On Mon, 2 Apr 2001, Benedict Bridgwater wrote: > Trent Piepho wrote: > > For instance, in libjpeg, there is this comment: > > > > * YCbCr is defined per CCIR 601-1, except that Cb and Cr are > > * normalized to the range 0..MAXJSAMPLE rather than -0.5 .. 0.5. > > * The conversion equations to be implemented are therefore > > > > Which would make you think that they use rec 601 Y'CbCr, wouldn't it? > > But then look at their equations: > > > > * Y = 0.29900 * R + 0.58700 * G + 0.11400 * B > > * Cb = -0.16874 * R - 0.33126 * G + 0.50000 * B + CENTERJSAMPLE > > * Cr = 0.50000 * R - 0.41869 * G - 0.08131 * B + CENTERJSAMPLE > > Well, if one can't trust the specs, then I guess the Bt848 datasheet is > just as suspect... particularly as I just realized that my "RGB to You can always decode the bt848 Y'CbCr output to RGB and see if it looks right. > Y'CbCr" routines actually use the above "Y'PbBr" (using the colorspace > FAQ terminolog) coefficients (I don't remember where I got them from), > yet the converted Bt848 YUV video looks entirely normal to me!!! That doesn't make sense. You say "RGB to Y'CbCr" routine, and then converted YUV video. If you take YUV as input, you need a "Y'CbCr to RGB" routine.
