VDP 3108
ADVANCE INFORMATION
2.4. Display Processor
black level expander are shown in Fig. 2–14 and Fig.
2–15.
In the display processor the conversion from digital
YC C to analog RGB is carried out. A block diagram is
shown in figure 2–18. In the luminance processing path
contrast and brightness adjustments and variety of fea-
tures such as black level expansion, dynamic peaking
and soft limiting are provided. In the chrominance path,
The tilt point L is a function of the dynamic range of the
t
r
b
video signal. Thus, the black level expansion is only per-
formed when the video signal has a large dynamic
range. Otherwise, theexpansiontoblackiszero. Thisal-
lows the correction of the characteristics of the picture
tube.
the C C signals are converted to 20.25 MHz sampling
r
b
rate and filtered by a color transient improvement circuit.
The YC C signals are converted by a programmable
matrix to RGB color space.
r
b
L
L
out
max
L
tr
The signals inserted via the YC C bus are identified by
r
b
their respective priority. The display processor provides
separate control settings for two pictures, i.e. different
coefficients for a ‘main’ and a ‘side’ picture.
L
t
BAM
BTLT
The digital RGB insertion circuit allows the insertion of
a 5 bit RGB signal. The color space for this signal is con-
trolled by a programmable color look up table (CLUT)
and contrast adjustment.
L
min
L
BTHR
L
in
tr
TheRGBsignalsandthedisplayclockaresynchronized
to the horizontal flyback. For the display clock a gate
delay phase shifter is used. The RGB signals are syn-
chronized by a FIFO. In the analog back-end, three 10-
bit digital-to-analog converters provide the analog out-
put signals.
Fig. 2–14: Characteristics of the black
level expander
L
max
a)
L
t
2.4.1. Contrast Adjustment
L
min
The 8 bit luminance input is multiplied by a factor of 0 ...
2 in 64 steps. A 2-bit noise shaping on the result is used
to increase the resolution of the luma signal. Contrast
adjustment is separate for main and side picture.
b)
2.4.2. Black Level Expander
L
t
The black level expander enhances the contrast of the
picture. Therefore the luminance signal is modified with
an adjustable, nonlinear function. Dark areas of the pic-
ture are changed to black, while bright areas remain un-
changed. The advantage of this black level expander is
that the black expansion is performed only if there is a
large dynamic range in the video signal and when it will
be most noticeable to the viewer.
Fig. 2–15: Black-level-expansion
a) luminance input
b) luminance output
The black level expander works adaptively. Depending
2.4.3. Dynamic Peaking
on the measured amplitudes ‘L ’ and ‘L
’ of the low-
min
max
pass-filtered luminance and an adjustable coefficient
Especially with composite input signals and notch filter
luminance separation, it is necessary to improve the lu-
minance frequency characteristics.
BTLT, a tilt point ‘L ’ is being established by
t
L = L
+ BTLT ( L – L ).
max min
t
min
Above this value there is no expansion, while all lumi-
nance values below this point are expanded according
to:
InDIGIT3000thelumaresponseisimprovedby‘dynam-
ic’ peaking. The algorithm has been optimized regarding
step and frequency response. It adapts to the amplitude
of the high frequency part. Small amplitudes are en-
hanced while large amplitudes stay nearly unmodified.
L
out
= L + BAM (L – L )
in in t
A second threshold, L , can be programmed, above
tr
which there is no expansion. The characteristics of the
MICRONAS INTERMETALL
13
MICRONAS [ MICRONAS ]
