Trent Piepho wrote: > The standard way it to use 9 tables of 256 entries, one for each combination > of (R, G, B) with (Y, U, V). Then you do something like > > Y = R_to_Y[R] + G_to_Y[G] + B_to_Y[B]; > U = R_to_U[R] + G_to_U[G] + B_to_U[B]; > V = R_to_V[R] + G_to_V[G] + B_to_V[B]; > > So instead of one table lookup, in a huge table, you do 9 lookups plus a few > additions. For more accuracy you would probably want to use fixed point > arithmetic. You don't need all 9 tables either, as some of them will end up > being the same. Yep, I scale all my precomputed tables up by 256, so it's all 16 bit integer additions rather than floating point, and then / 256 (>> 8) afterwards. I package it up as sample-at-a -time in-line conversion functions (effectively macros), so the net result is actually probably fairly competetive with an MMX conversion. Ben
