JP2935389B2 - Video signal processing device and nonlinear signal processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video signal processing device including a gamma correction circuit, a contour correction circuit, an auto knee circuit and the like, and a non-linear signal processing device used as an auto knee circuit.

[0002]

2. Description of the Related Art Conventionally, video signal processing devices such as video cameras have been used to reproduce faithful colors with a color picture tube.
A gamma correction circuit for compensating the light emission characteristics (gamma characteristics) of the color picture tube is provided. In addition, the video signal processing apparatus generates an aperture signal from an image signal (luminance signal) to clarify the outline of the image, and superimposes the aperture signal on the luminance signal to enhance the outline. A circuit is provided.

FIG. 7 is a block diagram showing a first example of a conventional video signal processing apparatus including an outline correction circuit. An outline correction circuit 2 is provided at a stage subsequent to a gamma correction circuit 1. The contour correction circuit 2 generates an aperture signal based on a difference between before and after the input luminance signal and the like.
And an adder 1C for adding the luminance signal added via the delay circuit 1B and the aperture signal from the aperture signal generation circuit 1A. However, when an aperture signal is generated from the output signal of the gamma correction circuit 1 as shown in FIG. 7, there is a problem that only a small aperture signal can be obtained because the high luminance portion is compressed by the gamma correction circuit 1.

FIG. 8 is a block diagram showing a second example of a conventional video signal processing device including an outline correction circuit. An outline correction circuit 2 is provided at a stage preceding the gamma correction circuit 1. However, in this case, there is a problem that the edge-enhanced luminance signal then passes through the gamma correction circuit 1 so that the aperture signal in the high-luminance portion is also compressed. Therefore, in such a circuit configuration, the outline of the high-luminance portion is lost, resulting in an unclear image.

FIG. 9 is a block diagram showing a third example of a conventional video signal processing device including an outline correction circuit. An aperture signal generation circuit 4 generates an aperture signal based on a luminance signal on the input side of a gamma correction circuit 1. The gamma correction circuit 1 generates the data and adds the generated data.
(See JP-A-55-92083 and JP-A-63-209373). However, in this case, while the high luminance portion of the luminance signal is compressed by the gamma correction circuit 1, the aperture signal is added irrespective of the luminance, so that it is necessary to balance the luminance signal and the aperture signal. There is a problem that is difficult.

FIG. 10 is a block diagram showing a fourth example of a conventional video signal processing device including an outline correction circuit. As shown in the drawing, only the high luminance signal is extracted by the high luminance detection circuit 3, the aperture signal is generated by the aperture signal generation circuit 4, and the aperture signal is added by the adder 5 at the subsequent stage of the gamma correction circuit 1. ing. Further, there is an apparatus that controls the gain of an aperture signal according to an input level (see Japanese Patent Application Laid-Open Nos. 61-15472 and 62-227279).

[0007]

However, a knee circuit may be added to the video signal processing apparatus in order to improve the reproducibility of a high luminance signal, and the magnitude of the aperture signal and the luminance signal is balanced. It was not easy. By the way, the knee circuit suppresses the amplitude of a luminance signal having a certain level or more as shown in the graph of FIG. 11 and outputs the signal. The conventional knee circuit sets the knee point by an input signal. Auto knee circuit to change (
Analog circuit) (see Japanese Patent Application Laid-Open No. Sho 62-157474), but there is no digital signal processing for changing the knee point.

A conventional digital processing knee circuit uses a shift / selector 6 as shown in FIG. 12, and among n-bit parallel inputs, the MBS (most significant bit D _n ) becomes “H”. When the input D of the bit below the MBS
_, D _n-2, ..., D _O are shifted by a preset number of stages and output to obtain an effect of equivalently suppressing a high-level signal. In this scheme,
The level at which the knee is applied (knee point level) is fixed to の of the input level of the circuit itself, and the setting of the suppression ratio is limited to ２ ，, ４, etc., and (１ ／) ^n. ,
The degree of freedom was low and the range of application was limited.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object of the present invention is to provide a good balance between the magnitude of an aperture signal and a luminance signal according to a shooting scene, and to change a knee point. Accordingly, it is an object of the present invention to provide a video signal processing device capable of improving the reproducibility of a high-luminance signal and providing a more natural image quality with a more natural resolution by providing a suitable aperture signal in conjunction with the high-luminance signal.

