JPH10290380A - Gradation improving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent unnatural coloring at low luminance generated by the error propagation processing at a post stage by replacing a part of color components with luminance signals at the part of low gradation corresponding to the distribution of a luminance signal level in a scene control circuit. SOLUTION: The scene control circuit 12 outputs threshold detection signals corresponding to the distribution of the luminance signal level of a field unit from the luminance signals Y. For the threshold detection signal, whether it is larger or smaller than a threshold value generated similarly inside the circuit 12 is compared and detected. The threshold value becomes a small value when the luminance signal level distribution is concentrated on the low luminance. When the luminance level is smaller than the threshold value of luminance replacement by the threshold detection signal, selection circuits 1B, 1C and 1D select and output the output signals of addition circuits 18, 19 and 1A. Thus, the unnatural coloring at the low luminance generated in an error propagation circuit 1E is made inconspicuous.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradation improving circuit for improving a gradation display characteristic of a video signal in an image display device.

[0002]

2. Description of the Related Art Conventionally, in a so-called error diffusion circuit, when an input signal level is at or near 0, an error is forcibly set to 0 and an error at low luminance associated with error diffusion processing is reduced. Problems such as natural coloring and floating of black level have been avoided.

Hereinafter, a conventional gradation improving circuit will be described with reference to the drawings. FIG. 4 is a block diagram of a conventional gradation improving circuit.

In FIG. 4, reference numeral 31 denotes an error diffusion processing of an n-bit digitized original pixel signal, and m (m ≦ n−
1) An error diffusion circuit that converts the data into bit data and outputs the data (m and n are arbitrary natural numbers). Reference numeral 32 denotes an addition circuit that adds the original pixel signal and an output signal of a prohibition circuit 35 described later. Reference numeral 33 denotes a diffusion level detection circuit which receives an output signal of the addition circuit 32 and determines whether or not to diffuse an error. Reference numeral 34 denotes an error generating circuit which receives an output signal of the adding circuit 32, outputs a reproduction error obtained by appropriately weighting and adding errors of an original pixel, such as a vertical upper pixel, a diagonally upper pixel, and a horizontal left pixel, to the original pixel. It is. An error prohibition circuit 35 forcibly sets the reproduction error to 0 or outputs the reproduction error as it is based on the output signal of the diffusion level detection circuit 33. A bit conversion circuit 36 receives an output signal of the addition circuit 32, converts the signal into m-bit data, and outputs the data.

The operation of the above-described gradation improving circuit will be described below. First, the addition circuit 32 adds the original pixel signal digitized to n bits and the output signal of the inhibition circuit 35. Next, the addition circuit 3 is added to the diffusion level detection circuit 33.
2, and outputs a closed signal if the signal level is 0 or a value close to it, and outputs an open signal otherwise. Next, the addition circuit 32 is added to the error generation circuit 34.
And outputs a reproduction error obtained by adding appropriate weights to the errors of the upper pixel, the upper diagonal pixel, the horizontal left pixel, and the like with respect to the original pixel. Next, the output signal of the error generation circuit 34 and the output signal of the diffusion level detection circuit 33 are input to the inhibition circuit 35, and when the output signal of the diffusion level detection circuit 33 is a closed signal, the value of the output signal of the error generation circuit 34 0, and outputs the output signal of the error generation circuit 34 as it is when the output signal of the diffusion level detection circuit 33 is an open signal. Next, the addition circuit 32 is added to the bit conversion circuit 36.
Is converted into m bits and output.

As described above, in the conventional error diffusion circuit, when the input signal level is 0 or close to it, the error is forcibly set to 0 and the unnatural color / black of low luminance accompanying the error diffusion processing is reduced. Problems such as floating levels have been avoided.

[0007]

However, in the above-described conventional configuration, when the input signal is 0 or a value close to 0, error diffusion is not performed. However, since the characteristics of low gradations are crushed, there is a problem that smooth gradation cannot be obtained, especially in a dark video portion, even though improvement of gradation display characteristics by error diffusion is desired.

[0008]

In order to solve the above-mentioned problems, a gradation improving circuit according to the present invention uses a scene control circuit in which a part of a color component is reduced in a low gradation part according to a distribution of a luminance signal level. Is replaced with a luminance signal, it is possible to prevent unnatural coloring at low luminance caused by the error diffusion processing in the subsequent stage.

