Count colored pixels of RenderTexture and get this data on CPU.

I need to calculate pixels of RenderTexture that are colored(alpha > 0). So I need to get pixels data inside C# script. My render texture is 16x16 pixels.

I have tried many things:

1. Texture2D.ReadPixels() - very slow.

2. Graphics.CopyTexture() - does not work with Texture2D.

3. AsyncGPUReadbackRequest - does not work on Android.

4. Texture2D.ReadPixels() but on a thread - works only on the main thread.

5. ComputeShader - does not work on low-end Android devices

6. Custom shader - can't read data directly from shader(GPU) so this also requires to read pixels from render texture.

So my guess that there is no way to get pixels to C# script fast. But maybe there is a way to just count colored pixels of the RenderTexture.

And again, the main problem is that reading pixels from RenderTexture to Texture is very slow. On Android it takes 10ms.