Another object of the present invention is to provide a non-linear signal processing device capable of freely setting a knee point level and a suppression rate by digital signal processing.

[0011]

According to the present invention, there is provided an automatic knee circuit for inputting an image signal and compressing and outputting a high-luminance portion having a predetermined knee point level or higher. A changeable auto knee circuit, a gamma correction circuit for inputting an output of the auto knee circuit and performing gamma correction and output, an aperture signal generation circuit for inputting the image signal and generating an aperture signal, and a gain coefficient to be input. A gain control circuit that controls a gain of the aperture signal based on the gain control circuit; an adder that adds the aperture signal whose gain is controlled by the gain control circuit to an output of the gamma correction circuit; Control means for lowering the gain coefficient while lowering the knee point of the auto knee circuit. It is a symptom.

In the above-mentioned video signal processing apparatus, when an auto knee circuit is not provided, when the brightness of the subject becomes brighter than a standard brightness, the gain factor becomes larger than a predetermined gain factor at the time of the standard brightness. A control means is provided for setting the gain coefficient to be smaller than a predetermined gain coefficient at the time of the standard brightness when the brightness becomes lower than the standard brightness.

[0013] Further, a nonlinear signal processing apparatus based on digital signal processing including an auto knee circuit is provided with knee point level setting means for setting a knee point level for an input digital signal, inputting the digital signal, and converting the digital signal into the knee signal. A subtracter for subtracting the knee point level set by the point level setting means, a first clip circuit for outputting only a positive digital signal among the subtraction results of the subtractor, and suppression of a digital signal equal to or higher than the knee point level A suppression rate setting means for setting a rate;
A multiplier for multiplying the output signal of the clipping circuit by the suppression rate set by the suppression rate setting means, and the digital signal being input, and the digital signal being a knee point level set by the knee point level setting means. , And an adder for adding the output of the second clip circuit and the output of the multiplier.

[0014]

According to the present invention, when the image becomes brighter than the standard brightness, the knee point of the auto knee circuit is lowered to improve the reproducibility of the high-brightness signal, and is linked to the change of the knee point (ie, Depending on the degree of compression of the high-brightness signal in the auto knee circuit), the gain of the aperture signal generated based on the image signal on the input side of the auto knee circuit is varied, and the gain adjusted aperture signal is output from the gamma correction circuit. Side. That is, when the knee point is low, the high-luminance signal is more compressed, and when the gain of the aperture signal is not controlled, the aperture amount with respect to the brightness appears to fluctuate on the screen. The gain is reduced so that the aperture does not get too unnatural.

In order to realize an automatic knee circuit or the like by digital processing, a preset knee point level is subtracted from an input digital signal, and the resulting signal is clipped to a zero-level clip via a first clip circuit. After that, the digital signal equal to or higher than the knee point level is multiplied by a desired suppression rate. Then, a digital signal which is non-linear to the input digital signal by adding the signal obtained by limiting the input digital signal via the second clipping circuit so as not to exceed the knee point level and the suppressed signal. I'm trying to get

According to another aspect of the present invention, when an auto knee circuit is not provided, when the brightness of a subject becomes brighter than the standard brightness, the gain of the aperture signal is increased to reproduce a highlight portion. When the brightness becomes darker than the standard brightness, the gain of the aperture signal is reduced to reduce noise.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a video signal processing device and a non-linear signal processing device according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing one embodiment of a video signal processing device according to the present invention. In FIG. 1, an image signal of a subject read from a solid-state imaging device (CCD) 10 is supplied to a sampling and holding circuit 12 and an A / D converter 1.
4 is applied to the luminance signal processing circuit 16. The luminance signal processing circuit 16 includes a trap circuit, a low-pass filter (L
PF), and generates a luminance signal from the input signal, and outputs the luminance signal to the adder 20 via the delay circuit 18.
The luminance signal is applied to an aperture signal generation circuit 22 and an auto iris circuit (AE circuit) 24.

