ADVANCE INFORMATION
VDP 313xY
2.10.Display Part
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.
In the display part the conversion from digital YCRCB
to analog RGB is carried out (see Fig. 2–17 on
page 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 4:4:4 format and filtered
by a color transient improvement circuit. The YCRCB
signals are converted by a programmable matrix to
RGB color space.
The black level expander works adaptively. Depending
on the measured amplitudes Lmin and Lmax of the low-
pass-filtered luminance (during a programmalbe verti-
cal window) and an adjustable coefficient BTLT, a tilt
point Lt is established by
Lt = Lmin + BTLT×(Lmax − Lmin).
The display processor can switch between two sepa-
rate control settings (main/side) for contrast,brightness
and matrix coefficients.
Above this value there is no expansion, while all lumi-
nance values below this point are expanded according
to:
Lout = Lin + BAM ×(Lin − Lt)
2.10.1.Luminance Contrast Adjustment
A second threshold, Ltr, can be programmed, above
which there is no expansion. The characteristics of the
black level expander are shown in Fig. 2–10and
Fig. 2–11.
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 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.
2.10.2.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
Lmax
Lmax
Ltr
Lout
a)
Lt
Lt
Lmin
BAM
BTLT
Lmin
b)
Lt
Lin
BTHR
Ltr
Fig. 2–10: Characteristics of the black level expander
Fig. 2–11: Black-level-expansion
a) luminance input
b) luminance input and output
Micronas
15
MICRONAS [ MICRONAS ]
