Circuit Descriptions, Abbreviation List, and IC Data Sheets
9.
The video processing is completely handled by the Hercules
•
IF demodulator.
•
Chrominance decoder
•
Sync separator.
•
Horizontal & vertical drive.
•
RGB processing.
•
CVBS and SVHS source select.
It has also built-in features like:
•
CTI.
•
Black stretch.
•
Blue stretch.
•
White stretch.
•
Slow start up.
•
Dynamic skin tone correction etc.
Further, it also incorporates sound IF traps and filters, and
requires only one crystal for all systems.
9.6
Columbus
9.6.1
Introduction
The Columbus is a combination of:
•
A
2D/3D Comb filter
for both PAL and NTSC, and
•
A
spatial/temporal noise reduction system
for both
colour and luminance signals.
The Columbus 3D Comb filter uses digitalised CVBS, U, and V
(or C) signals and can be used with or without an external 16
Mbit SDRAM. Without external 16Mbit SDRAM, 3D comb
filtering and temporal noise reduction are not possible.
The noise reduction part of the Columbus is controlled by the
FBX software using the SNERT interface. The 2D/3D Comb
filter part is controlled by the Main software using the I
2
C bus.
9.6.2
2D/3D Comb Filter
Introduction
The “3D Comb filter Columbus” is a combined 2D/3D Comb
filter function that is part of the Columbus chip (circuit diagram
B19, item 7M00). It is a comb filter for both PAL and NTSC.
The 3D Comb filter is used to separate chroma and luminance
components out of a CVBS signal. It is of no use when the
CVBS signal is a SECAM signal (SECAM signals cannot be
combed) The Columbus chip can be used with or without 16
Mbit external SDRAM (circuit diagram B10, item 7B01). When
an external SDRAM is connected to the IC, the Comb filter
function can work in combined 2D/3D processing (depending
on the detected pixel based motion). When no external
SDRAM is connected, only 2D Comb filtering is possible.
The Columbus can comb the following standard signals:
•
PAL B, PAL G, PAL H, PAL I, PAL D, PAL K: Colour
standard PAL, Colour carrier at 4.43 MHz, field frequency:
50 Hz
•
PAL M: Colour standard PAL, Colour carrier at 3.58 MHz,
field frequency: 60 Hz
•
PAL N: Colour standard PAL, Colour carrier at 3.58 MHz,
field frequency: 50 Hz
•
NTSC M: Colour standard NTSC, Colour carrier at 3.58
MHz, field frequency: 60 Hz
For NTSC signals, the PAL delay line must always be
bypassed.
The following signals CANNOT be combed:
•
Double Window signals or Multi PIP. For these signals,
only one part or even no part of the signal is in relation with
the burst. The part that is not in relation with the burst can
become very blurred when combed by the Columbus
Comb filter. Such a signal must be bypassed. Notch mode
is not even an option since e.g. in double window, one part
can be a PAL signal while the other part is NTSC or
SECAM.
•
In cases where a SECAM signal is presented to the
Columbus Comb filter; both the luminance and UV path
must be bypassed. The PAL delay line inside the
Columbus cannot be used for SECAM signals so it must
also be bypassed. The luminance path must have
luminance at its input instead of CVBS. A chroma delay line
outside Columbus must be used for SECAM signals.
Reason for this: the Columbus PAL delay line halves the
output of the chroma signals in case of SECAM.
•
Y/C, YPbPr, and RGB signals do not have to be combed.
So both the luminance and UV path must be bypassed.
The PAL delay line will also be bypassed.
•
In cases where the Columbus Comb filter does not receive
a CVBS signal with burst at the right place according to the
standard (this includes black and white signals without
burst), phase correction results become unpredictable and
the Comb filter must be set in bypass (= luminance path
bypassed, UV path bypassed, PAL delay line bypassed)
•
VCR signals cannot be combed and must be processed in
notch mode, or bypassed.
Columbus Modes
The several modes of the Columbus 3D Comb filter are:
•
Bypass mode.
•
Band-Pass-Notch mode.
•
2D Comb filter modes.
–
Simple median.
–
Median.
•
Field Comb filter mode.
•
Frame Comb filter mode.
Bypass Mode
The 3D Comb filter can be set in bypass mode. In this mode,
the CVBS, U and V signals are just bypassed to the output.
Band-Pass-Notch Mode
This is a mode where no Comb filtering is applied. A “Band
Pass Filter” is used to filter the chroma information out of the
CVBS signal. A “Notch Filter” is used to subtract the sub carrier
out of the CVBS in order to make a luminance signal without
chroma sub carrier.
In terms of cross colour and cross luminance, this mode has
the worst performance of all. It is only used on these signals
where no comb filtering can be applied (non-standard signals
and most VCR signals for example).
2D Comb Filter Modes
A Comb filter does an action on a current pixel and a delayed
pixel. When the delayed pixel is a line-delayed pixel, we talk
about a “Spatial or 2D Comb Filter” (for NTSC the delay must
be 1 line, for PAL it must be 2 lines).
Spatial or 2D Comb filters show problems on vertical colour
transients and on single coloured lines. For these situations,
extra hardware is added in the Columbus chip to avoid these
kinds of problems. However even with these extra measures,
there are still situations where the 2D Comb filter does not
perform optimally (diagonal resolution and single lines with
equal luminance content). In order to restrict the working area
of the 2D Comb filter to the frequencies where the sub carrier
is present, a horizontal band pass filter always precedes a 2D
Comb filter.
When a 2D Comb filter has no extra hardware to avoid
problems at vertical colour transients (or this extra hardware is
switched “off”), the Comb filter is called a “simple median filter”.
When there is extra hardware to avoid these kinds of problems,
the filter is called a “median filter”.
Field Comb Filter Mode
A Comb filter does an action on a current pixel and a delayed
pixel. When the delayed pixel is a field-delayed pixel, we talk
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