Gamma (LWF Method2)

[HMA_Steve]

Hello,
Finally getting round to having a look at this and I seem to have got my head round the general principles but do have a quick question:
I'm using Max 9 and 1.5 RC3. Most of the older posts ive read talk about changing the max prefs to use gamma at 2.2 but I notice in RC3 there is the option to specify a gamma value under the colour mapping for Linear Multiply. My question is can I just specify 2.2 here then use the colour correct map on any of my texture maps that are not at the correct gamma (all my old ones) and render? Surly it’s more complex than this?
Cheers,
Steve

[HMA_Steve]

okay so my method above would seem to be correct if i want the gamma 'burnt' into the image. It also seems there are numerous ways of doing this.

I have now calibrated my monitor and set everything up and using an old internal job have rerenderd (after reducing the light intensities beacuse of the increased brightness the gamma gives) i have to say that it tends to make images quite flat and lacking in contrast. Is this somthing that other have found?

[glorybound]

LWF .255

Good question.

I have been using this method with good results and I have gamma in max and color mapping set to 2.2. It has worked so far and it doesn't seem to make things flat.

[instinct]

when setting colourmapping gamma to 2.2 you burn in the gamma indeed. So you're rendering linear and save out the linear rendered image as sRGB. That's fine when working with non-linear enabled apps such as photoshop as they cant handle the linear images anyways. If you are working with linear apps (like nuke) then you would leave it off and work with the linear images throughout.

Regards,
Thorsten

[glorybound]

GAMMA

So working in MAX/VRAY/PS would you have both MAX and Vray's gamma set to 2.2?

[HMA_Steve]

if your using rc3 with the the gamma setting under colour mapping then you only need to change the gamma in one of the two, either vrays colour mapping or max prefs. if you do both im pretty sure your just applying the gamma correct twice. At least that my understanding.

[glorybound]

gamma

the next image I do I'll unceck max's and let you know.

[instinct]

mind you that they are the other way round. So if you set BOTH to 2.2 this is what happens :

The image is rendered linear and you need to take account for that in both your lights' brightnesses as well as your maps and color brightnesses. The rendering WILL be different though even when converted back to sRGB space as vray will render differently in LWF. By turning the colourmapping gamme o 2.2 what you do is actually INVERSING the Gamma on the final image (as a post process) to save out the correct gamma pic for using in PS etc. (same as the sRGB button in the VFB just for saving (the sRGB button is only for previewing in the VFB).

So leaving the max one of will lead to not rendering in LWF. and with the Gamma 2.2 in the colormapping this will brighten and de-contrast your image pretty heavily without actually rendering differently (colormapping is actually a post process unless you use "Affect adaption only" in newer betas.

If i am talking bullshit somebody pls correct me, but that's how i understood things and how we work.

Regards,
Thorsten

[glorybound]

gamma

I turned the gamma in vray off and my image is way dark. When I pick the sRGB in the frame buffer it returns to as if I had the gamma at 2.2 in vray.

[HMA_Steve]

Isnt gamma a post effect no matter which method you use?
My understanding of this whole LWF/Gamma corection thing is that basically you are rending the physical sceen much darker - which help vray in terms of speed and acuracy and then your apply the gamma correction to that darker image to bring up the brighness in a more acurate way post rendering? or have misunderstood this?

[instinct]

VRay actually behaves differently in LWF. If it was a pure postprocess then it would be rather pointless i'd guess. Esp. Shadow distribution is different in LWF. The sRGB button is a postprocess for viewing, the colormapping is a post-process that is burned in into the saved image. LWF does NOT help in terms of accuracy! Au contraire! Mostly it will actually undersample the image a lot, as it is darker and hence the sampler decides to use less samples. That's why there is a "Dont affect colors (adaption only)" switch in newer builds that allows you to make Vray use the gamma setting for the sampler only.

Regards,
Thorsten

[HMA_Steve]

so Lukx video tutorial is still the best way to set up LWF even in RC3 then?
thanks for your help

[lukx]

Okey let me expalin this a bit better. It works like this:

1
max preferences:
Gamma 2.2
Input gamma: 2.2

Bitmap files
Input Gamma : 2.2
Output Gamma: 1

vray color mapping settings:
gamma correction 2.2

rendering using VFB: you got burn in gamma 2.2
rendering using max frame buffer: image got double gamma but when saved from MFB it's with correct gamma 2.2




2
max preferences:
Gamma 2.2
Input gamma: 2.2

Bitmap files
Input Gamma : 2.2
Output Gamma: 1

vray color mapping settings:
gamma correction: 1 (or linear 1, doesn't really matter)

rendering using VFB: you got dark image with gamma 1
rendering using max frame buffer: image looks correct, got gamma 2.2 but when saved from MFB it's with gamma 1 (it's dark)




3
max preferences:
Gamma 2.2
Input gamma: 2.2

Bitmap files
Input Gamma : 2.2
Output Gamma: 2.2

vray color mapping settings:
gamma correction: 2.2

rendering using VFB: you got burn in gamma 2.2
rendering using max frame buffer: image got double gamma and when saved from MFB it's saved also with doubled gamma (wrong)




4
max preferences:
Gamma 2.2
Input gamma: 2.2

Bitmap files
Input Gamma : 2.2
Output Gamma: 2.2

vray color mapping settings:
gamma correction: 1 (or linear 1, doesn't really matter)

rendering using VFB: you got dark image with gamma 1
rendering using max frame buffer: image looks correct, got gamma 2.2 and when saved from MFB it's also with correct gamma 2.2



So i't up to you if you want to use burn in gamma, VFB or MFB or just the saves to be correct. Hope this helps.