As shown in FIG. 2, the aperture signal generating circuit 22 includes delay elements 22A and 22B, an adder 22C, a multiplier 22D and a subtractor 22E. Assuming that the luminance signal at the current input time is Y ₀ (FIG. 3A), the luminance signals Y ₁ and Y ₂ output from the delay elements 22A and 22B are shown in FIGS. 3B and 3C, respectively. It becomes a signal which is delayed with respect to the luminance signal Y ₀ as.

The adder 22C outputs the luminance signal Y₀And Y_Two
And outputs the result to the multiplier 22D.
The force signal is halved and output to the subtractor 22E. Subtraction
The other input of the device 22E has a luminance signal Y₁Has been added
The subtractor 22E outputs the luminance signal Y ₁From the output of the multiplier 22D
By subtracting the force, (Y₁− (Y₀+ Y_Two) /
An aperture signal (FIG. 3D) indicative of 2) is output.

The aperture signal thus generated is applied to multipliers 26 and 28 as shown in FIG. The AE circuit 24 integrates the luminance signal of a predetermined area in one screen from the input luminance signal and outputs a signal indicating the brightness of the subject to the central processing unit (CPU) 30.

A predetermined gain coefficient β is added to the other input of the multiplier 26. The multiplier 26 multiplies the input aperture signal by the gain coefficient β to reduce the gain of the aperture signal. Control is output to the adder 20. The adder 20 adds the luminance signal (the signal corresponding to the luminance signal Y ₁ in FIG. 2) added from the delay circuit 18 and the aperture signal whose gain has been controlled, and adds this to the auto knee circuit 32. Note that the addition of the aperture signal emphasizes the changing portion of the luminance signal (the contour portion of the image).

The automatic knee circuit 32 is capable of changing the knee point, and is constituted by a digital circuit shown in FIG. That is, the auto knee circuit 32
Is composed of a subtractor 32A, a clip circuit 32B, a zero clip circuit 32C, a multiplier 32D, a suppression rate setting unit 32E, and an adder 32F.

The luminance signal (digital signal) input from the adder 20 is supplied to a subtractor 32A and a clip circuit 32B.
Is added to A predetermined knee point level (digital signal) is applied from the CPU 30 (FIG. 1) to the other inputs of the subtractor 32A and the clip circuit 32B. The size of the knee point level will be described later. The subtracter 32A subtracts the knee point level from the input luminance signal, and outputs the subtracted signal a (FIG. 5A) to the zero clip circuit 32C. In FIG. 5A, a dashed line indicates a luminance signal before subtraction.

On the other hand, the clipping circuit 32B limits the input luminance signal so as not to exceed the knee point level, and outputs a signal b (FIG. 5B) which is restricted with respect to the input luminance signal. The zero clipping circuit 32C performs zero clipping so that a signal less than the zero level of the input signal a (FIG. 5A) is not output, and outputs a zero-clipped signal c (FIG. 5C) to the multiplier 32D. .

To another input of the multiplier 32D, a digital signal indicating a desired suppression rate is added from the suppression rate setting unit 32E, and the multiplier 32D multiplies the signal c by the suppression rate and calculates the product. The signal d shown in FIG. 5D is output to the adder 32F. The signal b (FIG. 4B) from the clip circuit 32B is added to the other input of the adder 32F.
The adder 32F adds these two inputs and outputs a signal e (FIG. 5E) indicating the sum.

According to the auto knee circuit 32 having the above configuration,
The knee point can be freely changed by the knee point level added from the CPU 30, and the suppression rate for digital signals exceeding the knee point level can be freely changed by the suppression rate setting unit 32E. The luminance signal whose high luminance portion has been suppressed by the auto knee circuit 32 is output to the gamma correction circuit 3 as shown in FIG.
4, and after being subjected to a predetermined gamma correction, is added to the adder 36.

On the other hand, the multiplier 28 multiplies the aperture signal applied from the aperture signal generation circuit 22 by a gain coefficient α applied from the CPU 30, thereby controlling the gain of the aperture signal and outputting it to the adder 36.
The adder 36 adds the luminance signal added from the gamma correction circuit 34 and the aperture signal gain-controlled by the multiplier 28 and outputs the result.

Next, the operation of the CPU 30 will be described. A signal indicating the brightness of the subject is added to the CPU 30 from the AE circuit 24. The CPU 30 changes the knee point level output to the auto knee circuit 32 according to the brightness of the subject, and changes the gain output to the multiplier 28. Change the coefficient α.

