Maya 8.5 Sun/Sky Rendering Bad

[Emil3d]

“But if I compare the 8bit render in RenderView with the 32bit render in Photoshop for some reason there is a difference. It’s not a BIG difference but there is. Why? In theory they should be exactly the same, don’t they?”

No, on theory they should not be the same.

[dagon1978]

There is nothing wrong in your setup. In your case the framebuffer gamma of 0.454 corrects the gamma of 8 and 16 bit textures. It will not have any affect if you don’t have these kind of textures in your scene. Another thing to be aware with this setup is that the color swatches do not mach the output. The colors will render lighter.

yep, and the displacement/bump maps are linearized too, so they works in the wrong way

[leif3d]

yep, and the displacement/bump maps are linearized too, so they works in the wrong way

So emil3d says the setup if fine, but dragon says that this setup will also linearize my displacement or bump which may work in the wrong way?

Was he referring to the swatches only?

Should I just stick to de-gammaing my color textures and not my value textures with gamma nodes and just keeping my framebuffer at 1?

I just want to have 32bit float control in post in the most color accurate way possible.

…I’m confused again…

[Emil3d]

leif3d, in other words, your setup is OK if everything in your scene is textured and you don’t have 8 & 16 bit textures that drive values like bump and displacement maps.

As I said, the color swatches will render wrongly. You can fix that, as you already know, by creating gamma nodes with correct color and 0.45 gamma and then plug them into the color input of the materials.

If you have 8 & 16 bit textures that drive values like bump and displacement maps, as Dagon noted, they will render wrongly too, since they don't need to be gamma corrected. In such case you shouldn’t use the Framebuffer gamma. You have to put it back to 1, and as an alternative, you have to attach gamma nodes to all 8 & 16 bit textures ([i]except value textures[/i]) in addition to the color swatches. 

I hope I’m not confusing you more, since I’m not very good at explaining things:)

[sixbysixx]

yep, and the displacement/bump maps are linearized too, so they works in the wrong way

No, I don’t think this is true.

As far as I know (and experienced it myself), setting the framebuffer gamma only affects color textures, but not parameter/value driving textures like bump or displacement.

Christoph

[Emil3d]

Christoph, honestly I haven’t tested this exclusively and I haven’t seen the effect of wrong displacement and bump, since all my displacement and bump textures are 32 bit created in Mudbox and this bypasses the problem. However what Dagon noted makes sense unless Mentalray is intelligent enough to see which texture is used for what. Are you sure that in your tests you displacement and bump were 8 bit textures?

Will this thread ever reach some unanimously accepted conclusion?

[dagon1978]

No, I don’t think this is true.

As far as I know (and experienced it myself), setting the framebuffer gamma only affects color textures, but not parameter/value driving textures like bump or displacement.

Christoph

I’m going to add my two cents here.

In case textures are involved, note that mental ray applies gamma correction to all output images that are not floating-point, and applies reverse gamma to all non-fp input textures.

AFAIK there is (at least in 8.5) currently no way to block the reverse gamma of non-fp input textures from within mrfM except by disabling gamma correction at all in mental ray.

p

…which is exactly what you want a good 99% of the time. Except for bump maps and displacement. So while this is a good try at “automatic under the hood”, it’s not 100% automatic under the hood.

The problem is that the color swatches in Maya aren’t gamma corrected, so the colors you “see” aren’t correct.

[…]

/Z

but you can see it by yourself, take a render with bump/displace and a lens shader with gamma 2.2 (so the textures are not linearized at all) and take it with fb gamma .45, you’ll get a different render

[sixbysixx]

but you can see it by yourself, take a render with bump/displace and a lens shader with gamma 2.2 (so the textures are not linearized at all) and take it with fb gamma .45, you’ll get a different render

Bloody Hell - I was sure I had figured this out. :rolleyes:

I did some testing again - this time with Displacement and Bump (in the past I tested only displacement)

Setup 1: a torus with a 16bit black to white gradient as a bump texture.
Result: there is indeed a big difference between rendering FB 0.45 Lens Gamma 1
and FB 1 Lens Gamma 2.2 - wow.

Setup 2: a torus with a 16bit black to white gradient as a displacement texture.
Result: there is a tiny shading difference between rendering FB 0.45 Lens Gamma 1
and FB 1 Lens Gamma 2.2, but I fail to register any difference in displacement between the two and that was also my conclusion from the past.

Did anybody else test this? Do you really see a difference in displacement between different frambuffer settings?

Cheers and sorry if I added to the confusion!

Christoph

[dagon1978]

Bloody Hell - I was sure I had figured this out. :rolleyes:

I did some testing again - this time with Displacement and Bump (in the past I tested only displacement)

Setup 1: a torus with a 16bit black to white gradient as a bump texture.
Result: there is indeed a big difference between rendering FB 0.45 Lens Gamma 1
and FB 1 Lens Gamma 2.2 - wow.

Setup 2: a torus with a 16bit black to white gradient as a displacement texture.
Result: there is a tiny shading difference between rendering FB 0.45 Lens Gamma 1
and FB 1 Lens Gamma 2.2, but I fail to register any difference in displacement between the two and that was also my conclusion from the past.

Did anybody else test this? Do you really see a difference in displacement between different frambuffer settings?

Cheers and sorry if I added to the confusion!

Christoph

i’ll investigate a little more on this subject tonight

[leif3d]

Thanks for the help everyone.

I’ll try and keep my value textures a 32bit float and my framebuffer at .454, because I don’t really care about my swatches. As long as it renders fine I’m ok.

