JP3072656B2 - Color temperature conversion circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color temperature conversion circuit, and more particularly, to a color temperature conversion circuit which increases the color temperature of a white portion of a video signal to enhance the image quality of white.

[0002]

2. Description of the Related Art It is generally known that human eyes are sensitive to skin color and white. When reproducing color images on a color cathode ray tube (CRT) or the like, the skin color and white are clearly and vividly displayed. In order to display a color image, a color temperature conversion process called a so-called dynamic color or the like is often performed.

FIG. 3 shows an example of this color temperature conversion circuit.
In FIG. 3, R (red), G (green), and B (blue) primary color signals are supplied to input terminals 51R, 51G, and 51B, respectively, and are extracted from output terminals 52R, 52G, and 52B, respectively. It has become. However, a variable gain amplifier (or gain control amplifier) 53 is inserted and connected between the input terminal 51B and the output terminal 52B. Each of these output terminals 52R, 52G, 52
The R, G, B output signals from B are supplied to each cathode of the CRT. Here, for each input R, G, B signal,
The white detection circuit 54 outputs a signal level having a ratio representing white,
That is, the signal level of R: G: B = 0.3: 0.59: 0.11 is detected, and the variable gain amplifier 53 according to the white signal level is detected.
Of the amplifier 53 by controlling the variable resistor 55
Control. Specifically, the color temperature of the output color signal is increased by 1.3 times 70 IRE or more of the B signal. This IRE means that the pedestal level is 0IR
E, a signal level unit such that the white peak is 100 IRE.

[0004]

In the above color temperature conversion circuit, a variable gain amplifier 53 is inserted and connected in the B signal transmission line, and gain control is performed.
There is a disadvantage that the frequency characteristics of the output signal deteriorate. This causes a problem of resolution degradation particularly when displaying a high-definition color image.

Further, since the so-called skin color is close to white, yellow or a high-brightness skin color may be erroneously detected only by the white detection circuit 54. For example, a color is reproduced to a bluish skin color having a high color temperature. This may cause deterioration of color reproducibility.

For this reason, for example, a configuration is required in which the skin color detection circuit 56 detects the skin color separately.
The skin color detecting circuit 56 detects a high skin color portion in a color image so as not to perform the white detection (disable), and by prohibiting the color temperature conversion process in the skin color portion. Although the reproduction of natural skin color is realized, it is necessary to add a skin color detection circuit 56.

Further, a cathode cutoff voltage E _{KCO of} each of R, G and B colors of the color CRT and a second grid voltage G ₂
In order to automatically add a so-called auto cut-off function for automatically correcting a shift in white balance due to a change with time, a reference pulse section using a horizontal scanning period in an overscan area outside an effective screen is used. A configuration is adopted in which the beam current of each color is detected and each DC (direct current) bias level is controlled so that the ratio of R, G, and B becomes a constant value. However, these R, G,
If the DC bias of the B signal changes, it becomes difficult to detect the signal level, and there is a disadvantage that the above-described white detection is adversely affected and the automatic cutoff operation is adversely affected. The present invention has been made in view of such circumstances, and can perform color temperature conversion without deteriorating the frequency characteristics of a video signal, particularly, a luminance signal. It is an object of the present invention to provide a color temperature conversion circuit capable of preventing a malfunction in a high skin color or yellow portion and preventing a deterioration in color reproducibility.

[0008]

SUMMARY OF THE INVENTION A color temperature conversion circuit according to the present invention comprises: a high luminance signal component detecting means for extracting a component having a predetermined level or more from an input luminance signal and outputting it as a high luminance component detection signal; First and second color difference signal level detecting means for detecting the level of each of the obtained RY and BY color difference signals as absolute values, and a high luminance component detection signal from the high luminance component detecting means. And a variable gain amplifier using the output from said first and second color difference signal level detecting means as a control signal, wherein the gain is increased when the output of said first and second color difference signal level detecting means becomes zero. The above-mentioned problem is solved by having a variable gain amplifying means set to be maximum and an adding means for adding an output signal from the variable gain amplifying means to the above-mentioned BY color difference signal.

Here, the detection threshold level of the high luminance component detecting means can be, for example, 70 IRE.
As the output control means, a gain control amplifier for controlling the gain of the high luminance component detection signal in accordance with the output signal from the color difference signal level detection means and outputting the signal can be used. Further, by adding the high-luminance component detection signal (the signal whose gain is controlled) to the BY color difference signal, the color temperature of the white portion of the video signal can be set to about 300 by 100 IRE.
It is preferable to increase by 0K. The IRE means that the pedestal level is 0 IRE and the white peak level is 100 IRE.
It is a unit of a video signal level such as RE, and K is a temperature unit Kelvin.