That is, when the subject has a standard brightness, the CPU outputs a knee point level at which the knee point becomes higher. This prevents the intermediate portion of the luminance signal from being compressed more than necessary. The gain coefficient α outputs a gain coefficient α that balances with the luminance signal output via the knee-point auto knee circuit 32 and the gamma correction circuit 34.

On the other hand, when the brightness of the subject becomes brighter than the standard brightness, the CPU outputs a knee point level smaller than the knee point level to the auto knee circuit 32 in order to lower the knee point. As a result, the compression ratio of the luminance signal is increased, and the information of the high luminance portion is not lost, and the reproducibility of the high luminance portion can be improved.

The high luminance portion is compressed as described above, and the aperture signal becomes relatively large with respect to the luminance signal output via the gamma correction circuit 34 while the gain coefficient α is fixed. The aperture will be unnaturally too large. Therefore, the CPU 30 lowers the knee point of the auto knee circuit 32, reduces the gain coefficient α, and also reduces the aperture signal.

As a result, the manner in which the aperture is attached changes in conjunction with the knee point, so that a more natural image quality with a sense of resolution can be obtained. FIG. 6 is a block diagram showing another embodiment of the present invention. The same reference numerals are given to the same parts as those in FIG. 1, and the detailed description is omitted.
In the embodiment shown in FIG. 6, the CPU 40 and the knee circuit 42
This is different from the CPU 30 and the automatic knee circuit 32 of the embodiment of FIG.

The CPU 40 responds to the signal indicative of the brightness of the subject from the AE circuit 24 by means of multipliers 28 and 26.
Are changed respectively. The knee circuit 42 is a normal knee circuit that does not change the knee point, but the knee circuit 42 is not always essential. Now, the CPU 40 changes the gain coefficients α and β according to the brightness of the subject as shown in the following table. That is, the gain coefficients α and β set when the subject has the standard brightness are set as reference (medium), and when the scene is darker than the standard, both the gain coefficients α and β are reduced. As a result, the aperture signal can be reduced, and the sense of noise in a dark scene accompanying the addition of the aperture signal is reduced.

Further, in a scene brighter than a standard having many highlights, the gain coefficient α is increased, thereby improving the reproducibility of the highlight portion. In this embodiment, although the aperture signal generation circuit 22 generates only one type of aperture signal, it goes without saying that the gain can be controlled for the two types of aperture signals in the horizontal and vertical directions as described above. No.

[0035]

As described above, according to the video signal processing apparatus of the present invention, the magnitude of the aperture signal and the luminance signal can be well balanced according to the shooting scene, and the knee point varies. Thus, the reproducibility of the high-brightness signal is improved, and by providing a suitable aperture signal in conjunction with this, it is possible to obtain a more natural image quality with a sense of resolution. Further, according to the nonlinear signal processing device of the present invention, it is possible to freely set the knee point of the input digital signal and the suppression rate for the signal exceeding the knee point. There is an advantage that it can be used as an auto knee circuit and can set and adjust detailed gradation characteristics of a luminance signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a video signal processing device according to the present invention.

FIG. 2 is a block diagram illustrating an example of an aperture signal generation circuit in FIG. 1;

FIG. 3 is a timing chart used to explain the aperture signal generation circuit of FIG. 2;

FIG. 4 is a block diagram showing details of an auto knee circuit in FIG. 1;

5 (A) to 5 (E) are graphs each showing the input / output relationship of signals of each unit in FIG. 4;

FIG. 6 is a block diagram showing another embodiment of the video signal processing device according to the present invention.

FIG. 7 is a block diagram showing a first example of a conventional video signal processing device including an outline correction circuit.

FIG. 8 is a block diagram showing a second example of a conventional video signal processing device including an outline correction circuit.

FIG. 9 is a block diagram showing a third example of a conventional video signal processing device including an outline correction circuit.

FIG. 10 is a block diagram showing a fourth example of a conventional video signal processing device including an outline correction circuit.

FIG. 11 is a graph showing an example of input / output characteristics of a knee circuit.

FIG. 12 is a diagram showing an example of a conventional knee circuit for performing digital processing.

