JPS632470A - Picture quality improving circuit - Google Patents

Abstract

PURPOSE:To obtain excellent correcting characteristics over the whole video band by using two signals formed by tracking and selecting the maximum and minimum levels out of levels indicating the same time between plural signals having a prescribed time delay and an original signal. CONSTITUTION:When respective signals S0-S2 are inputted to maximum and minimum level circuits 22, 23, outputs SMAX, SMIN are outputted from respective circuits 22, 23. The signal S1 becomes an outline correcting signal S1' through an outline correcting circuit 18. Thereby, the peak level of the signal S1' exceeds respective DC levels of the signals SMAX, SMIN. When respective signals SMAX, SMIN, S1' input a shoot waveform removing circuit 21, outputs S3', S4' are generated from maximum and minimum level output circuit 14, 15. The output of a maximum level output circuit 17 is the same as the signal SMAX. Thereby, the output S6 of the circuit 17 indicates a waveform obtained by slicing the signal S1 by the upper and lower DC levels based upon the signals SMAX, SMIN as shown by a solid line. The waveform includes the information of the original signal S0 and can be treated as the outline-corrected signal.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention relates to an image quality improvement circuit that performs, for example, contour correction of an image using a delay means. The present invention relates to an image quality improvement circuit that performs good correction over the entire band of a video signal without causing such a phenomenon.

(Prior Art) As a means of improving the sharpness of an image, there is an image quality improvement measure using a contour correction circuit. This circuit aims to improve the image quality by adding a second-order differential waveform to the waveform of the video signal and correcting the characteristic rounding of the rising and falling edges.

FIG. 6 shows an example of this type of image quality improvement circuit, and FIG. 7 is an explanatory diagram showing the operation of the circuit of FIG. 6.

FIG. 6 shows input signal a to delay circuit 1. The second-order differential waveform created by the second-order differentiator circuit 2 is inverted and amplified by the inverting amplifier 3, and this amplified inverted signal C is input to the adder circuit 4 as the signal from the delay circuit 1. Then, an output signal d (contour correction signal) with an enhanced contour is obtained.

FIG. 7 (a) is the input signal, (b) is the output of the delay circuit 1]
, and (C) shows the output of the inverting amplifier 3. and,
As shown in (d), the addition output of these signals S and C by the adder 4 has a second-order differential waveform added thereto, and its rising and falling portions have steep characteristics peculiar to the second-order differential waveform. It has been replaced by

In FIG. 8, two delay circuits 5 and 6 are connected in series, the input f= is set to e, and each output of the delay circuits 5 and 6 is set to f.

When the signal e and the signal f are input to the subtraction circuit 7, the signal f and the signal q are input to the subtraction circuit 8. The outputs of these subtracting circuits 7 and 8 are respectively input to an adding circuit 9, and the second-order differential waveform from the adding circuit 9 is amplified.
By appropriately amplifying io'c, the amplifier 10 generates a preshoot corresponding to the second-order differential waveform of FIG. 7 (see FIG. 7C).

and an overshoot waveform addition signal i are obtained. The above subtraction circuits 7, 8. And the calculation by the adder circuit 9 is (fe)+(f-g)...(1
). Then, by adding the signal i to the signal f in the addition σ circuit 11, an output signal j whose rising portion and falling portion have been corrected is obtained, similar to that shown in FIG. 7d.

The two circuits mentioned above both have preshoots and
By adding an overshoot and an overshoot, the outline of the image is emphasized and the clarity is increased.

However, in general, video signals with such shoot waveforms have the disadvantage that the image appears to have border lines and is warped, making it difficult to view.

By the way, in Japanese Patent Application No. 60-216395, there is
An improved circuit is disclosed in which the circuit shown in FIG. FIG. 9 shows one of the circuits listed in the above publication.

In FIG. 9, delay circuits 12 and 13 are connected in series, an input signal SO is input to the delay circuit 12 at the previous stage, a signal S1 is output from the delay circuit 12 as its delayed output, and a signal JP is output from the delay circuit 13 at the rear stage. ) S2 is outputting. Signal S
1 is input to a contour correction circuit 18 as shown in FIG. 6, for example, and the contour correction circuit 18 outputs a signal 3i = which is the input signal SO to which preshoot and overshoot are added.
Output.

