JP5783109B2 - Image display device - Google Patents

Description

  The present invention relates to an image display device including a liquid crystal image display that modulates illumination light according to video data.

  2. Description of the Related Art Projection-type image display devices are widely used in which illumination light is modulated according to video data by a liquid crystal image display, which is one of light modulation elements, and projected onto a screen.

Japanese Patent No. 4042603

  When displaying an image with a plurality of gradations expressed by an image display device, it is desired not to generate a moving image pseudo contour. It is also desirable to increase the number of gradations that are apparently expressed as much as possible. In the liquid crystal, the change in the light modulation output with respect to the voltage is small in the low gradation region and the high gradation region, while the change in the light modulation output with respect to the voltage is large in the intermediate gradation region. Therefore, a plurality of gradations from the low gradation part to the high gradation part may not be expressed well, or the image quality may be adversely affected. Therefore, it is desired to realize good gradation display characteristics and high image quality.

  In order to meet such a demand, the present invention does not generate a moving image pseudo contour and can increase the number of apparently expressed gradations as much as possible, thereby realizing good gradation display characteristics and high image quality. An object of the present invention is to provide an image display device that can be used.

  In order to solve the above-described problems of the conventional technology, the present invention provides a plurality of peripheral pixels with data having a predetermined lower number of bits in each pixel data constituting the first video data having the first number of bits. An error diffusion processing unit (2) that performs error diffusion and outputs as second video data having a second number of bits smaller than the first number of bits, and each pixel data constituting the second video data The subfield processing unit (3) for generating display data for subfield driving in which the pulse width monotonously increases or decreases in accordance with the grayscale level, and the grayscale level in the low grayscale range is determined within each frame period. The first emission intensity is set in the period and the period in which the gradation of the high gradation range is determined, and the second emission intensity lower than the first emission intensity is determined in the period in which the intermediate gradation range between them is determined. Luminous intensity An illumination source for emitting a bright light (6), to provide an image display apparatus comprising: a liquid crystal image display device (4) which modulates the said illumination light to the display data.

  The illumination light source includes a plurality of light sources (6a to 6d), a first light emission characteristic of the first set of light sources in the plurality of light sources, and a second of the second set of light sources of the plurality of light sources. The light emission characteristic is different, and the combined light of light emission by the first light emission characteristic from the first set of light sources and light emission by the second light emission characteristic from the second set of light sources is It is preferable to use illumination light. The plurality of light sources are preferably light emitting diodes.

  According to the image display apparatus of the present invention, it is possible to increase the number of gradations that are apparently expressed as much as possible without generating a moving image pseudo contour, and to realize good gradation display characteristics and high image quality.

It is a block diagram which shows one Embodiment of the image display apparatus of this invention. It is a figure for demonstrating operation | movement of the error diffusion process part 2 in FIG. It is a figure for demonstrating the operation | movement of the subfield process part 3 in FIG. 1, and the characteristic of the illumination light which the illumination light source 6 emits. FIG. 3 is a diagram for explaining the relationship between the gradation of display data input to the liquid crystal image display device 4 in FIG. 1 and the light modulation output intensity by the liquid crystal image display device 4. It is a figure which shows the example of an optical structure by one Embodiment of the image display apparatus of this invention. It is a perspective view which shows the specific structural example of the illumination light source 6 in FIG. It is a figure for demonstrating the light emission characteristic by the specific structural example of the illumination light source 6 shown in FIG. FIG. 6 is a partial perspective view of FIG. 5.

  Hereinafter, an image display apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 mainly schematically shows a circuit configuration of an image display apparatus 100 according to an embodiment. In FIG. 1, an image display apparatus 100 includes input terminals 1a to 1c, an error diffusion processing unit 2, a subfield processing unit 3, a liquid crystal image display 4, a light source control signal generation unit 5, an illumination light source 6, a polarizing plate 7, and a projection. A lens 8 is provided. Video data to be displayed by the image display device 100 is input to the input terminal 1a. A reference clock is input to the input terminal 1b, and a synchronization signal of video data is input to the input terminal 1c.

