JP2001136411A - Video signal processing circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a video signal processing circuit that uses a Y gamma correction circuit to effectively improve the contrast in dark parts as its major feature in a scene having many dark parts. SOLUTION: For example, on the basis of a comparison result between an input luminance signal and a dark point, a dark part detection circuit 15 detects the rate of the dark part shared in the input luminance signal. Then the output of the dark part detection circuit 15 controls 1st and 2nd gain control circuits 16a, 16b. Thus, the gain of a dark part expansion circuit 11 that amplifies a signal not higher than the gamma of the input luminance signal and the gain of a bright part compression circuit 12 that compressed a signal higher than the gamma of the input luminance signal are respectively automatically adjusted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated circuit for processing a video signal of a television receiver, and more particularly to a Y gamma correction circuit for performing gamma correction on a luminance signal (Y indicates a luminance signal).

[0002]

2. Description of the Related Art As is well known, one of integrated circuits for performing video signal processing of a television receiver is a Y gamma correction circuit for performing gamma correction on a luminance signal.

FIG. 10 shows a schematic configuration of a conventional Y gamma correction circuit.

The Y-gamma correction circuit includes, for example, a buffer 102 and a buffer 103 to which an input luminance signal (input Y) subjected to black expansion and black level correction by a black expansion / black level correction circuit 101 is supplied. Is provided between them. Then, the Y gamma correction of the luminance signal is configured to fix the gain and compress a signal having a gamma point or more (see FIG. 11). Incidentally, in FIG. 10, Q1 and Q2 are NPN transistors,
R1 to R4 are resistors, Ic is a constant current source, and SW is a switch for Y gamma correction on / off (ON / OFF).

However, the above-described Y gamma correction circuit compresses only a signal of the input Y which is higher than the gamma point. For this reason, for example, for a signal having a lot of luminance components (a scene with many bright parts) such as a human face illuminated in a studio, the differential gain is reduced, and as a result, the texture of the skin becomes solid and the detail is reduced. There was a problem that the feeling became worse.

Further, when the luminance level of an output luminance signal (output Y) with respect to an input luminance signal rises or falls due to a luminance signal correction process such as black expansion or gamma correction, color loss or color in a color difference signal becomes darker. Such a problem had occurred.

[0007]

As described above, in the prior art, gamma correction is performed by fixing only the gain and compressing only the signal at or above the gamma point. There was a problem that the sense of detail was lost.

Therefore, the present invention is effective for improving the contrast of a dark portion in a scene having many dark portions (a signal having a small brightness component) without losing the sense of detail even when there are many luminance components. It is an object to provide a simple video signal processing circuit.

[0009]

In order to achieve the above object, a video signal processing circuit according to the present invention receives an input luminance signal, and amplifies a signal of the input which is lower than a first level. A dark part expansion circuit, a light part compression circuit that operates complementarily to the amplifier operation of the dark part expansion circuit, and compresses a signal of the input luminance signal that is equal to or higher than the first level. A dark portion detection circuit for detecting a ratio of a dark portion to the input luminance signal based on a comparison result between the dark portion detection signal and the second level, and a gain for adjusting the gain of the dark portion expansion circuit in accordance with an output of the dark portion detection circuit. 1 gain control circuit, a second gain control circuit that adjusts the gain of the bright part compression circuit according to the output of the dark part detection circuit, and the output of the dark part decompression circuit and the output of the bright part compression circuit. And the output brightness It is composed of a summing circuit for generating a signal.

According to the video signal processing circuit of the present invention, it is possible to automatically adjust the Y gamma gain in accordance with the proportion of a dark portion in an input luminance signal, and to not only compress a signal having a gamma point or more, but also The signal below the gamma point can be amplified. As a result, it is possible to improve the contrast of the dark part while improving the deterioration of the detail feeling in a scene with many bright parts.

In particular, when the amplitude of the color difference signal is corrected based on the comparison output between the input luminance signal and the output luminance signal, if the luminance level changes by the luminance signal correction processing, This makes it possible to improve the problem of missing colors and darkening of colors.

[0012]

Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a schematic configuration of a dynamic Y gamma correction circuit according to a first embodiment of the present invention.

That is, the dynamic Y gamma correction circuit 10 receives, for example, input luminance signals that have been subjected to processing such as black expansion and black level correction by the black expansion / black level correction circuit 1 and inputs them to a dark portion. Circuit 11
The main part is constituted by the bright part compression circuit 12.

An output luminance signal is output to the buffer 2 via an addition circuit 13 for adding the output of the dark part expansion circuit 11 and the output of the light part compression circuit 12.

