Fusion 878A
2.0 Functional Description
PCI Video Decoder
2.4 Video Scaling, Cropping, and Temporal Decimation
100600B
Conexant
2-13
2.4.1.5 Chrominance
Scaling
A 2-tap, 32-phase interpolation filter is used for horizontal scaling of
chrominance. Vertical scaling of chrominance is implemented through
chrominance comb filtering using a line store, followed by simple decimation or
line dropping.
2.4.1.6 Scaling
Registers
The Horizontal Scaling
Ratio Register (HSCALE)
HSCALE is programmed with the horizontal scaling ratio. When outputting
unscaled video (in NTSC), the Fusion 878A produces 910 pixels per line. This
corresponds to the pixel rate at fCLK x 1 (4 × Fsc). This register is the control for
scaling the video to the desired size. For example, square pixel NTSC requires
780 samples per line, while CCIR 601 requires 858 samples per line.
HSCALE_HI and HSCALE_LO are two 8-bit registers that, when concatenated,
form the 16-bit HSCALE register. The method below uses pixel ratios to
determine the scaling ratio. The following formula should be used to determine
the scaling ratio to be entered into the 16-bit register:
Figure 2-11. Luma Peaking Filters with 2x Oversampling Filter and Luma Notch
(2 of 2)
HFILT = 01
HFILT = 11
HFILT = 10
HFILT = 00
Enhanced Resolution of Passband
879A_016a
Amplitude in dB [20*log10(ampl)]
Frequency in MHz
NTSC:
HSCALE = [ ( 910/P
desired
) – 1] × 4096
PAL/SECAM:
HSCALE = [ ( 1135/P
desired
) – 1] × 4096
where:
P
desired
= Desired number of pixels per line of video, including
active, sync and blanking.