JPH05292347A - Gamma correction circuit - Google Patents

Abstract

PURPOSE:To adjust the saturation without changing the gamma characteristic by applying an image pickup signal to a saturation adjustment circuit in which a low input level is subject to emphasis processing, applying the processed signal to a gamma correction section in which gamma correction is implemented to the image pickup signal. CONSTITUTION:An output level alpha or over is limited by a limiter 22 of the gamma correction circuit 10, a 1st limiter output (f) is obtained, an image pickup signal (e) is halved by an attenuator 24 and its signal (g) is limited for the output level alpha or over by a limiter 25 and a 2nd limiter output (h) is obtained. Both the outputs f, h are subtracted by a subtractor 26 and the gain of a correction signal (i) is adjusted by an amplifier 27 and the result is synthesized onto the current image pickup signal (e). A synthesis image pickup signal (j) includes a detection signal (i) for saturation adjustment and the signal is fed to a gamma correction section 30. Only a low input level of the gamma correction signal d' lower than a 1st inflexion point (x) is changed and unchanged entirely at a level higher than the level. The saturation is adjusted at the low input level. The amplitude of the correction signal is changed by controlling the gain of the amplifier 27 from an external control terminal 28 in the adjustment of the saturation to adjust the saturation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gamma correction circuit suitable for application to a television camera or the like.

[0002]

2. Description of the Related Art As is well known, the light emission characteristic of a color picture tube is a gamma characteristic (non-linear characteristic). ing.

FIG. 6 shows a conventional example of a gamma correction circuit 10 incorporated in a television camera, in which a terminal 10a is a CCD.
The image pickup signal a (see FIG. 7) is supplied to the attenuator 2 via the amplifier 11 and the input level thereof is appropriately attenuated.

The image pickup signal a is further supplied to a polygonal line approximation circuit 13 and converted into a signal c having a polygonal line characteristic as shown in FIG. The signal c is selected as an input / output characteristic such that it has a curve corresponding to a curve that is similar to a characteristic that is opposite to the gamma characteristic. Is approximated by.

This line-approximated image pickup signal c and the above-described attenuated image pickup signal a are used for level adjustment volume 1.
4 are supplied to both output terminals and are combined. Then, a signal having a curve d as shown in FIG. 7 is output from the mover side. The input / output characteristic of this signal is a curve similar to the characteristic opposite to the gamma characteristic, that is, a gamma correction curve. If the coefficient of the image pickup signal a is k, the coefficient k changes depending on the volume 14. Therefore, if the attenuated image pickup signal is A and the line-approximated image pickup signal is C, the combined gamma correction signal D is D = kA + (1-k) C However, 0 <k <1. Becomes

The image pickup signal d after synthesis is output to the output terminal 10b side through the amplifier 15. Since the gamma correction curve itself can be adjusted by adjusting the volume 14,
The gamma correction curve is adjusted according to the gamma value γ of the picture tube. The curve d in the figure shows the characteristics when γ = 0.45.

[0007]

By the way, in the case of controlling the saturation of the image projected on the picture tube on the image sending side, it would be better if only the saturation could be adjusted without changing the gamma characteristic itself. preferable. The saturation may be controlled by controlling the output characteristic on the low input level side, but in the example shown in FIG. 7, it is not possible to independently change only the low input level side. This is because if the saturation degree is adjusted, not only the characteristics of the rising portion of the input characteristics but also the characteristics of other portions change, so that the gamma value itself changes.

In order to improve this, it is necessary to change the gain of the amplifier 11, the curves a and c, and the gain of the amplifier 15, for example. This is not practical because the circuit configuration becomes complicated,
External control is also difficult.

Therefore, the present invention has solved such a conventional problem as described above, and allows the input / output characteristics on the low input level side to be arbitrarily changed to adjust the saturation without changing the gamma correction curve. It proposes a gamma correction circuit capable of performing the above.

