Abstract:
A contour emphasizing circuit and a contour emphasizing method, in which an image having sharpness and a clear image can be obtained, are provided. The contour emphasizing circuit provides a contour emphasizing signal generating means which outputs a delayed video signal, a contour emphasizing signal, and a plurality of differential signals by processing an inputted video signal, a signal level difference detecting means to which the plurality of differential signals outputted from the contour emphasizing signal generating means are inputted and which outputs a signal selecting control signal, and a signal selecting means to which the delayed video signal, the contour emphasizing signal, and the signal selecting control signal are inputted and which mixes the delayed video signal with the contour emphasizing signal in an arbitrary ratio and outputs a video output signal or which selects the delayed video signal or the contour emphasizing signal and outputs the selected signal as a video output signal.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a contour emphasizing circuit and a contour emphasizing method which are used in image processing. 
     DESCRIPTION OF THE RELATED ART 
     In a conventional contour emphasizing circuit used for image processing, a differential process is applied to an inputted signal and the resultant signal is added to the original inputted signal. 
     However, in the conventional contour emphasizing circuit, signals before and behind the contour part of an image are also amplified and emphasized. The emphasized region becomes wider than the contour part. Consequently, the image has reduced sharpness. Hence it is difficult to obtain a clear image with the conventional contour emphasizing circuit. 
     Further, the differential signal including noise or ringing is added to the original inputted signal, therefore, when the degree of the contour emphasizing is increased, there is a problem in that the signal to noise ratio (SNR) of a signal outputted from the contour emphasizing circuit is deteriorated. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a contour emphasizing circuit and a contour emphasizing method in which an image having sharpness and a clear image can be obtained. 
     According to a first aspect of the present invention, for achieving the objects mentioned above, there is provided a contour emphasizing circuit. The contour emphasizing circuit provides a contour emphasizing signal generating means which outputs a delayed video signal, a contour emphasizing signal, and a plurality of differential signals by processing an inputted video signal, a signal level difference detecting means to which the plurality of differential signals outputted from the contour emphasizing signal generating means are inputted and which outputs a signal selecting control signal, and a signal selecting means to which the delayed video signal, the contour emphasizing signal, and the signal selecting control signal are inputted and which mixes the delayed video signal with the contour emphasizing signal in an arbitrary ratio and outputs a video output signal or which selects the delayed video signal or the contour emphasizing signal and outputs the selected signal as a video output signal. 
     According to a second aspect of the present invention, in the first aspect, the contour emphasizing signal generating means provides a plurality of delaying means which delays the inputted video signal and generates a plurality of delayed video signals in which one of the plurality of delayed video signals is a delayed video signal that the inputted video signal is delayed and the other of the plurality of delayed video signals is a delayed video signal that the delayed video signal is further delayed, a plurality of primary differential signal outputting means in which the inputted video signal and one of the plurality of delayed video signal are inputted and outputs a differential signal, and one and the other of the plurality of delayed video signals are inputted and outputs another differential signal, a secondary differential signal outputting means to which the differential signals outputted from the plurality of primary differential signal outputting means are inputted and outputs a secondary differential signal, and an adding means to which the further delayed video signal and the secondary differential signal are inputted and outputs the contour emphasizing signal. 
     According to a third aspect of the present invention, a contour emphasizing method provides the steps of; delaying an inputted video signal and outputting a delayed video signal, delaying the delayed video signal and outputting a further delayed video signal, applying primary differential to the inputted video signal and the delayed video signal and outputting a primary differential signal, applying primary differential to the delayed video signal and the further delayed video signal and outputting another primary differential signal, applying secondary differential to the primary differential signals and outputting a secondary differential signal, adding the further delayed video signal and the secondary differential signal and outputting a contour emphasizing signal, comparing the primary differential signals and detecting changing range of inputted video signal level and outputting a signal selecting control signal, and outputting a video signal by mixing the further delayed video signal with the contour emphasizing signal obtained at the adding process in an arbitrary ratio or by selecting the further delayed video signal or the contour emphasizing signal based on the signal selecting control signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects and features of the present invention will become more apparent from the consideration of the following detailed description taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a diagram showing signals of a contour emphasizing circuit of the present invention; 
     FIG. 2 is a block diagram showing a structure of an embodiment of the contour emphasizing circuit of the present invention; 
     FIG. 3 is a flowchart showing operation of a first embodiment of the contour emphasizing circuit of the present invention; and 
     FIG. 4 is a flowchart showing operation of a second embodiment of the contour emphasizing circuit of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, embodiments of the present invention are explained in detail. In a contour emphasizing circuit of the present invention, a signal during a period when a signal level of a video signal is changing is replaced by a contour emphasized signal. With this, a high quality image with sharpness and without ringing and emphasizing unnecessary parts can be realized. 
