Why do I get color banding when using Color Dodge and a dark colored gradient?

Question

I am experiencing significant color banding when I use the Color Dodge blend mode with a very dark colored gradient layer style. I have even tried enabling dithering on the gradient layer style, with rather poor results. Here is what it looks like:

Here is a small PSD demonstrating what I'm experiencing.

This is my first time using the Color Dodge blend mode. It's my guess this either has something to do with this particular blend mode (I'm not familiar with how it works) or the gradient I'm using (which is extremely dark, possibly to the point that it creates precision issues).

How can I eliminate this color banding problem? Is there another configuration I can use that will get me nearly the same colors, but without the color banding?

Answer 1

The banding is due to the very low number of steps available to create the gradient and the very few colors available. At best, each color in RGB is limited to 256 steps (8 bits per channel = 2^8 steps per color) which is nearly always visible. ( see the examples in this thread for instance: How to produce a blurred abstract (frosted glass) background like this? )

In your particular case, increasing the number of levels to choose from by using 16 or 32 bits per channel, will afford you more on the order of 2^16 possible steps. [EDIT: image menu->mode->16 bits per channel]

You will need to export this to 8bpc RGB (since many applications do not support anything other than 8bit). Some filters and blend modes may not support 16- and 32-bit per channel modes and will not be available for use.