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PNX17XX Datasheet, PDF (592/832 Pages) NXP Semiconductors – Connected Media Processor | |||
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Philips Semiconductors
Volume 1 of 1
PNX17xx Series
Chapter 19: Memory Based Scaler
Decimation Filter
After horizontal processing, chrominance may be down sampled to reduce memory
bandwidth or allow for higher quality vertical processing that is not available
otherwise. Mirroring of samples at the ï¬eld boundaries compensate for run in and run
out conditions of the ï¬lter.
Normal Polyphase Filter Mode
The normal polyphase ï¬lter can be used to zoom out or downscale a video image.
Depending on the number of components, the ï¬lter uses 6 taps (three-component
mode) or 3 taps (four-component mode). For the normal polyphase ï¬lter, run-in and
run-out behavior are compensated by appropriate mirroring of samples at the ï¬eld
boundaries. In order to align the ï¬rst output pixel with the geometric location of the
ï¬rst input pixel, the start phase has to be chosen as:
dto_offset = 0x200 â
filter_length
(17)
Transposed Polyphase Filter Mode
The transposed polyphase ï¬lter can only be used to downscale. By reversing the ï¬ow
through the normal polyphase ï¬lter, the transposed ï¬lter takes the output pixels as
reference and accumulates input pixels. The advantage of the transposed polyphase
ï¬lter is the longer effective ï¬lter length which allows for ï¬ltering out high frequencies
that interfere with downscaling. A drawback of this approach is that the ï¬lter
coefï¬cients have to get optimized for the scaling ratio in order to avoid visible DC
ripples. Compensation for run-in and run-out behavior of the ï¬lter is not available. Use
of the transposed ï¬lter is limited to three components only.
The scaling ratio for the transposed polyphase HSP_ZOOM_0 = 0x1 0000h *
zoom_x, with zoom_x = pixel_out / pixel_in
Linear Phase Interpolation Mode (LPI)
In the linear phase interpolation mode, samples between two pixels are interpolated
by using the linear equation px = (1-phase) * xleft + phase * xright. Linear phase
interpolation creates adequate results especially when used with computer
generated graphics which, unlike motion video, is usually not bandwidth limited.
The LPI mode is enabled by setting HSP_PHASE_MODE = 7. Horizontal processing
mode has to be set to normal polyphase (HSP_MODE = 2) and four-component
mode has to be enabled (HSP_FIR_COMP = 1)
Color Space Matrix Mode
In addition to the normal and transposed polyphase ï¬ltering (scaling), the FIR ï¬lter
structure can instead be programed to perform color-space-conversion functions. A
dedicated set of registers holds the coefï¬cients for the color space matrix.
PNX17XX_SER_1
Preliminary data sheet
Rev. 1 â 17 March 2006
© Koninklijke Philips Electronics N.V. 2006. All rights reserved.
19-9
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