As shown in FIG. 2, for example, the dark part expansion circuit 11 amplifies (dynamically) only the signal below the gamma point (first level) of the input luminance signal in proportion.

As shown in FIG. 2, for example, the bright part compression circuit 12 compresses a signal having a gamma point or more of the input luminance signal.

The dynamic Y gamma correction circuit 10
Further includes a dark portion detection circuit 15, first and second gain control circuits 16a and 16b, and the like.

The dark part detecting circuit 15 detects the ratio (ratio) of the dark part in the input luminance signal. For example, the charge / discharge of the external capacitor 3 is controlled via the external pin 18 depending on whether the luminance level of the input luminance signal is equal to or less than the dark point (second level). And the potential (charging voltage) of the external capacitor 3 is
To the gain control circuits 16a and 16b.

The configuration and operation of the dark part detection circuit 15 will be described later. Also, the dark point may be at the same level as the gamma point,
The gamma point may have a magnitude relation.

First and second gain control circuits 16a, 16b
Is the output of the dark part detection circuit 15 (external capacitor 3
In order to automatically adjust the gain of the dark part expansion circuit 11 or the bright part compression circuit 12 in accordance with the potential of the dark part. The smaller the ratio of the dark part, the more the direction in which the gain does not change.

FIG. 3 shows the output characteristics of the dynamic Y gamma correction circuit 10 described above.

As shown in FIG.
The output of the bright part compression circuit 12 and the output of
Y gamma correction, which amplifies the signal below the gamma (γ) point and compresses the signal above the gamma point, of the input luminance signal that has been subjected to processing such as black expansion and black level correction by adding Becomes

As a result, Y gamma correction is not applied to a signal having a large luminance component (a scene with many bright parts), and conversely, a signal having a large dark part (a signal having a small luminance component) such as darkness is not applied. Can effectively improve the contrast of the dark part, and the detail feeling does not deteriorate.

Further, according to the ratio of the dark portion of the input luminance signal subjected to the processing such as the black expansion and the black level correction,
The Y gamma gain can be dynamically and linearly adjusted.

FIG. 4 shows an example of a circuit configuration of the dark part detecting circuit 15 described above.

For example, the dark part detection circuit 15
The N-transistors Q23 and Q25 compare the input luminance signal with a dark point which is a reference when detecting a dark part. If the luminance level is lower than the dark point, the PNP
The external capacitor 3 connected to the external pin 18 is charged via the transistors (current mirror circuits) Q21 and Q22 and the resistor R13.

In the dark part detection circuit 15, the charge voltage of the external capacitor 3 is compared with the ground potential (GND) by the PNP transistors Q28 and Q34, and the external capacitor 3 is charged to a level higher than the ground potential. During the period when the NPN transistor (current mirror circuit) Q3
2, Q33 is turned on.

As described above, in the case of the dark part detection circuit 15 of the present configuration, the charging voltage of the external capacitor 3 is controlled according to the ratio of the dark part to the input luminance signal. First and second gain control circuits 16
The gain control voltages a and 16b can be controlled.

The detection capability (detection reaction speed) of the dark part detection circuit 15 can be changed according to the time constant of the external capacitor 3 and the resistor R12. For example, when the scene is changed from a bright scene to a dark scene, the reaction can be immediately performed or a slightly delayed operation can be set by appropriately changing the time constant.

As described above, the Y gamma gain can be automatically adjusted according to the ratio of the dark part in the input luminance signal. In addition to compressing signals above the gamma point, signals below the gamma point can be amplified.

That is, the signal above the gamma point and the signal below the gamma point of the input luminance signal are complementarily compressed or amplified with an optimum gain according to the proportion of the dark part.

This makes it possible to apply Y gamma correction only to a signal having a small luminance component without applying Y gamma correction to a signal having a large luminance component.

Therefore, since the differential gain of a signal having many luminance components does not decrease, it is possible to improve the contrast of a dark portion in a scene with many dark portions while improving the deterioration of the sense of detail in a scene with many bright portions. It is.

In the dynamic Y gamma correction circuit 10 according to the first embodiment, the second gain control circuit 16b for automatically adjusting the gain of the bright part compression circuit 12 is replaced by a dark part detection circuit. Although the case has been described in which control is performed in accordance with the output of Fifteen, the present invention is not limited to this. For example, control may be performed by further using the output of the 100 IRE correction circuit.

(Second Embodiment) FIG. 5 shows a configuration example of a dynamic Y gamma correction circuit according to a second embodiment of the present invention. 2A is a schematic configuration diagram, and FIG. 2B is a circuit configuration diagram showing a part of the configuration more specifically.

