JPH04357790A - Color temperature conversion circuit - Google Patents

Abstract

PURPOSE:To perform color temperature conversion without deteriorating the frequency characteristic of a luminance (Y) signal. CONSTITUTION:The signal level in the positive and negative directions of color difference signals B-Y and R-Y is detected by color level detection circuit 21 and 24, absolute value conversion circuits 22 and 25, and an adder 23 and the gain of the variable gain amplifier 16 is controlled. Accordingly, the components more than 70IRE of the Y(luminance) signal from a color detection circuit 15 are mixed to the B-Y signal component in the only part without a color signal, and the color temperature of the video signal is raised. Thus, since mixed with the B-Y signal, the frequency characteristic of the Y signal will not deteriorate. There is no adverse effect on so-called automatic cut-off operation since the RGB output is not operated. Since the color temperature is not changed in the part having a color, the color reproducibility will not deteriorate.

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 that increases the color temperature of a white portion of a video signal to improve white image quality.

0002

[Prior Art] It is known that human eyes are generally sensitive to skin color and white, and when reproducing color images using a color cathode ray tube (CRT), etc., the skin color and white are clearly and vividly displayed. In order to display images in different colors, color temperature conversion processing called so-called dynamic color is often performed.

An example of this color temperature conversion circuit is shown in FIG. In FIG. 3, primary color signals of R (red), G (green), and B (blue) are supplied to input terminals 51R, 51G, and 51B, respectively, and are taken out 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 provided to each cathode of the CRT. Here, for each input R, G, B signal,
The white detection circuit 54 detects the signal level of the ratio representing white,
That is, a signal level of R:G:B=0.3:0.59:0.11 is detected, and the variable resistor 55 of the variable gain amplifier 53 is controlled according to this white signal level to adjust the gain of the amplifier 53 (gain ). Specifically, 70IR of B signal
E or more is multiplied by 1.3 to raise the color temperature of the output color signal. The IRE is a signal level unit in which the pedestal level is 0IRE and the white peak is 100IRE.

0004

By the way, in the above color temperature conversion circuit, the variable gain amplifier 53 is inserted and connected in the B signal transmission path and the gain is controlled.
This has the disadvantage that the frequency characteristics of the output signal deteriorate. This poses a problem of resolution deterioration, especially when displaying high-definition color images.

Furthermore, since the so-called skin color is close to white, the white detection circuit 54 alone may erroneously detect yellow or skin colors with high brightness.For example, the color may be reproduced to a bluish skin color with a high color temperature. There is a possibility that this may cause a serious deterioration in color reproducibility.

[0006] Therefore, it becomes necessary to have a configuration in which the skin color is separately detected by the skin color detection circuit 56, for example. This skin color detection circuit 56 detects a high skin color part in a color image and disables the white detection. Although the reproduction of natural skin color is realized, it is necessary to add a skin color detection circuit 56.

[0007] Furthermore, let us add a so-called auto cut-off function to automatically correct the deviation in white balance due to time-dependent changes in the cathode cut-off voltage EKCO of each color of R, G, and B of the color CRT and the second grid voltage G2. In this case, the beam current of each color is detected in the reference pulse period using the horizontal scanning period in the overscan area outside the effective screen, so that the ratio of R, G, and B becomes a constant value. A configuration is adopted to control each DC (direct current) bias level. However, these R
, G, and B signals, it becomes difficult to detect the signal levels, which has the drawback of adversely affecting the white detection and auto cutoff operation.

The present invention has been made in view of the above circumstances, and it is possible to perform color temperature conversion without deteriorating the frequency characteristics of video signals, especially luminance signals, and to prevent the adverse effects of so-called auto cutoff operation. It is an object of the present invention to provide a color temperature conversion circuit that can prevent malfunctions in skin-colored or yellow areas with high brightness and prevent deterioration of color reproducibility.

[0009]

[Means for Solving the Problems] A color temperature conversion circuit according to the present invention includes a white detection means for extracting a component of an input luminance (Y) signal at a predetermined level or higher, and an input R-Y and B-signal.
- color difference signal level detection means for detecting signal levels in the positive direction and negative direction of each of the Y color difference signals; and a white detection signal from the white detection means is controlled in accordance with an output signal from the color difference signal level detection means. The above-mentioned problem can be solved by having an output control means for extracting the white detection signal in a non-colored part, and an addition means for adding the output signal from this output control means to the B-Y color difference signal. Solve.

