JPS5927507B2 - Contour enhancement circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a signal corresponding to the contour part of a video signal,
The present invention relates to an edge enhancement circuit that improves image quality by modulating the scanning speed of a display element such as T and emphasizing an edge on a display screen.

Conventionally, in order to improve the image quality by emphasizing the outlines of the display screen on television receivers, etc., methods have been used to emphasize the high frequency parts of the video signal, or to emphasize the outlines by modulating the scanning speed according to the signal. There are ways to improve image quality.

Among these, the details of the scanning speed modulation method will be explained.

In FIG. 1, if the waveform of the video signal from the receiver is a, the differential waveform is b, and when this differential waveform is superimposed on the deflection current of the CRT, it becomes a waveform like c. When a signal a is applied to a CRT grid, etc., and the electron beam is deflected using a signal c, the differential waveform bl of b becomes smaller than the normal deflection speed.
In the period b2, the deflection speed becomes faster, and in the period b2, the deflection speed becomes slower. Therefore, the brightness distribution on the CRT screen will be darker in the part corresponding to bl than in the case without scanning speed modulation, and brighter in the part corresponding to b2, and ideally the brightness distribution will be like d. It should be. but,
In an actual CRT, the beam spot diameter of the electron beam increases as the beam amount increases, that is, in high-brightness areas (bright scenes), and the characteristics of the outline area deteriorate, causing the beam spot diameter of the electron beam to increase.
The brightness distribution on the screen is as shown in e. For this reason, there is a drawback that even if scanning speed modulation is performed, the effect of contour enhancement in high-brightness portions cannot be sufficiently achieved. FIG. 2 shows an actual circuit configuration for performing the operation shown in FIG. 1. In Fig. 2, 0 is the video signal input terminal, which is amplified by the video amplifier 1, passed through the video output stage 2, and applied to the CRTT, and the output signal of 1 is differentiated by the differentiating circuit 5. A waveform b is created and amplified by an amplifier 6. Regarding the deflection and high voltage circuits, a synchronization separation circuit 3 separates the synchronization signal, and a deflection/high voltage circuit 4 generates a signal and high voltage to be applied to the deflection coil and applies them to the deflection coil 9 and CRT 7. The scanning speed modulation signal obtained in step 6 is added to the scanning speed modulation coil 8 to perform scanning speed modulation.

As mentioned above, in a CRT, the beam spot diameter becomes large in the high-brightness portion, and the characteristics deteriorate. This situation is shown in FIG. Figure 3 shows the color CRT electron beam current of 10
This shows how the spatial frequency response changes when the voltage is 0 pA, 500 μA, 1000 μA, and 1500 μA. The characteristics deteriorate in the large current area (high brightness area), and Figure 1 For a video signal like a,
It can be clearly seen that even if the image is displayed on a CRT with scanning speed modulation, the screen will look like e, and the contours in the high-brightness areas will not be sufficiently emphasized. In view of the above-mentioned prior art, the present invention provides CR
This also compensates for the deterioration of the characteristics in the high-brightness portion of T, so that a sufficient edge enhancement effect can be obtained even in the high-brightness portion.

The details of the present invention will be explained below.

FIG. 4 shows an embodiment of the present invention. In Fig. 4, a is the input video signal, which is subjected to gasoma correction and the waveform of the video signal is shaped to create a waveform like b, that is, a waveform that has been gamma-corrected with a correction value greater than 1. This is differentiated to give a waveform like c. When this waveform c is superimposed on the deflection current as a scanning speed modulation signal, the waveform becomes as shown in d. a for CRT grids, etc.
When the signal of is added and the scanning speed is modulated by the signal of c, the brightness distribution on the CRT screen becomes e if it is ideal (that is, the characteristics of the CRT itself are ideal), but in an actual CRT,
As mentioned above, the beam spot diameter in a high brightness area is larger than that in a low brightness area, so in an actual scene, the brightness distribution will be as shown in f. As can be seen from this waveform, the edge enhancement effect is ideal, and there is no deterioration of characteristics in high brightness areas as in the conventional example shown in FIG. 1e. By gamma-correcting the input video signal and differentiating it to obtain a scanning speed modulation signal in this manner, the edge enhancement effect can be improved. Next, a simple means for performing this gamma correction and a means for enhancing contours using this signal will be specifically explained. FIG. 5 shows an example of this.