[0010]

In order to solve the above-mentioned problems, in the first invention, after the image pickup signal is supplied to the saturation adjustment circuit and the low input level side is emphasized,
It is characterized in that the gamma correction is supplied to the gamma correction section to perform gamma correction on the image pickup signal.

In the second aspect, the image pickup signal is supplied to the gamma correction section for gamma correction processing, and
The saturation level is adjusted by supplying the gamma-corrected image pickup signal to a saturation adjustment circuit and changing only the gamma characteristic on the low input level side of the image pickup signal. Is.

[0012]

The gamma correction circuit 10 shown in FIG. 1 will be described with reference to FIGS. The limiter 22 limits the output level α or higher to obtain the first limiter output f, the image pickup signal e is halved by the attenuator 24, and the output signal g is limited by the limiter 25 to the output level α or higher. As a result, a second limiter output h is obtained.

Both limiter outputs f and h are subtracted by a subtracter 26, and the subtracted correction signal i is gain-adjusted by an amplifier 27. After that, it is combined with the current image pickup signal e. The combined image pickup signal j is a signal including a correction signal i for saturation adjustment, and this is supplied to the gamma correction unit 30 having the same configuration as the conventional example. Therefore, the gamma correction signal of the curve d'of FIG. 4 is finally obtained.

This gamma correction signal d'changes only on the low input level side lower than the first inflection point x, and does not change at any level higher than that. The saturation is adjusted on the low input level side. To adjust the saturation, if the gain of the amplifier 27 is controlled from the external control terminal 28, the amplitude value of the correction signal changes, and the saturation can be adjusted with this.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a case where an example of the gamma correction circuit according to the present invention is applied to the signal processing system built in the above-mentioned television camera will be described in detail with reference to the drawings.

The gamma correction circuit 1 shown in FIG. 1 comprises a gamma correction section 30 and a saturation adjustment circuit 20. The gamma correction unit 30 has the same configuration as the conventional gamma correction circuit 10 shown in FIG.

In the example shown in FIG. 1, the saturation adjusting circuit 20 is provided in the preceding stage of the gamma correction unit 30. 2 and 3
The image pickup signal e output from an image pickup device (not shown) such as a CCD is supplied to the terminal 21, and the image pickup signal e is supplied to the first limiter 22 so that its input level changes to the first change. A low level from the bending point x, for example, z or more shown in FIG. 7 is limited to a predetermined value α.

As a result, an output corresponding to the input level is obtained below the low level z, and an output having a constant value α is obtained above the z. Therefore, this first limiter 22
From, the first limiter output f shown in FIG. 2 is obtained. The low input level z is selected as a value near the input level of the image pickup signal that contributes to the adjustment of the saturation.

The input image pickup signal e is further supplied to the attenuator 24, and its output level is reduced to, for example, 1/2 as a whole. The level-adjusted image pickup signal g is supplied to the second limiter 25, and the same limiter processing as described above is performed to obtain the second limiter output h.

These first and second limiter outputs f,
h is supplied to the subtractor 26, and the second limiter output h is subtracted from the first limiter output f to obtain the correction signal i as shown in FIG.

The correction signal i is supplied to the variable amplifier 27 and its gain is adjusted. By adjusting the gain, the correction signal i can be a correction signal such as i ″ as shown in FIG.
It is an input terminal of TL.

The level-adjusted correction signal i is added to the adder 29.
In addition, as a result of addition with the current image pickup signal e, a corrected image pickup signal j as shown in FIG. 3 is obtained. As is apparent from FIG. 3, the current image pickup signal e has a linear characteristic, whereas the corrected image pickup signal j has a nonlinear characteristic in which the low input level z or less is emphasized by the correction signal i, which will be described later. Further, the degree of saturation changes depending on the correction signal i.

How much the low input level z side is emphasized is controlled by the gain control signal CTL as described above. For example, when the correction signal is i ″, the corrected image pickup signal becomes j ″ (shown by a broken line) in FIG. 3, and the enhancement effect for a low input level is smaller than that of the corrected image pickup signal j.

