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I'm trying to post-process my render to achieve a low color depth look. For some reason the image becomes darker and the render do not really matches the look I want.

Exporting the not post-processed image and using the same algorithm on another program results in the look I want but it does not in Blender.

I would like to achieve the right image look using Blender. That will improve my working speed for my project because I won't need to use two programs.

How can I make Blender's compositing result match the right image?

Thanks for your help.

color reduction compositing postprocess issue

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Create stairs in an "RGB Curves" node. To make the line straight select "Vector Handle" on each dot. Hold CTRL and click on the line to create new dots. enter image description here

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  • $\begingroup$ Thanks for your answer. Im sorry but i still suffer the same image darkening. I think its not related to how i manage colors. No matter what node i use to replicate the color rounding the image allways goes darker. I tried colorramp too and i still have this issue. I think its probably something that it's not related to the nodes i use. $\endgroup$ – user81839 Oct 1 '19 at 17:51
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Your existing maths is actually rounding down due to the 'subtract 0.5', which will result in a darkening of the image (since everything rounds down to the next "step"). By re-arranging the nodes and using an Add at the end of the chain instead of in the middle, the logic will round to the nearest "step" and the final 'Add' will allow you to adjust the final 'offset' to get the desired result (you can also adjust the Multiply and Divide factors to scale the output).

Here are the adjusted nodes (note that I've added Value nodes to allow easier adjustment of all channels simultaneously) :

nodes

And here's the result :

result

Note also that I've adjusted the Multiply and Divide factors from your example of 7 and 6 to produce similar results since I didn't know your light settings for your original image (so had different starting levels).

Your original example split the image into 7 steps (due to the multiply by 7 before the 'round'), rounded down to the next lower step (with the subtract) then multiplied by 6 (so the result is actually lower than the original). In my adjusted nodes, the Add can be adjusted to regain some of the loss, or the Divide adjusted to change how the steps are converted back into the final range.

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