Note that the same parts in FIG. 5 as in FIG. 2 are given the same numbers. When the video signal output is added to the CRT7 grid,
As shown in Figure 6, CRT7 generally has gamma characteristics (γ
+2.2), and the beam current has a waveform like b for the input video signal a, so if this beam current waveform is detected by some means, gamma correction of the input signal a shown in Figure 4 can be performed. A waveform b can be obtained. For this reason, a resistor 10 is added to the cathode of the CRT 7, and the amount of beam current flowing through this resistor is extracted as a voltage. The signal appearing at both ends of this resistor 10 becomes a gamma-corrected signal as shown in FIG. 4b. By differentiating this signal by 5 in FIG. 5, a waveform as shown in c in FIG. 4 can be obtained. By amplifying this signal at 6 in FIG. 5 and modulating it at the scanning speed modulation coil 8, a fourth
An ideally edge-enhanced image as shown in FIG. f can be displayed. Next, another embodiment is shown in FIG.

In FIG. 7, the same numbers are given to the same parts as in FIG. 2. The video signal is amplified by 1 and applied to a video output transistor 11, the output of which appears across a load resistor 12. This output voltage drives the CRT 7 by 1, and the cathode voltage of the CRT is output from the transistor 11.
By adding a transformer 13 for signal extraction during connection, the amount of beam current of the CRT 7 can be detected. The signal detected by this transformer 13 indicates the amount of beam current of the CRT when an input video signal is applied to the CRT, and therefore has a waveform as shown in b in FIG. This signal is processed as in the previous embodiment, and the scanning speed modulation coil 8
In addition, the brightness distribution obtained on the CRT screen is the fourth
As shown in Figure f, the performance compensates for the deterioration of the characteristics in the high brightness portion of the CRT. It is obvious that this transformer 13 can also be used as a peaking coil for emphasizing the high frequency portion of the video signal. When the scanning speed is modulated in this way to emphasize outlines on the screen to improve image quality, the input video signal is gamma-corrected to compensate for the deterioration of CRT characteristics in high-brightness areas. This is differentiated and this differentiated signal is used as a scanning speed modulation signal.

That is, in order to gamma-correct the video signal, the gamma characteristics of the CRT are effectively used, the video signal is applied to the CRT, and the beam current flowing through the CRT, that is, the gamma-corrected signal, is extracted and used. This signal is differentiated and the differentiated signal is used as a scanning speed modulation signal. In addition to television receivers, the above embodiments can also be used in various display devices such as CRT display devices that display various images, characters, graphics, and the like.

As described above, the present invention provides a very simple method for obtaining a signal for use in gamma-corrected scanning velocity modulation of a video signal without adding any complicated and expensive circuitry.
It is possible to achieve an edge enhancement effect that compensates for the deterioration of characteristics in the high brightness portion of RT.

[Brief explanation of drawings]

Fig. 1 is a waveform diagram explaining the edge enhancement effect of the conventional scanning speed modulation method, Fig. 2 is a circuit diagram embodying the scanning speed modulation method of Fig. 1, and Fig. 3 shows the beam spot diameter of a CRT. Diagram showing spatial frequency response due to change, 4th
The figure shows a waveform diagram for performing scanning speed modulation that also takes into account the characteristics of a CRT, and a waveform diagram showing its effect. Figure 5 is a circuit configuration diagram of an embodiment of the present invention. Figure 6 shows the gamma characteristics of a CRT. FIG. 7 is a circuit configuration diagram showing another embodiment of the present invention. 1...Video amplifier, 2...Video output stage, 3...Synchronization separation circuit, 4...Deflection/high voltage circuit, 5...・Differential circuit, 6...
・Amplifier, 7...CRTl8...Scanning speed modulation coil, 9...Deflection coil, 10...
...Resistor, 11...Transistor, 12
...Resistor, 13...Transformer.

Claims (1)

[Claims] 1: a gamma correction circuit for gamma-correcting an input image signal with a correction value greater than 1; a differentiation circuit for differentiating the gamma-corrected image signal; and scanning of a cathode ray tube using the differentiated signal. 1. A contour enhancement circuit comprising: a scanning speed modulation circuit that modulates speed.