The corrected image pickup signal j is supplied to the gamma correction unit 30 as its input signal. The gamma correction unit 30 is shown in FIG.
A gamma correction signal d'similar to the gamma correction signal d as shown in FIG. The configuration of the gamma correction unit 30 is shown in FIG.
Since it has already been described in the above, its details are omitted.

Assuming that the output of the polygonal line approximation circuit 13 is c ', the polygonal line approximation processing is performed based on the corrected image pickup signal j as shown in FIG. 4, so that the polygonal line output c'is as shown in FIG. In this example in which the input level is lower than x, the z level or lower is emphasized.

As a result, the gamma correction signal d'output from the gamma correction unit 30 also has a characteristic in which the z level or lower is emphasized in this example in which the input level is lower than the first bending point x. Since the degree of saturation can be adjusted by adjusting the gamma correction level at a low input level, the desired degree of saturation can be easily obtained without changing the gamma correction signal itself, that is, without changing the gamma value γ.

When the value of the output level α supplied to the first and second limiters 22 and 25 is controlled, the peak value of the correction signal i shown in FIG. 3 shifts left and right, so that the low input level of the correction image pickup signal j is reduced. The degree of emphasis at will change. Therefore, the degree of saturation can also be adjusted by this output level α.

In the example shown in FIG. 1, the image pickup signal output from the image pickup device is first supplied to the saturation adjusting circuit 20 so that the level of the image pickup signal contributing to the saturation adjustment is adjusted in advance, and then the gamma correction process is performed. However, it is also possible to perform the opposite process to this process.

FIG. 5 is a system diagram at that time. Since the configuration is the same as that of FIG. 1, the detailed description of the operation is omitted, but the image pickup signal is supplied to the gamma correction unit 30 to be subjected to the gamma correction process, and the gamma-corrected image pickup signal is saturated. The saturation degree is adjusted by changing the gamma characteristic of the low-input level of the image pickup signal supplied to the adjusting circuit 20.

[0030]

As described above, in the gamma correction circuit according to the first aspect of the present invention, the image pickup signal is supplied to the saturation adjustment circuit to perform the enhancement processing on the low input level side, and then is supplied to the gamma correction unit. Then, the gamma correction is performed on the image pickup signal.

In the second aspect of the invention, on the contrary, the image pickup signal is supplied to the gamma correction section for gamma correction processing, and the gamma-corrected image pickup signal is supplied to the saturation adjustment circuit. The saturation level is adjusted by changing the gamma characteristic on the low input level side of.

According to this, in any case, the output level at the low input level of the image pickup signal can be emphasized,
It has a feature that the degree of saturation can be adjusted without changing the gamma characteristic. Therefore, the present invention is extremely suitable when applied to a gamma correction circuit of a television camera or the like.

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of a gamma correction circuit according to a first invention.

FIG. 2 is a characteristic diagram for explaining the operation.

FIG. 3 is a characteristic diagram for explaining the operation.

FIG. 4 is a characteristic diagram for explaining the operation.

FIG. 5 is a system diagram showing an example of a gamma correction circuit according to a second invention.

FIG. 6 is a system diagram of a conventional gamma correction circuit.

FIG. 7 is a characteristic diagram for explaining the operation.

[Explanation of symbols]

 1 Gamma Correction Circuit 13 Polygonal Line Approximation Circuit 20 Saturation Adjustment Circuit 22, 25 Limiter 24 Attenuator 27 Variable Amplifier 30 Gamma Correction Section

Claims (2)

[Claims] 1. An image pickup signal is supplied to a saturation adjustment circuit to carry out emphasis processing on the low input level side, and then is supplied to a gamma correction section to perform gamma correction on the image pickup signal. Characteristic gamma correction circuit. 2. The image pickup signal is supplied to a gamma correction section for gamma correction processing, and the gamma-corrected image pickup signal is supplied to a saturation adjustment circuit so that the gamma signal on the low input level side of the image pickup signal is supplied. A gamma correction circuit characterized in that its saturation is adjusted by changing only the characteristics.