The output 31' of the contour correction circuit 18 is inputted to each negative end of the first and second maximum level output circuits 14,15. Further, the above-mentioned signals So and 82 are the same as the above-mentioned signals So and 82. and second
The maximum level output circuits 14 and 15 are input to the other ends of the maximum level output circuits 14 and 15, and the third maximum level output circuit 16 is also input to the third maximum level output circuit 16, respectively. These maximum level output circuits 14.15.16
is for selectively outputting the maximum level among the levels presented by a plurality of inputs. And these first. to each output of the third maximum level output circuits 14 to 16] S3 to S
5 are respectively input to the minimum level output circuit 17. The minimum level output circuit 17, on the contrary, is a circuit that selects the minimum level signal.

The maximum level output circuits 14, 15, 16 and the minimum level output circuit 17 remove preshoot and overshoot from the signal 81 to generate waveforms with steep rising and falling waveforms. This will be described as a shoot waveform removal circuit.

FIG. 10 is an explanatory diagram showing the operation of the shoot waveform removal circuit, in which the delay circuits 12, 13 to 1, the input signal SO
A signal 81.32 that is temporally delayed by a predetermined time relative to the signal 81.32
occurs. As explained in FIG. 6, the contour correction circuit 18 outputs a signal 81' with an enhanced contour. The maximum level output circuit 14 compares the signals SO and 81- and selects and outputs the signal with the higher level, so the resulting output has a waveform as shown in S3. Sx is the signal SO(
Dotted line) and signal 5l- (solid line) are shown superimposed,
The operation of maximum level output circuit 14 is easily understood. Since the maximum level output circuit 15 also generates a signal in the same way as the maximum level output circuit 14, the waveform of the signal output becomes as shown in S4. - On the other hand, the maximum level output circuit 16 outputs the higher of the signals So and 82, so its output becomes a signal 9S5 including the signals So and 81.32, as shown by a waveform 85. Since the minimum level output circuit 17 selects a low level signal among the signals 33, 34, and 35, it is possible to output a signal 1336 whose rise and fall are Q steep.

However, the circuit of FIG. 9 operates as a trap circuit for the original signal when the frequency of the signal SO has a phase relationship with the signals 81 and S2 as shown in FIG. 11(a), and its output signal As shown in FIG. 11(b), S6 becomes a blasphemous signal that does not even indicate the information of the original signal.

(Problems to be Solved by the Invention) As described above, in the circuit shown in FIG. There have been cases where the waveform removal signal has a special phase relationship with the contour correction signal, making it impossible to remove each chute portion, making it impossible to properly perform contour correction.

An object of the present invention is to eliminate the above-mentioned problems and to provide a contour correction circuit that appropriately performs contour correction related to the frequency of a video signal.

[Structure of the invention] (Failure to solve the problem) The invention includes at least two delay circuits.

A delayed signal generating means for generating a plurality of signals each having a time delay relationship with respect to the original signal, the original signal and each signal from the delayed signal generating means are inputted, and one of the levels exhibited by each of these input signals is inputted. Maximum level detection means and minimum level detection means that always select and output the maximum level and minimum level in a tracking manner, and the contour correction signal from each of these detection means are supplied as inputs, and the contour correction signal as described above is supplied as output. By cooperating with circuit means for generating a signal with an improved waveform, an appropriate output waveform can be obtained even if the original signal has a specific frequency.

(Function) In an image quality improvement circuit using a delay circuit, a preshoot and a preshoot are applied to each of the rising and falling parts of the video waveform.
After obtaining a contour correction signal in which the characteristics of the waveform and the overshoot are sharpened, waveform shaping is performed to remove each of the above-mentioned shoot portions. When the original signal exhibits a specific frequency, the shoot waveform removal means that performs such shaping may act as a trap for the original signal and may not be able to properly perform contour correction. The reason for this is that the signal for removing the chute portion obtained by the delay circuit has a phase relationship with the contour correction signal that cannot be removed.The present invention allows information on the current signal to be stored even if such a phase relationship occurs. This allows a proper output signal to be obtained without any damage. That is, 1
In the present invention, the maximum level and the minimum level among the levels exhibited at the same time by a plurality of signals each having a predetermined delay time with respect to the original signal and the original signal are used as the reliability for removing the shoot portion. By using two signals that are each selected and formed in a tracking manner, when the original signal has a special frequency, the two signals act as upper and lower slice levels for the contour correction signal, so that the contour can be adjusted. A corrected signal can be obtained.

