JPH1165537A - Direct view liquid crtystal display for color image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To preserve image quality, even though the surrounding condition is changed by varying the color signals in accordance with the strength of an artificial light source, while employing a simple constitution. SOLUTION: An artificial light source receives electric power from a power supply 24, and the strength of the source is controlled by the intensity control circuit including a manual control element 26 or a luminance control circuit 22. The element 26 determines the strength of the source 16. The circuit 22 has an output 28 connected to an input 30 of an interface circuit 32, consisting of outputs 321 to 323 connected to inputs 341 to 343 of a circuit 34 for the control of the color of a panel 10 and for gamma compensation. The input 341 receives a signal control γR, i.e., γ with respect to a red(R) color. The inputs 342 and 343 respectively receives signal controls γG and γB, i.e., γ with respect to green(G) and blue(B) colors. A circuit 34 supplies color signals R, G, and B to the panel 10. Moreover, a manual adjustment is replaced by the automatic adjustment by the sensor connected to the control input of the circuit 22. The sensor detects the intensity of the environmental light beams.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a direct-view liquid crystal display for color images.

[0002]

2. Description of the Related Art Liquid crystal displays (LCDs) are used in various applications such as television (TV) receivers, portable computer displays called "laptop computers", and viewfinders for video cameras. Widely used. The most common display of this type is a direct-view LCD. This device usually consists of a light source behind the LCD panel. The light source is arranged to provide uniform or quasi-uniform illumination on the back of the panel, i.e., the surface facing the surface viewed by the user.

[0003] Control elements are usually provided for manual adjustment of the intensity of the light source. When the intensity of the ambient light actually changes, it is necessary to change the intensity in order to obtain a good contrast of the image. The intensity of this light source decreases (increases) the ambient light intensity
When you have to decrease (increase). The invention is based on the observation that the color of the displayed image changes with the intensity of the light source behind.

[0004]

An object of the present invention is to solve the above-mentioned problems.

[0005]

According to the present invention, the color control circuit of the LCD comprises means for changing the color signal according to the intensity of the artificial light source behind it. It is known to provide a means for varying the intensity of natural light used as a light source behind. However, natural light has color components that vary over a wide range depending on its intensity. Artificial light sources do not have such color component changes. However, the inventor has found that, despite this relatively small variation, the color of the displayed image varies with the intensity of the light source behind the artificial.

[0006] The color control circuit is preferably provided with a control input for receiving a signal representative of the intensity of the light source behind. According to the present invention, it is always possible to automatically obtain the same color for a given image. In an embodiment of the invention, the intensity or brightness of the light source behind is controlled manually or automatically, and the intensity control circuit has an output connected to the control input of the color control circuit.

Color is controlled directly or through a gamma correction circuit. Television signals are usually transmitted with gamma correction. This correction takes into account the non-linear characteristics of a cathode ray tube (CRT): the CRT is supplied with a luminance signal which varies non-linearly with the input signal. The broadcasted gamma correction is CRT
Make a linear response. However, the response is different for one tube and another. Therefore each tube has an additional γ
It has correction means. However, LCDs inherently provide a linear characteristic. They therefore comprise circuitry to compensate for the broadcasted gamma correction.

The color control circuit comprises three γ inputs,
One is for each color (red R, green G, blue B), and an interface circuit is provided with an input for receiving a signal representing the intensity of the light source behind, and this interface circuit is provided with R, G,
It has three outputs that provide a gamma control signal for B.
The interface is, for example, a ROM (read only memory) that contains a table that provides a gamma curve for each of the three colors for each value of light intensity.

[0009] Computer displays are not intended to receive TV signals, and such displays are not provided with gamma correction circuits. In such a case, the color is directly controlled by the light intensity.

[0010]

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the invention are explained in more detail below by way of example with reference to the figures. FIG. 1 shows a prior art direct view LCD. The display comprises a liquid crystal panel 10 having a front surface 12 and a back or back surface 14. This back surface is formed by the combination of an artificial light source 16 (for example in the form of an elongated lamp with several branches), a diffuser 18 between the light source 16 and the back surface 14 and a reflector 20 behind the light source 16. Provided.

According to the embodiment of the present invention shown in FIG. 2, the intensity of the light source 16 is controlled by an intensity control circuit or brightness control circuit 22 that receives power from a power supply 24 and includes a manual control element 26. This element 26 determines the intensity of the light source 16.
Input of the intensity control circuit 22 is input 34 ₁ of the color control and gamma correction circuit 34 of the panel 34, 34 _2, 34 ₃ are connected respectively output 32 _1, 32 _2, 32 ₃ made of the interface circuit 32 30 Output 28 connected to
Having.

