VCT 38xxA
ADVANCE INFORMATION
2.9. Macrovision Detection
2.10.2.Black-Level Expander
Video signals from Macrovision encoded VCR tapes
are decoded without loss of picture quality. However, it
might be necessary in some applications to detect the
presence of Macrovision encoded video signals. This
is possible by reading the Macrovision status register
(FP-RAM 0x170).
The black-level expander enhances the contrast of the
picture. Therefore the luminance signal is modified
with an adjustable, non-linear function. Dark areas of
the picture are changed to black, while bright areas
remain unchanged. The advantage of this black-level
expander is that the black expansion is performed only
if it will be most noticeable to the viewer.
Macrovision encoded video signals typically have AGC
pulses and pseudo sync pulses added during VBI. The
amplitude of the AGC pulses is modulated in time. The
Macrovision detection logic measures the VBI lines
and compares the signal against thresholds.
The black-level expander works adaptively. Depending
on the measured amplitudes ‘Lmin’ and ‘Lmax’ of the
low-pass-filtered luminance and an adjustable coeffi-
cient BTLT, a tilt point ‘Lt’ is established by
The window wherein the video lines are checked for
Macrovision pulses can be defined in terms of start
and stop line (e.g. 6-15 for NTSC).
Lt = Lmin + BTLT (Lmax - Lmin).
Above this value there is no expansion, while all lumi-
nance values below this point are expanded according
to:
2.10.Display Processing
Lout = Lin + BAM (Lin - Lt)
In the display processing the conversion from digital
YCrCb to analog RGB is carried out. A block diagram is
shown in Fig. 2–18 on page 24. In the luminance pro-
cessing path, contrast and brightness adjustments and
a variety of features, such as black-level expansion,
dynamic peaking and soft limiting, are provided. In the
chrominance path, the CrCb signals are converted to
4:4:4 format and filtered by a color transient improve-
ment circuit. The YCrCb signals are converted by a
programmable matrix to RGB color space.
A second threshold, Ltr, can be programmed, above
which there is no expansion. The characteristics of the
black-level expander are shown in Fig. 2–11and Fig.
2–12.
Lmax
Ltr
Lout
The display processor provides separate control set-
tings for two pictures, i.e. different coefficients for a
‘main’ and a ‘side’ picture.
Lt
BAM
BTLT
Lmin
The digital OSD insertion circuit allows the insertion of
a 5-bit OSD signal. The color space for this signal is
controlled by a partially programmable color look-up
table (CLUT) and contrast adjustment.
The OSD signals and the display clock are synchro-
nized to the horizontal flyback. For the display clock, a
gate delay phase shifter is used. In the analog back-
end, three 10-bit digital-to-analog converters provide
the analog output signals.
Lin
BTHR
Ltr
Fig. 2–11: Characteristics of the black-level expander
The tilt point Lt is a function of the dynamic range of
the video signal. Thus, the black-level expansion is
only performed when the video signal has a large
dynamic range. Otherwise, the expansion to black is
zero. This allows the correction of the characteristics of
the picture tube.
2.10.1.Luma Contrast Adjustment
The contrast of the luminance signal can be adjusted
by multiplication with a 6-bit contrast value. The con-
trast value corresponds to a gain factor from 0 to 2,
where the value 32 is equivalent to a gain of 1. The
contrast can be adjusted separately for main picture
and side picture.
18
Micronas
MICRONAS [ MICRONAS ]
