Television – Image signal processing circuitry specific to television – Hue control
Reexamination Certificate
2000-06-21
2003-02-04
Miller, John (Department: 2614)
Television
Image signal processing circuitry specific to television
Hue control
C348S649000, C348S651000, C348S659000, C348S653000
Reexamination Certificate
active
06515714
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hue adjustment circuit used in TV sets.
BACKGROUND OF THE INVENTION
In NTSC TV sets, a hue adjustment (TINT) circuit is nearly indispensable in order to correct a tint shift caused when demodulating a chroma signal.
On the other hand, devices such as digital video disks (DVDs) have spread in recent years. In order to connect these devices to a TV set, capability of inputting a YUV signal (color difference signal) besides a composite video signal to a TV set is being demanded.
When the YUV signal is input, it is not demodulates and consequently a hue adjustment circuit should be essentially unnecessary. For the purpose of delicate tint adjustment, it is also requested to hue adjust the YUV signal (color difference signal) as well.
The present invention aims at implementing such a hue adjustment on the color difference signal using a compact configuration.
The conventional art will now be described.
FIG. 2
is a diagram showing the conventional art.
In
FIG. 2
, numeral
1
denotes a 90° phase shift circuit for shifting the phase of a sub-carrier signal (hereafter referred to as fsc signal) by 90°,
2
a TINT phase shift circuit for shifting the phase of the fsc signal in order to adjust the hue,
3
a
a circuit for multiplying the fsc signal subjected to phase adjustment in the TINT phase shift circuit
2
by the fsc signal subjected to phase shift in the 90° phase shift circuit
1
.
In
FIGS. 2
,
4
a
,
4
b
,
4
c
and
4
d
are circuits for multiplying output signals of multiplier circuits
3
a
and
3
b
by a color difference signal (a R—Y signal and a B—Y signal), and
5
a
and
5
b
are circuits for addition and subtraction of outputs of the multiplier circuits
4
a
,
4
b
,
4
c
and
4
d.
FIG. 3
is a diagram showing a vector (hue) of a chroma signal.
FIG. 4
is a vector diagram showing phase relations among a burst signal, an original fsc signal FSC(0), a fsc signal FSC(90) subjected to phase shift in the 90° phase shift circuit
1
, and a fsc signal subjected to phase adjustment FSC(&agr;) subjected to phase adjustment in the TINT phase shift circuit
2
.
In
FIG. 3
, it is provisionally assumed that the vector (hue) of a chroma signal of a certain color is A and its angle is &thgr;. The angle of the burst signal is 180°.
When a chroma signal having a hue A is multiplied by the fsc signal and thereby demodulated to the color difference signal (R—Y and B—Y), the R—Y signal and the B—Y signal can be represented as sin &thgr; and cos &thgr;, respectively.
When the hue A is changed to a hue A′ by changing the phase by &agr;, the color difference signal R—Y and B—Y demodulated by the fsc signal become sin (&thgr;+&agr;) and cos (&thgr;+&agr;).
From the addition theorem, the following equations (1) and (2) are derived.
sin (&thgr;+&agr;)=sin &thgr; cos &agr;+ cos &thgr; sin &agr; (1)
cos (&thgr;+&agr;)=cos &thgr; cos &agr;− sin &thgr; sin &agr; (2)
Therefore, hue adjustment can be conducted by arithmetic operations on the color difference signals R—Y (sin &thgr;) and B—Y (cos &thgr;) and hue correction components sin &agr; and cos &agr;.
The hue correction components sin &agr; and cos &agr; can be generated from the fsc signal by using the 90° phase shift circuit
1
and the TINT phase shift circuit
2
as shown in FIG.
2
.
Hereafter, its principle will be described.
Typically, demodulation from the chroma signal to the color difference signal (R—Y signal and B—Y signal) is conducted by multiplying two fsc signals, synchronized in phase to the burst signal and differing in phase by 90°, by the chroma signal.
The two fsc signals differing in phase by 90° are obtained from the original fsc signal (hereafter abbreviated to FSC(0)) and a fsc signal (hereafter abbreviated to FSC(90)) shifted in phase by 90° from FSC(0) in the 90° phase shift circuit
1
.
FIG. 4
shows phase relations among the burst signal, FSC(0), FSC(90).
Here, in the TINT phase shift circuit
2
, the phase of FSC(0) is changed by &agr;. The output of the TINT phase shift circuit
2
is FSC(&agr;) .
FIG. 4
shows phase relations among the burst signal, FSC(0), FSC(90), and FSC(&agr;).
If FSC(0) is multiplied by FSC (&agr;) in the multiplier circuit
3
a
of
FIG. 2
, a component cos &agr; a is obtained from its output.
In the same way, if FSC(90) is multiplied by FSC(&agr;) in the multiplier circuit
3
b
of
FIG. 2
, a component sin &agr; is obtained from its output.
Results of these multiplication operations are evident from
FIG. 4
as well. Since cos &agr; and sin &agr; are scalar quantities obtained from multiplication of vectors, it is understood that they are direct current signals having neither frequency components not phase components.
As described above, the hue correction components sin &agr; and cos &agr; can be obtained from the fsc signal.
On the other hand, the multiplier circuits
4
a
and
4
b
, the adder circuit
5
a
, and the subtracter circuit
5
b
are circuits for implementing the equations (1) and (2).
As a result of computation operations conducted in the multiplier circuits
4
a
and
4
b
, the adder circuit
5
a
, and the subtracter circuit
5
b
, the R—Y signal changed in hue by &agr; (sin (&thgr;+&agr;)) and B—Y signal changed in hue by &agr; (cos (&thgr;+&agr;)) can be obtained.
If the conventional art is used in a TV set, however, a circuit for generating the hue adjustment components sin &agr; and cos &agr; is separately needed. This results in a drawback that the circuit scale becomes large and the system itself becomes complicated.
SUMMARY OF THE INVENTION
It is an object of the present invention to facilitate circuit implementation and make the circuit scale smaller by using the chroma signal demodulation circuit in the TV set as the hue adjustment circuit as well.
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patent: 4118741 (1978-10-01), Gomi et al.
patent: 4197556 (1980-04-01), Isono et al.
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patent: 4679072 (1987-07-01), Takayama
patent: 4695875 (1987-09-01), Kishi
patent: 4788586 (1988-11-01), Eckenbrecht
patent: 5381185 (1995-01-01), Ohki et al.
patent: 5654768 (1997-08-01), Hatano
patent: 59-163995 (1984-09-01), None
patent: 1-155795 (1989-06-01), None
patent: 1-288192 (1989-11-01), None
patent: 2-143789 (1990-06-01), None
Leydig , Voit & Mayer, Ltd.
Miller John
Natnael Paulos
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