AMD SC2200 manual Horizontal Downscaler with 4-Tap Filtering

32580B Video Processor Module

7.2.2.2Horizontal 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 downscaler 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.

Bypass

		To Line
		Buffers
Video	4-Tap	Horizontal
Input
	Filtering	Downscaler

4x4

Coefficients

Downscale

Factors

Figure 7-8. Horizontal Downscaler Block Diagram

328 AMD Geode™ SC2200 Processor Data Book