Also, here, in the configuration according to the first embodiment described above (see FIG. 1), the second gain control circuit 16b is controlled according to the output of the dark part detection circuit 15 and the output of the 100 IRE correction circuit 21. 1 is shown as an example, and the same parts as those in FIG.
A brief description will be given.

This dynamic Y gamma correction circuit 10 '
Is a summing circuit 13 for adding the output of the dark part expanding circuit 11 and the output of the light part compressing circuit 12, and a second gain control circuit 1 for automatically adjusting the gain of the light part compressing circuit 12.
6b, a 100IRE correction circuit 21 is further provided.

The 100 IRE correction circuit 21
This is for aligning the pp value of the IRE reference voltage with the output (correcting a 100 IRE shift between the input and the output). The output of the adding circuit 13 (see FIG. 6) is used as an input, and the Y gamma correction is performed. Based on the result of comparing the output luminance signal with the 100 IRE reference voltage, the second gain control circuit 1
6b.

That is, the 100IRE correction circuit 21
100 IRE inserted for an arbitrary period (T period) anywhere in the blanking period of the output luminance signal
The corresponding voltage is compared with a reference voltage of 100 IRE by a comparison circuit (not shown). And the above 100I
When the voltage corresponding to RE is higher than the reference voltage of 100 IRE, an internal capacitor (not shown) is charged by the control voltage, and when it is lower, the capacitor is discharged.

As the internal capacitor, one having a time constant enough to hold the control voltage at least during the picture period is prepared.

If the potential (charging voltage) of the internal capacitor is higher than a certain comparison voltage, the current flowing through the bright part compression circuit 12 increases, and the compression gain increases. Conversely, if the potential of the internal capacitor is lower than a certain comparison voltage, the current flowing through the bright part compression circuit 12 decreases, and the compression gain decreases.

FIG. 7 shows the above-mentioned 100 IRE correction circuit 2
1 shows a comparison operation between the output luminance signal and the 100 IRE reference voltage.

In this case, 100IR during the blanking period
By inserting the E reference voltage, the output luminance signal (1
(A voltage corresponding to 00IRE) and a 100IRE reference voltage are compared.

Finally, the current flowing through the bright part compression circuit 12 is increased or decreased so that the output luminance signal (the signal after gamma correction) becomes 100 IRE, and the compression gain is automatically adjusted. .

As described above, the adjustment is automatically performed during the blanking period, so that 10
There is no shift of 0IRE. That is, when the input luminance signal is 100
If it is an IRE, the output luminance signal will be 100 IRE. Therefore, performing the dynamic Y gamma correction in the state where the 100 IRE correction has been performed can prevent a disadvantage that the input luminance signal is shifted by 100 IRE in the output.

The adjusted 100 IRE correction circuit 21
The internal capacitor holds a control voltage during the picture period. Also, the inserted 100IRE reference voltage needs to be removed at a later stage.

Here, the operation of the dynamic Y gamma correction circuit 10 'including the 100 IRE correction circuit 21 will be briefly described with reference to FIG.

In the dark part expanding circuit 11, the signal obtained by level-shifting the input luminance signal and the voltage obtained by level-shifting the gamma point are supplied to PNP transistors Q11 and Q12.
Are compared by

When the input luminance signal is below the gamma point, the base voltage of NPN transistor Q8 (base voltage of PNP transistor Q11 + Vbe) changes linearly. Conversely, when the input luminance signal is equal to or higher than the gamma point, the base voltage of the NPN transistor Q8 (base voltage of the PNP transistor Q12 + Vbe) becomes a fixed voltage.

On the other hand, the base voltage (reference voltage) of NPN transistor Q7 is equal to D when no input luminance signal is input.
C level + voltage for level shift by level shift circuit +
Vbe is set.

Therefore, when the input luminance signal is below the gamma point, the output of the dark part detection circuit 15
The NPN transistor Q5 of the first gain control circuit 16a
After Q6 is controlled, a linear current flows through the transistor Q8, and the gain of the dark part expansion circuit 11 also becomes linear.

On the other hand, when the input luminance signal is equal to or higher than the gamma point, a current fixed to the transistor Q8 flows, and the gain of the dark part expansion circuit 11 is also fixed.

Similarly, in the bright part compression circuit 12, the signal obtained by level-shifting the input luminance signal and the voltage obtained by level-shifting the gamma point are supplied to the NPN transistor Q1.
3, Q14.

When the input luminance signal is equal to or lower than the gamma point, the NPN transistor Q14 is turned on, and the bright part compression circuit 12 does not operate.

Conversely, when the input luminance signal is equal to or higher than the gamma point, the NPN transistor Q13 turns on. The output of the dark part detection circuit 15 controls the NPN transistors Q3 and Q4 of the second gain control circuit 16b, and the 100IRE correction circuit 21 controls the NPN transistors Q3 and Q4.
The transistors Q9 and Q10 are controlled, and the bright part compression circuit 12 operates.

That is, the bright part compression circuit 12 operates only when the input luminance signal is equal to or higher than the gamma point, and the current flowing through the transistor Q10 is made variable by the 100IRE correction circuit 21.
The gain is automatically adjusted so as to be equal to 100 IRE.

As described above, when the input luminance signal is equal to or higher than the gamma point and when the input luminance signal is equal to or lower than the gamma point, the gains of the dark part expanding circuit 11 and the light part compressing circuit 12 are appropriately controlled. Based on being connected to the inverting input and the non-inverting input, they operate complementarily to each other.

According to the dynamic Y gamma correction circuit 10 'having such a configuration, it is possible to obtain an effect equal to or higher than that of the dynamic Y gamma correction circuit 10 according to the first embodiment.

That is, the Y gamma gain can be dynamically and linearly adjusted in accordance with the proportion of the dark portion of the input luminance signal that has been subjected to processing such as black expansion and black level correction. It is possible to effectively improve the contrast of a dark portion in a scene having many dark portions, such as darkness, while preventing the image quality from deteriorating.

In particular, since the second gain control circuit is controlled by using the output of the 100 IRE correction circuit, it is possible to prevent such a problem that the 100 IRE is shifted.

The circuit composed of NPN transistors Q9 and Q10 in the second gain control circuit 16b
The OIRE correction circuit 21 is provided by providing the OIRE correction circuit 21. For example, as shown in FIG.
In the case of the dynamic Y gamma correction circuit 10 without the RE correction circuit 21, it can be omitted.

Accordingly, the configuration and operation of the dynamic Y gamma correction circuit 10 according to the first embodiment are basically the same as those of the dynamic Y gamma correction circuit 10 'according to the second embodiment. It is.

In the dynamic Y gamma correction circuits 10 and 10 'according to the first and second embodiments described above, a change in the luminance level of the luminance signal due to the Y-system correction processing causes It is also possible to configure so as to be able to improve the problem of missing colors and darkening of colors.

(Third Embodiment) FIG. 8 shows a schematic configuration of a dynamic Y gamma correction circuit according to a third embodiment of the present invention. Here, an example is shown in which the color difference amplitude correction circuit is further provided in the configuration according to the above-described second embodiment (see FIG. 5A). The same parts as those in FIG. 5A are denoted by the same reference numerals, and detailed description thereof will be omitted.

This correction circuit includes the dynamic Y gamma correction circuit 10 ′ and the color difference amplitude correction circuit 31. The color difference amplitude correction circuit 31 includes a comparison circuit 32
And a third gain control circuit 33 for correcting the output luminance signal with respect to the input luminance signal in the Y system (here,
The amplitude of the in-phase color difference signal is corrected in accordance with a change in the luminance level due to black expansion or gamma correction.

That is, the comparison circuit 32 of the color difference / amplitude correction circuit 31 outputs an output luminance signal (a signal after Y-system correction) which has been subjected to processing such as Y gamma correction, which is the output of the dynamic Y gamma correction circuit 10 '. And an input luminance signal (a signal before Y-system correction) before being subjected to black expansion and black level correction, which is an input of the black expansion and black level correction circuit 1, and the comparison result is referred to as a third signal. To the gain control circuit 33 of FIG.

The third gain control circuit 33 of the chrominance amplitude correction circuit 31 receives the comparison result of the comparison circuit 32 as an input, and if there is a change in the luminance level, the chrominance signal for the chrominance signal is changed according to the amount of the change. It controls the gain (gain) of the amplitude correction.

For example, when the luminance level of the output luminance signal is higher than that of the input luminance signal, the color of the color difference signal becomes lighter, so that the gain of the color difference amplitude is increased (FIG. 9).
(A)). Conversely, when the luminance level of the output luminance signal is lower than that of the input luminance signal, the color of the color difference signal becomes darker, so that the gain of the color difference amplitude is reduced (FIG. 9).
(B)).

Normally, the luminance level is lowered by black extension. With this configuration, even if the luminance level of the output luminance signal changes with respect to the input luminance signal due to the Y-system correction processing, the amplitude gain of the in-phase color difference signal is linked to the luminance level change. As a result, it becomes possible to improve the disadvantages such as color omission and dark color in the color difference signal.

Therefore, in the above-mentioned scenes having many dark areas such as dark areas, the contrast of the dark areas can be effectively improved, and it is possible to prevent the detail from being deteriorated. In addition to dynamically and linearly adjusting the Y gamma gain in accordance with the proportion of dark areas in the input luminance signal that has undergone processing such as correction, the luminance signal and the color difference signal can be corrected in a well-balanced manner, eliminating discomfort. Is possible.

Of course, various modifications can be made without departing from the scope of the present invention.

[0073]

As described above in detail, according to the present invention, even when there are many luminance components, the sense of detail is not lost, and in a scene with many dark parts such as darkness (a signal having a small luminance component). Thus, a video signal processing circuit effective for improving the contrast in dark areas can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an example of a dynamic Y gamma correction circuit according to a first embodiment of the present invention.

FIG. 2 is an operation characteristic diagram for explaining an outline of the dynamic Y gamma correction circuit.

FIG. 3 is an output characteristic diagram for explaining the operation of the dynamic Y gamma correction circuit.

FIG. 4 is a circuit diagram showing an example of a dark part detection circuit in the dynamic Y gamma correction circuit.

FIG. 5 is a schematic configuration diagram illustrating an example of a dynamic Y gamma correction circuit according to a second embodiment of the present invention.

FIG. 6 is an output characteristic diagram of the dynamic Y gamma correction circuit.

FIG. 7 is a schematic characteristic diagram similarly illustrating the operation of the 100IRE correction circuit in the dynamic Y gamma correction circuit.

FIG. 8 is a schematic configuration diagram illustrating an example of a dynamic Y gamma correction circuit according to a third embodiment of the present invention.

FIG. 9 is a schematic characteristic diagram for explaining the operation of the color difference amplitude correction circuit in the dynamic Y gamma correction circuit.

FIG. 10 is a schematic configuration diagram of a Y gamma correction circuit shown to explain a conventional technique and its problems.

FIG. 11 is an output characteristic diagram for explaining the operation of the conventional Y gamma correction circuit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Black expansion and black level correction circuit 2 ... Buffer 3 ... External capacitor 10,10 '... Dynamic Y gamma correction circuit 11 ... Dark part expansion circuit 12 ... Light part compression circuit 13 ... Addition circuit 15 ... Dark part detection circuit 16a ... 1 gain control circuit 16b second gain control circuit 18 external pin 21 100IRE correction circuit 31 color difference amplitude correction circuit 32 comparison circuit 33 third gain control circuit

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Echiko Matsuo 3-3-9 Shimbashi, Minato-ku, Tokyo Toshiba Abu-E Co., Ltd. F-term (reference) 5C021 PA03 PA17 PA53 PA58 PA66 PA76 PA96 RA06 RB03 XA34 XA61

Claims (7)

[Claims] 1. An input luminance signal is input, and the input
A dark part expansion circuit for amplifying a signal of a first level or less; a light circuit for operating a complementary operation to the amplifying operation of the dark part expansion circuit to compress a signal of the input luminance signal of the first level or more. A partial compression circuit, a dark part detection circuit that detects a ratio of a dark part in the input luminance signal based on a comparison result of the input luminance signal and a second level, and according to an output of the dark part detection circuit, A first gain control circuit that adjusts the gain of the dark part expansion circuit; a second gain control circuit that adjusts the gain of the light part compression circuit in accordance with the output of the dark part detection circuit; and an output of the dark part expansion circuit And an output circuit for adding an output of the bright part compression circuit and generating an output luminance signal. 2. The video signal processing circuit according to claim 1, wherein the dark section expansion circuit proportionally amplifies the signal of the first level or lower. 3. The video signal processing circuit according to claim 1, further comprising a 100 IRE correction circuit for adjusting the pp value of the 100 IRE reference voltage at the output. 4. The apparatus according to claim 1, wherein the 100IRE correction circuit compares the output luminance signal with a 100IRE reference voltage, and controls the second gain control circuit according to the comparison result. Item 4. The video signal processing circuit according to Item 3. 5. A comparison circuit for comparing an input luminance signal with an output luminance signal and outputting a change in luminance level of the output luminance signal with respect to the input luminance signal, and an amplitude of a color difference signal based on the comparison output. 4. The video signal processing circuit according to claim 1, further comprising: a third gain control circuit for controlling a gain for correcting the gain. 6. The video signal processing circuit according to claim 5, wherein the input luminance signal is a signal before black extension and black level correction. 7. The video signal processing circuit according to claim 5, wherein the output luminance signal is a signal subjected to Y gamma correction.