Matrox Electronic Systems Matrox RT.X2 - Manual (Page 166)

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Chapter 5, Using Matrox RT.X2 with Video for Windows Programs
5 Under 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 the 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).
6 Under 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.
7 Select the Force Frame-based DCT setting to render macroblocks as
frames rather than as fields. In some cases, graphics will yield less artifacts if
this option is selected.
8 Click 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.