According to the present invention, even when the input signal has a value of 0 or a value close to 0, the error diffusion processing is not inhibited, so that the gradation display characteristics of a dark video signal portion can be improved.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a luminance substitution circuit which receives a video signal and suppresses unnatural coloring at a low luminance generated in an error diffusion circuit at the subsequent stage, and improves a gradation display characteristic of the video signal. And an error diffusion circuit for performing an error diffusion in order to perform the error diffusion. A luminance replacement circuit that replaces a part of a color component with a luminance signal, and an error diffusion circuit that performs error diffusion for improving a gradation display characteristic of an output video signal of the luminance substitution circuit. It relates to a gradation improving circuit.

According to a second aspect of the present invention, there is provided a gradation improving circuit comprising:
A luminance replacement circuit, which receives a color input video signal and outputs a luminance signal, and a luminance level detection circuit, which receives the luminance signal,
A scene control circuit that outputs a delayed luminance signal, a threshold detection signal, a primary color multiplication coefficient, and a luminance multiplication coefficient,
A storage element for receiving the color input video signal and delaying the color input video signal by a predetermined time to output a color delayed video signal;
east significant bit (hereinafter LS)
B) and an appropriate number of bits of the delayed luminance signal, and a first multiplication circuit that multiplies the appropriate number of bits of the delayed luminance signal by the primary color multiplication coefficient output from the scene control circuit. A second multiplication circuit for multiplying the output signal of the first multiplication circuit and the output signal of the second multiplication circuit, A selection circuit for switching the output signal of the adder circuit with a threshold detection signal output from the scene control circuit and outputting the selected signal.

According to a third aspect of the present invention, there is provided a luminance level detecting circuit for inputting a red input video signal, a green input video signal, and a blue input video signal and outputting a luminance signal, and receiving a luminance signal and outputting a delayed luminance. A scene control circuit that outputs a signal, a threshold detection signal, a primary color multiplication coefficient, and a luminance multiplication coefficient, a storage element that inputs a red input video signal, a green input video signal, and a blue input video signal, and outputs the signal after delaying for a predetermined time; A first multiplication circuit for multiplying an appropriate number of LSB bits of the red delayed video signal by a primary color multiplication coefficient, and a second multiplication circuit for multiplying an appropriate number of LSB bits of the green delayed video signal by a primary color multiplication coefficient A third multiplication circuit for multiplying an appropriate number of LSB bits of the blue delayed video signal by the primary color multiplication coefficient, and multiplying an appropriate number of LSB bits of the delayed luminance signal by the luminance multiplication coefficient A fourth multiplier circuit, a first adder circuit for adding an output signal of the first multiplier circuit and an output signal of the fourth multiplier circuit, and an output signal of the second multiplier circuit and a fourth multiplier circuit A second addition circuit for adding the output signal of the third multiplication circuit, a third addition circuit for adding the output signal of the third multiplication circuit and the output signal of the fourth multiplication circuit, a red delayed video signal and the first
A first selection circuit for switching the output signal of the adder circuit of FIG.
A second selection circuit for switching the output signal of the adder circuit of FIG.
2. A gradation improving circuit according to claim 1, further comprising a luminance replacement circuit comprising a third selection circuit for switching an output signal of said addition circuit with a threshold detection signal. By substituting a part of the color component with the luminance signal in the low part, it is possible to prevent unnatural coloring at low luminance caused by the error diffusion processing in the subsequent stage.

According to a fourth aspect of the present invention, there is provided a luminance level detection circuit for inputting a red input video signal, a green input video signal, and a blue input video signal and outputting a luminance signal, and receiving a luminance signal and outputting a delayed luminance. A scene control circuit that outputs a signal and a primary color multiplication coefficient, a storage element that receives a red input video signal, a green input video signal, and a blue input video signal and outputs the delayed signal for a predetermined time, and a delayed luminance signal from a red delayed video signal A first subtraction circuit for subtracting a color difference signal and outputting a red color difference signal;
A second subtraction circuit that subtracts the delayed luminance signal from the green delayed video signal and outputs a green color difference signal, a third subtraction circuit that subtracts the delayed luminance signal from the blue delayed video signal and outputs a blue color difference signal, and a red color difference First to multiply the signal by the primary color multiplication coefficient
, A second multiplication circuit for multiplying a green color difference signal by a primary color multiplication coefficient, a third multiplication circuit for multiplying a blue color difference signal by a primary color multiplication coefficient, and an output signal of the first multiplication circuit and delayed luminance A first addition circuit for adding the signals, a second addition circuit for adding the output signal of the second multiplication circuit and the delayed luminance signal, and a third addition circuit for adding the output signal of the third multiplication circuit and the delayed luminance signal. 3. A gradation improving circuit according to claim 2, further comprising a luminance replacement circuit comprising an adder circuit of (1) and (2), wherein the number of multiplication circuits can be reduced by changing a calculation method of the luminance replacement.

