Beer glass scene creation
This course contains a little bit of everything with modeling, UVing, texturing and dynamics in Maya, as well as compositing multilayered EXR's in Photoshop.
# 1 03-11-2011 , 03:08 PM
goggles's Avatar
Registered User
Join Date: Sep 2011
Posts: 219

White background Render problem. Mental Ray Final Gather & HDRI light studio 2.0

I have been testing some render settings for final gather and HDRI image based lighting, to get a perfect result. I would like to use this setup for my white background white floor with soft shadows or reflections. But I am getting an unwanted white highlight below the object and a white hue problem.

My workflow and settings:

1- Create two spheres. Apply basic mia_material, change color to red. The rest of the settings for mat is default.
2- Create a plane, apply "use_background" on the plane. In the "use background attributes" i set the specular color, reflectivity and reflection limit to 0.
3- Create a camera, position it. In the camerashape1 > mental ray settings, i add a mia_exposure_simple for lens shader. Set pedestal to -0.01
4- Open up render settings, and in common tab> render options i uncheck "Enable Default Light"
5- Under "Indirect Lighting" tab i check "Final Gathering"
6- Final Gather Settings: Accuracy:300 Point Density:6000 Point Interpolation: 40 Secondary Diffuse Bounces:2
7- Under Quality tab, Raytrace/Scanline Quality > Max sample lvl: 2
8- Under Quality tab > Frame Buffer > Data Type: RGB(Float)3X32, Gamma : 0.45
9- Under Indirect Lihting, I create an Image Based Lighting sphere and add an HDRI image created in HDRI light studio with a single 500 watt light source (the one seen on reflection on picture)

Now if i hit render, i will get a plane reflection on the spheres. But the result will be like this, without any bottom sphere highlight or a white hue at the bottom half of the sphere. The reflection of the floor on the spheres is actually blocking the white hue at the bottom half of sphere, but still if you look carefully you can see the continuing white hue on top of the floor reflection border.

user added image

To get rid of the floor reflection on the sphere i go to pplaneshape render stats, and uncheck "visible in reflections." When i render like this, i have good soft shadows on the floor, but theres a white hue on the red sphere. And a white border highlight at the bottom of the sphere.

user added image

I need to get this hue and highlight dissappear and make the background and floor white without blowing the gamma and hdri light gain.

Now i think its a floor+gamma or exposure setting issue. But further this point when i try to change settings, gamma or IBL color gain settings to get a white background, i cant get a balance....

If anybody can give me a tiny little information othis it would be great. Thanks user added imageuser added image

# 2 03-11-2011 , 04:37 PM
honestdom's Avatar
The Nurb Herd
Join Date: Oct 2007
Location: London
Posts: 2,381
Hey there,
I'm not very clear on what you are saying but from what i can gather you want rid of the grey on the bottom of the sphere?
did you try unchecking final gather cast on the plane render stats? I'm quite crap at working out what the problem is if i don't have the scene in front of me.

btw, if you ask me your FG setting are massively high and you don't need to use a "useBackground" shader.

# 3 03-11-2011 , 05:14 PM
goggles's Avatar
Registered User
Join Date: Sep 2011
Posts: 219
Hi. Thanks for your reply and advice. I changed the FG settings low. Accuracy: 50, density 0.5. Also frame buffer back to 1. The problem is, i dont have a light in the scene. The only thing i use is FG and the Image Based Lighting (the built in option) sphere.
I changed the floor to a plane with white colored lambert. Turned off cast FG, and visiblty on reflections.
Now i get this grey background and white floor. The reason i get this grey background is bec i created a grey background image in HDRI light studo 2.0.
In maya i try to set the color offset value of IBL, to pure white from black. But this time i get blown whites on sphere.
By the white hue i mean, theres a white reflection on the second image i posted. And at the bottom of the sphere theres a white highlight at the borders. (Shouldnt it be black?) I am confused.... I need to solve this white background photorealistic image lighting soon. Hope we can solve this : /

# 4 03-11-2011 , 06:01 PM
daverave's Avatar
The thin red line
Join Date: Aug 2009
Location: England
Posts: 4,472
There is nothing stopping you from putting a light in there to cast shadow, from the same direction as you image light..........dave

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