When OnRenderImage(RenderTexture src, RenderTexture dst) is called does the src RenderTexture come with transparency data? In other words, is the src an RGBA buffer or an RGB buffer?
It just depends on how the original camera render texture was setup. In this example (Unity - Scripting API: RenderTexture.Create) it sets up a 32-bit render texture for the camera to use. If it’s set to
RenderTextureFormat.ARGB32 then it will include alpha/transparency data.
Thanks!