Here, the detection threshold level of the white detection means can be set to, for example, 70 IRE, and the output control means controls the gain of the white detection signal according to the output signal from the color difference signal level detection means. It is possible to use a gain control amplifier that outputs Further, it is preferable to increase the color temperature of the white portion of the video signal by about 3000 K at 100 IRE by adding a white detection signal (a gain-controlled signal thereof) to the B-Y color difference signal. In addition, IRE refers to the pedestal level as 0IRE.
, is a unit of video signal level such that the white peak level is 100 IRE, and K is the temperature unit Kelvin.

[0011]

[Operation] Since the Y (luminance) signal of the video section having no color difference signal component is added and mixed with the B-Y 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 manipulated, it does not adversely affect the auto cutoff operation. Furthermore, since the color temperature is not changed in a certain part of the color signal, color reproducibility does not deteriorate.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, 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 receives a Y (luminance) signal, and the input terminals 12 and 13 receive B-Y and R-Y color difference signals.
Each is supplied. The Y (luminance) signal is taken out as it is from the output terminal 14 and is also sent to the white detection circuit 15.
components with a level of 70 IRE or higher are detected. The luminance signal component at a level of 70 IRE or higher from the white detection circuit 15 is sent to an adder (mixer, mix circuit) 17 via a variable gain amplifier (or gain control amplifier) 16 as an output control means. The adder 17 is supplied with the B-Y color difference signal from the input terminal 12 via the hue control circuit 27, and the output from the adder 17 is supplied from the terminal 18 with the B-Y color difference signal (which has undergone color temperature conversion processing). taken out as a signal. Further, from the output terminal 19, a signal obtained from the RY color difference signal of the input terminal 13 via the hue control circuit 27 is taken out.

The BY color difference signal from the input terminal 12 is sent to a color level detection circuit 21, which converts the component near the reference 0 level into a color level detection signal and sends it to an absolute value conversion circuit 22. As shown in the input/output characteristic diagram in the circuit block in FIG. is 0, and input components exceeding this predetermined range are output. Further, when the input level exceeds another predetermined range outside this predetermined range, the output is saturated and is so-called limited. This color level detection circuit 2
Since the output from 1 appears in the positive direction and the negative direction, the absolute value is taken by the absolute value conversion circuit 22. This is done considering that the level of the B-Y color difference signal is approximately 0 for non-colored signals such as white, and the output is 0 in the white part of the image.
Therefore, a signal is obtained whose value increases and becomes saturated depending on the degree of coloring. The output signal from this absolute value conversion circuit 22 is sent to an adder 23.

Similarly, for the R-Y signal from the input terminal 13, the color level detection circuit 22 and the absolute value conversion circuit 25
As a result, a signal is obtained in which the output is 0 in the white part of the image, the value increases depending on the degree of coloring, and becomes saturated as the color increases, and this 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, and this resistance value is variably controlled. This variable gain amplifier 16 has a characteristic that the gain decreases as the output level from the adder 23 increases, and when the output from the adder 23 is 0, that is, uncolored white. In part,
The gain of the amplifier 16 is maximized. This variable gain amplifier 1
Since the output from 6 is sent to the adder 17 and added and mixed with the B-Y 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 a white portion in the video signal where there is no color signal is increased by about 3000 K (K indicates the temperature unit Kelvin) at 100 IRE, for example. Alternatively, for example, the color temperature of the white part of 9500K is increased to about 12000K with 70 IRE or more. As a result, the white portion within the display screen can be displayed as a more vivid white. Further, since the luminance (Y) signal supplied to the input terminal 11 is sent to the output terminal 14 without any processing, color temperature conversion can be performed without deterioration of frequency characteristics or the like and without deterioration of resolution.

Furthermore, even if a so-called auto cutoff function is added that automatically corrects white balance deviations caused by changes in the cathode cutoff voltage EKCO of each color of the color CRT and the second grid voltage G2 over time, the R, G , B output is not manipulated, so there is no adverse effect. This automatic cutoff operation will be explained with reference to FIG. 2.

Each input terminal 31, 32, 33 in FIG.
, Y from each output terminal 14, 18, 19 in FIG.
(brightness) signal, BY (color difference) signal, and RY (color difference) signal are each supplied. The Y signal is supplied to the matrix circuit 34, and the BY signal and the RY signal are supplied to the matrix circuit 34 via color control circuits 35 and 36, respectively. These color control circuits 35 and 36 are similar to the hue control circuits 27 and 2 in FIG.
8 may be used in common.

