158
Chapter 5, Using Matrox RT.X2 with Video for Windows Programs
5Under Zig Zag Order, select one of the following:
$Regular Sets the regular (default) zig zag scanning pattern of the AC
coefficient of the DCT block as defined in the ISO/IEC 13818-2
(figure 7-2) specification documentation.
$Alternate Sets an alternate zig zag scanning pattern of th e AC coefficient
of the DCT block as defined in the ISO/IEC 13818-2 (figure 7-3)
specification documentation. Use this setting when capturing or rendering
video at a high data rate (for example, at a data rate of 100 Mb/sec or higher).
6Under Rounding Type, select one of the following:
$MPEG-2 Rounds the AC coefficients up to the nearest whole number
when calculating the quantization coefficient.
$Matrox Custom Truncates the AC coefficients to the lowest whole
number when calculating the quantization coefficient. In some cases, this
setting may yield less artifacts in graphics.
7Select the Force Frame-based DCT setting to render macroblocks as
frames rather than as fi elds. In some cases, g raphics will yield less artifacts if
this option is selected.
8Click OK to save your settings. The settings you selected will be used each
time you render material with your program, until you change the settings
again.