RGBA_8888 is an actual format. Each pixel is 4 bytes, with 8 bits of red, green, blue, and transparency information.
The other two are used when specifying a type of format to use, but not an actual format. TRANSPARENT means there there must be at least 1 alpha bit, but that whatever format is chosen doesn't need to support full blending- it just needs to be able to be transparent or non-transparent. For example, a JPEG has transparency. TRANSLUCENT means it can be partially transparent and should have alpha blending applied. RGBA_8888 is translucent, the alpha channel describes how to blend it in. Translucency is a superset of transparency.
The other two are used when specifying a type of format to use, but not an actual format. TRANSPARENT means there there must be at least 1 alpha bit, but that whatever format is chosen doesn't need to support full blending- it just needs to be able to be transparent or non-transparent. For example, a JPEG has transparency. TRANSLUCENT means it can be partially transparent and should have alpha blending applied. RGBA_8888 is translucent, the alpha channel describes how to blend it in. Translucency is a superset of transparency.