The input 34 ₁ is a signal control γ _R , that is, a red (R) signal.
Receives γ for color. Inputs 34 ₂ and 34 ₃ receive signal controls γ _G and γ _B , respectively, γ for the green (G) and blue (B) colors. The circuit 34 supplies the color signals R, G, B to the panel 10. This circuit is, for example, from Sony
RGB marketed under the model number XA1785 AR
Decoder / driver.

[0013] In the embodiment shown in FIG. 3 manual adjustment is replaced by the automatic adjustment provided by the sensor 40 connected to the control input 22 ₁ of the intensity control circuit 22. This sensor 40 detects the intensity of ambient light. A further embodiment (not shown) relates to a display for a computer rather than a TV, wherein the signal from the brightness controller 22 or the sensor 40 is supplied to the control input of a color control circuit similar to the circuit 34 of FIGS. Is done. Such color control circuits usually have manual adjustment. In this case, the signal from the brightness controller or sensor is applied to an input that receives a signal generated by manual adjustment in conventional circuits.

The interface circuit 32 comprises a ROM type memory in which data is recorded as a table corresponding to a curve. More precisely, the signal at input 30 is divided inside circuit 32 into a given number of value ranges. Each range corresponds to a set of three curves γ _R , γ _G and γ _B.
The curve γ _R (or γ _G or γ _B ) is a table that provides the value of the red signal for each quantized value of the R (or G or B) signal provided to the input 36 of the color control circuit 34.

If the sensor 40 or the circuit 22 provides a normal or average value, the color control circuit 34 will appear through the interface circuit 32 so that the colors on the screen 12 are the most practical and most realistic for the viewer. Provides nominal values for γ _R , γ _G and γ _B. In circuit 32, the table provides a correction that maintains color as the intensity of the ambient light or the intensity of the artificial background light source changes.

More precisely, as the intensity decreases, the ratio of the red component of the light increases with respect to the ratio of the G and B components. In that case the correction must be made so that the ratio of the nominal values is maintained. This is achieved by reducing the R component or increasing the G and B components. If the light intensity increases with respect to the nominal value, the ratio of the blue (B) component is increased with respect to the ratio of the R and G components. It is therefore necessary to reduce the B component with respect to the other components, more specifically the red (R) component.

All of the above embodiments of the present invention provide a simple means for color control of a liquid crystal display without a significant increase in power consumption. The image quality is preserved even when the surrounding conditions change. In a further embodiment (not shown) the interface circuit comprises a RAM-type memory in which a set of gamma curves γ _R , γ _G and γ _B corresponding to the current intensity of the ambient light or the light source 16 is stored. I have. These curves are provided by a central memory of the computer (for example, a ROM or a hard disk), in which all the γ _R , γ _G and γ _B curves corresponding to different intensities are stored.

[Brief description of the drawings]

FIG. 1 is a schematic view of a direct-view color LCD.

FIG. 2 is a block diagram of one embodiment of the present invention.

FIG. 3 is a block diagram of another embodiment of the present invention.

[Explanation of symbols]

10,34 panel 12 circuit on the front 14 back 16 an artificial light source 18 diffuser 20 reflector 24 power supply 26 manual control elements 22 the intensity control circuit 34 for gamma correction 30,34,34 _1, 34 _2, 34 ₃ inputs 28, 36, 32 ₁ , 32 ₂ , 32 ₃ outputs 32 interface circuit 40 sensor

Claims (8)

[Claims] 1. An LCD panel (10) and an artificial light source (16;
20 and 18) and a color circuit means (34) for controlling the color of the panel, which is a direct-view liquid crystal display for a color image, wherein the color control means (3
An indicator comprising means (32) for controlling (4). 2. A means (2) for controlling the intensity of a light source (16).
2. A display according to claim 1, wherein the signal representative of the light source intensity is generated by said means (22, 26) for controlling the intensity of the light source. 3. The light source intensity control means comprises a manual adjustment element (26) for controlling the intensity.
Display of description. 4. shows the intensity of the ambient light, according to claim 1, characterized in that it comprises a control input of the light source intensity control means (22) (22 ₁₎ detector for generating a signal to be supplied to the (40) Indicator. 5. The color circuit means (34) includes a gamma correction circuit, the means for controlling the color circuit means providing gamma correction for each color, wherein the gamma correction for each color reduces the intensity of the light source. 5. The display according to claim 1, wherein the display depends on the value of the signal to be represented. 6. A means for controlling a color circuit.
6. The display of claim 5, wherein 2) includes a memory storing a table representing gamma correction curves for each color at various values of the signal representing the intensity of the light source. 7. The display according to claim 6, wherein said memory is a read-only memory. 8. The memory stores three values for the current intensity of the light source.
One of storing correction curve, the display of these curves according to claim 6, characterized in that provided by the central memory of the computer to store all of the gamma _R, gamma _G and gamma _B curves corresponding to various intensities vessel.