On Tue, 16 Feb 2010 17:15:37 -0300 Luiz Americo Pereira Camara <luiz...@oi.com.br> wrote:
> While trying to get the RGB values (bytes) of a TFPColor i got confused > about the format of TFPColor > > Some hardcoded colors (unit FPImage) like colGray, colTea sets the high > byte value of Red, Green, Blue fields with the corresponding byte value > of RGB and leaves the low byte with 0. > > Other colors like colWhite or colFuchsia sets both low and high byte of > the fields with the corresponding RGB values. > > So whats the correlation of RGB byte values and TFPColor? RGB, TColor uses range of 0-$ff and TFPColor uses Word so range is 0-$ffff, so you can multiple each by $101. Another way is to copy the byte (c shl 8+c). Note: The reverse is *not* to divide by $101. (e.g. $fffe div $101 = $fe, but it should be mapped to $ff). The reverse is to divide by $100 (or "shr 8"). And note that this is a "per pixel" conversion, which might not be the best way. > Should colWhite be redefined as colWhite : TFPColor = (Red: $ff00; > Green: $ff00; Blue: $ff00; Alpha: alphaOpaque) No. That's not fully white. $ff*$101 = $ffff > or > > colGray be redefined as colGray : TFPColor = (Red: $8080; Green: > $8080; Blue: $8080; Alpha: alphaOpaque) ?? Yes, although this rarely makes a difference. > This info will help to fix http://bugs.freepascal.org/view.php?id=15793 IMO the bug report is misleading. Converting a TFPColor to RGB looses bits. You should not assume that the 48bit FPColor constants support 24 bit RGB. The FPColor constants don't support other RGB formats like 5-6-5 neither and there are many different algorithms to scale picture resolutions. Mattias _______________________________________________ fpc-devel maillist - fpc-devel@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-devel