  The error diffusion processing unit 2 is supplied with video data, a reference clock, and a synchronization signal. It is assumed that the number of bits of video data input to the error diffusion processing unit 2 is m bits. A subfield processing unit 3 to be described later performs processing to generate display data for driving the liquid crystal image display 4 in a subfield based on n-bit video data having a bit number smaller than m bits. Therefore, the error diffusion processing unit 2 uses lower (mn) bit data in each pixel data as an error, and as an example, as shown in FIG. 2, the error in the pixel P is assigned a weighting coefficient to a plurality of peripheral pixels. Multiply and spread.

  The error in the pixel to which the error has been added is further diffused by multiplying a plurality of peripheral pixels by a weighting coefficient, so that the error is cumulatively added to each pixel. In the error diffusion processing in the error diffusion processing unit 2, if the accumulated error is within a certain range, the gradation of the pixel is maintained, and if the accumulated error exceeds the certain range, the gradation of the pixel is changed to a gradation one higher. By doing so, gradation that cannot be displayed originally is reproduced in a pseudo manner as a spatial collection of pixels with coarse display gradation.

  The n-bit video data output from the error diffusion processing unit 2 is input to the subfield processing unit 3. The subfield processing unit 3 generates display data having a pulse width corresponding to the gradation of each pixel data in the video data. The subfield processing unit 3 drives the liquid crystal image display 4 in a subfield with display data having a pulse width corresponding to the gradation of each pixel data.

  FIG. 3A shows the minimum basic unit of the subfield. As shown in FIGS. 3B to 3D, the subfield processing unit 3 has a shorter pulse width as the gradation of the pixel data is lower and a longer pulse width as the gradation of the pixel data is higher. Display data is generated. Assuming that FIG. 3D shows the longest pulse width, the subfield processing unit 3 performs the processing from the minimum basic unit shown in FIG. 3A to the longest pulse width shown in FIG. 3D within one frame period. Display data having a pulse width corresponding to the gradation of the pixel data in the range is generated.

  In this way, the subfield processing unit 3 monotonously increases or decreases the pulse width of the display data for subfield driving according to the gradation. Therefore, in the image display apparatus according to the present embodiment, no moving image pseudo contour is generated.

  In so-called pulse width modulation driving, in which the pulse width of display data, which is a display period by a subfield, is monotonously increased or decreased according to the gradation, the number of gradations that can be expressed is limited by the total number of subfields. For example, 256 subfields are required to perform 8-bit, 256-gradation representation. However, in order to realize 256 subfields, an extremely high operation rate is required, which is difficult to realize. Therefore, the subfield processing unit 3 generates display data of about several tens of subfields.

  The error diffusion processing unit 2 is provided in front of the subfield processing unit 3 and the number of gradations that can be expressed in a pseudo manner by the error diffusion processing unit 2 is increased only by the subfield processing unit 3 that performs pulse width modulation driving. This is because the number of gradations that can be expressed is reduced. In the present embodiment, since the error diffusion processing unit 2 and the subfield processing unit 3 that performs pulse width modulation driving are provided, the number of gradations that are apparently expressed can be increased as much as possible without generating a moving image pseudo contour. .

  The display data generated by the subfield processing unit 3 is input to the liquid crystal image display 4 which is a reflection type light modulation element. The liquid crystal image display 4 also receives a driving signal such as a timing signal for pixel addressing and a driving clock generated by a driving signal generation circuit (not shown). The liquid crystal image display 4 receives polarized light described later. The liquid crystal image display 4 modulates the incident polarized light according to the display data and outputs it.

  The light source control signal generator 5 is supplied with the synchronization signal input to the input terminal 1c. The light source control signal generation unit 5 generates a light source control signal for controlling the illumination light emitted from the illumination light source 6 to switch the emission intensity to a plurality of levels in time in synchronization with one frame period of the video data. The light source control signal is input to the illumination light source 6. The illumination light source 6 emits illumination light whose emission intensity varies with time as shown in FIG. 3E based on the light source control signal.

