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Old 04-05-2010, 02:28 PM   #1
nectario
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Default What is wrong with this Porsche?

Hi,

I have a black Porsche model, which I am trying to render it using mental ray in Maya 2011. I'm placing it with Sun and Sky created in mental ray. I selected the all the maximum quality settings: Production Quality, Global Illumination, Final Gather, Refractions, etc. etc.. When I render it, the car comes out grayish/blueish. Below is an example:

http://www.nektarios.com/Black_Porsche.jpeg

Even though the car is black, why does it look grayish/blueish? I tried everything to make it look black, but to no avail. Keep in mind this only happens with the Sun and Sky setting turned on in Mental ray. Your helps is appreciated! Btw, the material on the paint is Phong.

Thank you!

-Nektarios
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Old 04-05-2010, 03:17 PM   #2
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thats exactly how its meant to look...when you use Physical sun and sky you will get the ambient bleed of the sky which of course is blue , to make it less noticable change the time of the day so the sun is lower in the sky to either morning or evening and possibly change it to a winter month too . If you want it black then you need to do a studio render .
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Old 04-05-2010, 03:28 PM   #3
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Thanks. So how can I get the shadows in the Porsche appear blacker then? I still need it at an outdoor setting.

Cheers,

-N.
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Old 04-05-2010, 03:44 PM   #4
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You could lower the gamma. If you open up the hypershade and goto the utilities tab you should find a node called mia_exposure_simple. If you click on this it will open up the settings where you can try lowering the gamma to make the render darker.
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Old 04-05-2010, 03:49 PM   #5
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Thank you! :-)
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Old 04-05-2010, 04:35 PM   #6
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I really wish that the physical sky was implemented properly because everyday someone will run into this problem. When the physical sky is created, it attaches a lens shader to the camera to control the exposure(else you'll see exactly how bright the sun is) and that lens shader also has a gamma property and that is set to 2.2 which is the default gamma on monitors (the physical sky setup assumes you are working in a space where the gamma is 1.0 also known as linear space).

The thing is, when you choose colors from the color picker or use or your jpeg and other 8 bit textures they already have a gamma of 2.2 embedded (or else they won't look normal and pretty to human eyes), so now, you have your colors and textures being hit twice by a gamma of 2.2 which causes the washed out look. You can fix this by countering the embedded gamma, plug in gamma utilities(as you would with any other texture) into your shader(excluding bump, normal and displacement maps) then you can use the gamma node's value to plug the textures or change the color. The gamma node's "gamma" should be set to the inverse of 2.2 which is .45454545454 or you can round that to .455

Apart from that, I think part of your problem is the fact that your car is highly and equally reflective regardless of viewing angle so it's showing a lot of everything else but it's diffuse color and car paint doesn't do that. If you were to browse the mental ray materials section of the hypershade you should see carpaint shaders.
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Old 04-05-2010, 04:53 PM   #7
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Wow! Thank you!!! VERY insightful! I will do that and see what the outcome looks like... :-)
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Old 05-05-2010, 01:32 AM   #8
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I re-rendered with all suggestions. Much better! :-) See image below!
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Old 05-05-2010, 03:45 AM   #9
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Huge improvement, good job!:nod:
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