|
|
Vray Tutorials |
|
|
Please don't translate or copy these tutorials elsewhere. I don't like the tutorials to float around in 10 different versions and places on the net. Feel free to link to this page of course! (see also Terms of Use)
This is a free tutorial!
Please click on the Paypal donate button if you want to support this site and help me creating new tutorials.
|
|
|
| Back to Vray tutorials page |
Standard studio lighting setup |
| Page 1 - Page 2 |
Before you start
If you discovered this Vray tutorial page through a direct link or search engine, please note that you're on page 2 of the tutorial! Please complete page 1 first if you haven't done so.
|
|
8. Noise!
You're probably wondering why the images are so noisy and take pretty long to render. This is because Vray area lights produce raytraced area shadows, and these are very processor intensive. The noise is coming from the low subdiv value in the lights properties.
Because we are using adaptive qmc AA, it is necessary to use high subdivs values for the area lights to get rid of the noise. Try 30 subdivs for both lights and render again. You can see the result in image 1 (click to enlarge)
Now go to the anti aliasing settings and change to adaptive subdivision AA with min/max=0/2. With this anti aliasing sampler, you can use lower subdivs than with adaptive QMC to have a similar noise quality. So change the lights subdivs both to 10 and render again. This is image 2 (click to enlarge)
|
 |
9. subdivision vs QMC
At first sight, you might think the adaptive subdivision image is better (less noisy). But if you look closely, the noise is just different, not 'better'. In the shadow area you get a 'blotchy' kind of noise, compared to the QMC example which is sharp constant noise.
The top image is the adaptive subdivision AA, the bottom one is the adaptive QMC AA.
|
 |
10. Reduce the noise
We will now try to reduce the noise for both image samplers to see which one is the fastest for high quality images.
Set image sampler to adaptive subdivision AA, min/max=0/2
Adjust subdivs for both lights to 30 and render.
The image is noise free. If you zoom in a lot, you can see a tiny bit of the blotchiness.
Now change to adaptive QMC AA, min/max=1/4
Adjust lights subdivs to 36.
In the QMC sampler rollout, change the noise threshold to 0.002. The adpative QMC AA is very sensitive to the QMC sampler settings. The noise threshold is the most important one. (QMC sampler controls the quality of all 'quasi monte carlo' related calculations. In short, all subdivs settings are qmc related, except for lightcache subdivs)
If you zoom in here, you can also see a bit of noise, but sharper and smoother than the blotchiness of adapt subdiv AA.
But in this case, adaptive subdiv AA wins from adapt QMC AA. When you will add more complex materials like glossy ones, and more area lights, fine textures, displacement maps etc, rendertimes for adaptive QMC will not rise as fast as rendertimes with adaptive subdiv AA. Usually when you have lots of glossy effects (also DOF, motion blur,...) it is better to use adaptive QMC AA. |
 |
11. Store with irradiance map option
Like I said, the reason for the noise are the raytraced area shadows. Especially for test rendering, we can easily disable them.
The light coming from a Vraylight (or also from standard Max lights) is called 'direct' light. This means it is not GI light (first or secondary bounce). Once this direct light hits a surface, it bounces back a bit (depending on how dark and reflective that surface is). That bounce is called the 'first' bounce, and it is calculated by the irradiance map (because we have set first bounce GI engine to irradiance map).
But the Vraylight has an option 'store with irradiance map'. This option actually means 'treat direct light as first bounce GI light'. Instead of casting direct light, the Vray light will now cast first bounce GI light and thus it will be calculated by the irradiance map. This also means that when it hits a surface, and bounces back, it will become secondary GI light, and it will be calculated by the secondary GI engine, QMC GI in this case.
So by setting the Vraylight to 'store with IR map', the result will be that there is no direct light anymore, only GI light. This means that all shadows will also be created by the GI light. The consequence of this is, that shadow quality doesn't depend on the Vraylight subdivs anymore, but the it is controlled by the GI settings, namely the irradiance map (and QMC GI for secondary bounces). This is important, the Vraylight subdivs do absolutely nothing if 'store with IR map' is checked!
(note that this option only works if IR map is set as first bounce GI engine. If you have for example QMC GI for first and second bounce, and lights with the 'store with IR map' turned on, these lights will not cast any light!)
To illustrate the store with IR map option, I rendered two images with the 'show GI only' option (global switches rollout). This option renders the image only with the GI light, so without any direct light that may be present in the scene.
The first one is with normal Vraylight (without 'store with IR map' option).
The second one with the 'store with IR map' option turned on.
You clearly see that in the first example, with the direct light extracted, there is not that much GI light to be calculated. And in the seond example, all light is GI light.
This step is very very important, you should really understand the difference between 'store with IR map' turned off or on, and the difference between direct/first bounce and secondary bounces. |
 |
12. Store with irradiance map option (2)
The disadvantage of this option is that there will be more first bounce GI light, but worse, also more secondary bounced GI light (calculating detailed GI light, especially second bounce, is very processor intensive). This means you have to rely on IR map and QMC GI calculations for the creation of nice shadows. In product renders this is not such a big problem, because there will not be much secondary bounces anyway. Light that hits the top of the spheres for example (=first bounce), will bounce back (second bounce) right into the sky. So this second bounce will have no effect on the rendering. Only a bit will bounce in between floor and objects, or from one object to the other. But the secondary bounces will not have such a big influence on lighting and shadow creation.
This will become more of a problem in interior scene lighting. There, the second bounce will not go to the sky, but it will probably hit a ceiling or wall, bouncing again and again... So in these scenes, the secondary bounces do have a great impact on final lighting look and shadows. So in this case, it would be a good idea to reduce the amount of GI light, by replacing the first bounce by direct light ('store with IR map' turned off). Think about it, instead of relying on first bounce GI light to start with, you now start with direct light which will illuminate a lot of the scene already (quality is perfect, it is direct light), then there is first bounce (ir map) and then second bounce. I will show this in the interior lighting tutorial.
To summarize, for product renders you can greatly benefit from the store with IR map option, as there are not much secondary light bounces. You will need to improve the IR map settings, resulting in longer GI calculation, but the actual rendering of the image will be a lot faster, as there are no difficult area shadows to render anymore. The total rendertime (GI calculation + raytracing the image) will be a lot lower than when you use true raytraced area shadows (here GI calculation will go faster, but actual raytracing will take a lot longer, so combined total result is much longer).
See top image with following settings:
- adaptive QMC AA 1/4
- noise threshold=0.002 in QMC sampler rollout
- IR map: see settings below top image
As you can see, rendertimes are cut in half, and compared to the raytraced area shadows examples, there is absolutely no noise at all! But shadows are a bit less precise.
Go to the IR map settings and change the min/max to -4/-3 and the hsph subdivs to 20. In the QMC sampler rollout set noise threshold to 0.005 again. These are very fast testrender values. Render the image again. Notice how less detailed the shadows are now (bottom image, spheres look like they float a bit). But hey, 11.3 seconds is not bad for a fully antialiased image :-) |
 |
13. The end
This concludes the studio setup tutorial.
By now, you should better understand the difference between adaptive subdivision AA and adaptive QMC AA, the effect of the 'store with IR map' option, and how to create a simple efficient studio lighting setup.
Save this scene so you can reuse it in some of the other tutorials still to come. |
|
| Page 1 - Page 2 |
| Back to Vray tutorials page |
|
|
|
)
)
)
)
)
)
)
)
)
)
)