Philips Semiconductors
Preliminary specification
YUV one chip picture improvement based on luminance
vector-, colour vector- and spectral processor
The maximum and minimum gain of each segment is
limited. Apart from the adaptive white-point stretching the
black and white references are not affected by the
non-linear processing. The amount of non-linearity can be
controlled by the I
2
C-bus non-linearity DAC:
bits NL5 to NL0.
V
ARIABLE GAMMA
On top of the histogram conversion a variable gamma
function is applied for an alternative brightness control, or
for factory adjustment. It is intended as an alternative for
the DC-offset of the classic brightness user control.
It maintains the black and white references. The gamma
ranges from 0.5 to 1.5. The gamma can be set by the
I
2
C-bus variable gamma DAC: bits VG5 to VG0.
C
UE FLASH
In the present TV environment there is a lot of measured
information like ambient light and noise. This information
can be used to make an update of settings of the several
algorithms after a picture has changed. The cue flash
signal detects when a picture changes significantly. When
the picture content has changed, the I
2
C-bus bit CF is set
to logic 1 in the status register. After reading the status
register, bit CF is reset to logic 0. On the output pin CF the
cue flash information is present (active LOW) for only one
line in the vertical retrace part. This pin is configured as an
open drain output and therefore should be pulled up to the
5 V supply.
Spectral processor
In the spectral processor the luminance transfer is
controlled by smart peaking, colour dependent sharpness
and luminance transient improvement, defined by the
sharpness improvement processor. The colour transfer is
controlled by a colour transient improvement circuit; an
additional output is available to provide a SCAVEM circuit.
A
DJUSTABLE CHROMINANCE DELAY
The colour vector processor drives a delay line for
correcting delay errors between the luminance input signal
and the chrominance input signals (U and V).
The chrominance delay can be adjusted in 6 steps of
12 ns (1f
H
) or 6 ns (2f
H
) by the I
2
C-bus bits CD2 to CD0.
S
HARPNESS IMPROVEMENT PROCESSOR
The sharpness improvement processor increases the
slope of large luminance transients of vertical objects and
enhances transients of details in natural scenes by contour
correction.
1999 Sep 24
7
TDA9178
It comprises three main processing units: the step
improvement processor, the contour processor and the
smart sharpness controller.
Transient improvement processor
The step improvement processor (see Fig.11) comprises
two main functions:
•
MINMAX generator
•
MINMAX fader.
The MINMAX generator utilizes all taps of an embedded
luminance delay line to calculate the minimum and
maximum envelope of all signals momentarily stored in the
delay line. The MINMAX fader chooses between the
minimum and maximum envelopes, depending on the
polarity of a decision signal derived from the contour
processor. Figures 12, 13 and 14 show some waveforms
of the step improvement processor and illustrate that fast
transients result with this algorithm. The MINMAX
generator also outputs a signal that represents the
momentary envelope of the luminance input signal.
This envelope information is used by the smart sharpness
controller.
Line width control (also called aperture control) can be
performed by I
2
C-bus line width DAC: bits LW5 to LW0.
This control can be used to compensate for horizontal
geometry errors caused by the gamma, for blooming of the
spot of the CRT, or for compensating SCAVEM.
Contour processor
The contour processor comprises two contour generators
with different frequency characteristics. The contour
generator generates a second-order derivative of the
incoming luminance signal which is supplied to the smart
sharpness controller. In the smart sharpness controller,
this signal is added to the properly delayed original
luminance input signal, making up the peaking signal for
detail enhancement. The peaking path features a low
peaking frequency of 2 MHz (at 1f
H
), or a high peaking
frequency of 3 MHz (at 1f
H
), selectable by I
2
C-bus
bit CFS.
The contour generators utilize three taps of the embedded
luminance delay line. Figure 15 illustrates the normalized
frequency transfer of the filter.
PHILIPS [ NXP SEMICONDUCTORS ]
