display gamma in RT

[simmsimaging]

devin: I understood your issue to be one of matching framebuffers and gamma, not comparing the two rendering engines, so I'm sure your gamma stuff is fine. The differences you are showing there can probably be tightened up by matching your GI engines and some upping the tracing.

Not sure what Chaos Group's position would be, but it's probably worth remembering that this is billed as a *preview* engine, so differences are to be expected, and it seems obvious to me that *some* test renders and fine-tuning are to be expected - just fewer of them. If that RT preview is unacceptable for you then your margin on it is far tighter than mine, but it's your call of course.



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[devin]

No I'm not saying it's unacceptable I just wanted to know if the RT preview is supposed to match what is coming out of the VFB. If it's not supposed to and there are going to be slight differences then I can accept that, I just want to be clear.

[rmejia]

I just wanted to know if the RT preview is supposed to match what is coming out of the VFB.

There are some comments regarding that in this thread:

http://www.chaosgroup.com/forums/vbu...ad.php?t=45628

Posts #16 and #19

[simmsimaging]

My experience so far has been that there can be slight differences, but it's hard to predict in advance what they will be, other than that they are usually minor. I tend to run RT for a while and when I'm getting close to happy with a mat or light position (say 90% there) I run a quick Vray render to see how it stacks up and make sure I'm on target. If all is good I go back to RT. If not I may keep the difference in mind and continue with RT for a while anyway for speed, or at that point I switch to VRay to finalize. All depends on what I'm doing.

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[vlado]

Here ya go.

The differences you are seeing are because of the differences between the sRGB and gamma 2.2 color space. While both images are quite close in linear space, they are displayed differently in the V-Ray VFB and the 3ds Max ActiveShade window. The differences are typically most noticeable in the dark regions of an image.

Best regards,
Vlado

[devin]

That's good to know, thanks Vlado and everyone else I appreciate your help.

[jujubee]

I'm pretty sure I use the same method as Steve and Devin. The point of this method is to 'burn in' LWF into the final image versus applying sRGB afterwards.

Gamma & LUT Preference settings:
1) Enable Gamma/Lut Correction.
2) Gamma 2.2
3) Affect Material Editor
4) Input Gamma: 2.2
5) Output Gamma: 1.0

Vray Settings:
1) Max FB: off
2) Vray FB: on
3) Dark Multiplier: 1.0
4) Bright Multiplier: 1.0
5) Gamma: 2.2
6) Affect Background: checked

Results:
1) The intended result is rendered directly in the VrayFB. This is LWF burned in.
2) This method does NOT using the sRGB button at all.
3) If you use the MaxFB, the image will be double-corrected using this method. Hence it is turned off.
4) ActiveShade preview looks 'washed out.' It is directly affected by Max Preference Gamma setting set to 2.2.

I am having the same problem as the original poster. The ActiveShade is much brighter/washed out then rendering to the VFB. In this example, I'm using a Vrayblend material. You can see that the sky is darker in the VFB, the ground is a slightly darker, and the carpaint is blown out.

I just threw together the scene quickly - didn't really mess with camera and lighting settings.

[stevesideas]

I'm pretty sure I use the same method as Steve and Devin. The point of this method is to 'burn in' LWF into the final image versus applying sRGB afterwards.

Gamma & LUT Preference settings:
1) Enable Gamma/Lut Correction.
2) Gamma 2.2
3) Affect Material Editor
4) Input Gamma: 2.2
5) Output Gamma: 1.0

Vray Settings:
1) Max FB: off
2) Vray FB: on
3) Dark Multiplier: 1.0
4) Bright Multiplier: 1.0
5) Gamma: 2.2
6) Affect Background: checked

Results:
1) The intended result is rendered directly in the VrayFB. This is LWF burned in.
2) This method does NOT using the sRGB button at all.
3) If you use the MaxFB, the image will be double-corrected using this method. Hence it is turned off.
4) ActiveShade preview looks 'washed out.' It is directly affected by Max Preference Gamma setting set to 2.2.

I am having the same problem as the original poster. The ActiveShade is much brighter/washed out then rendering to the VFB. In this example, I'm using a Vrayblend material. You can see that the sky is darker in the VFB, the ground is a slightly darker, and the carpaint is blown out.

I just threw together the scene quickly - didn't really mess with camera and lighting settings.

Thats exactly right. This is the exact setup I have for the vrayFB. I dont use the maxFB and dont have to press the SRGB button as the gamma is burnt in. However, the vrayRT is definately producing a double gamma image. Could a gamma parameter be added to the vrayRT rollout ?

[vlado]

Thats exactly right. This is the exact setup I have for the vrayFB. I dont use the maxFB and dont have to press the SRGB button as the gamma is burnt in. However, the vrayRT is definately producing a double gamma image. Could a gamma parameter be added to the vrayRT rollout ?

Yep, we'll have to figure a way around this.

Best regards,
Vlado

[jujubee]

However, the vrayRT is definately producing a double gamma image. Could a gamma parameter be added to the vrayRT rollout ?

I'm not sure if it's quite double gamma. It seems very 'close' to double gamma. The reason I say that is because when I did hit the sRGB button, it was slightly brighter than the VrayRT preview.

If there was only some way to render ActiveShade within a VFB instead of MaxFB... (independent docking.)

[devin]

Oh, ok, I see now.

What I normally do is:

(*) have 3ds Max display gamma to 2.2, sRGB button in the VFB ON, V-Ray gamma 2.2 and "Don't affect colors" to on, OR
(*) have 3ds Max display gamma to 1.0, sRGB button in the VFB OFF, V-Ray gamma 2.2 and "Don't affect colors" off.

In both of these cases the RT preview accurately reflects the rendered image. However in your case it is more complicated, I have to think a little if it can be adjusted to show the ActiveShade/regular 3ds Max RFW properly.

Best regards,
Vlado

Vlado,
I have gone back and changed my settings to reflect what you suggested and although the VFB and the Active Shade images are much closer in appearance there are still significant differences when compared side by side. Your comments lead me to believe that when you view these images together there is no difference, if that's true then I must still be doings something wrong because I've yet to be able to get a accurate result. It's not just material colors that are different, lighting is different even if I use Brute Force. So is simmsimaging correct that because this is a preview engine we shoulden't expect it to match up with what's comming out of the VFB?

[vlado]

Can you send me an email to vlado@chaosgroup.com with some more details about your setup? Ideally a scene that demonstrates the issue would be best. It would also help me to determine what needs to be changed/fixed in order to avoid the problem, if there is any.

Best regards,
Vlado

[simmsimaging]

So is simmsimaging correct that because this is a preview engine we shoulden't expect it to match up with what's comming out of the VFB?

Just to be clear - it's not that I don't think it should match, and be quite close. I just think there's some acceptable room for variation.



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[devin]

I understand what you're saying, it's just my belief that if your using this to figure out what your scene is going to look like it should match up with the final output. Unless there is a technical reason it can't do this then it should match.

[simmsimaging]

No arguments there - not much point in it otherwise However, expecting a super exact match is tantamount to expecting Vray to be more or less obsolete (assuming RT is not just limited to lo-res etc.)

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