOF subdivs are 10 and multiplied by 30 (this is equivalent to 55 subdivs). Even at 55 subdivs the coins are not clean.

[Thomas An._cg]

Caustics quality

This time I wanted to find out if it is possible to do nice cautics using GI only (no photons) and how far would the settings would have to go to achieve this. I like GI caustics because they are easier to test with region render.

It turns out the most consuming part are the caustics that fall on the blurry parts of the coins. Those coins had to be boosted to 80 subdivs and the noise is still slightly there. It takes 15min/bucket to finish these coins

Overall the quality came out ok but the render time is not too good (18hours ). I do not think the use photon mapped caustics would improve the time by match... when I use Wouter's method (at 12500 subD) it takes my PC 4hours just for the photon map and then we have to go through the cautics on the blurry coins again (and we still have to boost the metals to 80 subDvs or more). So basically by using the photon method we are gaining some speed from the GI calculation but we are loosing it again on the photon map (in both cases we need lightcache and in both cases we need high definition materials for the blurry/caustic effects and in both cases the caustics on the coins will be the most time consuming operation).

[Thomas An._cg]

Caustics quality

It seems, this scene is my right of passage to Vray. If I can get this down to 2hours or less (at "milky smooth" quality) then I feel I can do anything with Vray...