In the next tutorial I will try to explain what parameters you need to control in order to obtain realistic caustic effects with 3ds max and vray.

Open the “caustics start” scene that you will find in this zip file.
As you can see, the glass material is already prepared:
-reflect 213:213:213 with fresnel reflections checked.
-refract 238:238:238
-IOR 1.44
-Affect shadows – checked

First, go to the “Vray: caustics” rollout and activate it by checking the box next to it.
If you render it at this stage you will end up with something like this:

The caustics effects are already visible but they have a fake look and lack definition.

The most important parameter that we need to adjust is the “caustics subdivisions” that are emitted by the light. For this, you need to right click on the direct light, choose vray properties and increase the “caustics subdivisions” from 1500 to 20000 and render it again.

The caustics are starting to look more real.
Now let’s see what other parameters do…

If we change the “search distance” parameter to 0.02 we will end up with something like following:

As it can easily be observed, smaller values produce much sharper caustics but a lot more noisy.
Higher values result in smoother caustic effects, but at the same time the higher the values, the blurrier they get.

After several tests, I am happy with a search distance value of 0.09 for this scene. The caustics still look a bit noisy, but we will try to adjust this by tweaking the “max density” parameter.

Max density is probably the trickiest parameter, and if you don’t understand how it really works, you can end up with unexpected and undesired results.

First, let’s do a test; increase the max density from “0” to “1” and look what happens:

Where did all the caustic effects go?
Take a look at the following diagrams:

If max density is greater than “0”, when vray needs to store a new photon, it will look if there is another photon within the radius specified by this parameter. If it finds one, it will just add the energy to the one in the map, in order to keep the photon map at a smaller size (case 2 of the diagram). If the area is too large the end result will look like there are no caustics in the rendering.
If no other photon is found within that radius, the new photon will be stored in the photon map (case 1 of the diagram).
After doing some tests, I think that a value of 0.002 works just fine for this scene.

In order to realize just how tricky this max density can be, leave it at 0.002 (that works fine at the moment, as seen in the rendering above) and increase the caustics subdivisions of the direct light to 50000 and run another test rendering.

You would expect better results, right? WRONG! The result looks exactly like the one with max density set to “1”. Basically by increasing the caustics subdivisions we ended up with more photons acting like “case 2” of the diagram.

Other parameters:
Multiplier – it makes the caustics brighter if increased, or less bright if a value lower than “1” is assigned to it. In theory you should leave it at “1” since it is supposed to give physically correct results.

Max photons – somewhat similar to “search distance”, but instead of using the distance between photons to interpolate, it uses a higher or a lower number of photons.

Mode – works almost like the irradiance map. You can choose “new map” to calculate it again, or you can save it once you are happy with it and load it later for further renderings.

Another important factor to keep in mind is that the looks of the caustics depend a lot on the geometry of the objects that cast them. For example if you want to render a swimming pool with caustics you need to model a realistic water surface (or at least a really good displacement map), otherwise it will not look natural.

Here is a list of 15 vray tutorials that I think everybody should read. It covers everything from materials and shaders to illumination and rendering settings.

(And yes, I have included 3 of mine tutorials in the list )

1) Critical vray  settings
Without any doubt, this should be the first one on the list. It’s an in-depth analysis of all the critical vray settings that affect your scene one way or the other. It covers topics like irradiance map settings, image sampler, lightcache settings and more.

http://3dats.com/Images/Tutorials/Critical_VRay_Settings_Part_I.pdf

2) How to create incredibly realistic grass
Although you will need a really powerful workstation in order to use the technique shown in this tutorial (especially if you have large areas of grass in your scene), the results are truly amazing.

http://www.peterguthrie.net/blog/2009/04/vray-grass-tutorial-part-2/

3) How to create a lampshade material
A tutorial that explains how to use the vray2sided material in order to obtain materials like lampshades, curtains, etc.

http://www.cgdigest.com/index.php/creating-a-lamp-shade-material-in-vray/

4) How to setup a sky scrapper rendering
This is a very interesting tutorial that shows you a very unconventional way to setup a rendering of a skyscraper at night.

http://www.pixelab.be/blog/2008/03/09/tutorialmaking-of-vincent-van-duysen-tower-in-beirut/

5) Night exterior illumination
A tutorial that explains, in a systematic way, how to setup the illumination for a night time rendering of a small villa.

http://www.cgdigest.com/index.php/night-rendering-tutorial-vray/

6) Daytime exterior lighting
A tutorial that reveals a method to light an exterior scene in vray, using image based lighting.

