Television – Camera – system and detail – Combined image signal generator and general image signal...
Reexamination Certificate
1997-07-11
2001-07-24
Garber, Wendy R. (Department: 2612)
Television
Camera, system and detail
Combined image signal generator and general image signal...
Reexamination Certificate
active
06266088
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an edge crispening circuit and, more particularly, to a method of performing edge crispening by an out-of-green system in a color image sensor and a circuit for carrying out the same.
Heretofore, color cameras equipped with edge crispening devices have been proposed. Where an image signal from a color camera is processed by an edge crispening method in the prior art edge crispening circuitry, edge crispening circuits are provided for green (G), blue (B), and red (R) signals, respectively. These edge crispening circuits create edge crispening signals for the edges or contours of an image. These edge crispening signals are superimposed on the R,. G,and B signals, thus obtaining an edge-enhanced color image.
This conventional method needs three edge crispening circuits. Hence, large-sized circuitry is necessary. Also, the cost is increased. Therefore, this method has been mainly used for high-grade cameras such as those used in broadcasting stations.
In recent years, domestic video movies have become widespread. Therefore, there is a need for more compact low-cost color cameras. Also, an edge crispening circuit of a smaller size has been required.
An out-of-green edge crispening circuit is available as a means for accomplishing an edge crispening circuit of a smaller size, and is described in the “Prior Art Technique” column of Japanese Patent Laid-Open No. 285778/1990. In this prior art out-of-green edge crispening device, an edge crispening signal is created from the image signal from the green color image sensor device and superimposed on blue and red signals. In this way, edge crispening is performed for each color signal.
However, the prior art edge crispening device utilizing the out-of-green method has the following problems. Since the edge crispening signal is created from the green signal, the level of the edge crispening signal relative to all the R, G, and B signals is determined by the ratio of the green signal component contained in the imaged subject. Therefore, the edge crispening effect is affected greatly by the color of the subject.
For example, where the subject is a totally blue pattern, the G signal level is low and so the level of the edge crispening signal DTL
1
is low. As a result, sufficient edge crispening effect cannot be obtained.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an edge crispening method capable of producing a good edge crispening effect irrespective of the colors of the subject.
It is another object of the invention to provide an edge crispening circuit capable of producing good edge crispening effect irrespective of the colors of the subject.
In accordance with one aspect of the present invention, there is provided an edge crispening method in which an edge crispening signal is created from the green (G) signal. This edge crispening signal is superimposed on the three primary color signals, i.e., green (G), blue (B), and red (R), to crispen the edges of a reproduced image. This method is characterized in that the magnitude of the edge crispening signal superimposed on the R, G, and B signals is controlled according to the ratios of the levels of the B and R signals to the level of the G signal.
In accordance with another aspect of the present invention, there is provided an edge crispening method in which an edge crispening signal is created from the green (G) signal. This edge crispening signal is superimposed on the three primary color signals, i.e., green (G), blue (B), and red (R), to crispen the edges of a reproduced image. This method is characterized in that coefficients, or weighting factors, are calculated from the ratios of the levels of the B and R signals to the level of the G signal and that the edge crispening signal is multiplied by the coefficients. The resultant signals, hereinafter referred to as the weighted edge crispening signals, are superimposed on the R, G, and B signals. Preferably, the levels of the R, G, and B signals are found from their respective amplitudes.
In accordance with the present invention, there is provided an edge crispening circuit which comprises arithmetic means, a decision means, and superimposing means. The arithmetic means calculate the ratio of the level of the blue (B) signal to the input green (G) signal, as well as the ratio of the level of the red (R) signal to the level of the green (G) signal. The decision means produces coefficients, or weighting factors, used to control the magnitudes of the edge crispening signal superimposed on the R, G, and B signals. The coefficients are found from the ratios described above. The superimposing means superimpose the weighted edge crispening signals to the R, G, and B signals.
Preferably, the edge crispening circuit in accordance with the present invention further includes comparator means and a level-varying means. The aforementioned arithmetic means comprise first and second arithmetic means. The first arithmetic means produces a coefficient k
1
from the levels of the G and B signals. The second arithmetic means produces a coefficient k
2
from the levels of the G and R signals. The comparator means compares the magnitudes of the coefficients k
1
and k
2
and selects a larger one. The decision means compares the coefficient k
1
or k
2
selected by the comparator means with a reference value &agr; and produces a coefficient k. The level-varying means preferably varies the level of the edge crispening signal according to the coefficient k produced by the decision means.
Other objects and features of the invention will appear in the course of the description thereof, which follows.
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patent: 5298981 (1994-03-01), Topper et al.
patent: 5515112 (1996-05-01), Penney
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Foley & Lardner
Garber Wendy R.
Moe Aung S.
NEC Corporation
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