
Brooktree
213
DISPLAY REFRESH CONTROLLER
Video Data Path
L2166_A
Bt2166
Graphics/Video Controller
Replicative Vertical
Upscaling
When upscaling in this mode, the combination of initial and increment values pro-
grammed must be such that the number of DDA carry-outs equals the source line
count, and the last DDA carry-out occurs while the last source line/pixel is being
processed.
2-Tap Vertical Upscaling
When doing 2-tap interpolative video upscaling, only one hardware video window
is supported, as the second video path is used for processing the lower line of video
line pairs. The video plane 1 path is used for processing the upper line of each in-
terpolated line pair; the video plane 2 path is used for processing the lower line of
each interpolated line pair.
The following video plane 1 and 2 registers should contain identical values:
Video Control Format Field
Video Size Value
Video Pitch Values
Video Count Values
Video Bump Modulus Values
For interpolative upscaling, the combination of initial and increment values pro-
grammed must be such that the number of DDA carry-outs is one less than the
number of source line count, and the last DDA carry-out occurs while the last
source line/pixel pair is being processed.
The increment value for interpolative upscaling may be computed by using the
following expression:
The source pixel count is the source window height or width, as given by
Table 14. The destination pixel count is the size of the onscreen video window
plane height or width. The destination pixel count equals the number of pixels for
which the video plane extents are dened.
As is true for horizontal 2-tap upscaling, seven intermediate steps of interpola-
tion are provided for all of the video formats; all channels are linearly interpolated
in RGB formats. In YCrCb formats only luminance is interpolated; chrominance is
replicated from top to bottom.
3-Tap Vertical Upscaling
As in 2-tap mode, the video plane 2 path is used for processing the "second" line.
The graphics fo provides the lowest line of a line triad; hence, graphics may not
be displayed when doing 3-tap vertical upscaling.
As is true for 3-tap horizontal upscaling, this mode is valid only for 4:2:2 video.
The weighting is identical to the weighting shown for horizontal 3-tap upscaling,
shown in Table 166 on page 214.
Upscale Initial and
Increment Computation
The system needs to pre-calculate and provide the DDA constants required for the
desired scale factor and initial starting values and load these values into the appro-
priate X and Y increment and initial registers.
Increment
4095 SourcePixelCount
1
–
()
DestinationPixelCount
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