(Example) The present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a circuit diagram showing an embodiment of an image quality improvement circuit according to the present invention.

In FIG. 1, the block 21 shown within the dotted line is the maximum level output circuit 14-16 of FIG. and a minimum level output circuit 17, and in this embodiment, the contour correction signal 81- from the contour correction circuit 18 is input to the shoot waveform removal circuit 21.
In addition, the original signal 30. Output 31 of delay circuit 12. and a maximum level output circuit 22, which receives the output S2 of the delay circuit 13, respectively. It is characterized by using signals 3HAX and 5HIN from the minimum level output circuit 23.

That is, the original signal SO is input to the delay circuit 12,
The signal S1 is then delayed by the delay time and is input to the delay circuit 13 at the subsequent stage. The output S of this delay circuit 13
2 is a signal delayed by the delay time of the delay circuit 13 with respect to the signal S1.

The signal Sl, 32 and the original signal SO obtained in this way are
Maximum level output circuit 22. and is input to the minimum level output circuit 23. The maximum level output circuit 22 is the maximum level output circuit 14 in the shoot waveform removal circuit 21.
The minimum level output circuit 23 is configured similarly to the minimum level output circuit 17 in the shoot waveform removal circuit 21.

These maximum level output circuits 22. The minimum level output circuit 23 selectively outputs the highest level and the lowest level among the levels exhibited by the three inputs at the same time.

In the shoot waveform removal circuit 21, the maximum level output circuit 2
The signal 3 WAX from 2 is input to the maximum level output circuits 14 and 16, and the signal 5 from the minimum level output circuit 23 is inputted to the maximum level output circuit 14 and 16.
HIN is input to the maximum level output circuit 15° and the maximum level output circuit 16, respectively. Then, the output $3' of the maximum level output circuit 14 and the maximum level output circuit 1
The outputs S4- of 5 are input to the minimum level output circuit 17, respectively.

The signal S5 = from the maximum level output circuit 16 is also input to the minimum level output circuit 17, and the minimum level output circuit 17 derives an output signal S6.

Note that the contour correction circuit 18 uses, for example, a configuration that adds waveforms for two or more machines as shown in FIG. 6, and inputs the original signal SO,
An output 81' is outputted by adding preshoot and overshoot to the signal.

The present embodiment is configured as described above, and its operation will be explained next.

FIG. 2 is a diagram showing the operation waveforms of each part when the relationship between the signals SO to S2 does not have the phase relationship as shown in FIG.
In the figure, the delay times set in each of the delay circuits 12 and 13 are the same τ, but this is not an essential matter of the circuit and may be different.

First, when signals 80, 31, and 82 each having a predetermined delay time relationship are input to the maximum level output circuit 22 (see FIG. 2 a, b, clJ), the maximum level output circuit 22
Among the levels that each of the signals SO to S2 exhibit at the same time, the highest one is selected and output. Therefore, as shown in FIG. 2(d), the output 5HAX of the same circuit 22 is a signal whose rise time coincides with the signal SO and whose fall time coincides with the signal qS2 (if the original signal SO is a pulse signal, the logical sum output). In addition, the minimum level output circuit 23 is
Among the levels exhibited by S2 at the same time, the lowest one is selected and the next one is output. Therefore, the output 5H of the same circuit 23
As shown in FIG. 2(e), IN becomes a signal (AND output) whose rise time matches the signal $2 and whose fall time matches the signal SO.

On the other hand, the contour correction circuit 18 performs contour correction on the signal S1.
Contour correction signal 81' (Pi, P3: Brishoot) shown in FIG. 2(f) with waveforms for several machines added.

Therefore, although this signal 81' is a signal that roughly matches the signal S1 in terms of time, the time required for rising and falling is longer for signal 81'. shorter than 81.

Next, the maximum level output circuit 14 of the shoot waveform removal circuit 21 inputs the signal @3HAX and the contour correction signal $1°, so its output 83' is output from the preamplifier as shown in FIG. Shoottro 1. Overshoot P4 is removed and the rise and fall times become S3°, which matches SHAX. Also, the output 8 of the minimum level output circuit 15
4' is the preshoot section P1.4' based on the signal St'. Overshoot P4 is removed, and the rising and falling edges are signal 8.
The signal shown in FIG. 2(h), which corresponds to 1-, is obtained. Furthermore,
The output 85' of the maximum level output circuit 16 is the signal SHA
It becomes equivalent to X.