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a gradation improving circuit showing one embodiment of the present invention.

In FIG. 1, reference numeral 11 denotes a luminance level detection circuit which receives a red input video signal, a green input video signal, and a blue input video signal and outputs a luminance signal. Reference numeral 12 denotes a scene control circuit that receives a luminance signal and outputs a delayed luminance signal, a primary color multiplication coefficient, a luminance multiplication coefficient, and a threshold detection signal. Reference numeral 13 denotes a storage element that receives a red input video signal, a green input video signal, and a blue input video signal, and outputs a red delayed video signal, a green delayed video signal, and a blue delayed video signal with a predetermined delay. Reference numeral 14 denotes a first multiplication circuit that multiplies an appropriate number of LSB bits of the red delayed video signal by a primary color multiplication coefficient. Reference numeral 15 denotes a second multiplication circuit that multiplies an appropriate number of LSB bits of the green delayed video signal by a primary color multiplication coefficient. Reference numeral 16 denotes a third multiplication circuit for multiplying an appropriate number of LSB bits of the blue delayed video signal by a primary color multiplication coefficient. Reference numeral 17 denotes the delayed luminance signal
Fourth for multiplying an appropriate number of bits of the t significant bit (hereinafter referred to as LSB) by a luminance multiplication coefficient.
Is a multiplication circuit.

Reference numeral 18 denotes a first adder for adding the output signal of the first multiplier 14 and the output signal of the fourth multiplier 17. Reference numeral 19 denotes a second addition circuit that adds the output signal of the second multiplication circuit 15 and the output signal of the fourth multiplication circuit 17. 1A is a third adding circuit that adds the output signal of the third multiplying circuit 16 and the output signal of the fourth multiplying circuit 17.

Reference numeral 1B denotes a first selection circuit that switches between the red delayed video signal and the output signal of the first addition circuit 18 according to a threshold detection signal. 1C is a second selection circuit that switches between the green delayed video signal and the output signal of the second addition circuit 19 according to a threshold detection signal. 1D is
This is a third selection circuit that switches between the blue delayed video signal and the output signal of the third addition circuit 1A according to a threshold detection signal. 1E is the output signal of the first selection circuit 1B and the second
Is an error diffusion circuit that receives the output signal of the selection circuit 1C and the output signal of the third selection circuit 1D, performs error diffusion, and outputs a red output video signal, a green output video signal, and a blue output video signal.

The operation of the gradation improving circuit configured as described above will be described below with reference to FIG.

First, a red input video signal R, a green input video signal G, and a blue input video signal B are input to a brightness level detection circuit 11 and a brightness signal Y is output. Actually, a luminance signal Y is output by performing an arithmetic processing such as Y = 0.30R + 0.59G + 0.11B (1). next,
The luminance signal Y is input to the scene control circuit 12, and a delayed luminance signal, a distribution of luminance signal levels in field units are checked, and a threshold detection signal corresponding to the distribution of luminance signal levels, a primary color multiplication coefficient, and a luminance multiplication coefficient are output. .

Here, the threshold detection signal is compared and detected as to whether it is larger or smaller than a threshold value generated inside the scene control circuit 12. The threshold value is a threshold value of the luminance signal Y that determines whether part of the primary color signal component is replaced with the luminance signal Y or not. When the luminance signal level distribution is concentrated on low luminance, the threshold value is controlled to a small value, otherwise, the threshold value is controlled to a large value. For example, in a video scene, the threshold value is "8"
Then, the threshold detection signal outputs “0” when the luminance signal Y is smaller than “8”, and outputs “1” when the luminance signal Y is higher than “8”.

The primary color multiplication coefficient and the luminance multiplication coefficient are
Each value of 0 or more and 1 or less satisfies the relationship of primary color multiplication coefficient + luminance multiplication coefficient = 1. Therefore, if the primary color multiplication coefficient is k, the luminance multiplication coefficient is (1-k). When the luminance signal Y is equal to or smaller than the threshold value, a part of the primary color signal component is replaced with the luminance signal Y in a low gradation part, so that the primary color multiplication coefficient
Is a value corresponding to the luminance level. On the other hand, when it is larger than the threshold value, the primary color multiplication coefficient k is always “1”.

