Vray 2.0: Physical cam v.s. exposure control? Vray color mapping? confused!

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  05 May 2011
Vray 2.0: Physical cam v.s. exposure control? Vray color mapping? confused!

Hi guys,

I am a bit of a newbie to Vray after being a long time MR user within 3ds (max 2010 currently).

I briefly used Vray 1.5 before recently upgrading to 2.0. In 1.5 I understood that you got your exposure control only via using the Vray Physical Camera, since there was no Vray specific global exposure control (such as the excellent MR Photographic Exposure, although I suppose you could use one of the other exposure control systems, i.e. "Logarithmic Exposure Control" but they all seem poor). With the advent of Vray 2.0 I see this has been rectified and Vray has ity's own fully featured exposure control to use via the "Exposure control" dialogue within Environment and Effects window.

Am I to take it that this makes the Vray physical cam basically redundant? I certainly find it easier to use exposure control globally like this, rather than tying it to a single camera (and therefore any renders done in my standard and often used Perspective view come out wrong). Is there any point in using the Vray Physical cam at all? I know perhaps this is an easy way to get motion blur / DoF, however I still find doing this kind of stuff in post more sensible/flexible.

On top of this, where should "Vray Color Mapping" come into the equation? I am not used to this feature as there was no real equivilent within MR (it seems like the kind of stuff that MR exposure control deals with, Burns/Midtones/Shadows etc). I see in older tutorials it is common to use Vray Color mapping, but with more fully featured exposure control is this another thing that is redundant?

I am just trying to get a feel for a good workflow here - I don't want to learn the ins and outs of the Color mapping if it is on it's way out!

Any help or general advise would be most appreciated!
John
 
  05 May 2011
Yes, its redundant, just another option to do the same thing. If you prefer a global exposure control, thats what it is made for, but its also good to have the option of using exposure in the camera like it used to be, sometimes you have a scene with great difference in light intensity from different places, so in this case its nice to have different cameras with different exposures in the same scene.

And about the color mapping, the equivalent in mental ray is indeed the "Burns/Midtones/Shadows", its just a another way to translate the pixel intensity from the render to RGB levels. The default is to work in linear space, thats the way I like to work, but I agree that lots of people like to tweak the color mapping, that is like working with curves on post and thats why I don't like to use it in the render, I also rather to do this kind of post work in the post production.

Also you may like to read aversys tutorial about vray and gamma, I work much the same way its describe there to get a "pure" render from vray and tweak what its needed in post:
http://www.aversis.be/tutorials/vra...al_gamma_01.htm
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  05 May 2011
Thanks that is all really helpful! good to clarify the use of the Color mapping in particular (your link makes clear that there are advantages to doing Color mapping with Vray rather than just in post).

So you tend to set the max gamma/LUT to 2.2, as well as the VFB to 2.2, with input/output as 1.0? Does this mean your images rendered in your frame buffer look different to what max outputs, and you have to tweak them in post (or save them with the 2.2 change burnt in)?

I must admit all this gamma stuff has always confused me a little, I have a rough grasp but I don't see why more of this stuff can't just be under the bonnet (you put in a figure of 2.2 and it does all the rest of the work for you, making sure your all your texture bitmaps are 2.2 regardless of whether they are 1.0 or 2.2 or anything else on input, and making sure your final rendered image is 2.2 as well).

Cheers
John
 
  05 May 2011
In my case it will depend on what I will be doing in post and how much time I have to finish a job. If I'm in a hurry, I just use max frame buffer and set the output to 2.2.
When I have time to work in post production, I render to EXR in 16-bit or 32-bit and in this case it will be linear 1.0.
Most of the time I leave the gamma in max to be input/output in 2.2 and use the override in the bitmap dialog to choose when I need to import a displace or output an EXR with gamma 1.0.
Just remember to enable the sRGB button on the vray frame buffer, and these are the other settings I use most of the time:


Cheers!

Flavio
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  05 May 2011
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