Hi Guys,

I have added the gamma correction a background (Surface shader) with 0.4545. And with the mental ray physical sun & sky created. It auto created mia_exposure_simple gamma correction node for me.

A) My question, is the surface shader appear darker when the MR sun & sky is used. Is there anyway I work around other than adjust the gamma on the lens shader, mia_exposure_simple on my camera.
I tried to tweak the gain, it managed to adjust it to picture original color & tone but. everything else is over exposed now.

B) And is it a bug or something that MR sun & sky doesn’t work well with surface shader?

C) Are there any ways to solve this issue? ( I know we could handle it in post using render layers and mask it out)

Thanks in advance!

OceanCookie 12 May 2011 01:11 PM

B) And is it a bug or something that MR sun & sky doesn’t work well with surface shader?

No, it’s user error.  A surface shader does no shading calculation of any kind.

I’m not at my Maya computer at the moment so I can’t test this, but my guess is that the Surface Shader uses RGB values of 0 to 1.  When you are using Physical Sun & Sky the values are much much much bigger.  You should be able to keep the Physical Sun & Sky and the Exposure settings at their default, and just go into the Surface Shader “out color” and crank up the “V” value to something very high.  Try V = 10, 50, 200, 500....etc… until you start to see it in the render.

3ds Max 2013, Maya 2013
Windows 7 Ultimate 64 Bit
Core i7, 12GB RAM
Nvidia Quadro FX 3700 (Driver 267.17)

Valen Wagner 12 May 2011 02:55 PM

I’m not at my Maya computer at the moment so I can’t test this, but my guess is that the Surface Shader uses RGB values of 0 to 1.  When you are using Physical Sun & Sky the values are much much much bigger.  You should be able to keep the Physical Sun & Sky and the Exposure settings at their default, and just go into the Surface Shader “out color” and crank up the “V” value to something very high.  Try V = 10, 50, 200, 500....etc… until you start to see it in the render.

Thanks Valen, I think my earlier message was a little confusing. What I meant was I actually attached a node file to the surface shader’s out color; it’s a picture to use as a background.

It was working fine with the brightness and tone everything with the spot light & MR Image Based Lighting. Except the MR Physical Sun & Sky.

Thanks

In that case try cranking up the “V” value for the “Color Gain” and/or “Alpha Gain” within the “Color Balance” section of your file texture.

3ds Max 2013, Maya 2013
Windows 7 Ultimate 64 Bit
Core i7, 12GB RAM
Nvidia Quadro FX 3700 (Driver 267.17)

Valen Wagner 12 May 2011 04:31 PM

In that case try cranking up the “V” value for the “Color Gain” and/or “Alpha Gain” within the “Color Balance” section of your file texture.

It works! I tweak the colour gain V value to 2.5. it get the results I want. Thanks!
But mean while I found out the main cause of the issue; mia_exposure_simple, but I don’t really know how to solve it under its own tab.

I realize that the default gamma correction to the lens shader, mia_exposure_simple is set to default. (As I stick to the linear workflow, gamma correction.)

Pedestal: 0
Gain: 1.0
Knee: 0.5
Compression 2.0
Gamma 2.2

I tried to tweak the Knee to 0.5 to 1.0, the surface shader picture looks as good, just like the result of the method you suggested but everything just over exposed. (without the MR sun &sky )

Then I realize, when I created the MR physical sun & sky, it auto replaces my lens shader with the new mia_exposure_simple but the values are different:

Pedestal: 0
Gain: 0.2
Knee: 0.75
Compression 3
Gamma 2.2

With this value, the things as mentioned is too under exposed.
So I tweak the same value as the default one but everything except the surface shader picture, just over exposed again.  But if I let it remain and just tweak the Colour Gain V value, it works well.

I also found out that mia_exposure_simple shader created with the mr physical sun & sky is connected. The connection is mia_exposure_simple3> mia_phsycialsky1.miskyexposure. But I couldn’t find the connection under the attribution tab,

Is there anyway we could tweak the connection like replace with another lens shader?

So after all the best way is the adjust the V” value for the “Color Gain” ? :D

So in conclusion of the solution, basically, I just tweak colour gain value from 2.5, And the values of lens shaders, mia_exposure_simple, I let it be default, be it Mr physical sun & sky or just other lighting methods.

Thanks for the helps!  :)

I am curious - how exactly are you using a Surface Shader as a “background”...?

Another lens shader is the mia_exposure_photographic.  I like this one better - it has more options.  But you will have to manually set it up after creating the Physical Sun & Sky.  Here is a link to a very useful script that sets it up for you.

http://kobayashystips.blogspot.c...ographic-ae-template.html

3ds Max 2013, Maya 2013
Windows 7 Ultimate 64 Bit
Core i7, 12GB RAM
Nvidia Quadro FX 3700 (Driver 267.17)

Hi Valen,

So sorry for the late reply, i was busy with other works. Here a sample of it, i didn’t do much after it.

I was supposed to create a realistic ocean, so I intented to use a surface shader as my background for sampling, please let me know if you have better ways. ^^

(Mountains is a jpg with surface shader, then the ocean is the maya shader)
Thats how’s it supposed to use, but i don’t know if it’s good or worse for using this method. Thanks again

Do you have a piece of geometry that you’re using as a background?  Your surface shader is assigned to that?  Were you first using “Image Based Lighting” and then later you clicked the “Sun & Sky” button?

Do you mind zipping and uploading your project to this site?

3ds Max 2013, Maya 2013
Windows 7 Ultimate 64 Bit
Core i7, 12GB RAM
Nvidia Quadro FX 3700 (Driver 267.17)

Valen Wagner 24 May 2011 05:39 PM

Do you have a piece of geometry that you’re using as a background?  Your surface shader is assigned to that?  Were you first using “Image Based Lighting” and then later you clicked the “Sun & Sky” button?

Do you mind zipping and uploading your project to this site?

Sure, my work isn’t that good :D I only spent hrs tweaking the ocean but it still doesn’t look real yet :D (let me sort out and zip it, could I delete and add files from my profile? )

I have a polygon, then attached a surface shader to it, and the surface shader’s file is the mountain & sky that you seen in the picture.

Actually, i couldn’t remember, if i don’t remember wrongly, i tried both ways, images based lighting & the sun & sky, both way 1st follow by e other, as long it’s physical sun & sky, it will affect the lens shader.
(the new mia_simple_exposure’s setting is tweaked and link to the sun shader & the lens, along the way, it affects the surface shader, i guess the only way is to create my own custom physical sun & sky shader, since there’s no ways to tweak in Maya hypershade nodes.)

Do you want to see the shader nodes difference when the physical sun & sky is created?