Next, the red input video signal R is supplied to the delay element 13.
And a green input video signal G and a blue input video signal B,
It outputs a red delayed video signal, a green delayed video signal, and a blue delayed video signal. Here, the time for delaying the red input video signal, the green input video signal, and the blue input video signal is set to coincide with the time required for the scene control circuit 12 to output the delayed luminance signal.

Next, the first multiplication circuit 14 multiplies an appropriate number of LSB bits of the red delayed video signal by a primary color multiplication coefficient k. At a luminance level at which achromatization is not performed, a selection circuit described later is switched to directly output a red delayed video signal using a threshold detection signal. For example, when the threshold value is “8”, the above equation (1) is used. According to the above, when the red input video signal R is “27” or more,
Since the luminance signal Y always exceeds the level “8”, the number of bits of the red delayed video signal input to the first multiplication circuit 14 is sufficient in the lower 5 bits.

Next, the second multiplication circuit 15 multiplies the appropriate number of LSB bits of the green delayed video signal by the primary color multiplication coefficient k. Similarly, when the threshold value is 8, and when the green input video signal G is 14 or more, the luminance signal Y is always at level 8 or more, so the number of bits of the green delayed video signal input to the second multiplication circuit 15 , The lower 4 bits are sufficient.

Next, the third multiplication circuit 16 multiplies the appropriate number of LSB bits of the blue input video signal by the primary color multiplication coefficient k. Similarly, when the threshold value is 8, and when the blue input video signal B is 73 or more, the luminance signal Y always goes to the level 8 or more, so the number of bits of the blue delayed video signal input to the second multiplication circuit 16 , The lower 7 bits are sufficient.

First multiplier circuit 14, second multiplier circuit 1
5. The determination of the appropriate number of bits in the third multiplication circuit 16 is controlled by the scene control circuit 12.

Next, in a fourth multiplication circuit 17, an appropriate number of LSB bits of the delayed luminance signal and a luminance multiplication coefficient (1-k)
And multiply by For example, when the threshold value is “8”, the lower 3 bits are sufficient for the number of bits of the delayed luminance signal input to the fourth multiplier 17. The appropriate number of bits is also controlled by the scene control circuit 12.

Next, the output signal of the first multiplication circuit 14 and the output signal of the fourth multiplication circuit 17 are added by the first addition circuit 18. Next, the output signal of the second multiplication circuit 15 and the output signal of the fourth multiplication circuit 17 are added by the second addition circuit 19. Next, the output signal of the third multiplication circuit 16 and the output signal of the fourth multiplication circuit 17 are added by the third addition circuit 1A. Next, the first selection circuit 1B compares the red delayed video signal and the output signal of the first addition circuit 18 with the threshold detection signal, and when the luminance level is smaller than the threshold value of the luminance replacement, the output of the first addition circuit 18 is output. Signal
When the luminance replacement threshold value is exceeded, a red delayed video signal is selected and output.

Similarly, the second selection circuit 1C switches between the green delayed video signal and the output signal of the second addition circuit 19 according to the threshold detection signal. Similarly, the third selection circuit 1D switches between the blue delayed video signal and the output signal of the third addition circuit 1A according to the threshold detection signal. Finally, the output signal of the first selection circuit 1B, the output signal of the second selection circuit 1C, and the output signal of the third selection circuit 1D are input to the error diffusion circuit 1E, and the error diffusion is performed to perform a red output image. A signal, a green output video signal and a blue output video signal are output.

As described above, in the gradation improving circuit according to the first and second aspects of the present invention, a part of the color component is replaced with a luminance signal in a part where the gradation is low, so that the error diffusion in the subsequent stage is performed. It is possible to prevent unnatural coloring at low luminance caused by the processing. According to the present invention, even when the input signal is “0” or a value close thereto, the error diffusion processing is not inhibited, so that the gradation display characteristics of a dark video signal portion can be improved.

Further, the distribution of the luminance signal level in the field unit is examined by the scene control circuit, and the threshold value for replacing the color component with the luminance component is controlled in accordance with the distribution of the luminance signal level, so that the color component is excessively damaged. Is prevented.

(Embodiment 2) An example of another embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a block diagram of a gradation improving circuit according to a third embodiment of the present invention. In FIG. 3, points different from the configuration described in Embodiment 1 will be described.

