I would guess 3 colour channels at 16bit (i.e. 2 bytes)
(2^32)÷(1920×1080×4×3×2) = 86
Where does the 4 come from? I thought it was R+G+B+A, but you already have 3 colour channels in that calculation
Where does the 4 come from? I thought it was R+G+B+A, but you already have 3 colour channels in that calculation