JP2009229646A - Display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance display quality. <P>SOLUTION: A mirror device 30 modulates light from a light source 10 based on a luminance signal and emits a reflection image. The reflection image by the mirror device 30 is resolved to respective color components of RGB and made incident on liquid crystal panels 10R, 10G, 10B respectively, The liquid crystal panels 10R, 10G, 10B corresponding to RGB modulate light respective color components in the mirror device 30 based on respective color signals. A dichroic prism 130 combines transmission images of the liquid crystal panels 10R, 10G, 10B, and a projection lens group 140 projects the composite image onto a screen. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for realizing high quality display.

In recent years, display devices that form a reduced image by irradiating light from a light source onto a display panel that changes the transmittance (or reflectance) of light for each pixel, and enlarge and project the reduced image using an optical system are becoming widespread. . In such a display device, a technique for changing the luminance of the light source in accordance with the average brightness of the entire screen has been proposed in order to increase the contrast ratio of the displayed image in appearance (Patent Document 1). reference).
JP 2004-354717 A

However, in the above technique, the contrast ratio is determined by a combination of the range of transmittance (or reflectance) in the display panel and the range of light source luminance. However, since the light source can be controlled only in a relatively narrow range, the contrast ratio is increased. It was not possible to enlarge.
The present invention has been made in view of the above-described circumstances, and one of its purposes is to provide a display device capable of displaying a high contrast ratio.

In order to achieve the above object, a display device according to the present invention includes a luminance modulator that modulates and emits light from a light source based on a luminance signal, and corresponds to different primary colors, and emitted light from the luminance modulator. Comprising: first to third optical modulators for modulating the light based on the respective color signals; and a combining means for generating a combined image of the light respectively modulated by the first to third optical modulators. Features. According to the present invention, the brightness of the composite image is represented by the product of the brightness of the light modulated by the brightness modulator and the brightness of the light modulated by the first, second, or third light modulator. Therefore, it is possible to ensure a high contrast ratio.

Here, from a luminance signal corresponding to an image to be displayed, a luminance average value calculation circuit that calculates an average value of luminance in the image, a light source control circuit that controls the luminance of the light source according to the calculated average value, A luminance processing circuit that converts luminance indicated by a luminance signal corresponding to an image to be displayed and supplies the luminance modulation circuit to the luminance modulator may be further included. According to this configuration, the brightness of the light source is controlled according to the average value of the brightness of the image to be displayed, and the brightness of the light modulated by the brightness modulator is controlled, so that the local brightness control of the screen is performed. Is possible.
In the present invention, the first to third optical modulators may be liquid crystal panels corresponding to red, green, and blue, respectively. In the present invention, the projector may further include projection means for enlarging and projecting a composite image by the synthesis means.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating an optical configuration of a projector 100 that is a display device according to a first embodiment of the present invention and that projects a display image on a screen in an enlarged manner.
As shown in this figure, when the projector 100 is viewed around the dichroic prism 130, the liquid crystal panels 10R, 10G,
10B is arranged.

The light source 102 includes a halogen lamp, a parabolic reflector, and the like, and emits substantially parallel white light.
The mirror device 30 has mirror elements corresponding to a plurality of pixels, and each mirror element reflects light incident from the light source 102 in the direction of 9 o'clock in FIG. In the (Off) state, the light is reflected in the direction of about 8 o'clock.
Since the mirror device 30 is PWM-driven for each pixel based on the luminance signal as will be described later, the reflected image in the on-state direction becomes brighter and darker for each pixel when viewed from one vertical scanning period. Will have. For this reason, the mirror device 30 functions as a luminance modulator.
Further, as viewed from the mirror device 30, a light absorber 32 is provided in the 8 o'clock direction so as to absorb the light reflected by the mirror element in the off state.

The dichroic mirror 104 reflects G (green) and B (blue) light of white light in the 6 o'clock direction and transmits light of other colors in the 9 o'clock direction.
The mirror 106 reflects the light transmitted through the dichroic mirror 104, that is, R (red) light in the 6 o'clock direction and guides it to the liquid crystal panel 10R. The dichroic mirror 108 is
Of the G and B light reflected by the dichroic mirror 104, the G light is reflected in the 9 o'clock direction, guided to the liquid crystal panel 10G, and the light of other color components is transmitted in the 6 o'clock direction.

The relay lens system 120 includes an entrance lens 121, a relay lens 122, and an exit lens 123.
And two mirrors 126 and 127, and light transmitted through the dichroic mirror 108,
That is, the B light is guided to the liquid crystal panel 10B.
The reason why the relay lens system 120 is provided only for the B light is to prevent the loss of the B optical path to the liquid crystal panel 10B compared to other R and G.