Therefore, these signals 83', 84- and 85
The output S6 of the minimum level output circuit 17 which manually outputs the overshoot P2. The preshoot P3 is removed by selecting the level of the signal S5- during the shoot period, and the rising and falling edges of the signal S3- are detected by the signal 84.
By selecting the rising and falling edges of ', a signal as shown in FIG. 2(j) is obtained, which is removed. As a result, all preshoot and overshoot are removed from the output 36G of the minimum level output circuit 17, resulting in a sharp rise and fall characteristic.

Next, referring to FIG. 3, the operation when the signals SO to S2 have a special phase relationship as shown in FIG. 11 will be described.

In FIG. 3, the reference levels of (a) to (e) are the same. (a) shows the phase relationship of the signals So, 81, and S2. With this phase relationship, the maximum level output circuit 22. When each signal SO-$2 is input to the minimum level output circuit 23, the maximum level output circuit 22 outputs a signal with a predetermined amount of DC increased from the reference level as an output SHAX, as shown in FIG. 3(b). is generated, and the minimum level output circuit 23 generates a signal as the output S MIN whose level is reduced to approximately the same level as the DC component as shown in FIG. 3(C). On the other hand, since the signal S1 is amplified by the amplification function of the contour correction circuit 18, the contour correction signal 81' is a signal at a higher level than Sl shown in (a) (see FIG. 3d).
becomes. Therefore, the peak peak level of the signal S1- is naturally equal to the DC level of the signal 3 HAX and the signal S H
Exceeds the IM DC level.

Each signal SHAχ, 5HIN,
and Sl- are input to the shoot waveform removal circuit 21,
The output S3- of the maximum level output circuit 14 is as shown in FIG. 3(e).
It appears as a waveform as shown in the maximum level output circuit 15.
The output 34- appears as a waveform shown in FIG. 3(f). Note that the output 85' of the maximum level output circuit 16 is the same as the signal SHAX.

As a result, the output S6 of the minimum level output circuit 17 has a waveform obtained by slicing the signal S1- by the upper and lower DC levels of the signals SHAX and 5HIN, as shown by the solid line in FIG. 3(Q). It will be done. This waveform is the original signal SO
, and the contour can be treated as if it had been corrected to the question and answer in the case of FIG. 2.

Next, the maximum level output circuit 22, the maximum level output circuits 14 to 16, and the minimum level output circuit 2 used in the above embodiment will be explained.
A specific configuration example of 3.17 will be explained.

FIG. 4(a) shows the maximum level output circuits 14 to 16,
The collectors of the two transistors Ql and Q2 are connected in common, the emitters are connected in common, the common collector is connected to the power supply of DC voltage Vcc, and the common emitter is connected to the resistor R1.
The input signal that is higher in level than the input signal applied to the base input lx of the transistor Q1 and the input signal applied to the base input hay of the transistor Q2 is connected to the ground point through the transistor Q1 and Q2. Output from Etsumita.

FIG. 4(b) shows the minimum level output circuit 17, in which the common emitters of three PNP transistors Q3, Q4, and Q5 are connected to a power source of DC voltage ■cC via a resistor R2, and the common collector is connected to the ground point. The lowest level input signal for three input signals applied to the respective base input terminals x, y, and z of transistors Q3, Q4, and Q5 is outputted from the common emitter.

Note that the maximum level output circuit 22 may include additional transistors equivalent to the transistors Ql and Q2 in FIG. 4(a). Further, the minimum level output circuit 23] can be constructed by the same circuit as that shown in FIG. 4(b). In this way, in this embodiment, even if the original signal SO has a specific frequency, the obtained output waveform does not lose the information of the original signal and has a rising edge.

and the falling edge has been corrected.

The above embodiment is just an example, and for example, the shoot waveform removal circuit 21 can be modified in various ways, as shown in FIG.
The maximum level output circuits 14 to 16 are connected to the minimum level output circuit 2.
4 to 26, and the minimum level output circuit 17 may be replaced with the maximum level output circuit 27.