The only crappy thing with that workflow is that I can’t use procedutal textures, because I would have to de-gamma everything and keep the framebuffer at 1…which is what I’m trying to avoid with really heavy textured scenes.

But oh well…you can’t have everything you want…

[JayHoo]

Hi,
how can I improve my renderings with regard to the contrast? Is the mia_exposure_simple node the thing to play with? With area lights I get good results but I need the physical sun in this still.

Thanks for your advices.

[leif3d]

The mia_exposure_simple lens shader will give you necessary control for contrast and brightness to produce a nice render.

There is very detailed information on the docs regarding each option and functionality.

[yagaio]

Well, it works for me… all I did was unchecking ‘Preview Tonemap Tiles’ in the render globals, choosing a 32bit buffer and openEXR as file format.

But you can clearly see the problems occuring when doing a gamma correction using the lens shader. Instead, leave the mia_exposure’s gamma at 1.0, and set the framebuffer’s to 0.455 and you should be fine. I’ve attached the edited scene.

first,if i say wrong,please correct me.

i think you havenot anser his question at all~,you just solve it in other way,i think the pivot is not here,his box colour is set=1,the gamma corecction is not do anything to col=0 and 1,just take effects in (0-1,not include 0 and 1),if his box col =0.5,i think the node"gamma correct"will take effects. he will see different between use node"gamma correct"to box’s col and not use

this is 2009’,i have just seen the all of this ,thank for all you have done!
and i think he has know the anser in 2007,my anser is too late~

[EightBit]

THANK YOU THANK YOU THANK YOU
for this thread. It took me an hour and a half to read just half of it, but I wouldn’t have figured this stuff out in a million years.
For anyone else who finds their way here, here are the minimum settings (in the MR Render Settings Tab) to gamma correct your renders and preview them correctly when liting and texturing.

Once rendered the linear gamma must be accounted for in other apps.
To change the gamma to 2.2 in PShop, Image/Adjustments/Exposure/Set Gamma to 2.2
and in After Effects, Interpret Footage/Main/Color Management Tab/Interpret as Linear Light set to On.

[Aneks]

Should I just stick to de-gammaing my color textures and not my value textures with gamma nodes and just keeping my framebuffer at 1?

This is really a key thing that I am trying to get my head around. From what I have read on LAMRUG and on 3Dlight blog and other sources I am fairly certain that changing the Framebuffer gamma is not the right way to work.

I really wish mental images and Autodesk would come out and do some sort of official tutorial or documentation on this. Rather than leaving it for the user base to stumble through their confusing controls proceedures and naming.

Anyway. I did a bit of an email with Zap Anderson mentioned I was using framebuffer gamma set to 1 and mia_simple_exposure gamma set to 1 and was told that this was correct.

My question is to people like Dragon and Floze who seem to have a really good handle on this.

I am guessing that framebuffer gamma .454 is just a convenient way to remove gamma from textures globally rather than an ideal workflow?

How does framebuffer gamma .454 effect non-colour channel textures such as specularity, bump/displace and prebaked occlusion ?

I don’t work as a 3d lighting TD so I am still trying to come to grips with all this !

[Hamburger]

Anyway. I did a bit of an email with Zap Anderson mentioned I was using framebuffer gamma set to 1 and mia_simple_exposure gamma set to 1 and was told that this was correct.

Okay, now you have really confused me!

Personally I just use this method:

Framebuffer gamma: .454
Lens gamma (mia_photographic): 1

This way there is no gamma correction nodes involved with textures which dramatically cuts down on workload and also gets rid of those annoying error messages when rendering. I only have to add gamma correct nodes with swatches which is no big deal compared to the amount of textures in a scene. Also…David Johnson discovered that textures blend differently when using different methods and that framebuffer does work the best.

http://www.djx.com.au/blog/2008/10/06/linear-workflow-and-gamma-update/

This is my take on it and it works for me, however the best way is to not use any sort of gamma correction until post and render to 32bit. That’s the “true” way I guess.

[Aneks]

hey,

I have been reading his blog, really great work. Have learnt a lot from it. Looked at the comparison he did between colour blending at 2.2, 1 and .454. I think its a great comparison but personally I think the light banding effect you get at .454 is undesirable. Similarly wouldn’t putting framebuffer .454 effect all bump/displacement/spec shaders as well ?

If the ideal workflow is .454 in mental ray I am prepared to be wrong and work accordingly !

I am just trying to bring out a ‘true’ linear workflow. Am used to working this way with renderman and as I am a film compositor have been dealing with this stuff in Shake and Nuke for many many years ! It just seems Autodesk is being very lax in their implementation and that there is a real lack of official information about this stuff !

PS I see he is from Melbourne as well ! Represent

[_LuxX1]

OKe i got an other problem with the sky and sun.

I have an animation where a ship is sailing trough the ocean.
( just an normal ocean with wake and emiter)
When the ship sails it will give a foam trail, only here comes the problem.
everything is rendered correctly ( i setted the frame buffer) Only the foam isnt white but transparant grey or something like that.

i tryed with light linking, setting textures etc etc… how do i get this foam to the normal colour?

[djx]

With sun/sky you get much brighter illumination, and you rely on the exposure node to make it look right. The problem is that the foam is like a surface shader and is not affected by the lights, so it’s color value needs to be increased to bring it into the same exposure range as everything else. You can make the foam color super white. I just tried it with mia_exposure_photographic and a foam color value of 50000 looked about right, but it is very much dependant on how you have your scene setup, so just try some bigger numbers until it looks right.

– David

[_LuxX1]

Superb!!.. i was just watching a tutorial where they also explained that it was possible to crank up withe. i putted it to 20 now and it looks good

great men thnx!