Android: Preparing textures for 16-bit compression

I have several PNG textures that Unity imports as RGBA32. If compression is enabled, the PNG will be RGBA16. The compressed textures will have noticeable banding in gradients (see link for pic). I’m trying to find a way to prepare the textures for 16-bit compression, or at least minimize the banding effect.

I’m familiar with index-dithering, which is a technique that tries to simulate gradients as best it can with the provided palette. But I’m not familiar with any 16-bit dithering effects. Or perhaps there are other techniques that I could try?

link to image

If you’re using Photoshop, download the Telegraphics 5/6/5 filter.