http://en.9jcg.com/comm_pages/blog_content-art-150.htm

7) How to render an architectural scene with hdri
A classic way to light an architectural rendering using hdri

http://www.cgarena.com/freestuff/tutorials/max/hdri-vray/index.html

Night interior rendering tutorial
An interior rendering tutorial that explains  how to setup a night illumination rig with vray

http://www.cgdigest.com/index.php/night-interior-rendering-tutorial-using-vray-and-3d-max/

9) How to render realistic snow with vray displacement

http://www.3dtotal.com/team/Tutorials_3/snow_displacement/snow_displacement_01.php

10)  How to setup and render convincing materials like chrome, silver, stone and glass

http://cg-india.com/tutorials/3dsmax_makkingof02.html

11) How to use hdr images (hdri) in vray
A tutorial that takes you through all the necessary steps to use hdr images in your scenes

http://www.aversis.be/tutorials/vray/basic_hdri_01.htm

12) How to render a liquid in a glass
Rendering a liquid in a glass can prove to be problematic. If you model it like in real life, the polygons located at the interior of the glass will be microscopically close to the geometry of the liquid, which can result in coplanar faces and therefore, artifacts when rendering.
Checkout this tutorial to see how you can avoid all that trouble.

http://www.spot3d.com/vray/help/150R1/tutorials_glassinterface.htm

13) Gamma 2.2 or Linear Workflow (LWF)
A very well documented tutorial that talks about every aspect of working with gamma set at 2.2
When this concept was introduced for the first time, it generated a lot of buzz. Most people couldn’t get it to work right and their resulting renderings had either the colors or textures washed out. This type of workflow is a bit different than the traditional way, so if you miss a step you get unexpected results.
Fortunately, this tutorial explains each and every step very clearly and it also sheds some light on the theory behind the concept of linear workflow.

http://www.aversis.be/tutorials/vray/essential_gamma_01.htm

14) Vray studio lighting tutorial
A comprehensive tutorial that explains how to create a studio lighting in rig in vray.
This is especially helpful for art directors or furniture designers.

http://cg-india.com/Tutorials/V-Ray/3dsMax_tutorial_SL_01.html

15) How to create various reflective shaders and caustics

http://www.cgarena.com/freestuff/tutorials/max/differentshaders/index.html

If you know more vray tutorials that you think I should add to the list, feel free to post a comment with links to them.

Even after a few years since linear workflow (also known as gamma 2.2 method) first “appeared”, there still is quite a lot of confusion around the subject.

This is caused by the fact that there are several methods to achieve the same result and several tutorials on the internet most of them explaining different workarounds.

In this tutorial I will try to show all the steps that I use for linear workflow (working with 3ds max and vray) and keep things as simple as possible.

Bellow there are 2 images; the first one is rendered without linear workflow while the other one is rendered using this method. Although the second one looks much more natural, due to the even illumination and without color bleed, both of the scenes have exactly the same number of lights with the same light multipliers.

Click on the image to view a higher resolution rendering

Step 1
Go to “Customize”, “Preferences” and click the “gamma and lut” tab.
Check “Enable gamma /lut correction”, type 2.2 in the field next to “Gamma”.
Under “Materials and Colors” check both “Affect Color Selectors” and “Affect Material Editor”.

Step 2
In the material editor, select one of the materials and click on the texture in the diffuse channel. In the Bitmap Parameters rollout, click on the path of the bitmap and in the pop up window, under “Gamma” check override and type 2.2

If you haven’t started the scene from scratch and you are using an older scene, you must repeat the step above for all the textures that you have used.
This is what most people forget to do and as a result they end up with washed out textures.

Step 3
Believe it or not, you are now ready to render
The only thing that you need to do when the rendering process is ready, is to save the file as an .exr format (you need a 32 bit image, not an 8 image).
If you need to convert it to a jpg, open the exr file in photoshop, click on “image”, “mode” and choose 8bits/channel.

Just out of curiosity, you can try to save the image as a jpg directly from the render. You will end up with a dark rendering. This is because the gamma is not burnt in the image, but with the settings shown in the previous steps, you have set 3ds max to display it correctly.

If for some reason you need to burn the gamma into the image, you need to activate the Vray frame buffer, and under the color mapping options change the gamma from 1 to 2.2
I really don’t recommend doing this tough, because of the loss of quality.

The advantages of working with gamma 2.2 are obvious… less lights are needed to setup a lighting rig for an interior scene, less color bleed, faster rendering times, etc.
I use this for almost every daylight interior scenes; for interiors with night illumination I tend not use it since I find it easier to get more “drama” in the renderings, the old fashion way.