The matrix circuit 34 has a luminance-color difference (Y,
B-Y, RY) signals into three primary color signals of R, G, and B, and the obtained R, G, and B signals are sent to contrast control circuits 41R, 41G, and 41B, respectively. In the contrast control circuits 41R, 41G, and 41B, the dynamic range of each signal is commonly and variably controlled in accordance with the contrast control signal from the control terminal 42. Next drive bias control circuit 43R, 43G, 43B
The DC (direct current) bias value (black level) is commonly controlled for each color in accordance with the brightness control signal from the control terminal 44, and the control terminal 45R for each color,
According to the drive control signals from 45G and 45B, R,
Amplitude for each primary color signal of G and B (contrast for each color)
is now under control.

Drive bias control circuit 43R, 43G
, 43B are sent to the DC shift circuits 46R, 46G, 4 for adding the above-mentioned auto cutoff function.
Sent to 6B. These DC shift circuits 46R,
46G and 46B control the DC level for each color in accordance with the control signal from the sequencer 47. For example, one horizontal scanning line in the overscan part at the top of the screen outside the effective screen part of the video signal is used. , the beam currents for each R, G, and B are detected in a 4-field cycle sequence in which R, G, and B are sequentially switched in each field and a dark current is caused to flow in the next field, and the beam currents for each R, G, and B are detected at a constant ratio. It is controlled so that In this case, each R, G is sent from each DC shift circuit 46R, 46G, 46B to output terminal 49R, 49G, 49B via an amplifier, respectively.
, the beam current value of the B signal is detected by the current detection means 48R, 48
G and 48B are detected and sent to the sequencer 47. Note that each output signal from the output terminals 49R, 49G, and 49B is sent to each R, G, and B cathode of a color CRT (cathode ray tube, not shown).

As explained above, in the luminance (Y)-color difference signal processing stage, the positive and negative signal levels of the B-Y and R-Y color difference signals are detected by the color level detection circuits 21 and 2.
4. By controlling the gain of the variable gain amplifier 16 by detecting it with the absolute value conversion circuits 22, 25 and the adder 23, the white detection circuit 15 slices the components of 70 IRE or more of the Y signal and converts it into a color signal. This is done by extracting only the portions that are not present and mixing them with the B-Y signal component. As a result, the white color temperature of the video signal can be increased by, for example, 10
It is possible to raise the power by about 3000K at 0IRE.

[0022] Therefore, since the color temperature is increased by mixing the Y signal of the video section having no color signal component with the BY signal, the frequency characteristics of the Y signal do not deteriorate. Also, R, G,
Since the B output is not manipulated, the auto cutoff operation described above is not adversely affected. Furthermore, since the color temperature is not changed in a certain part of the color signal, the color reproducibility of yellow, flesh color, etc. does not deteriorate.

It should be noted that the present invention is not limited to the above embodiments; for example, the threshold value of the white detection circuit 15 is 70
It is not limited to IRE, and various input/output characteristics etc. can be set. Furthermore, instead of the variable gain amplifier 16, a gate circuit may be used that allows the white detection signal to pass only through the non-colored portion. Furthermore, as each color level detection circuit 21, 24, a circuit that discriminates based on a predetermined color level may be used.

[0024]

Effects of the Invention As is clear from the above description, according to the color temperature conversion circuit according to the present invention, the input luminance (Y
) A white detection signal from a white detection means for extracting a component of a signal with a predetermined level or higher is output from a color difference signal level detection means for detecting the positive direction and negative direction signal levels of each color difference signal of R-Y and B-Y. By controlling according to the output signal,
Since the white detection signal from the non-colored portion is extracted and added to the B-Y color difference signal to increase the color temperature, the frequency characteristics of the Y signal do not deteriorate. Furthermore, since the R, G, and B signals are not manipulated, 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 explanation of the drawing]

FIG. 1 is a block circuit diagram showing a schematic configuration of an embodiment of a color temperature conversion circuit of 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 showing a schematic configuration of an example of a conventional color temperature conversion circuit.

[Explanation of symbols]

11...Y (luminance) signal input terminal 12...
B-Y color difference signal input terminal 13...R-Y color difference signal input terminal 15...White detection circuit 16...Variable gain amplifier 17...Adder 21, 24... ...Color level detection circuits 22, 25...
... Absolute value conversion circuit 23 ... Adder

Claims (1)

[Claims] 1. A white detection means for extracting a component of an input luminance signal at a predetermined level or higher, and a color difference detecting means for detecting the signal level in the positive direction and the negative direction of each input R-Y and B-Y color difference signal. signal level detection means; and output control means for extracting the white detection signal in a non-colored area by controlling the white detection signal from the white detection means in accordance with the output signal from the color difference signal level detection means. , and addition means for adding the output signal from the output control means to the B-Y color difference signal.