JPH0332170A - Circuit equipment for correcting aperture of video signal due to digital form - Google Patents

Abstract

PURPOSE: To variously adjust a video signal at a cost as low as possible by introducing an adjustable signal for changing a characteristic curve to multiplying circuits provided on the address input side and data output side of a memory. CONSTITUTION: A pattern characteristic curve is stored in a memory 13, an aperture correction signal is introduced through a first multiplying circuit 12 to the address input side of the memory 13, and a corrected aperture correction signal can be extracted from the data output side of the memory 13 through a second multiplying circuit 14. Moreover, an adjustable signal for changing the characteristic curve is introduced to the multiplying circuits 12 and 14. Thus, the smooth characteristic curve can be formed and adjusted even when a storage place is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a circuit arrangement for aperture correction in digital form of video signals. In this case, an aperture correction signal in digital form is derived from the video signal and further modified using a circuit with an adjustable non-linear characteristic curve, and this modified aperture correction signal is added to the video signal, and in this case , the non-linear characteristic curve progresses such that if the aperture correction signal has a small value, the modified aperture correction signal is substantially O, and then increases as the value of the aperture correction signal increases.

Prior Art Aperture correction of video signals improves image sharpness by compensating for degradation in the frequency characteristics of the image recording device. Furthermore, if the correction is excessive in some cases, frequency components that are important for the subjective perception of sharpness will be enhanced. However, in order to avoid the increase in noise caused by the aperture correction signal in a flat image area,
The aperture correction signal has been modified using a threshold characteristic curve. This method is also called Coring.

A proposal for implementing this method by digital signal processing is given by M. Jacobsen and L. 1elters.
"Digital signal processing by processor control in PAL-color television receiver" by J. Bach, 1981
It is described on pages 429 to 457 of the minutes of the 9th FKTG annual conference held from September 21 to 24, 2008, particularly in Figure 7 on page 450. However, a characteristic curve is shown which has a flat course below the threshold value and a linearly increasing course otherwise. Characteristic curves of this kind can certainly be easily realized with digital circuits, but in the case of digital signals, which does not always lead to satisfactory results, the realization of characteristic curves with an arbitrary course can be achieved by addressing the signal to be modified. This is done in a simple manner per se by forming a signal which is guided to the memory and the value stored at the respective address is modified. However, this requires a large amount of memory if an adjustment is required that allows the characteristic curve to be selected as freely as possible. For this purpose, a large number of corresponding characteristic curves must be stored. To be able to adjust, for example, 8 bits for the threshold and 4 bits each for the slope of the positive branch and the slope of the negative branch of the characteristic curve, 65536 complete characteristic curves must be stored. Must.

OBJECTS TO BE SOLVED BY THE INVENTION Therefore, it is an object of the present invention to provide a circuit arrangement for aperture correction which can be adjusted in a wide variety of ways and achieves a smooth characteristic curve at the lowest possible cost. .

Means for Solving the Problem This problem consists of a pattern characteristic Ilh line being stored in a memory, an aperture correction signal being led to the address input side of said memory via a first multiplier circuit, and a modified aperture correction signal being introduced to the address input side of said memory. A signal is transmitted from the data output side of the memory to the second
The problem is solved in that it can be tapped off via a multiplier circuit, and that an adjustable signal for changing the characteristic curve is led to said multiplier circuit.

Advantages of the invention A circuit arrangement according to the invention having the features of claim 1 comprises:
It has the advantage that a smooth characteristic curve and its adjustment can be realized even if the storage space is kept very small. A further advantage of the circuit arrangement according to the invention is that by inputting the adjustment values separately for the threshold value and the slope (if necessary separately for the positive and negative branches of the characteristic curve), it is possible to The point is that you can make adjustments accordingly. This ensures that each incoming video signal, for example depending on its signal-to-noise ratio and the slope of its edges, on the one hand avoids deterioration of the signal-to-noise ratio and, on the other hand, improves the sharpness as optimally as possible. Adjustments can be made separately so that

Advantageous embodiments according to claim 1 are possible with the features described in claim 2 and subsequent claims.

Embodiments of the invention are illustrated using several drawings,
DESCRIPTION OF THE EMBODIMENTS DESCRIPTION OF THE PREFERRED EMBODIMENTS In a digital circuit for aperture correction, which is shown as a block diagram in FIG.

B is led to an analog/digital converter 2, at the output of which digital color value signals Rd, GdBd appear.

By using the digital filter 3, the color value signal G
d, an aperture correction signal C is obtained by a method known per se.
ORin is derived. This signal is called Corin
g characteristic curve and, after post-processing in block 5, which primarily performs amplification adjustment, is led to an adder circuit 6 as signal CORout. On the other input side of the adder circuit 6, color value signals Rd, Gd, Bd whose elapsed time has been adjusted in advance in a delay circuit 7 to the elapsed time of the signals from circuits 3 to 5 are applied. an aperture-corrected color value signal Rd from the output side of the adder circuit 6;
, Gd-1 and Bd- are sent out. If necessary, these signals can be converted into analog signals R=, G'' and B' using a digital/analog converter 8 and taken off at the output of the circuit arrangement of FIG. 1.Aperture correction Instead of the color value signal Gd, a luminance signal can also be used for deriving the signal, which is usually formed by using a suitable matrix circuit.

