Rendering problem with reflections.

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Old 01 January 2013   #1
Rendering problem with reflections.

Hello,
I have a problem with rendering. It happened to me quite often, that parts of the rendered picture doesn´t look good - especially materials with one color and reflections. See the enclosed picture. What might it be? It happens even if I render in 16bit. These two examples have AA best 8x8 and GI with IR+QMC medium quality.
Thank you in advance!
Jiri
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File Type: jpg render_problem.jpg (30.8 KB, 62 views)
 
Old 01 January 2013   #2
There is definitely something going on with reflections. They appear to be posterized.

We ran a test just a few days ago because we were getting posterized output in our reflection passes when doing multipass renders.

We tried in R14 physical and standard render and in R13 as well.

The reflection pass always looks posterized.

It's puzzling and I'm surprised we had never noticed it until very recently.
 
Old 01 January 2013   #3
if its the same problem i think its the normal lights (if you have any in scene)
the more lights you add the better the render looks.
even if you just duplicate the 1 light and just lower the intensity so your using multiple lights for 1 light source.
im just saying this as a workaround
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Old 01 January 2013   #4
Confirmed here...
Just ran a test though and a 32 bit reflection pass does not seem to be posterized.

Anyone else?
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Old 01 January 2013   #5
I found that when rendering multipass with linear workflow, you needed to also use linear output in the 'save' area of the render settings. This stopped banding in the multi-pass (non multipass/ RGBA render was always fine).
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Old 01 January 2013   #6
Hello,

thanks everybody for the advice. It seems to be really some problem with multipass image (and linear workflow). If I save the output in 32bit Multipass then everything works fine. If I save it in simple PNG, everything works as well.
The problem is with 16bit or 8bit multipass image (or even with the RGBA layer!). The reflections there seem to be really posterised.
Thats pitty. My 8bit Multipass has 120MB, 32bit multipass has 1,9GB :(

Jiri
Attached Images
File Type: jpg render_problem_02.jpg (39.9 KB, 8 views)
 
Old 01 January 2013   #7
I think this is the same issue I was describing. It is fixed by outputting in linear colour space too.
Under the Render Settings -> Save -> Image Colour Profile, the default is sRGB. So you work in linear space then output to sRGB.

If you change it to Linear, then you are working in linear & outputting in linear.
When you do this, you will see banding in the picture viewer but when you open your render in photoshop or other application (as linear workspace), you will see there is no banding anymore (you must be at 100% zoom).

This affects only multipass renders. I had the same issue & it took some googling & tests to find out how to fix it.

If I'm wrong, I apologise but it does sound exactly the same issue.
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Old 01 January 2013   #8
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