pixelated and artifacts when compositing in photosho

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  10 October 2013
pixelated and artifacts when compositing in photosho

I did my first propper atempt to composit my render passes and layers. I rendered in Maya and composited in Photoshop, using layer mask, levels, color corrections, etc. When i did it, it started to pixelate and get ugly colored artifacts here and there, not smooth and nice.
So does anyone have any suggestions or tips for me how to avoid or work around this? Im thinking the issue might be in rendering, but i dont know. I dont have alot experience with rendering yet either.
  10 October 2013
It sounds to me like you're using some destructive techniques in 8-bits per channel mode. Every time you apply a color correction to an 8-bit image, you lose a little bit of color fidelity. This adds up very quickly, resulting in banding, noise, and halos. Take a look at your histogram—if it has a sawtooth appearance, then you have probably been throwing away data.*

You can mitigate the problem in three ways: Use adjustment layers rather than applying color corrections with the Image / Adjustments menu. This allows non-destructive color operations.

Convert your layers to Smart Objects, so that filters are also non-destructive.

Work in 32 bits/channel mode to avoid data during color corrections. Even if your original layers are only 8-bit, you still get a lot of benefit from using the higher precision color space.

Unfortunately, putting your work into 32-bit mode disables a lot of tools. Photoshop is seriously lagging behind the rest of the world in that respect.

*Here's an experiment to see exactly what benefit 32-bit mode gives you. Create a new 8-bit document and fill it with a gradient. Open Levels. You should see a pretty smooth, filled in curve in the histogram. Move the gamma up or down drastically and apply it, then open Levels again. You'll see the sawtooth pattern in the histogram that I mentioned.

Now do the same experiment, only in 32-bit mode. When you open Levels the second time, you should still see a filled-in histogram—no sawtooth. A 32-bit channel has enough values that you can perform color operations as much as you like and never have to throw away data—thus, fewer artifacts. Obviously, you can still make a right hash out of the image with destructive changes, but at least you won't have banding and halos!
Bryan Ray
  10 October 2013
Thanks for that answer, i will experiment some with this. I just wonder as i dont have much experiene yet on this area, just to be sure, to work in 23 bit channel, is that something i have to set before i render or just switch it over in Photoshop?
  10 October 2013
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