[Explanation of symbols]

 Reference Signs List 16 luminance signal processing circuit 20, 32F, 36 adder 22 aperture signal generation circuit 24 AE circuit 26, 28, 32D multiplier 30, 40 CPU 32 automatic knee circuit 32A subtractor 32B clip circuit 32C ... Zero clip circuit 32E ... Suppression ratio setting unit 34 ... Gamma correction circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-123575 (JP, A) JP-A-4-42668 (JP, A) JP-A-4-32372 (JP, A) JP-A-62-1987 157474 (JP, A) JP-A-3-106269 (JP, A) JP-A-4-22275 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04N 5/14-5 / 217

Claims (6)

(57) [Claims] 1. An auto knee circuit which receives an image signal and compresses and outputs a high-brightness portion having a predetermined knee point level or higher, wherein the auto knee circuit is capable of changing a knee point. A gamma correction circuit for inputting, gamma correcting and outputting, an aperture signal generating circuit for inputting the image signal to generate an aperture signal, and a first controlling a gain of the aperture signal based on an input gain coefficient A gain control circuit; a first adder for adding an aperture signal whose gain is controlled by the first gain control circuit to an output of the gamma correction circuit; and an auto knee circuit when a subject becomes brighter than a standard brightness. Control means for lowering the knee point and reducing the gain coefficient. Place. 2. A gain control means for controlling a gain of an aperture signal output from the aperture signal generation circuit based on a predetermined gain coefficient, and an aperture whose gain is controlled by the second gain control circuit. The video signal processing apparatus according to claim 1, further comprising: a second adder that adds a signal to an image signal input to the auto knee circuit. 3. The image signal is a digital signal, the auto knee circuit includes: a knee point level setting unit configured to set a knee point level for an input digital signal; A subtracter for subtracting the knee point level set by the point level setting means, a first clip circuit for outputting only a positive digital signal among the subtraction results of the subtractor, and suppression of a digital signal higher than the knee point level Suppression rate setting means for setting a rate; a multiplier for multiplying the output signal of the first clipping circuit by the suppression rate set in the suppression rate setting means; and inputting the digital signal. A second clock for limiting the output so as not to exceed the knee point level set by the knee point level setting means. The video signal processing apparatus according to claim 1, further comprising: a lip circuit; and an adder that adds an output of the second clip circuit and an output of the multiplier. 4. A gamma correction circuit for inputting an image signal, performing gamma correction and outputting the same, an aperture signal generating circuit for receiving an image signal on the input side of the gamma correction circuit and generating an aperture signal, A first gain control circuit that controls a gain of the aperture signal based on a gain coefficient of 1; and a first gain control circuit that adds an aperture signal whose gain is controlled by the first gain control circuit to an output of the gamma correction circuit. When the brightness of the subject becomes higher than the standard, the first gain coefficient is made larger than a predetermined gain coefficient at the time of the standard brightness, and when the brightness becomes darker than the standard, the first gain coefficient becomes the first gain coefficient. A first control unit for setting a coefficient smaller than a predetermined gain coefficient at the time of standard brightness. 5. A second gain control circuit for controlling a gain of the aperture signal based on an input second gain coefficient, and the gamma correction of the aperture signal whose gain is controlled by the second gain control circuit. A second adder for adding to the image signal input to the circuit; and a second adder for setting the second gain coefficient to be smaller than a predetermined gain coefficient at the time of the standard brightness when the brightness of the subject becomes darker than the standard. 5. The video signal processing device according to claim 4, comprising: 6. Knee point level setting means for setting a knee point level for an input digital signal; and inputting the digital signal, and subtracting the knee point level set by the knee point level setting means from the digital signal. A subtractor, a first clip circuit that outputs only a positive digital signal among the subtraction results of the subtractor, a suppression ratio setting unit that sets a suppression ratio of a digital signal equal to or higher than a knee point level, A multiplier for multiplying the output signal of the clipping circuit by the suppression rate set in the suppression rate setting means; and the digital signal is input, and the digital signal sets the knee point level set by the knee point level setting means. A second clip circuit that outputs the signal while limiting the output so as not to exceed, and an output of the second clip circuit and the output of the multiplier. A non-linear signal processing device comprising: an adder for adding an output to the output signal.