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•
Dynamic Contrast. To make the contrast (black/white)
range wider, Philips has invented Dynamic Contrast. It
uses the digital memory used in 100 Hz sets. It measures
every A-field (25 x per second), and digitally analyses
where on the greyscale most of the image is located. If it is
a relatively dark image, the lighter part of that image is
stretched towards white, so that more contrast will become
visible in that picture. If it is a relatively light image, the
darker part of that image is stretched towards black, so that
these darker parts will have more contrast. When the
image is in the middle of the greyscale, both dark and light
parts are stretched.
9.8.4
Eagle (Diagram B3c)
Introduction
Some strong picture improvements are carried out inside the
Eagle, which all contribute to the excellent picture quality.
These improvements are:
•
LTI (both horizontal and vertical).
•
CTI (only horizontal).
•
Peaking (both horizontal and vertical).
•
More pixels per line.
•
More lines per frame.
•
Better colour transitions.
By means of over sampling, the video signals get a sample
frequency of 64 MHz, a bandwidth of 20 MHz, and 1680 pixels
per line (was 32 MHz, 10 MHz and 840 pixels/line). This
requires two extra field memories (MEM4 and MEM5).
The Eagle can handle four different modes:
•
Digital Natural Motion (PAL): 100 Hz, 2
(1680 pixels x 625 lines)
•
Pixel Plus (PAL): 75 Hz, 2
833 lines)
•
Double Lines (PAL): 50 Hz, 2
x 1250 lines)
•
Pixel Plus (NTSC): 60 Hz, 2
1050 lines)
LTI (Luminance Transient Improvement)
The main objective of LTI is a steeper slope at contrast
transitions (e.g. from 10 mV to 900 mV within 3 pixels i.s.o. 5
pixels for one detail). It is based on waveform altering around a
signal jump.
Important: The LTI, as used in the Eagle, is designed for
interpolated picture contents. This means that for pixel/line
doubling, one of the two pixels/lines is an interpolated value.
When a picture jump is interpolated, you will get extra room to
make it steeper (you get extra pixels to describe the slope).
Without interpolation, you cannot use this kind of LTI.
•
LTI can add "ears" to the waveform at the jump (a kind of
controlled overshoot).
•
LTI "estimates" the frequency of the jump and will adapt the
amplification to this frequency.
•
LTI is applied both horizontal as vertical.
•
LTI is amplitude dependent. This means that only "big"
jumps are processed. It works with a threshold, which is
coupled to the noise meter via the Auto TV software.
•
LTI is also frequency dependent. This means that it is
distributed over the slopes. When there are many steep
slopes in the signal, LTI will only process the steepest
ones. If there are only a few slopes, LTI will process all of
them. This is fully hardware implemented.
Circuit Descriptions and Abbreviation List
, 2:1 Interlace
fH
, 2:1 Interlace (1680 pixels x
fH
, 2:1 Interlace (1680 pixels
fH
, 2:1 Interlace (1680 pixels x
fH
EM5A P/M
Luminance Y
D'
C'
A
B
C
D
Figure 9-15 Horizontal LTI
For horizontal LTI, the number of pixels is doubled (64 MHz) by
means of interpolation. Pixel A at the transition will keep its
luminance value, while the (new) pixels B can have a
luminance value of zero to max. 31. For example:
•
Pixels B can keep the same value (gain = 0)
•
Pixels B can get the value of C and C' (gain = 8), which will
give a steeper slope.
•
Pixels B can also get the value of D and D' (gain = 31),
which will give an even steeper slope with the so-called
"ears". These "ears" will give a contrast improvement.
For CTI, the same principle is used, in order to get better
colour transitions.
detail
833
samples
Figure 9-16 Vertical LTI
The principle for vertical LTI is the same as for horizontal LTI.
The shift from 625 to 833 lines is done by means of a scaler.
With these extra interpolated samples, it is possible to create
steeper slopes, possibly with "ears".
Peaking/Coring
The objective of "peaking" is contrast improvement (e.g. from
50 mV
to 70 mV
for one detail).
PP
PP
It uses a noise threshold (coring = non-linear filtering around
zero-level), thus it works everywhere in the picture (except
below the threshold level).
The added difference signal is frequency dependent, which
results in frequency dependent contrast improvement. When
the difference signal becomes too large, the peaking is reduced
(smartness).
Amplitude
PEAKING
2.3Mc
4Mc
8Mc
Frequency
A
B
C
Figure 9-17 Peaking
9.
EN 127
Original slope
Added interpolated
pixels
B
gain=0
gain=8
gain=31
spatial X or Y
CL 16532149_083.eps
061201
Original samples
Added interpolated
samples
CL 16532149_084.eps
071201
'ear'
'ear'
CL 16532149_085.eps
131201
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