SAA7146AH NXP Semiconductors, SAA7146AH Datasheet - Page 67

• Manufacturer Part Number: SAA7146AH
• Manufacturer: NXP Semiconductors

Specifications of SAA7146AH

• Lead Free Status / Rohs Status: Compliant

Philips Semiconductors
7.9.2.4
The vertical scaler performs the vertical downscaling of the
input data stream to a randomly number of output lines.
It can be used for input line lengths up to 768 pixels/line
and has to be bypassed, if the input line length exceeds
this pixel count.
For the vertical scaling there are two different modes:
7.9.2.5
For vertical scales down to icon size the ACCU mode can
be used. In this mode the parameter YSCI controls the
scaling and the parameter YACL the vertical anti-aliasing
filtering.
The output lines are generated by a scale-dependent
variable averaging of (YACL + 2) input lines. In this way a
vertical FIR filter is build for anti-aliasing, with up to
maximum 65 taps.
YSCI defines the output line qualifier pattern and YACL
defines the sequence length for the line averaging.
For accurate processing the sequence has to fit into the
qualifying pattern. In case of misprogramming YACL,
unexpected line dropping occurs.
Where:
2004 Aug 25
handbook, full pagewidth
The ACCU mode (vertical accumulation) for scales
down to icon size and
The Linear Phase Interpolation (LPI) mode for scales
between 1 and
N
N
Multimedia bridge, high performance
Scaler and PCI circuit (SPCI)
OL
IL
= Number of Input Lines.
= Number of Output Lines and
Vertical scaler
ACCU mode (scaling factor range 1 to 1/1024;
YACM = 1)
1
line 1
line 2
2
.
scaling factor S = 1/3: vertical accumulation of 4 lines (1 line overlap)
1st sequence
2nd sequence
3rd sequence
Fig.20 Example: vertical accumulation.
optimal weighting factors:
1
2
2
1
2
2
1
2
2
1
67
the YSCI (scaling increment), YACL (accumulation length;
optimum: 1 line overlap) and YP (scaling start phase) have
to be set according to the equations below, see Fig.20.
In order to get a unity amplitude gain for all sequence
lengths and to improve the vertical scaling performance,
the accumulated lines can be weighted and the amplitude
of the scaled output signal has to be renormalized. In the
given example (see Fig.20), using the optimal weighting,
the gain of a sequence results in 1 + 2 + 2 + 1 = 6.
Renormalization (factor
Normally, the weighting would be 2 + 2 + 2 + 2. In this
case the gain can be renormalized simply with
DCGY2 to DCGY0 = ‘010’ (factor
examples for register settings depending on a given scale
ratio.
YSCI = INT {1024
YACL = INT {(1 - S)/S}
YP x = INT {YSCI/16}
YACL = TRUNC [N
length; i.e. number of lines per sequence, that are not
part of overlay region of neighbouring sequences
(optimum: 1 line overlapped)
YSCI = INT [1024
YPx = INT [YSCI/16] scaling start phase (fix; modified in
LPI mode only).
By gain reduction using BCS control (brightness,
contrast, saturation) down to
for DCGY2 to DCGY0 which may result in a loss of
signal quantization, or
By gain emphasizing using BCS control up to
and selecting factor
may result in a loss of signal detail due to limiting in the
BCS control.
(1 - S)}
IL
(1
1
/N
8
1
OL
6
for DCGY2 to DCGY0 which
= 2 (dotted lines)
= 42
= 682
) can be done
N
OL
1] accumulation sequence
/N
4
MGD697
6
IL
1
and selecting factor
)] scaling increment
8
). Table 58 gives
Product specification
SAA7146A
8
6
1
4