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VDP3104B

Video Processor Family

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PRELIMINARY DATA SHEET

VDP 31xxB

2.8. Display Part

In the display part the conversion from digital YCrCb to

analog RGB is carried out. A block diagram is shown in

Figure 2–20. In the luminance processing 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 20.25 MHz sampling rate

and filtered by a color transient improvement 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 con-

trolled by a partially programmable color look-up table

(CLUT) and contrast adjustment.

The OSD signals and the display clock are synchronized

to the horizontal flyback. For the display clock, a gate

delay phase shifter is used. In the analog backend, three

10-bit digital-to-analog converters provide the analog

output signals.

2.8.1. Luma Contrast Adjustment

The contrast of the luminance signal can be adjusted by

multiplication with a 6-bit contrast value. The contrast

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.

2.8.2. 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 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 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 coefficient

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. 2–13 and Fig.

2–14.

The tilt point Lt is a function of the dynamic range of the

video signal. Thus, the black level expansion is only per-

formed when the video signal has a large dynamic

range. Otherwise, the expansion to black is zero. This al-

lows the correction of the characteristics of the picture

tube.

a)

Lout

Lmax

Ltr

Lt

b)

BAM

BTLT

Lmin

Lmax

Lt

Lmin

Lt

Ltr

BTHR

Lin

Fig. 2–13: Characteristics of the black level expander

Fig. 2–14: Black-level-expansion

a) luminance input

b) luminance input and output

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