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NXP Semiconductors
PNX15xx/952x Series
Volume 1 of 1
Chapter 12: Video Input Processor
PNX15XX_PNX952X_SER_N_4
NXP B.V. 2007. All rights reserved.
Product data sheet
Rev. 4.0 — 03 December 2007
12-439
Enabling the Dither Units
Immediately after the Dither unit is enabled or after a reset, the unit waits for the
beginning of a newly-captured image. Only then the unit starts dithering.
Once the Dither unit is operational (enabled), it keeps track of the order in which the
images arrive: we refer to the very rst image at the unit dither as the
even image, the
second image as the
odd image, and so on. A frame here is dened as two images:
an even image followed by an odd image. This maintained state does not depend on
the selected alternation options, it is maintained as long as the Dither unit is enabled.
Any alternative activity corresponds to the internally-maintained state of a frame and
eld (even or odd) and has nothing to do if the signal is coming from the top or the
bottom eld.
Dithering operation also distinguishes between even and odd pixel-components of
the same type (either Y, U or V) in a line.
The rst occurrence of a Y or U or V component in the rst line in the rst received
image is considered to be an even occurrence (or
set).
2.5.5
Horizontal Video Filters (Sampling, Scaling, Color Space Conversion)
Interpolation Filter (Upsampling)
All horizontal video processing is based on equidistant sampled components. All
4:2:2 video streams, therefore, have to be upsampled before being scaled
horizontally. The interpolation FIR lter used can interpolate interspersed or co-sited
chroma samples. Mirroring of samples at the eld boundaries compensate for run-in
and run-out conditions of the lter.
The following coefcients are used:
co-sited: A=(1) and B=(-3,19,19,-3)/32
interspersed: C=(-1,5,13,-1)/16 and D=(-1,13,5,-1)/16
Decimation Filter (Downsampling)
After horizontal processing, the chrominance may be down-sampled to reduce
memory bandwidth or allow a higher-quality vertical processing not available
otherwise. Mirroring of samples at the eld boundaries compensate for run in and run
out conditions of the lter.
The following coefcients are used:
co-sited: low pass A=(1,2,1)/4 or sub-sample A=(0,1,0)
interspersed: B=(-3,19,19,-3)/32
Normal Polyphase Filter (Horizontal Scaling)
The normal polyphase lter can be used to zoom up (upscale) or downscale a video
image. Depending on the number of components, the lter is used with 6 taps (three-
component mode) or 3 taps (four-component mode).