JP2009244809A - Image display apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control output light quantity while holding white balance in an image display apparatus having a plurality of solid state light-emitting elements each of which emits monochromatic light of different wavelength. <P>SOLUTION: The image display apparatus includes: a plurality of light sources (solid state light-emitting elements) 60, 61, 62 each of which emits monochromatic light of different wavelength; a light source control circuit (dimming means) 40 for independently dimming each of the light sources 60, 61, 62; a display device (light modulation means) 30 for modulating monochromatic light emitted from each of the light sources 60, 61, 62 in accordance with an image signal; and an image forming lens 70 for forming a display image by image-forming the modulated light modulated by the display device 30. The light source control circuit 40 controls the luminance of the display image while holding the white balance of the display image. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image display apparatus including a plurality of solid state light emitting elements that emit monochromatic light.

  2. Description of the Related Art Conventionally, in the field of televisions and projectors, a technique for adjusting (dimming) the amount of output light according to an image signal and environment has been proposed. For example, Patent Document 1 describes a technique for improving the contrast of a display image by controlling an aperture stop according to an image signal.

  Patent Document 2 describes a technique for adjusting the amount of output light by driving a fluorescent lamp serving as a backlight in a liquid crystal television by PWM (Pulse Width Modulation) according to an image signal.

JP 2006-133750 A JP 2006-53520 A

  By the way, in the technique described in Patent Document 1, since the amount of light is adjusted using an aperture stop, the F value of the optical system changes according to the adjustment of the amount of output light. Therefore, when an optical element having an angle characteristic is used in the optical system, there is a problem that the color of the display image changes when light control is performed.

  In particular, when white is output, there is a problem that the white balance is lost depending on the light control. Therefore, it is desired to adjust the amount of light emitted from the light source itself without using the opening / closing diaphragm to adjust the amount of light output in the image display device.

  In the technique described in Patent Document 2, a fluorescent lamp that is a backlight light source of a liquid crystal television is dimmed, but the backlight using a white fluorescent lamp is targeted. This is done only with the PWM signal. The fluorescent lamp is controlled with reference to only the vertical period signal from the image signal processing circuit.

  However, for example, when dimming a solid state light emitting device that emits monochromatic light such as a light emitting diode (LED), the light emission characteristics of the solid state light emitting device are different. The problem that the white balance is lost occurs.

  Therefore, the present invention provides an image display apparatus having a plurality of solid state light emitting elements that emit monochromatic lights each having a different wavelength, the output light quantity being adjustable while maintaining the white balance of the display image. The purpose is to provide.

  Another object of the present invention is to provide an image display apparatus in which the output light amount is dynamically adjusted according to the image signal, and the contrast of the display image is improved.

  In order to solve the above-described problems and achieve the above object, an image display apparatus according to the present invention has any one of the following configurations.

[Configuration 1]
A plurality of solid-state light emitting elements each emitting monochromatic light of a different wavelength, dimming means for dimming each solid-state light-emitting element independently, and light that modulates monochromatic light emitted from each solid-state light-emitting element according to an image signal A modulation means; and an imaging means for forming a display image by forming an image of the modulated light modulated by the light modulation means, and the light control means adjusts the brightness of the display image while maintaining the white balance of the display image. It is characterized by controlling.

[Configuration 2]
In the image display device having the configuration 1, the luminance control of the display image by the light control unit is performed based on the image signal.

  In the image display device according to the present invention having the configuration 1, the dimming means for independently dimming the plurality of solid-state light emitting elements each emitting monochromatic light having different wavelengths, while maintaining the white balance of the display image, Since the brightness of the image is controlled, the white balance of the display image is maintained regardless of the image signal and the environment.

  In the image display device according to the present invention having the configuration 2, since the brightness of the display image is controlled by the light control means based on the image signal, the optimum brightness is output to the image signal to improve the contrast feeling. Can do.

  That is, the present invention provides an image display device having a plurality of solid-state light emitting elements each emitting monochromatic light having different wavelengths, and capable of adjusting the amount of output light while maintaining white balance. It is something that can be done.

  Further, the present invention can provide an image display apparatus in which the output light amount is dynamically adjusted according to the image signal, and the contrast feeling of the display image is improved.

  Hereinafter, the configuration of an image display device according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of an image display apparatus according to the present invention.

  As shown in FIG. 1, the image display apparatus according to the present invention has an image signal processing circuit 10 to which an input image signal is supplied. The image signal processing circuit 10 generates RGB three primary colors (red, green, and blue) image signals and the like from the input image signal, and outputs them to the display device drive circuit 20. Further, the image signal processing circuit 10 calculates a control parameter from the image signal in order to perform dimming of the light source suitable for the content (scene) of the display image, and controls the control parameter for the light source control circuit 40 serving as dimming means. And a vertical synchronizing signal.

  The display device drive circuit 20 converts the input image signal into a drive signal for the display device 30 serving as a light modulation unit, and outputs the drive signal to the display device 30. On the other hand, the light source control circuit 40 generates a signal for driving the light source from the input control parameter, and each of the plurality of solid state light emitting elements emits monochromatic light (red, green, and blue) having different wavelengths. The light sources 60, 61, 62 are driven. The light source drive signals 71 for driving the light sources 60, 61, and 62 are independent from each other, and the light source control circuit 40 dims the light sources 60, 61, and 62 independently. The light source drive signal 71 for driving each light source 60, 61, 62 is updated every vertical period of the image signal.

