Exposure Control and Render Elements (Mental Ray)

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  10 October 2012
Exposure Control and Render Elements (Mental Ray)

Hey guys, I'd appreciate some help with something our team has been struggling with the last few days.

We need to kick out several render elements for one of our animations, such as specular, reflection, diffuse, indirect lighting etc. Our normal render comes out fine, but when I examine the render elements themselves, they are very blown out (and very orange.) After a little investigation it turns out that the exposure control is the culprit. Everyone seems to be suggesting that the solution is to turn off exposure control, or to correct these images in post. I've been kicking them out as 32BIT EXR, which has been useful correcting them in After Effects, however I've never achieved a very good way of getting the colour back to the original render, it's always slightly off. It feels like I'm doing it in a bit of a hacky way, and I'd appreciate if someone could let me know if I'm doing the wrong thing. I'm using exposure and Levels on separate channels to get the colour back to normal levels.

And if I turn the exposure controls off, this goes against a lot of stuff that I've learnt in Max. Does it really matter? Is it ok to have your lights just really dark or really bright to compensate for the lack of exposure control.

What's the best way to go about this? Ideally I'd like to have exposure control, and a simple way to correct the images in After Effects.

A little enlightenment would be greatly appreciated, thank you.
  10 October 2012
Hi Harry,

the problem is the physical scale value. If you exposure the image need you the correct physical scale for the render elements (passes), because the passes are rendering without exposure controll. In Photostudio have you the option "delete BG overbright". This options adjust the physical scale value for the new exposure. Then can you render the passes this correct brightness.

Photo Studio Free Version: http://www.infinity-vision.de/page/ps_free_version

hot chip
  10 October 2012
Ah brilliant, thank you very much! It seems to be working, the images are of the correct exposure, however the Temperature value doesn't seem to affect the render elements? They're still really orange.
  10 October 2012
Hi Harry,


"Highlihts burn" + "Midletone" + "Shadow" + "Temperature" + "Vignetting", must you do in the Post production.
  10 October 2012
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