koobas.hobune.stream
PVRTC RGB same size as RGBA
I've been trying to reduce the texture footprint of my project and I stumbled accross this...
Based on the numbers in Unity and the console output from an iOS build, adding an alpha channel to a PVRTC texture doesn't increase the ammount of memory it takes up?
Just wanted to confirm this and maybe get an explanation as to how this texture compression format works.
Thanks.
Just wanted to confirm this since it s
PVRTC uses premultiplied alpha and is a compressed-in-memory format. The reason adding an alpha channel doesn't increase the memory is because it was always there in the first place. PVRTC incorporates the alpha channel into the other channels.
However every PVR image I've ever seen that has alpha has looked absolutely terrible on the device.
It's by design. PVRTC 4bpp, means that it has 4 bits per pixel, no matter whether your texture is with or without Alpha. Check out this spec: http://blog.imgtec.com/powervr/pvrtc-the-most-efficient-texture-compression-standard-for-the-mobile-graphics-world, or this image more specifically which explains the amount of bits per channel: 
As you can see when you have alpha your pixel still takes 4 bits, but it has less bits per channel.