FIG. 2 shows the output signal CORin for the input signal CORin.
4 shows a suitable characteristic curve of circuit 4 as a function of out;

In this case, for a relatively small input signal, CORou
t=0, and within the range of thresholds -UC and +Uc, it increases slowly at first and then rapidly. At multiples of the threshold value -m-Uc to 10m-Uc, the characteristic curve takes on a relatively gradual, almost linearly increasing course.

The double-headed arrow means that it is adjustable by the circuit arrangement according to the invention. Double-headed arrow symbol Sp,
Sn corresponds to the symbol of the signal used for the adjustment in question in the circuit arrangement of FIG.

In the case of the embodiment according to FIG. 3, the aperture correction signal COR
in is led to a multiplier circuit 12 via an input 11. The output side of the multiplier circuit 12 is preferably a read-only memory (
It is connected to the address input side of a memory configured as (FROM). The data output side of this memory 13 is connected to the input side of a second multiplier circuit 14, and at its output side 15 a modified aperture correction signal CORo
You can take out the ut.

A pattern characteristic curve is stored in the memory 13, which has, for example, the course shown in the second flash. In order to change the pattern characteristic curve to a characteristic curve formed comprehensively based on this pattern characteristic curve, three encoding switches 16, 17, and 18 are provided, and each of these switches changes the desired value and pattern characteristic curve. can be adjusted to the corresponding value.

The encoding switch 16 is used to adjust the threshold value Uc for the pattern characteristic curve threshold value Ucm. The digital signal C=U c / U cm, for example 8 bits wide, produced by the coding switch 16 is directed to the address of a further read-only memory 19, in which the address corresponding to each value of the signal C has its reciprocal. Stored.

Each reciprocal 1/C is directed to a multiplier 12.

By multiplication of the aperture correction signal with signal 1/c,
Actually, the axis reference for the aperture correction signal CORin in FIG. 2 is changed. Accordingly, the threshold value Uc and the slope of the course beyond the positive and negative branches of the characteristic curve change. To compensate for the latter, the signal read out from memory 13 is not only multiplied by the signal S·p that determines the slope, but also by the signal C. For this purpose the signals Sp and C
A table stored in the read-only memory 20 is used for this purpose. In this case the address is formed from the bits of both signals C and S.

A further encoding switch 18 for adjusting the signal Sn and a read-only memory for forming the product C-8n, in order to be able to adjust the slope of the positive branch and the slope of the negative branch separately. 21 are provided. The controllable changeover switch 22 has a read-only memory 20.2
One of the one output signals is transferred to the multiplier circuit 14 depending on the polarity sign of the aperture correction signal.

Instead of the coding switch, other arrangements for inputting the adjustment values can also be provided, for example a digital interface 23 from which a corresponding signal can be derived from a computer if necessary.

Effects of the Invention The circuit arrangement according to the invention makes it possible to form smooth characteristic curves and to adjust them even with a very small storage space. Further, with the circuit device of the present invention, it is possible to separately adjust the threshold value and the slope adjustment value.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a known aperture correction circuit device, FIG. 2 is a diagram of an example of a so-called Coring characteristic curve, and FIG. 3 is a block diagram of a circuit device according to the present invention.

Claims (1)

[Claims] 1. A circuit device for aperture correction in digital form of a video signal, in which case the aperture correction signal in digital form is derived from the video signal and further has an adjustable nonlinear characteristic curve. modified using a circuit and this modified aperture correction signal is added to the video signal, further in this case said non-linear characteristic curve is
For aperture correction in digital form of the video signal, the modified aperture correction signal is essentially 0 if the aperture correction signal has a small value, and then increases as the value of the aperture correction signal increases. In the circuit arrangement, the pattern characteristic curve is stored in the memory (13), and the aperture correction signal is sent to the first multiplier circuit (13).
2) to the address input side of said memory (13) and further modified aperture correction signal is passed from the data output side of said memory (13) to a second multiplier circuit (14).
can be taken out via the multiplication circuit (1
2.14) A circuit arrangement for aperture correction in digital form of a video signal, characterized in that an adjustable signal for changing the characteristic curve is introduced. 2. A signal (1/C) for adjusting the threshold of the characteristic curve is led to the first multiplier circuit (12), and the second multiplier circuit (14
) includes a reciprocal of the signal (C) for adjusting the threshold value and a signal (S) for adjusting the slope of the characteristic curve exceeding the threshold value.
2. The circuit arrangement according to claim 1, wherein a signal formed by multiplication with p, Sn) is derived. 3. A signal for adjusting the threshold value, and a product of a reciprocal of the signal for adjusting the threshold value and a signal for adjusting the slope are stored in the memory (19, 20) in a table format. 2. The circuit device according to 2. 4. Depending on the polarity sign of the aperture correction signal, a signal (Sp) for adjusting the slope of the positive part of the characteristic curve or a signal (Sn) for adjusting the slope of the negative part of the characteristic curve is derived. 3. The circuit device according to claim 2. 5. As another table (21), the product of the reciprocal of the signal for adjusting the threshold and the signal (Sn) for adjusting the slope of the negative part of the characteristic curve is stored, and a changeover switch (22) is provided, the polarity sign of the aperture correction signal is guided as a control signal to the changeover switch, and the product read from the table is led to the input side of the changeover switch, and 4. The circuit arrangement according to claim 3, wherein the output side is connected to a second multiplier circuit (14). 6. The circuit device according to claim 2, wherein signals for adjusting the threshold value and the slope are input using encoding switches (16, 17, 18). 7. Claim 2, wherein a signal for adjusting the threshold and the slope is input using a digital interface.
The circuit arrangement described.