Panasonic EURO 4 Chassis, Техническое руководство

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17.6. Scaler Stage
The luma and chroma signals output from the colour
decoder are fed to the following scaler stage and the
Skew filter.
17.6.1.Skew Filter
The skew filter is used to ensure that the signal
being processed is at the same timing as the system
clock.
As there is no way for the VDP
IC601 to know
whether the signal that it is processing is a standard
signal or a non-standard signal, e.g. VCR input, the
system clock is free running.
The skew filter which is controlled by the internal
Horizontal Phase Lock Loop1 (PLL1), (located in the
sync and deflection block discussed later), produces
a phase shift which ensures that the system clock
and source signal are at the same timing.
The luma and chroma signals are then fed to the
Horizontal scaler.
17.6.2.Horizontal Scaler
The 4:2:2 YC
r
C
b
signal is fed to the horizontal scaler.
The horizontal scaler is used to fit a picture with 4:3
format on a 16:9 screen by stretching the picture
geometry at the borders, the inverse effect can also
be produced by the scaler. A summary of the scaler
modes is given below.
Mode Scale Factor Description
Compression
4:3 -> 16:9
0.75 linear 4:3 source displayed on a 16:9
tube, with side panels
Panorama
4:3 -> 16:9
non-linear
compression
4:3 source displayed on a 16:9
tube, Borders distorted
Zoom 4:3 ->
4:3
1.33 linear Letterbox source (PAL+)
displayed on a 4:3 tube, vertical
overscan, borders distorted, no
cropping
Panorama
4:3 -> 4:3
non-linear
zoom
letterbox source (PAL+)
displayed on a 4:3 tube, vertical
overscan, borders distorted, no
cropping
The scaler itself contains a programmable
decimation filter, a 1-line delay FIFO memory and a
programmable interpolation filter.
The controlling of the scaler being performed by the
internal Fast Processor.
17.6.3.Black-Line Detector
When a letterbox format signal is processed black
areas at the top and bottom of the picture are visible.
To over come this the picture is either zoomed or
shifted.
The VDP3120 IC601 supports this feature using a
letterbox detector. The detector is used to detect
black video lines by measuring the signal amplitude
during active video. For every field the number of
black lines are measured, compared to the previous
measurement and the result is stored in the I
2
C
register BLKLIN. To adjust the picture amplitude the
external controller reads this register, calculates the
vertical scaling co-efficients (vertical sawtooth
parameters, horizontal scaling etc.) and transfers
the new settings to the VDP IC601 .
The letterbox signals containing logos on the left and
right side of the black areas are processed as black
lines, while subtitles inserted in the black areas are
processed as non-black lines. Therefore the
subtitles are visible on the screen. Dark video
scenes with a low contrast level compared to the
letterbox area are indicated by a BLKPIC bit.
Skew
Filter Horizontal
Scaler
BlackLine
Detector
Luma
Chroma
From
Colour Decoder
To
Display
Processor
Luma
Chroma
Scaler Stage