[0010]

Since the Y (luminance) signal of the video section having no color difference signal component is added and mixed with the BY signal to increase the color temperature, the frequency characteristics of the Y signal do not deteriorate. Also, R, G,
Since the B signal is not operated, the auto cutoff operation is not adversely affected. Further, since the color temperature is not changed in a portion where the color signal exists, the color reproducibility does not deteriorate.

[0011]

FIG. 1 is a block circuit diagram showing a schematic configuration of a color temperature conversion circuit according to an embodiment of the present invention.

In FIG. 1, the input terminal 11 has a Y
(Brightness) signals are input to the input terminals 12 and 13 for BY, R-
Each of the Y color difference signals is supplied. The Y (luminance) signal is taken out from the output terminal 14 as it is, and sent to a high luminance component detection (or white detection) circuit 15 to detect a component having a level of 70 IRE or more. A luminance signal component having a level of 70 IRE or more from the high luminance component detection circuit 15 is sent to an adder (mixer, mix circuit) 17 via a variable gain amplifier (or gain control amplifier) 16 as output control means. I have. A BY color difference signal from the input terminal 12 is supplied to the adder 17 via the hue control circuit 27.
Output from terminal 18 is B- (color temperature converted).
Extracted as a Y signal. The output terminal 19 outputs the RY color difference signal of the input terminal 13 to the hue control circuit 27.
Is obtained.

The BY color difference signal from the input terminal 12 is sent to a color level detection circuit 21 and sent to an absolute value conversion circuit 22 as a color level detection signal from which components near the reference 0 level have been removed. As shown in the input / output characteristic diagram in the circuit block in FIG. 1, the color level detection circuit 21 has an output (vertical axis) level within a predetermined positive / negative range near an input (horizontal axis) level reference 0. Is 0, and an input component exceeding this predetermined range is output. When the input level exceeds another predetermined range outside the predetermined range, the output is saturated, so-called limited. This color level detection circuit 2
Since the output from 1 appears in the positive and negative directions, the absolute value conversion circuit 22 takes the absolute value. This takes into account that the level of the BY color difference signal is substantially zero for non-colored signals such as white, and the output is zero in the white portion of the image.
Thus, a signal is obtained in which the value increases according to the degree of color and saturates. The output signal from the absolute value conversion circuit 22 is sent to the adder 23.

Similarly, for the RY signal from the input terminal 13, the color level detection circuit 22 and the absolute value conversion circuit 25
As a result, in the white portion of the image, the output becomes 0, the value increases in accordance with the degree of coloration, and a signal that saturates when the color is added is obtained. The signal is sent to the adder 23.

The signal from the adder 23 is sent as a gain control signal to a variable resistor 26 for changing the gain of the variable gain amplifier 16 to variably control the resistance value. This variable gain amplifier 16 has such a characteristic that the gain (gain) decreases as the output level from the adder 23 increases, and when the output from the adder 23 is 0, that is, when there is no white color In part,
The gain of the amplifier 16 becomes maximum. This variable gain amplifier 1
Since the output from 6 is sent to the adder 17 and added and mixed with the BY signal, the signal level of the B (blue) component increases in the white portion, and the color temperature increases.

As a specific numerical value, the color temperature of the white portion of the video signal where there is no color signal is increased by, for example, about 3,000 K (K indicates Kelvin in temperature unit) at 100 IRE. Alternatively, for example, the color temperature of the white portion of 9500K at 70IRE or more is increased to about 12000K. Thereby, the white portion in the display screen can be displayed as brighter white. Further, since the luminance (Y) signal supplied to the input terminal 11 is sent to the output terminal 14 without performing any processing, the color temperature conversion can be performed without deterioration of the frequency characteristic and the resolution.

Further, even if a so-called auto cut-off function for automatically correcting a shift in white balance due to a temporal change of the cathode cut-off voltage E _KCO and the second grid voltage G ₂ of each color of the color CRT is added, , G and B outputs are not operated, so that there is no adverse effect. This automatic cutoff operation will be described with reference to FIG.

Each input terminal 31, 32, 33 in FIG.
The Y from each of the output terminals 14, 18, and 19 in FIG.
A (luminance) signal, a BY (color difference) signal, and an RY (color difference) signal are supplied. The Y signal is supplied to a matrix circuit 34, and the BY signal and the RY signal are supplied to the matrix circuit 34 via color control (color control) circuits 35 and 36, respectively. These color control circuits 35 and 36 correspond to the hue control circuits 27 and 2 in FIG.
8 may be shared with each other.

The matrix circuit 34 has a luminance-color difference (Y,
(B, Y, R-Y) signals are converted into R, G, B primary color signals, and the obtained R, G, B signals are sent to contrast control circuits 41R, 41G, 41B, respectively. In the contrast control circuits 41R, 41G, and 41B, the dynamic range of each signal is variably controlled in accordance with the contrast control signal from the control terminal.
Next drive bias control circuits 43R, 43G, 43B
The DC (direct current) bias value (black level) is commonly controlled for each color according to a brightness control (brightness control) signal from the control terminal 44, and the control terminal 45R for each color is controlled.
In response to drive control signals from 45G and 45B, R,
Amplitude for each of G and B primary color signals (contrast for each color)
Is controlled.

