Image analysis – Image enhancement or restoration – Intensity – brightness – contrast – or shading correction
Reexamination Certificate
1999-12-28
2003-12-02
Do, Anh Hong (Department: 2724)
Image analysis
Image enhancement or restoration
Intensity, brightness, contrast, or shading correction
C382S263000
Reexamination Certificate
active
06658165
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a contrast enhancing apparatus for a video signal, and in particular to a contrast enhancing apparatus which is capable of significantly enhancing a contrast of a video signal by enhancing(amplifying or attenuating) a video signal inputted.
2. Description of the Background Art
In a method for enhancing a contrast of a video signal, a boundary portion of a video signal is selected, and the boundary portion is enhanced for thereby enhancing a contrast of the same. In another method therefor, a light and darkness ratio between a light portion and a darkness portion is enhanced using a homomorphic filter for thereby enhancing a contrast.
As shown in
FIG. 1
, the contrast enhancing apparatus of a video signal formed of a conventional homomorphic filter includes an algebraical conversion unit
100
for converting a video signal Yin into an algebra form (log), a wave filtering unit
200
for separating an algebraically processed video signal Ylog
1
into a low frequency component Y
1
pf
1
and a high frequency component Yhpf
1
, a first multiplier
300
for attenuating the low frequency component Y
1
pf
1
using an attenuation coefficient “a”, a second multiplier
400
for amplifying the high frequency component Yhpf
1
using an amplifying coefficient “b”, a summing unit
500
for summing the attenuated low frequency component Y
1
pf
1
and the amplified high frequency component Yhpf
1
, and an exponential conversion unit
600
for converting the signal Ylog
2
summed by the summing unit
500
to a video signal.
The operation of the conventional contrast enhancing apparatus for a video signal will be explained with reference to the accompanying drawings.
First, the video signal Yin inputted from the algebraical conversion unit
100
is algebraically processed, and the thusly algebraically processed video signal Ylog
1
is divided into the low frequency component Y
1
pf
1
and the high frequency component Yhpf
1
by the wave filtering unit
200
. At this time, the low frequency component Y
1
pf is multiplied by the attenuating coefficient “a” and is attenuated by “a” times for enhancing the contrasts of the low frequency component Y
1
pf
1
and the high frequency component yhpf
1
, and the high frequency signal Yhpf
1
is amplified by the second multiplier
400
by the amplifying coefficient “b”. Here, since the attenuating coefficient “a” and the amplifying coefficient “b” have fixed values, the contrast of the video signal Yin is enhanced by uniformly attenuating or amplifying the inputted low frequency component Y
1
pf
1
and the high frequency component Yhpf
2
.
In addition, since the signal Ylog
1
that the low frequency component Y
1
pf
1
attenuated by the first multiplier
300
and the high frequency component Yhpf
1
amplified by the second multiplier
400
are summed by the summing unit
500
is an algebraically converted signal, the signal is inputted into the exponential conversion unit
600
and is exponentially converted and is recovered as a video signal Yout.
Therefore, in the homorphic filter, the contrast of the video signal is enhanced by attenuating the low frequency component Y
1
pf
1
of the input video signal Yin and amplifying the high frequency component Yhpf
1
using the fixed amplifying or attenuating coefficients “a” and “b”. However, since the above-described coefficients “a” and “b” have a fixed value, all video signals are amplified or attenuated by the fixed values, it is impossible to properly enhance the contrast of all video signals.
In addition, in the method in which the coefficients “a” and “b” are differently set in accordance with the video signal Yin, it is difficult to adapt in real time, and in the case that the low frequency component Y
1
pf
1
is attenuated, since a transition of the DC level occurs, the final output Yout must be scaled again, and the minimum and maximum values of the signal component must be obtained, so that a real time process is not implemented.
Since the video sinal is not processed in a real time, it is impossible to uniformly enhance the contrast of the video signal.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a contrast enhancing apparatus for a video signal which is capable of determining an enhancing coefficient of the low frequency component using a high frequency component level and a low frequency component level in a method for enhancing the low frequency component of the video signal, compensating the thusly determined coefficient using a DC level, obtaining a low frequency component, and the determining the enhancing coefficient of the high frequency component based on the enhancing coefficient of the low frequency component. In addition, the enhancing coefficient of the high frequency component and the enhancing coefficient of the low frequency component are given an off-set value in accordance with a control signal of a user, so that it is possible to enhance a light darkness ratio by variably amplifying or attenuating the contrast of the video signal in accordance with the levels of the high frequency component and low frequency component.
To achieve the above objects, there is provided a contrast enhancing apparatus for a video signal which includes an algebraical conversion unit for algebraically converting an inputted video signal, a wave filtering unit for separating the algebraically converted video signal into a low frequency signal and a high frequency signal, a low frequency coefficient mapping unit for generating a level of a high frequency signal which is an output of the wave filtering unit and a level of the low frequency signal and a low frequency enhancing coefficient based on a user's adjustment, a high frequency coefficient mapping unit for generating a high frequency enhancing coefficient which is in inverse proportion to the low frequency enhancing coefficient, a first multiplier for multiplying the low frequency signal and the low frequency enhancing coefficient, a low frequency signal processing compensation unit for receiving an output of the low frequency mapping unit and an output of the first multiplier and compensating a low frequency level, a second multiplier for multiplying the high frequency signal and the high frequency enhancing coefficient, a summing unit for summing an output of the low frequency amplifying compensation unit and an output of the second multiplier, and an exponential conversion unit for exponentially converting an output of the summing unit.
Additional advantages, objects and features of the invention will become more apparent from the description which follows.
REFERENCES:
patent: 4187519 (1980-02-01), Vitols et al.
patent: 4204226 (1980-05-01), Mistretta et al.
patent: 4829380 (1989-05-01), Iadipaolo
patent: 5359675 (1994-10-01), Siwoff
patent: 5546135 (1996-08-01), Okamoto et al.
patent: 6172718 (2001-01-01), Alvarez et al.
Schulze et al., “A morphology-Based Filter Structure for Edge-Enhancing Smoothing”, IEEE International Conference, vol. 2, Nov. 1994, pps. 530-534.
Do Anh Hong
Fleshner & Kim LLP
LG Electronics Inc.
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