The above is correct calculation. But please take care about real system implementation. If you implement on 32-bit system, and do you want high performance ? Because 32-bit system can work with 32-bit data for read/write. 3-byte (24-bit) operation may difficult and reduce performance. So you may use 4-byte (32-bit) for 1 pixel, That means 1024*1280*4 = 5 MB.