Further, the number of delay circuits is not limited to two.

Maximum level output circuit 22. and minimum level output circuit 23
This is because the more the number of signals input to the signal S MAX and S HIN in the case of FIG. 4 becomes flat, the better the contour correction can be performed.

[Effects of the Invention] As explained above, according to the present invention, in correcting the rise and fall characteristics of a video signal without preshoot and overshoot, it is possible to prevent correction from becoming impossible at a specific frequency. , there is an effect that good correction characteristics can be obtained over the entire video band.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the image quality improvement circuit according to the present invention, FIGS. 2 and 3 are operation waveform diagrams showing the operation of FIG. 1, and FIG. A circuit diagram showing an example of a level output circuit and a minimum level output circuit, FIG. 5 is a circuit diagram showing another embodiment, FIG. 6 is a circuit diagram showing an example of a conventional contour correction circuit, and FIG. 7 is a circuit diagram showing an example of a conventional contour correction circuit. 6 is a waveform diagram for explaining the operation, FIG. 8 is a circuit diagram showing another example of the conventional contour correction circuit, FIG. 9 is a circuit diagram showing an example of the image quality improvement circuit according to the earlier application of the present invention, and FIG. 10 and 11 are operation explanatory diagrams for explaining the operation of the circuit shown in FIG. 9. 12.13...Delay circuit, 14~16.22°27
...Maximum level output circuit, 17.23~26...
Minimum level output circuit, 18... Contour correction circuit, 21.
...Shoot waveform removal circuit, SO...original signal, 81
-...Contour correction signal, Q1-Q5...Transistor. (0) (b > Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11

Claims (5)

[Claims] (1) A contour correction means for obtaining a contour correction signal with an enhanced contour by adding preshoot and overshoot to the rising and falling portions of the waveform of the original signal, respectively, and at least two delay circuits; Delayed signal generation means for generating a plurality of signals that are each delayed in time from the signal, and inputting the original signal and each signal from the delayed signal generation means, and calculating the level that these input signals exhibit at the same time. Maximum level detection means and minimum level detection means for selectively outputting the maximum level and minimum level among them, and the signal from the maximum level detection means, the signal from the minimum level detection means, and the contour correction signal are respectively supplied as inputs. and a shoot waveform removing means that generates as an output a signal having a waveform in which preshoot and overshoot added to the contour correction signal are removed and whose rising and falling parts are steeper than the original signal. It is equipped with an image quality improvement circuit. (2) The shoot waveform removal means includes a first maximum level output circuit that inputs the signal from the maximum level detection means and the contour correction signal, compares both signals, and outputs a maximum level signal; a second maximum level output circuit that inputs the contour correction signal and the signal from the minimum level detection means, compares both signals, and outputs a maximum level signal; A third maximum level output circuit inputs each signal, compares both signals, and outputs a maximum level signal, and inputs each output signal from the first, second, and third maximum level output circuits, and a first minimum level output circuit that compares the three signals and outputs the minimum level signal.
Image quality improvement circuit described in section. (3) The shoot waveform removal means includes a second minimum level output circuit that receives the signal from the maximum level detection means and the contour correction signal, compares both signals, and outputs a minimum level signal; a third minimum level output circuit that receives the contour correction signal and the signal from the minimum level detection means, compares both signals, and outputs a minimum level signal; a fourth minimum level output circuit that inputs each signal, compares both signals, and outputs a minimum level signal, and inputs each output signal from the second, third, and fourth minimum level output circuits, and a fourth maximum level output circuit that compares the three signals and outputs the maximum level signal.
Image quality improvement circuit described in section. (4) The maximum level detection means described above comprises a plurality of NPN transistors each having a different signal input to its base, a collector connected to a common voltage source, and an emitter connected to a reference potential point via a common emitter resistance. 2. The image quality improving circuit according to claim 1, wherein the image quality improving circuit has a common emitter of each transistor and extracts a maximum level signal from a common emitter of each transistor. (5) The above minimum level detection means comprises a plurality of PNP transistors each having a different signal input to its base, a collector connected to a common reference potential point, and an emitter connected to a voltage source via a common emitter resistance. 2. The image quality improvement circuit according to claim 1, wherein the image quality improvement circuit has a common emitter of each transistor and extracts a minimum level signal from a common emitter of each transistor.