  The display device 30 is driven by the display device drive circuit 20 and modulates monochromatic light emitted from each of the light sources 60, 61, and 62 according to an image signal. Then, the modulated light modulated by the display device 30 is imaged by the imaging lens 70 to form a display image. The display image is controlled in luminance by the light source control circuit 40, but is always performed while maintaining white balance.

  FIG. 2 is a waveform diagram showing a light source drive signal in the image display apparatus according to the present invention. In FIG. 2, V represents a vertical synchronizing signal, A represents a waveform when the light source is dimmed by voltage or current, and D represents a waveform when the light source is dimmed by PWM drive, that is, a duty ratio (% : The ratio of the ON period) shows the waveform of the pulse wave.

  In this image display device, as shown in FIG. 2, the light emission output of each of the light sources 60, 61, 62 is controlled by parameters output from the image signal processing circuit 10 to the light source driving circuit 40. That is, this parameter determines the white balance. The light source control circuit 40 calculates the optimal light emission output of each light source 60, 61, 62 based on the image signal, and derives the parameters of each light source 60, 61, 62 from this calculation result.

  FIG. 3 is a graph showing emission characteristics of LEDs that emit red, green, and blue light actually measured. In FIG. 3, the horizontal axis represents the duty ratio (%) in PWM drive, and the vertical axis represents the value obtained by normalizing the brightness.

  Table 1 shows examples of parameters derived by the light source control circuit 40.

  For example, as shown in [Table 1], when the luminance of the light source is dimmed in 50 levels using PWM drive, it is created in advance from the light emission characteristics of the light sources 60, 61, 62 as shown in FIG. By holding the table in the light source control circuit 40, it is possible to independently control the duty ratio (%), which is a parameter of each light source 60, 61, 62, and maintain the white balance of the light source. .

  In this way, by performing optimum driving for each of the light sources 60, 61, 62, it is possible to avoid the loss of white balance due to the difference in the light emission characteristics of the light sources 60, 61, 62 described above.

  Note that these parameters can be calculated not only by using a table but also by calculation by incorporating a formula prepared in advance in the light source control circuit 40. The light source control circuit 40 calculates light source dimming control parameters for each vertical period, but when the brightness of the light source changes abruptly, unnatural appearance occurs. Therefore, a visually natural control parameter can be calculated by calculating the control parameter with reference to the value of the control parameter in a plurality of past vertical synchronization periods.

For example, _let P _{n be} the control parameter for the current vertical synchronization period, and _let P _n−1 , P _n−2 , P _n−3 ,..., P _n−k be the control parameters for the past k vertical synchronization periods. Also, _let P ′ _n be a control parameter calculated from these k + 1 parameters. At this time, as shown in [Equation 1], it can be calculated from the average value of a plurality of past control parameters. That is, _let P ′ _n be the average value of the control parameters in the current vertical synchronization period and the control parameters in the past k vertical synchronization periods.

  The control parameter averaged in advance by the image signal processing circuit 10 may be output to the light source control circuit 40.

Further, as shown in [Expression 2], it is also possible to calculate by weighting a plurality of past control parameters. As control parameters closer to the current vertical sync period, it performs weighting on the control parameter in the parameter P 'to effect on _n increases k + 1 single vertical synchronization period is calculated.

  In such a method of calculating an actual parameter from a plurality of parameters, the light source control circuit 40 calculates the control parameter of the current vertical synchronization period from the control parameters of the plurality of past vertical synchronization periods, whereby the image signal processing circuit 10 It is also effective against signal noise that may occur in the transmission line between the light source control circuit 40 and the like. In other words, even when the light source control circuit 40 suddenly receives an inappropriate control parameter due to the influence of noise, the light source control circuit 40 is smoothed by the control parameters of the past plurality of vertical synchronization periods. Avoiding light.

  Note that the control of each light source in the image display device according to the present invention described above is intended to avoid the loss of white balance caused by the difference in the light emission characteristics of the light sources 60, 61, 62. When the image signal is a single color or an image signal having only two color components, the light source corresponding to the color component not included in the input image signal may be always turned off.

It is a block diagram which shows the structure of the image display apparatus which concerns on this invention. It is a wave form diagram which shows the light source drive signal in the image display apparatus which concerns on this invention. It is a graph which shows the light emission characteristic of LED which emits red, green, and blue actually measured.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image signal processing circuit 20 Display device drive circuit 30 Display device 40 Light source control circuit 60 Light source (red)
61 Light source (green)
62 Light source (blue)
70 Imaging lens

Claims (2)

A plurality of solid state light emitting elements each emitting monochromatic light of a different wavelength;
A dimming means for dimming each solid-state light emitting element independently;
Light modulating means for modulating the monochromatic light emitted from each of the solid state light emitting elements according to an image signal;
Imaging means for forming a display image by imaging the modulated light modulated by the light modulation means,
The light control means controls the luminance of the display image while maintaining the white balance of the display image. The image display apparatus according to claim 1, wherein the brightness control of the display image by the light control unit is performed based on the image signal.

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