Caustics and linear workflow?

[marvsweden]

I've been trying to create good looking caustics for a pool. Read all the tutorials I could find and started create my own model but I wasn't able to create good looking caustics. After days (!) of tweaking all settings for caustics, the v-ray sun and displacement maps I found out that the linear workflow option seems to play a big part in the equation. Can someone explain that? When I deactivate "Linear workflow" in the Color mapping settings the caustics become ugly. I figured it was down to the displacement map's gamma value, which I believe is the only thing in my model that's being affected by the linear workflow tick-box, but applying a 0.454 value to it doesn't have a noticeable effect on the caustics. If I go the other way applying let's say a gamma 2 value it makes things even worse. Is there something I'm missing regarding caustics and linear workflow, gamma and/or color mapping settings?

Here's an image of the Linear workflow tick-box activated except for the middle section of the image where that same box is un-ticked. All other settings the same.

[peerman]

I'm not behind my computer right now, but you could try to enable refractive Gi under the GI tab. Maybe it helps.

Regards

[marvsweden]

Thanks peerman.

Your input was very interesting. I didn't think of GI being involved since I thought caustics was only affected by direct lighting.
Here's a new screenshot. This time all other settings are the same and I did no tweaking of the displacement map. It's quite clear that the GI-settings has an effect on how the caustics are perceived.



I still can't get my head around this. Maybe the "problem" isn't a big one and I could just tick the linear workflow box, live with it, and the caustics are all good. However, I would like to know why the caustics are affected by the tick-box and I'm used to working without it, using universal settings for my rendering and so on.

I thought the linear workflow tick-box "only" applied the inverted gamma to the materials in the scene. If so, I would be able to create the same look of the caustics without the linear workflow tick-box active by applying the inverted gamma-value of the materials in the scene, right? They all have gamma = 1. What value should I apply then?

Any input is much appreciated.

[fpedrogo]

In term of gamma, we have to control or correct the gamma for two thing, color and textures. In V-Ray for Sketchup we have two way to control the gamma. One is to correct the color and textures separated using "Correct LDR texture" (to correct just the texture) and the "Correct RGB color" (to correct just the colors). The other method is using the "linear workflow". As you mentioned, this liner workflow will apply the invert of the gamma to the colors and textures at the same time. Which is what we need to get the correct result. Otherwise we are going to be over gamma. By default, in the texture editor it said that the gamma is 1.0 for all the textures. However this is not the actual gamma value of the textures. As you know most of the images that we use as textures on the materials has gamma 2.2 baked on it. So, that value 1.0 in the gamma means that we are going to use whatever the gamma of the images are, as my default gamma, which it is 2.2. So, gamma 1.0 in the texture editor, really means gamma 2.2. There are some exceptions in term of the default gamma for textures. In V-Ray for Sketchup and Rhino don't correct HDRI, EXR, nor images any other images format when you are using them on GI(skylight), Reflection/Refraction (background), lights and emissive material. That is why if you use for example a .jpg in the emissive layer, you will have to manually invert the gamma in the texture editor (instead of 1.0, we should use .4545 or select sRGB as the gamma mode) to get the correct result.
V-Ray also use the gamma for the sampling process. If the gamma is not correct the sampling process will be different. In the test that you are doing, the render with the correct gamma (using linear workflow) the caustic is good. The other renders have the incorrect gamma (over gamma, brighter) V-Ray has to sampler those render different in term of the amount of samples, etc. That is why the caustic look over bright (wrong gamma).
The reflective and refractive caustics check box are to produce caustics through the GI (GI caustics). The secon test where the caustics is over bright with the Refractive check box enable make sense, because you are calculating GI caustic (from the GI) and direct caustics (from the sun). An again, it is over bright, because the wrong gamma (over gamma). If you compare the color and gamma of the wood texture with the color and gamma of the renders, you will notice the gamma issue.

Please see attached images

Best
Fernando

[marvsweden]

Thank you so much for clarifying things Fernando!

If I'm not reading your reply wrong, it would mean that I would be able to create the same looking caustics without the active Linear Workflow tick-box as long as I apply correct gamma to both textures and colors (of the materials that only use a diffuse layer with RGB-colors), right?
That would make the sampling process work and make sure my colors and textures look the same?

[fpedrogo]

Why you don't want to use Liner workflow or Correct LDR textures and Correct RGB colors? Why you want to correct everything manually if V-Ray can do that work for you? If you want to save the images in linear space (gamma 1) then you just have to enable the option "Don't affect colors (adaptation only). This will use correct gamma for the sampling, but it will not bake the gamma on the image. Then you can save the image as .exr to have a 32 bit image.\
But, to answer your question, yes. If you manually correct everything, you should get the same result as if V-ray correct the gamma for you. The problem are the colors. You will need to use a texture with the color that you want to correct in order to be able to manually correct the gamma to that color.

[marvsweden]

Thanks again Fernando,

I'm still learning here. Somewhere along the line I started disabling Linear workflow since I thought my textures became over saturated. I just felt that they looked better with Linear workflow off but maybe I was wrong and maybe it had to do with lighting or some other settings, I'm not sure. I never liked how colors and textures were displayed in the Sketchup viewport. I think I'm starting to get the hang of it now, thanks to your replies.

[fpedrogo]

Hi
At the end of the day, this is why I love V-Ray. You have the freedom to get what ever the effect you want. If you like to disable linear workflow and correct the textures manually, go for it. It is about taste.