     FIG. 1 is a diagram showing signals of a contour emphasizing circuit of the present invention. As shown in FIG. 1, at the contour emphasizing circuit, a signal selecting control signal S 8  and a contour emphasizing signal S 7  are generated by an inputted video signal S 1 , a delayed video signal S 2 , and a delayed video signal S 3 . And a video output signal S 9  whose contour is emphasized can be obtained by that the signal selecting control signal S 8  makes the delayed video signal S 3  and the contour emphasizing signal S 7  change over optimally. 
     FIG. 2 is a block diagram showing a structure of an embodiment of the contour emphasizing circuit of the present invention. As shown in FIG. 2, the embodiment of the contour emphasizing circuit of the present invention consists of a contour emphasizing signal generator  7 , a signal level difference detector  8 , and a signal selector  9 . The contour emphasizing signal generator  7  consists of a delay element  1 , a delay element  2 , a first subtracter  3 , a first subtracter  4 , a second subtracter  5 , and an adder  6 . 
     FIG. 3 is a flowchart showing operation of a first embodiment of the contour emphasizing circuit of the present invention. Referring to FIGS. 1,  2 , and  3 , the operation of the first embodiment of the contour emphasizing circuit of the present invention is explained. First, an inputted video signal S 1  is delayed at the delay elements  1  and  2 , and delayed video signals S 2  and S 3  whose delayed amounts are different from each other are generated (step s 101 ). The three video signals S 1 , S 2 , and S 3  are inputted to a primary differential circuit composed of the first subtracters  3  and  4 , and as shown in FIG. 2, a primary differential signal S 4  is generated from the video signals S 1  and S 2  at the first subtracter  3 , and a primary differential signal S 5  is generated from the delayed video signals S 2  and S 3  at the first subtracter  4  (step s 102 ). 
     The primary differential signals S 4  and S 5  generated respectively at the first subtracters  3  and  4  are inputted to the second subtracter  5 , and a secondary differential signal S 6  is generated (step s 103 ). And this secondary differential signal S 6  and the delayed video signal S 3  are inputted to the adder  6 , and a contour emphasizing signal S 7  is generated (step s 104 ). The operation mentioned above is performed at the contour emphasizing signal generator  7 . 
     The primary differential signals S 4  and S 5  are inputted to the signal level difference detector  8  and compared, and the changing range of inputted video signal level is detected and the detected result is outputted as a signal selecting control signal S 8  (step s 106 ). 
     At the signal selector  9 , the level of the signal selecting control signal S 8  is examined (step s 107 ), and either the contour emphasizing signal S 7  or the delayed video signal S 3  is selected in response to the change of the inputted video signal level. As shown in FIG. 1, when the signal selecting control signal S 8  is low level, the delayed video signal S 3  is selected as a video output signal S 9  (step s 105 ). And when the signal selecting control signal S 8  is high level, the contour emphasizing signal S 7  is selected as the video output signal S 9  (step s 108 ). 
     As mentioned above, the video output signal S 9  can be obtained by selecting either the contour emphasizing signal S 7  or the delayed video signal S 3  which has the same delayed amount that the contour emphasizing signal S 7  has, based on the signal selecting control signal  8  which shows the change of the inputted video signal level. That is, the contour emphasizing signal S 7  is selected as the video output signal S 9  in a period shortly after the inputted video signal S 1  level is changing and the delayed video signal S 3  is selected as the video output signal in at other times. At this video output signal S 9 , the period of the contour emphasizing signal S 7  is short, therefore even when the degree of the emphasizing is increased, the ringing does not occur. Therefore, the SNR of the video output signal S 9  is not deteriorated. The differential circuits composed of subtracters that are used at the present invention, can be replaced by other circuits having the same function. 