The liquid crystal panels 10R, 10G, and 10B each have a transmissive liquid crystal element corresponding to the pixels in the same arrangement as the mirror device 30, and each function as an optical modulator that modulates incident light for each pixel. The liquid crystal panels 10R, 10G, and 10B are driven based on R, G, and B color signals as described later. For this reason, the transmission image of the liquid crystal panel 10R shows an R component image, and similarly, the transmission images of the liquid crystal panels 10G and 10B show an image of a G component and a B component, respectively.

The dichroic prism 130 has dichroic surfaces 13R and 13B orthogonal to each other. Of these, the dichroic surface 13R reflects R light incident from the 12 o'clock direction, emits it in the 9 o'clock direction, and transmits light of other colors. The dichroic surface 13B reflects B light incident from the 6 o'clock direction, emits it in the 9 o'clock direction, and transmits light of other colors. For this reason, the G light incident from the 3 o'clock direction passes through the dichroic surfaces 13R and 13B and is emitted as it is in the 9 o'clock direction.
Accordingly, the R, G, and B component images are combined by the dichroic prism 130 to become a color image and are emitted in the 3 o'clock direction.
The projection lens group 140 is an optical system that enlarges and projects the color image synthesized by the dichroic prism 130 onto the screen 150.

Next, the electrical configuration of the projector 100 will be described with reference to FIG.
The separation circuit 52 separates the composite video signal supplied from the host device (not shown) into a luminance signal, an RGB color signal, and a synchronization signal.
The luminance average value calculation circuit 54 calculates the average value Avg of the brightness of the image to be displayed for each vertical scanning period based on the luminance signal and the synchronization signal separated by the separation circuit 52.
The light source control circuit 56 controls the luminance of the light source 102 to have a characteristic as shown in FIG. 3, for example, according to the average value Avg calculated by the luminance average value calculation circuit 54. In detail
First, when the average value Avg is not less than the first threshold and not more than the second threshold, the light source control circuit 56
When the luminance is constant at N, and secondly, when the average value Avg is lower than the first threshold value, the average value Avg is controlled to become lower than N as the average value Avg becomes lower than the first threshold value. And average value Avg
Is higher than the second threshold value, the average value Avg is controlled to be higher than N as the average value Avg becomes higher than the second threshold value.

The luminance processing circuit 58 converts the luminance signal separated by the separation circuit 52 according to the average value Avg calculated by the luminance average value calculation circuit 54. Specifically, the luminance processing circuit 58 firstly sets the luminance indicated by the luminance signal to a constant value n corresponding to the luminance N by the light source 102 when the average value Avg is not less than the first threshold and not more than the second threshold. Second, when the average value Avg is lower than the first threshold value and the luminance indicated by the luminance signal is higher than a predetermined value, the average value Avg is gradually higher than the predetermined value n as the luminance increases. Third, when the average value Avg is higher than the second threshold value and the luminance value indicated by the luminance signal is lower than the predetermined value, the constant value n increases as the luminance decreases. Convert to be gradually lower than.

Actually, the luminance average value calculation circuit 54 must be obtained when at least one vertical scanning period has not elapsed.
Cannot calculate the average luminance value Avg indicated by the luminance signal supplied during the vertical scanning period. For this reason, when the supplied luminance signal is converted based on the calculated average value Avg, the vertical scanning period is shifted, but it is considered that the difference can be ignored even for a normal moving image. If it cannot be ignored, a delay circuit for adjusting the supply timing of the luminance signal to the calculated average value Avg may be provided.

The device control circuit 60 drives and controls the mirror device 30 in accordance with the luminance signal converted by the luminance processing circuit 58 and the synchronization signal separated by the separation circuit 52. Specifically, the device control circuit 60 is set so that each mirror element in the mirror device 30 is turned on only during a period corresponding to the luminance indicated by the converted luminance signal in one vertical scanning period (1 V). PWM (pulse width modulation) control.

On the other hand, the panel control circuit 62 drives and controls the liquid crystal panels 10R, 10G, and 10B based on the RGB color signals and the synchronization signals separated by the separation circuit 52, respectively. Specifically, the panel control circuit 62 performs the following for each liquid crystal capacitor in the liquid crystal panel 10R.
Control is performed so that the voltage corresponding to the gradation indicated by the R color signal is sequentially written in accordance with the synchronization signal. Similarly, the G and B color signals are indicated for the liquid crystal capacitors in the liquid crystal panels 10G and 10B. Control is performed so that the voltage corresponding to the gradation to be written is sequentially written according to the synchronization signal.