Drive bias control circuits 43R, 43
The primary color signals from the G and 43B are supplied to the DC shift circuits 46R, 46G,
46B. These DC shift circuits 46
R, 46G, and 46B control a DC level for each color in accordance with a control signal from the sequencer 47. For example, one horizontal scan line of an overscan portion above a screen outside an effective screen portion in a video signal R, G, and B are sequentially switched for each field, and a beam current for each of R, G, and B is detected and fixed at a four-field cycle sequence in which a dark current flows in the next field. Is controlled so as to satisfy the following ratio. Each DC in this case
The beam current values of the R, G, and B signals sent from the shift circuits 46R, 46G, and 46B to the output terminals 49R, 49G, and 49B via the amplifiers are respectively detected by current detection means 48.
R, 48G, and 48B, respectively.
7 The output terminals 49R, 49G, 49B
Are sent to respective R, G, B cathodes of a color CRT (cathode ray tube, not shown).

As described above, at the stage of luminance (Y) -color difference signal processing, the signal levels of the BY and RY color difference signals in the positive and negative directions are detected by the color level detection circuits 21 and 2.
4. By controlling the gain of the variable gain amplifier 16 by detecting the signals by the absolute value conversion circuits 22 and 25 and the adder 23, the high luminance component detection circuit 15 slices a component of 70 IRE or more of the Y signal, Only a portion having no color signal is taken out, and this is mixed with the BY signal component. Thereby, the color temperature of white of the video signal can be raised by about 3000 K at 100 IRE, for example.

Accordingly, since the Y signal in the video section having no color signal component is mixed with the BY signal to increase the color temperature, the frequency characteristics of the Y signal do not deteriorate. Also, R, G,
Since the B output is not operated, the above-described auto cutoff operation is not adversely affected. Further, since the color temperature is not changed in a portion where the color signal is present, the color reproducibility of yellow, skin color, etc. does not deteriorate. Note that the present invention is not limited to only the above-described embodiment. For example, the threshold value of the high luminance component detection circuit 15 is not limited to 70IRE, and various input / output characteristics can be set. Also, instead of the variable gain amplifier 16,
A gate circuit that allows the high luminance component detection signal to pass only in the non-colored portion may be used. Further, as each of the color level detection circuits 21 and 24, a circuit that discriminates at a predetermined color level may be used.

[0023]

As is clear from the above description, according to the color temperature conversion circuit of the present invention, the high-luminance component detecting means for extracting a component of the input luminance (Y) signal having a predetermined level or higher. RY and B
The output from the first and second color difference signal level detecting means for detecting the level of each color difference signal of -Y as an absolute value is 0.
When the variable gain control is performed so that the gain becomes maximum, the high-luminance component detection signal in the non-colored portion is extracted, and this signal is added to the BY color difference signal to obtain a color difference signal. Since the temperature is raised, the frequency characteristics of the Y signal do not deteriorate. In addition, since the R, G, and B signals are not operated, the auto cutoff operation is not adversely affected. Furthermore, since the color temperature is not changed in a certain part of the color signal,
Color reproducibility does not deteriorate.

[Brief description of the drawings]

FIG. 1 is a block circuit diagram illustrating a schematic configuration of an embodiment of a color temperature conversion conversion circuit according to the present invention.

FIG. 2 is a block circuit diagram showing an example of an RGB signal processing circuit to which an output signal from the color temperature conversion conversion circuit of the embodiment is supplied.

FIG. 3 is a block circuit diagram illustrating a schematic configuration of an example of a conventional color temperature conversion conversion circuit.

[Explanation of symbols]

11 Y (luminance) signal input terminal, 12 BY color difference signal input terminal, 13 R-Y color difference signal input terminal, 15
High brightness detection circuit, 16 variable gain amplifier, 17 adder, 21, 24 color level detection circuit, 22, 25
Absolute value conversion circuit, 23 adder

Claims (1)

(57) [Claims] 1. A high-luminance signal component detecting means for extracting a component of a predetermined level or more of an input luminance signal and outputting the component as a high-luminance component detection signal; First and second color difference signal level detecting means for detecting a level as an absolute value, and a high luminance component detection signal from the high luminance component detecting means as an input, and a first and a second color difference signal level detecting means. A variable gain amplifier using the output of the first and second color difference signal level detection means as a control signal, wherein the gain is set to be maximum when the output of the first and second color difference signal level detection means becomes zero, An adder for adding an output signal from the variable gain amplifier to the BY color difference signal.