     Next, a second embodiment of the contour emphasizing circuit of the present invention is explained. The structure of the second embodiment is the same as the first embodiment shown in FIG.  2 . In the first embodiment, the signal selector  9  generates the video output signal S 9  being the contour emphasized signal by selecting either the contour emphasizing signal S 7  or the delayed video signal S 3 , based on the signal selecting control signal  8  which responds to the change of the inputted video signal level. In the second embodiment, when the change of the level of the delayed video signal S 3  is large, that is when the differential signal level of the inputted video S 1  is large, a video output signal S 9  is a mixed signal, in which the component of the contour emphasizing signal S 7  is made to be large and the component of the delayed video signal S 3  is made to be small. As mentioned above, in the second embodiment of the present invention, the video output signal S 9 , in which the mixing ratio of the contour emphasizing signal S 7  to the delayed video signal S 3  is changed in response to the differential signal level of the inputted video signal S 1 , can be outputted. With the second embodiment, the same effect as the first embodiment can be achieved. In the second embodiment, the primary differential signals S 4  and S 5 , or the secondary differential signal S 6  can be used as the differential signal which is used at the signal selector  9  to decide the mixing ratio. Or a combined signal, in which the primary differential signals S 4  and S 5  are combined with the secondary differential signal S 6 , can be used as the differential signal. Further, the nondifferential signals such as the inputted video signal S 1 , the delayed video signal S 2 , and the delayed video signal S 3 , can be combined with the primary differential signal S 4  and S 5  or the secondary differential signal S 6 , and used as the differential signal. 
     FIG. 4 is a flowchart showing operation of the second embodiment of the contour of the second embodiment of the contour emphasizing circuit of the present invention is explained. First, as in the first embodiment, an inputted video signal S 1  is delayed at the delay elements  1  and  2 , and delayed video signals S 2  and S 3  whose delayed amounts are different from each other are generated (step s 111 ). These three video signals S 1 , S 2 , and S 3  are inputted to a primary differential circuit composed of the first subtracters  3  and  4 , and as shown in FIG. 2, a primary differential signal S 4  is generated from the video signals S 1  and S 2  at the first subtracter  3 , and a primary differential signal S 5  is generated from the delayed video signals S 2  and S 3  at the first subtracter  4  (step s 112 ). 
     The primary differential signals S 4  and S 5  generated respectively at the first subtracters  3  and  4  are inputted to the second subtracter  5 , and a secondary differential signal S 6  is generated (step s 113 ). The secondary differential signal S 6  and the delayed video signal S 3  are inputted to the adder  6 , and a contour emphasizing signal S 7  is generated (step s 114 ). The operation mentioned above is performed at the contour emphasizing signal generator  7  as in the first embodiment. 
     The primary differential signals S 4  and S 5  generated at the contour emphasizing signal generator  7  are inputted to the signal level difference detector  8  and compared, and the changing range of the inputted video signal level is detected and the detected result is outputted as a signal selecting control signal S 8  (step s 119 ). 
     The delayed video signal S 3  and the contour emphasizing signal S 7  are inputted to the signal selector  9  (step s 115 ). And the change of the level of the signal selecting control signal S 8  (the change of the inputted video signal level) is examined at the signal selector  9  (step s 116 ). 
     The mixing ratio of the delayed video signal S 3  to the contour emphasizing signal S 7  is decided at the signal selector  9  (step s 117 ). A video signal S 3  with the contour emphasizing signal S 7  at the signal selector  9  and outputted (step s 118 ). 
     As mentioned above, in the second embodiment of the contour emphasizing circuit of the present invention, the mixing ratio of the contour emphasizing signal S 7  to the delayed video signal S 3  is changed in response to the difference between the inputted video signal level from the secondary differential signals S 4  and S 5 . That is, the second embodiment has a function that judges the level of the differential signals. 
     According to the first embodiment of the present invention the contour emphasizing signal S 7  is only used when the inputted video signal level is changing. Therefore, contour emphasizing with high definition can be achieved. And even with the degree of the contour emphasizing increased, ringing does not occur and the SNR is not deteriorated. 
     Further, in the second embodiment of the present invention, the contour emphasizing circuit of the present invention can adjust the mixing ratio of the delayed video signal S 3  to the contour emphasizing signal S 7  in response to the inputted video signal level. Therefore, the contour emphasizing with high definition can be achieved. And even with the degree of the contour emphasizing increased, ringing does not occur and the SNR is not deteriorated. 
     While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by those embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.