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VCT38XXA

Video/Controller/Teletext IC Family

Micronas 

VCT 38xxA

ADVANCE INFORMATION

2.9. Macrovision Detection

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).

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 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).

2.10.Display Processing

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.

The display processor provides separate control set-

tings for two pictures, i.e. different coefficients for a

‘main’ and a ‘side’ picture.

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.

2.10.2.Black-Level Expander

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.

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

Lt = Lmin + BTLT (Lmax - Lmin).

Above this value there is no expansion, while all lumi-

nance values below this point are expanded according

to:

Lout = Lin + BAM (Lin - Lt)

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.

Lout

Lmax

Ltr

Lt

BAM

BTLT

Lmin

Ltr BTHR

Lin

Fig. 2–11: Characteristics of the black-level expander

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.

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.

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