Mini-Tutorial | How to reduce banding in exported renders

EarthQuake · Aug 2014

I've seen banding in the backgrounds in a lot of Toolbag 2 renders, so I figured I would write a short post explaining why it happens and how to fix it.

First off, the underlying issue is a problem of bit-depth, there simply isn't enough values in an 8-bit image to represent a perfectly smooth gradient. The effect of this is amplified if you have a low contrast or flat color background, and a low contrast vignette.

To solve the banding/bit-depth issue, some sort of dithering needs to happen. Dithering is basically adding some noise so to break up the pattern and avoid the typical stair-stepping effect. In Toolbag 2 we do this by default by setting the grain value in the camera post effect options to 0.04, this adds a very small amount of noise that helps to dither the render. A bit of noise also helps to generally make renders look more natural, and at the default setting its such a small amount that it shouldn't make a noticeable difference to your actual model.

Here are some comparison images in PNG format:

First off, is a standard 8-bit image with the grain effect turned off. You can see the nasty stair stepping effect clearly here.

Secondly we have an image exported at 16bit, and then down converted to 8-bit in photoshop, which should do some dithering in the conversion. This helps a small amount, however it isn't enough with a subtle vignette like we have here.

Lastly, we have an 8-bit image with grain on at the default value of 0.04. This looks much, much better with no visible banding. There is a small amount of noise visible in the background, however this is very much preferable to the alternative (nasty banding artifacts).

We realize it may be a little confusing that grain effect is essentially required to get the best quality renders, so we may look into doing some sort of dithering that is not tied to the grain effect.

Here is the same image, but jpeg(quality 9) this time: