JPH0758983A - Dynamic gamma correction circuit - Google Patents

Abstract

PURPOSE:To supply a circuit which timewise averages the luminance of a picture and executes gentle gamma correction. CONSTITUTION:An amplification/clamping part 6 inputting a luminance signal, and A/D conversion part 9 inputting the output of the amplification/clamping part 6 through an integrator 8 and a latch circuit 15 inputting one side output of the A/D conversion part 9 to a comparator 11 and the other side output to the address input terminal of a gamma correction circuit 2 and latching the output signal of an A/D conversion part 1 are provided. The output of the latch circuit 15 is inputted to a comparator 11. One side output of the comparator 11 is inputted to a holding/active circuit 18 and the other side output is inputted to the holding/active circuit 18. The output of the holding/active circuit 18 is inputted to the base of a transistor 22 through a resistor, and the collector output of the transistor 22 is inputted to the amplification/clamping part 6.

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 for correcting the brightness according to the brightness distribution of a brightness signal.

[0002]

2. Description of the Related Art When displaying with a display device other than a cathode ray tube such as a liquid crystal, the relationship between the brightness and the applied voltage is different from that of the cathode ray tube. Conventionally, this difference was corrected by γ correction. In the γ correction, when the luminance distribution is divided within a range of a predetermined gradation, a reference value is set for each frequency of the luminance distribution, and some curve patterns are provided based on the reference value. The correction is performed by selecting a table. However, the above method makes it difficult to finely adjust the contrast because the same correction is performed for both small and large changes in the frequency of the luminance distribution with a predetermined level value as a boundary.

[0003]

As described above, in the conventional γ correction method, for example, when an image having a high frequency of low luminance is changed to an image having a low frequency, and when an image having a low frequency of luminance is slightly high. The same γ correction is performed when the number of images is changed to a small number, and the screen has a problem of flickering each time. The present invention solves the above problems,
An object of the present invention is to provide a γ correction circuit that can change the correction value depending on the brightness level of the previous screen.

[0004]

In order to solve the above-mentioned problems, the present invention inputs an A / D conversion section for inputting a video signal and a value obtained by the A / D conversion section to a part of its input terminal. Γ correction circuit, a D / A conversion unit for inputting γ-corrected data to a predetermined brightness level, a video signal is taken out from the output of this D / A conversion unit, and the brightness signal is input to the amplification / clamp unit. The output of this amplifying / clamping unit
A / D conversion unit, the output of the A / D conversion unit is input to a comparator, and at the same time, it is input to a part of the address input terminal of the γ correction circuit to latch the output of the A / D conversion unit. A latch circuit and an output of the latch circuit are input to the comparator, a first output of the comparator is input to a first input terminal of a hold / active circuit, and a second output of the comparator is held / active. The second input terminal of the circuit is input, the output of the hold / active circuit is input to the base of the transistor through a resistor, and the collector output of the transistor is input to the control terminal of the amplification / clamp section. .

[0005]

In this way, by storing the data value of the low luminance level corresponding to the low address value of the γ correction circuit and the data of the high luminance level corresponding to the high address value, the past The address is controlled so as to be changed according to the average value of the luminance signal of, for example, when the past is bright, the increase rate of the current brightness is suppressed so that it does not become extremely bright, and when the past is dark, the current Keep the brightness reduction rate of to prevent it from getting extremely dark.

[0006]

Embodiments of the image processing apparatus according to the present invention will be described in detail below. FIG. 1 is a block diagram of essential parts of an embodiment of an image processing apparatus according to the present invention. In the figure, 1 is A /
The video signal is input to the D converter, the output of the A / D converter is input to a predetermined n bits of the address terminal 3 of the γ correction circuit 2, and the output of the γ correction circuit 2 is D / A converted. It is input to the unit 4 and the output video signal is taken out from the D / A conversion unit 4. The luminance signal 5 is input to the amplification / clamp unit 6,
The output 7 of the amplifying / clamping unit 6 is passed through the integrator 8 to A
Input to the A / D conversion unit 9 and output 10 from the A / D conversion unit 9.
Is input to one input terminal 12 of the comparator 11 and is input to the remaining m-bit address input terminal 13 of the γ correction circuit 2. The other output terminal 14 of the A / D converter 9 is input to the latch 15, and the output 16 of the latch 15 is input to the other input terminal of the comparator 11. One output 17 of the comparator 11 is input to one input terminal 19 (S2) of the hold / active circuit 18, and the other output 20 of the comparator 11 is the other input terminal 21 of the hold / active circuit 18. Input in (S1).
Output level of the hold / active circuit 18 (S
3) is input to the base of the transistor 22 via a resistor, and the collector output of the transistor 22 is amplified /
Input to the control terminal 23 of the clamp section 6. still,
Reference numeral 24 is a clock signal supplied to the A / D converters 1 and 9 and the latch.

Next, the operation of each part of the image processing apparatus will be described. The analog video signal (R, G, B) is A / D converted by the A / D converter 1, and this digital value is input to a predetermined n bits of the address terminal 3 of the γ correction circuit 2. The gain / clamping unit 6 adjusts the gain and clamp level of the luminance signal 5, and the adjusted luminance signal is integrated by the integrator 8 to become an APL signal, and the A / D conversion unit 9 further / D converted. This A / D converted value is input to the remaining address terminals of the γ correction circuit 2 in m bits, and the latch 15 latches this signal with the A / D conversion clock and delays it by one clock. The value is D (n-1). The comparator 11 compares the delayed value D (n-1) with the current A / D converted value D (n), and inputs the comparison result to the hold / active circuit 18.

Next, the hold / active circuit 18
The relationship between the level input to the input terminals 19 (S1) and 21 (S2) and the output level (S3) will be described. The value D (n) obtained by A / D converting the current brightness level is
If it is larger than the previous value D (n-1) (increase in brightness), the "L" level is output to the output S3, and conversely, D (n) is larger than D (n-1). If it is small (the brightness is reduced), the "H" level is output. D (n)
Is equal to D (n-1), the previous value D (n-1) is directly output to the output S3 as (no change in brightness).

Output S3 of the hold / active circuit
Is input to the base of the transistor 22 via the resistor. Since the bias point of the transistor 22 is set in the non-saturation region, for example, when D (n) becomes smaller than D (n-1) (luminance decreases),
The "L" level is applied to the base of the transistor 22, which raises the level of the collector of the transistor 22 and gradually decreases the gain of the amplifying / clamping unit 6 connected from the collector through the resistor. As the value is increased, the value of the clamp level for A / D conversion is gradually increased so that the brightness decreases slowly.
In this way, by storing the data value of the low level value corresponding to the low address of the γ correction circuit and storing the data of the high level value corresponding to the high address, the average value of the past luminance signals is stored. Since the address changes depending on the past, for example, if the past was bright, suppress the increase rate of the current brightness to prevent it from becoming extremely bright, and if the past was dark, suppress the decrease rate of the current brightness. You can prevent it from getting extremely dark.

[0010]

As described above, according to the image processing apparatus of the present invention, for example, when the current brightness is to be γ-corrected, the correction value to be γ-corrected is changed according to the past brightness value. Since it is possible to have such a hysteresis, the screen will not become extremely bright or dark by γ correction,
It becomes a smooth γ correction that is averaged over time, and it is possible to provide an easy-to-see screen with little change in contrast.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an embodiment of an image processing apparatus according to the present invention. 1 A / D conversion section 2 Gray scale detection section 3 Address terminal 3 4 D / A conversion section 5 Luminance signal 6 Amplification / clamp section 7 Output 8 Integrator 9 A / D conversion section 10 Output 11 Comparator 12 Input terminal 13th 3 memory part 14 output terminal 15 latch 16 terminal 17 output 18 hold / active circuit 19 input terminal 20 output 21 input terminal 22 transistor 23 control terminal 24 CLK

Claims (1)

[Claims] 1. An A / D conversion section for inputting a video signal, a γ correction circuit for inputting the A / D converted signal to a part of an input terminal of a γ correction circuit, and a γ correction circuit, and this γ correction circuit. In the D / A conversion unit for inputting the input data and the one for extracting the video signal from the output of the D / A conversion unit, the amplification / clamp unit for inputting the luminance signal and the output of the amplification / clamp unit are connected to the integrator. The A / D conversion unit input via the A / D conversion unit and the output of the A / D conversion unit are input to the first input terminal of the comparator, and also input to a part of the address input terminal of the γ correction circuit. A latch circuit for latching the output of the D conversion unit, an output of the latch circuit is input to the second input terminal of the comparator, and a first output of the comparator is input to the first input terminal of the hold / active circuit. Hold / act the second output of the comparator Input to the second input terminal of the input / output circuit, and the value of the output level of the hold / active circuit is changed by the combination of the input first and second input signal levels. To the base of the transistor,
A dynamic γ correction circuit characterized in that the output level of the collector is inputted to the control terminal of the amplification / clamp section.