Contour emphasizing circuit

Details Contour emphasizing circuit Contour emphasizing circuit

1999-09-24

2002-08-13

Hsia, Sherrie (Department: 2614)

Television

Image signal processing circuitry specific to television

Transition or edge sharpeners

C348S630000

Reexamination Certificate

active

06433836

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a contour emphasizing circuit, wherein a digital contour-emphasized video signal, on the basis of the input of an analog signal, is output, and is employed to produce contour-emphasized color video signals by a display device (for example, matrix type display device) which is digitally driven, such as a plasma display (referred only to as PDP) and liquid crystal display (referred only to as LCD).
BACKGROUND ART
In conventional CRT (Cathode Ray Tube) display device, contour emphasizing processing is carried out to achieve high picture quality implementation and high-pass characteristic compensation. The contour emphasizing circuit for carrying out this contour emphasizing processing is, as shown in
FIG. 1
, composed of a Y/C separation circuit
10
, a color demodulation circuit
12
, a contour extracting circuit, phase adjustment circuits
16
,
18
and
20
, an adder
22
and a matrix circuit
24
.
The Y/C separation circuit
10
separates a Y (luminance) signal and a C (color) signal from the composite video signal (for example, compound color television signal) input to an input terminal
26
, and the color modulation circuit
12
separates a Y signal, an R−Y (color difference) signal and a B−Y (color difference) signal on the basis of a Y signal and a C signal.
The contour extracting circuit
14
extracts the contour component Ye which is a high-pass component of a video signal on the basis of an adder
22
.
The matrix circuit
24
prepares a signal adding the contour component Ye to the R (red), G (green) and B (blue) signals, respectively, on the basis of (Y+Ye) signals added by the adder
22
, an (R−Y) and a (B−Y) signal phase-adjusted by phase adjustment circuits
18
and
20
. That is to say, the matrix circuit
24
prepares R+Ye, G+Ye and B+Ye on the basis of the operations in following equations (1), (2) and (3). By outputting these R+Ye, G+Ye and B+Ye to the CRT-display device by means of output terminals
28
r,
28
g
and
28
b,
videos contour-emphasized by this CRT display device are displayed.
(
R−Y
)+(
Y+Ye
)=
R+Ye
  (1)
(
G−Y
)+(
Y+Ye
)=
G+Ye
  (2)
(
B−Y
)+(
Y+Ye
)=B+Ye  (3)
(G−Y) in the above equation (2) is generated by the following equation (4).
When a video contour-emphasized by the matrix type display device driven by digital video signals (for example, R, G and B signals) like PDP and LCD is displayed, each signal of (R+Ye), (G+Ye) and (B+Ye) obtained in output terminals
28
r
,
28
g
and
28
b
in
FIG. 1
is output to the display device after being digitized by the A/D (analog/digital) conversion circuit. However, in such a prior example, when a large amplitude signal is input to an input terminal
26
, or when the contour emphasizing quantity (or contour emphasizing coefficient, the description is omitted, as it is similar afterwards) is “large”, there is a problem that the correct operation cannot be obtained over the dynamic range of the A/D conversion circuit.
For example, when a large amplitude signal is input to the input terminal
26
, by outputting a signal over the dynamic range of the A/D conversion circuit as shown at the left-hand side in FIG.
2
(
a
) from output terminals
28
r
,
28
g
and
28
b
, there are problems that signals exceeding an upper conversion reference voltage value VRT (for example, 5 volts) in the dynamic range, as shown at the right-hand in said FIG. (a), are cut, resulting in producing white crushing or signals under the lower conversion reference voltage value VRT (for example, 3 volts) in the dynamic range are cut, resulting in producing black crushing.
Further, when the contour emphasizing quantity of the contour extracting circuit
14
is “large”, there are problems that signals over the dynamic range of the A/D conversion circuit as shown at the left-hand side in FIG.
2
(
b
) are cut, resulting in producing white crushing or signals under the lower conversion reference voltage value VRB are cut, resulting in producing black crushing.
The present applicant simultaneously proposes a contour emphasizing circuit as shown in
FIG. 3
as a separate application to solve the above mentioned problems. That is to say, by generating a Y signal after converting analog color video signals to digital signals by the A/D conversion circuit and by constituting so that digital video signals which are contour-emphasized will be obtained from adding the contour component extracted from this Y signal to digital color video signals from the A/D conversion circuit, it has been designed so that the contour emphasizing component, unlike the conventional example, will not surpass the dynamic range of the A/D conversion circuit.
However, when a signal processing circuit is added to carry out the signal processing like picture element number, gamma correction, etc. to this proposed contour emphasizing circuit, there is a problem that the contour emphasizing effect is reduced by half according to the position for adding this signal processing circuit.
For example, as shown in
FIG. 3
, when the signal processing circuit
35
for carrying out the picture element number conversion and gamma correction is added to the back stage of contour adders
34
r
,
34
g
and
34
b
, there is a problem.
The circuit shown in
FIG. 3
is constituted by A/D conversion circuits
30
r
,
30
g
and
30
b
, a first phase adjustment circuit
31
composed of line memories
31
r
,
31
g
and
31
b
, a second phase adjustment circuit
33
, contour adders
34
r
,
34
g
and
34
b
, a signal processing circuit
35
, a Y signal generation circuit
36
, a contour extracting circuit
38
, a gain controller
40
for the contour components, and a coefficient multiplication circuit
42
.
Hence, analog R, G and B signals input to input terminals
44
r
,
44
g
and
44
b
are converted to digital signals by A/D conversion circuits
30
r
,
30
g
and
30
B, phase-adjusted by first and second phase adjustment circuits
31
and
33
, and input to contour adders
34
r
,
34
g
and
34
b
. The Y signal generation circuit generates Y signals from digital R, G and B signals, the contour extracting circuit
38
extracts a contour component from a Y signal, this extracted contour component enters in contour adders
34
r
,
34
g
and
34
b
through the gain controller
40
and the coefficient multiplication circuit
42
, and are added to the original digital R, G and B signals. For digital R, G and B signals contour-emphasized by those contour adders
34
r
,
34
g
and
34
b
, the signal processing like picture element number conversion, gamma correction, etc. is carried out by the signal processing circuit
35
and supplied to the display device through output terminals
86
r
,
86
g
and
86
b
, and contour-emphasized videos are displayed.
At this time, contour adders
34
r
,
34
g
and
34
b
add contour components as shown in the same figure (b) output from multipliers
86
r
,
86
g
and
86
b
of the coefficient multiplication circuit
42
to input signals R, G and B as shown in FIG.
4
(
a
) from the second phase adjustment circuit
33
, and output R, G and B signals contour-emphasized as shown in the same figure (c). However, there is a problem that the contour emphasizing effect comes to be reduced by half by the signal processing circuit
35
at the later stage.
Next, functions that the contour emphasizing effect as described above is reduced by half will be explained employing
FIGS. 5 and 6
.
FIG. 5
shows a case that the picture element number conversion is carried out to adjust the sampling picture element number to the display picture element number of the display device, and if the rate conversion is carried out making the sampling picture element number to ½, as shown in the same figure (
b
), against the original signal shown in the same figure (
a
), signals output from output terminals
86
r
,
86
g
and
86
b
beco

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