AMD Geode SC3200 - Manual (Page 318)

318 AMD Geode™ SC3200 Processor Data Book
Video Processor Module 32581C
7.2.2.2 Horizontal Downscaler with 4-Tap Filtering
The Video Processor implements up to 8:1 horizontal
downscaling with 4-tap filtering for horizontal interpolation.
Filtering is performed on video data input to the Video Pro-
cessor. This data is fed to the filter and then to the down-
scaler. There is a bypass path for both filtering and
downscaling logic. If this bypass is enabled, video data is
written directly into the line buffers. (See Figure 7-8.)
Filtering
There are four 4-bit coefficients which can have pro-
grammed values of 0 to 15. The filter coefficients can be
programmed via the Video Downscaler Coefficient register
(F4BAR0+Memory Offset 40h) to increase picture quality.
Horizontal Downscaler
The Video Processor supports horizontal downscaling. The
downscaler can be implemented in the Video Processor to
shrink the video window by a factor of up to 8:1, in 1-pixel
increments. The downscaler factor (m) is programmed in
the Video Downscaler Control register (F4BAR0+Memory
Offset 3Ch[4:1]). If bit 0 of this register is set to 0, the down-
scaler logic is bypassed.
The horizontal downscaler supports downscaling of video
data input format YUV 4:2:2 only.
The downscaler supports up to 29 downscaler factors.
There are two types of factors:
• Type A is (1/m+1). One pixel is retained, and m pixels
are dropped. This enables downscaling factors of 1/16,
1/15, 1/14, 1/13, 1/12, 1/11, 1/10, 1/9,1/8, 1/7, 1/6, 1/5,
1/4, 1/3, and 1/2.
• Type B is (m/m+1). m pixels are retained, and one pixel
is dropped. This enables downscaling factors of 2/3, 3/4,
4/5, 5/6, 6/7, 7/8, 8/9, 9/10, 10/11, 11/12, 12/13, 13/14,
14/15, and 15/16.
Bit 6 of the Video Downscaler Control register
(F4BAR0+Memory Offset 3Ch) selects the type of down-
scaling factor to be used.
Note: There is no vertical downscaling in the Video Pro-
cessor.
Figure 7-8. Horizontal Downscaler Block Diagram
Bypass
4-Tap Horizontal
4x4 Downscale
Video
Input
Filtering
Coefficients
Downscaler
Factors
To Line
Buffers