L64105 LSI Logic Corporation, L64105 Datasheet - Page 312

• Manufacturer Part Number: L64105
• Description: Mpeg-2 Audio/video Decoder
• Manufacturer: LSI Logic Corporation

9.8 Horizontal Postprocessing Filters
9-20
Since the first field is not available after it has been displayed, RMM
cannot fully support all of the freeze modes. In RMM, only Freeze Last
Field is supported on B pictures because the second field of data is
overwritten in memory. In addition, when performing pulldown the second
field, instead of the first field, is repeated during the display of B-frames.
The Display Controller integrates two separate horizontal postprocessing
filters, a simple 2:1 horizontal decimation filter and an 8-tap interpolation
filter. These filters are provided for scaling images horizontally along the
scan line.
The decimation filter is a simple bilinear averaging filter that decimates
two pixels down to one along the horizontal scan line. This filter may be
used in conjunction with the 0.5 letterbox filter for displaying pictures at
1/4 resolution. Such an application may require a four-frame store system
to account for the higher bandwidth requirements. The decimation filter is
enabled by setting the Horizontal Decimation Filter Enable bit in Register
274
should be programmed to the number of frame-store reads required to
reconstruct the picture, i.e., twice the picture width.
Regardless of the input picture resolution, the horizontal interpolation
filter can provide up to 720 pixels on each line. In addition to its
interpolation features, the filter also provides fine-scale horizontal pan
and scan to within 1/8th of a pixel during pan and scan operation. This
filter is used for both luminance and chrominance data.
The interpolation filter is implemented using an 8-tap polyphase filter.
The filter is capable of generating up to eight, unique, subpixel values
between two consecutive pixels on a scan line. The generation of pixels
depends upon the ratio between the width of the source image and the
target image. Typically, the target image width is 720 pixels.
Figure 9.9
horizontal interpolation filter. To activate the horizontal filter, the host
must first enable the filter by setting the Horizontal Filter Enable bit in
Register 276
setting (response A) or clearing (response B) the Horizontal Filter Select
bit in the same register.
Video Interface
(page
4-61). When using the decimation filter, the main reads per line
through
(page
Figure 9.12
4-63). The desired filter response is selected by
illustrate the characteristics of the