According to the present embodiment, the brightness of each pixel in the composite image by the dichroic prism 130 is simply the brightness of the light source 102, the brightness of the reflected light in the on-state direction by the mirror device 30, the liquid crystal panel 10R, It can be expressed by the product of the brightness of 10G and 10B transmission images.
When the average value Avg calculated by the luminance average value calculation circuit 54 is not less than the first threshold and not more than the second threshold, the luminance of the light source 102 is N, and the brightness of the reflected light in the ON state direction by the mirror device 30 is Since all pixels have a value corresponding to the constant value n, the brightness of each pixel in the composite image is determined only by the RGB color signals.

Further, in the present embodiment, the light source 1 is selected according to the average brightness value Avg in the image to be displayed.
The brightness of 02 is controlled and the reflected light from the mirror device 30 is locally controlled for each pixel.
In detail, when the average value Avg of the luminance of the image to be displayed is lower than the first threshold and there is a bright highlight portion in a part of the image, the luminance of the light source 102 becomes low. The dark portion becomes darker, while the highlight portion is controlled to be relatively bright in the mirror device 30, so that the phenomenon that the highlighted portion of the image projected on the screen 150 becomes dark is avoided. .
On the other hand, when the average value Avg of the luminance of the image to be displayed is higher than the second threshold and there is a dark shadow portion in a part of the image, the luminance of the light source 102 is increased, so that the bright portion Since the shadow portion is controlled to be relatively dark in the mirror device 30, while the shadow portion is controlled to be relatively dark, the phenomenon that the shadow portion of the image projected on the screen 150 becomes bright (black floating) is avoided. Is possible.

In the embodiment, the luminance of the light source 102 is controlled according to the average value Avg and the luminance indicated by the separated luminance signal is converted according to the average value Avg. However, the luminance of the light source 102 is made constant. The mirror device 30 may be driven and controlled without converting (or appropriately compressing) the luminance indicated by the separated luminance signal.
Here, the maximum value of brightness expressed by each pixel of the mirror device 30 is wd, and the minimum value is Bd.
And the maximum value of brightness expressed by each pixel of the liquid crystal panels 10R, 10G, 10B is Wp,
When the minimum value is expressed by Bp, the brightness of each pixel when viewed from the composite image by the dichroic prism 130 is simply the mirror device 30 if the light source 102 has a constant luminance.
Can be represented by the product of the brightness of the reflected light in the on-state direction and the brightness of the transmitted images of the liquid crystal panels 10R, 10G, and 10B.
Since the contrast ratio is expressed by the ratio between the maximum value and the minimum value of brightness, it is Wp / Bp in the configuration in which only the liquid crystal panels 10R, 10G, and 10B are provided as in the related art. On the other hand, in the present embodiment, in addition to the liquid crystal panels 10R, 10G, and 10B, the mirror device 3 is provided in the preceding stage.
Since 0 is provided, the contrast ratio is (Wd · Wp) / (Bd · Bp).
Therefore, even when the luminance of the light source is not changed, the liquid crystal panels 10R, 10G, 1
A higher contrast ratio than the conventional configuration of only 0B is possible.

In the embodiment, the mirror device 30 is exemplified as the luminance modulator. However, any device that changes the luminance (brightness and darkness) for each pixel may be used. For example, a transmissive or reflective liquid crystal panel is also applicable. Further, the liquid crystal panels 10R, 10G, and 10B are not limited to the transmission type,
The reflection type is also applicable.
In the embodiment, the projector has been described as an example, but the present invention can also be applied to a rear projection type television.

It is a top view which shows the optical structure of the display apparatus which concerns on embodiment of this invention. It is a block diagram which shows the electrical structure in the display apparatus. It is a figure which shows the light source control in the display apparatus.

Explanation of symbols

10R, 10G, 10B ... Liquid crystal panel, 30 ... Mirror device, 52 ... Separation circuit, 54 ...
Luminance average value calculation circuit 56 ... Light source control circuit 58 ... Luminance processing circuit 60 ... Device control circuit 100 ... Display device 130 130 Dichroic prism 140 140 Projection lens group

Claims (4)

A luminance modulator that modulates and emits light from a light source based on a luminance signal;
First to third optical modulators corresponding to mutually different primary colors and modulating emitted light from the luminance modulator based on respective color signals;
Combining means for generating combined images of the lights modulated by the first to third optical modulators,
A display device comprising: A luminance average value calculation circuit for calculating an average luminance value in the image from the luminance signal corresponding to the image to be displayed;
A light source control circuit for controlling the luminance of the light source according to the calculated average value;
A luminance processing circuit that converts luminance indicated by a luminance signal corresponding to an image to be displayed and supplies the luminance modulator to the luminance modulator;
The display device according to claim 1, further comprising: The display device according to claim 1, wherein the first to third light modulators are liquid crystal panels corresponding to red, green, and blue, respectively. Projecting means for enlarging and projecting a composite image by the combining means,
The display device according to claim 1, further comprising:

Images