A scene control circuit 22 receives a luminance signal and outputs a delayed luminance signal and a primary color multiplication coefficient. Reference numeral 24 denotes a first subtraction circuit that subtracts the delayed luminance signal from the red delayed video signal and outputs a red color difference signal. 2
Reference numeral 5 denotes a second subtraction circuit that subtracts the delayed luminance signal from the green delayed video signal and outputs a green color difference signal. Reference numeral 26 denotes a third subtraction circuit that subtracts the delayed luminance signal from the blue delayed video signal and outputs a blue color difference signal.

A first multiplication circuit 27 multiplies the red color difference signal by the primary color multiplication coefficient. Reference numeral 28 denotes a second multiplication circuit that multiplies the green color difference signal by the primary color multiplication coefficient. 29
Is a third multiplication circuit that multiplies the blue color difference signal by the primary color multiplication coefficient.

2A is a first adder for adding the output signal of the first multiplier 27 and the delayed luminance signal. 2B
Is a second adder for adding the output signal of the second multiplier 28 and the delayed luminance signal. 2C is a third addition circuit that adds the output signal of the third multiplication circuit 29 and the delayed luminance signal. 2D is the output signal of the first adder 2A and the second
Is an error diffusion circuit which receives the output signal of the addition circuit 2B and the output signal of the third addition circuit 2C, performs error diffusion, and outputs a red output video signal, a green output video signal, and a blue output video signal. .

The operation of the thus configured gradation improving circuit will be described below. The luminance signal Y is input to the scene control circuit 22, and a delayed luminance signal and a distribution of a luminance signal level in a field unit are checked, and a primary color multiplication coefficient corresponding to the luminance signal level distribution is output.
Next, the first subtraction circuit 24 subtracts the delayed luminance signal from the red delayed video signal and outputs a red color difference signal (RY). Next, the second subtraction circuit 25 subtracts the delayed luminance signal from the green delayed video signal and outputs a green color difference signal (G-Y). Next, the third subtraction circuit 26 subtracts the delayed luminance signal from the blue delayed video signal and outputs a blue color difference signal (BY).

Next, the first multiplication circuit 27 multiplies the red color difference signal (RY) by the primary color multiplication coefficient k. Next, the second
Multiplies the green color difference signal (GY) by the primary color multiplication coefficient k. Next, the third multiplication circuit 29 multiplies the blue color difference signal (BY) by the primary color multiplication coefficient k.

Next, the output signal of the first multiplication circuit 27 and the delayed luminance signal are added by the first addition circuit 2A. next,
The output signal of the second multiplication circuit 28 and the delayed luminance signal are added by the second addition circuit 2B. Next, the third adder circuit 2C
Then, the output signal of the third multiplying circuit 29 and the delayed luminance signal are added.

Finally, the error diffusion circuit 2D receives the output signal of the first addition circuit 2A, the output signal of the second addition circuit 2B and the output signal of the third addition circuit 2C, and performs error diffusion. And outputs a red output video signal, a green output video signal, and a blue output video signal.

As described above, in the gradation improving circuit of this embodiment, αS + (1−α) Y = α (SY) + Y (S: R,
Paying attention to the equation (Either G or B), the number of multiplication circuits can be reduced as compared with the gradation improvement circuit described in the above (Embodiment 1).

[0041]

As described above, the low-luminance achromatic circuit of the present invention replaces a part of the color component with a luminance signal in a low-gradation part, thereby reducing the low luminance generated by the error diffusion processing in the subsequent stage. Unnatural coloring in the image can be made inconspicuous. Since the error diffusion processing is not inhibited even when the input signal is 0 or a value close to it as in the conventional example, the gradation display characteristics of the dark video signal portion can be improved by the error diffusion processing.

Further, the scene control circuit checks the distribution of the luminance signal level on a field basis, and controls the threshold value for replacing the color component with the luminance component according to the distribution of the luminance signal level, so that the color component is excessively damaged. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram of a gradation improving circuit according to an embodiment of the present invention.

FIG. 2 is an operation waveform diagram for explaining the operation of the circuit.

FIG. 3 is a block diagram of a gradation improving circuit according to a third embodiment of the present invention;

FIG. 4 is a block diagram of a conventional gradation improving circuit.

