JPH0369477B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention can shorten the transient period of a color difference signal and make the rise and fall steep.
The present invention relates to a color transient correction circuit that can obtain clear images with sharp outlines and less color fringing.

Prior Art FIGS. 3 and 4 show a block diagram of a conventional color transient correction circuit and waveforms of each part. Figure 3b is obtained by differentiating and full-wave rectifying the two color difference signals of red and blue.
A pulse-like waveform that captures the transient period of the color difference signal is obtained. The two pulsed signals obtained in this way are added together to create a composite signal, which is further subjected to processing such as waveform shaping to create a color transient correction pulse d, which turns on switch 1 in the figure. Turn off. During the period when the pulse is at a high level, the switch 1 is turned off to cut off the input, and the storage capacitor 2 is discharged to maintain the previous state. Then, at the same time that the pulse changes to low level, switch 1 is turned on to charge storage capacitor 2, and the output reaches the same level as the input.

Due to this operation, a color difference signal having a transient as shown in FIG. 2A is improved to a color difference signal having a steep rise as shown in FIG. (IEEE
TRANSACTIONS ON CONSUMER
ELECTRONICS NOVEMBER 1983
(See VOLUME CE29 NUMBER4) Problems to be Solved by the Invention However, with this method of simply adding together the pulsed signals obtained from the two color difference signals, there is a difference in the transient period of the two color difference signals. If this occurs, the pulse width will expand, resulting in the following problems, for example.

Assume that there is a narrow red color difference signal with a width of about 1 μsec as shown in FIG. 4a. The waveform obtained by differentiating and full-wave rectifying the signal is shown in b in the same figure, and the color difference signal after color transient correction is shown in c in the same figure. There is no problem if the phases and transient periods of the red and blue color difference signals match, but if the blue color difference signal is
In the case where the red color difference signal and the transient period are shifted, the signal obtained by adding the red and blue differentials + full-wave rectified wave will be as shown in the figure f, and Therefore, the red color difference signal subjected to the color transient correction becomes a signal with a narrow width and amplitude, as shown in g in the figure, compared to the ideally corrected signal c in the figure. This causes a phase shift between the luminance signal and the color difference signal and a decrease in color saturation.

The present invention solves these conventional problems and alleviates the disadvantages that appear when color transients are corrected.

Means for Solving the Problems The present invention provides a method for combining pulse-like signals obtained by differentiating and full-wave rectifying red and blue color difference signals to create a composite pulse signal. The pulsed signals obtained from the other color difference signals are mainly used, and the pulsed signals obtained from other color difference signals are added to compensate for the deficiency.

Operation By using the circuit of the present invention, each color difference signal is corrected using a pulsed signal obtained by mainly differentiating and full-wave rectifying the red difference signal as a correction switching pulse. Therefore, it is possible to reduce adverse effects such as a decrease in color saturation and a phase shift between the color difference signal and the luminance signal, which are caused by a difference in the transient period with other color difference signals.

In addition, even if the amplitude change of the red difference signal is so small that no pulse can be detected, if there is an amplitude change in another color difference signal, a corresponding pulse is added, so the red amplitude change will be detected. Color transients can be corrected even when no color is available.

Embodiment Hereinafter, a circuit according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of one embodiment of the present invention. In the figure, reference numeral 3 denotes a comparator, and one of its inputs receives a pulse-like waveform obtained by differentiating the red difference signal and undergoes full-wave rectification, and the other input receives a voltage slightly higher than the lowest potential of the pulse-like waveform as a reference voltage.
When the potential of the pulse waveform is higher than the reference voltage, the output of the comparator becomes low level and the switch 4 is turned off. Conversely, when the potential of the pulse waveform is lower than the reference voltage, the output of the comparator becomes high level and switch 4 is turned on.
A pulsed waveform obtained by differentiating and full-wave rectifying the blue difference signal is added. This results in a blue pulse being added to the red pulse wave only when it is smaller than a certain standard.

FIG. 2 is an example of a circuit that realizes this. The transistors 5 and 6, the resistors 7 and 8, and the current source 15 constitute a comparator. A pulse obtained by differentiating and full-wave rectifying the red difference signal is input to the base of transistor 5, and a reference voltage is applied to the base of transistor 6. Comparing the two potentials, if the base potential of the transistor 5 is higher than the base potential of the transistor 6, the transistor 5 is turned on, and the collector potential is lowered by the voltage drop across the resistor 7, and the transistors 13, 14 and the resistor 11 are , 12 is turned off. Conversely, when the base potential of transistor 5 is lower than the base potential of transistor 6, transistor 5 is turned off, the collector potential becomes high, and the switch circuit is turned on. By adding such a circuit, color transient correction is performed mainly by pulses generated during the transient period of the red difference signal, and the amplitude change of the red difference signal is small and other Only when the amplitude change of the color difference signal is large, color transient correction is performed by a pulse generated during the transient period of the color difference signal having a large amplitude change.

Effects of the Invention As described above, the color transient correction circuit of the present invention mainly uses the pulse signal obtained from the red difference signal when adding up each pulse signal obtained by differentiating and full-wave rectifying each color difference signal. Therefore, the pulse signal obtained from other color difference signals is only added to compensate for this. Therefore, even if there is a slight deviation in the transient period between each color difference signal, the pulse width will be less likely to spread and will not be seriously affected.
It becomes possible to reduce damage such as a phase shift between a color difference signal and a luminance signal and a decrease in color saturation.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a color transient correction circuit according to an embodiment of the present invention, Fig. 2 is a specific circuit diagram of its main parts, and Fig. 3 is a block diagram of a conventional color transient correction circuit and its various parts. Waveform diagram FIG. 4 is a waveform diagram for explaining conventional problems. 3...Comparator, 4...Switch, 5,
6, 13, 14...transistor, 7-12...
Resistor, 15... Current source.

Claims (1)

[Claims] 1. First and second switch circuits that receive red and blue color difference signals as input, capacitors provided at other terminals of the first and second switch circuits, and input signals from the red and blue color difference signals. A differential full-wave rectifier circuit that generates third and fourth correction pulses, a comparison circuit that receives the third correction pulse and the reference voltage as input, and a differential full-wave rectifier circuit that generates only the third and fourth correction pulses. a synthesis circuit that receives input via a fifth switch circuit, and controls the first and second switch circuits with the output pulse of the synthesis circuit;
A color transient correction circuit characterized in that said fifth switch circuit is controlled by an output pulse of said comparison circuit.