[Explanation of symbols]

 Reference Signs List 21 luminance level detection circuit 22 scene control circuit 23 storage element 24 first subtraction circuit 25 second subtraction circuit 26 third subtraction circuit 27 first multiplication circuit 28 second multiplication circuit 29 third multiplication circuit 2A Addition circuit of 1 2B Second addition circuit 2C Third addition circuit 2D Error diffusion circuit

Claims (4)

[Claims] 1. A luminance replacement circuit for inputting a video signal and replacing a part of a color component in a low gradation part with a luminance signal according to a distribution of a luminance signal level, and an output video signal of the luminance substitution circuit. And an error diffusion circuit for performing error diffusion for improving the gray scale display characteristics of the gray scale. 2. A luminance replacement circuit comprising: a luminance level detection circuit for receiving a color input video signal and outputting a luminance signal; a luminance level detection circuit for receiving the luminance signal; a delayed luminance signal, a threshold detection signal, a primary color multiplication coefficient, and a luminance multiplication coefficient. , A storage element that receives the color input video signal and outputs a color-delayed video signal after a predetermined time delay, and a least significant b of the color-delayed video signal.
a first multiplication circuit for multiplying an appropriate number of bits of it (hereinafter referred to as LSB) by a primary color multiplication coefficient output from the scene control circuit; an appropriate number of bits of LSB of the delayed luminance signal and the scene control; A second multiplication circuit for multiplying a luminance multiplication coefficient output from the circuit, an addition circuit for adding an output signal of the first multiplication circuit and an output signal of the second multiplication circuit, and the color delayed video 2. The gradation improving circuit according to claim 1, further comprising a selection circuit for switching and outputting a signal and an output signal of the adding circuit by a threshold detection signal output from the scene control circuit. 3. A luminance replacement circuit, comprising: a luminance level detection circuit that receives a red input video signal, a green input video signal, and a blue input video signal and outputs a luminance signal; A scene control circuit that outputs a detection signal, a primary color multiplication coefficient, and a luminance multiplication coefficient; a red delay video signal and a green color that are input with the red input video signal, the green input video signal, and the blue input video signal, and are delayed by a predetermined time; A storage element for outputting a delayed video signal and a blue delayed video signal;
a first multiplying circuit for multiplying an appropriate number of bits of a significant bit (hereinafter referred to as LSB) by the primary color multiplication coefficient, and multiplying an appropriate number of bits of an LSB of the green delayed video signal by the primary color multiplication coefficient; A second multiplying circuit, a third multiplying circuit for multiplying an appropriate number of LSB bits of the blue delayed video signal by the primary color multiplication coefficient, and an appropriate number of LSB bits of the delayed luminance signal and the luminance multiplication A fourth multiplying circuit for multiplying the coefficient by a coefficient;
A first adding circuit for adding the output signal of the multiplying circuit of the above and the output signal of the fourth multiplying circuit, and adding the output signal of the second multiplying circuit and the output signal of the fourth multiplying circuit. A second addition circuit, a third addition circuit for adding an output signal of the third multiplication circuit and an output signal of the fourth multiplication circuit, and a third addition circuit for adding the red delayed video signal and the first addition circuit. A first selection circuit for switching an output signal according to the threshold detection signal, a second selection circuit for switching the green delayed video signal and an output signal of the second addition circuit according to the threshold detection signal, and the blue delay 2. The gradation improvement circuit according to claim 1, further comprising a third selection circuit that switches between a video signal and an output signal of the third addition circuit according to the threshold detection signal. 4. A luminance replacement circuit which receives a red input video signal, a green input video signal, and a blue input video signal and outputs a luminance signal, receives the luminance signal, and outputs a delayed luminance signal and a primary color signal. A scene control circuit that outputs a multiplication coefficient; and a red delayed video signal, a green delayed video signal, and a blue delayed video signal that receive the red input video signal, the green input video signal, and the blue input video signal and delay the same for a predetermined time. A first subtraction circuit for subtracting the delayed luminance signal from the red delayed video signal and outputting a red color difference signal; and a green color difference signal for subtracting the delayed luminance signal from the green delayed video signal. A third subtraction circuit that subtracts the delayed luminance signal from the blue delayed video signal and outputs a blue color difference signal; a second subtraction circuit that outputs the blue color difference signal; A first multiplication circuit that multiplies a color multiplication coefficient, a second multiplication circuit that multiplies the green color difference signal and the primary color multiplication coefficient, and a third multiplication circuit that multiplies the blue color difference signal and the primary color multiplication coefficient. A first addition circuit that adds the output signal of the first multiplication circuit and the delayed luminance signal, a second addition circuit that adds the output signal of the second multiplication circuit and the delayed luminance signal, The gradation improving circuit according to claim 1, further comprising a third adding circuit that adds an output signal of a third multiplying circuit and the delayed luminance signal.