  As shown in FIG. 3E, the illumination light source 6 has a first emission intensity in a period for determining a gradation in a low gradation region and a period in which a gradation in a high gradation region within one frame period, Illumination light having a second light emission intensity lower than the first light emission intensity is emitted during the period in which the gradation of the intermediate gradation region between them is determined. The emission intensity of general illumination light is constant within one frame period as indicated by a broken line.

  The illumination light emitted from the illumination light source 6 enters the polarizing plate 7. The polarizing plate 7 is disposed at an angle of 45 ° with respect to the traveling direction of the illumination light. The polarizing plate 7 reflects, for example, an S-polarized component, which is one polarized component, and makes it incident on the liquid crystal image display 4. The liquid crystal image display 4 modulates the incident S-polarized component according to the display data and outputs it as modulated light of the P-polarized component which is the other polarized component. The modulated light of the P-polarized component emitted from the liquid crystal image display 4 passes through the polarizing plate 7 and enters the projection lens 8. The projection lens 8 projects the incident modulated light onto a screen (not shown) and displays an image.

  In the present embodiment, the liquid crystal image display 4 is a reflection type light modulation element, but may be a transmission type light modulation element.

  FIG. 4A shows the gradation represented by the on-period of the subfield and the light of the liquid crystal image display 4 when the light emission intensity of general illumination light is set as indicated by a broken line in FIG. The relationship with the modulation output intensity is shown. 4A and 4B, nine gradations are used for simplification, but in actuality, a larger number of gradations are expressed by the subfield processing unit 3.

  As shown in FIG. 4A, due to the voltage / modulation rate characteristics of the liquid crystal, generally, the light modulation output intensity of the liquid crystal image display 4 is relative to the effective value of the drive voltage applied to the liquid crystal image display 4. S-shaped characteristics. That is, the change rate of the light modulation output intensity with respect to the voltage change is small in the low gradation range that is the rising edge of the modulation from black to dark. The change rate is steep in the intermediate gradation range. In the high gradation region near the white peak (saturation level), the rate of change becomes gentle again.

  For this reason, the difference in light modulation output intensity when the on-period of the subfield, which is the pulse width of the display data, changes is large, for example, ΔL1 in the intermediate gradation region, and in the low gradation region and the high gradation region. Get smaller. When the error diffusion processing is performed by the error diffusion processing unit 2, the error diffusion noise tends to be emphasized in the intermediate gradation region if the characteristics as shown in FIG. The intermediate gradation area is an area in which the shadow of the person's face is expressed, and has a great influence on the texture of the image. Therefore, in order to realize a high quality display, it is required to improve the image quality in the intermediate gradation range.

  Therefore, in the present embodiment, as described with reference to FIG. 3E, the emission intensity of the illumination light from the illumination light source 6 is determined based on the period for determining the gradation of the low gradation area within one frame period and the high gradation area. The first emission intensity is used in the period for determining the gradation, and the second emission intensity is lower than the first emission intensity in the period for determining the gradation of the intermediate gradation range between them. Accordingly, the relationship between the gradation and the light modulation output intensity has a characteristic as shown in FIG.

  As shown in FIG. 4B, the difference of the light modulation output intensity when the on-period of the subfield is changed is ΔL2 smaller than ΔL1 in the intermediate gradation region. This corresponds to equivalently reducing the weighting in the subfield of the intermediate gradation range. As shown in FIG. 4B, the relationship between gradation and light modulation output intensity is closer to a linear characteristic than in FIG. In the present embodiment, error diffusion noise is not emphasized in the intermediate gradation range, and high-quality display can be realized by improving the image quality in the intermediate gradation range.

  Next, details of the optical configuration of the image display apparatus 100 according to the embodiment will be described with reference to FIG. 5, the same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted as appropriate. In FIG. 5, the illumination light emitted from the illumination light source 6 is collected by the collimator lens 101 and is incident on the integrator 102 composed of a pair of fly-eye lenses. As an example, the illumination light source 6 includes four light emitting diodes (LEDs) 6a to 6d, which are semiconductor light sources, as shown in FIG. The LEDs 6 a to 6 d are driven by drive signals Sda to Sdd from the light source control signal generation unit 5.

  The light source control signal generation unit 5 causes the LEDs 6a and 6d to emit light with the light emission characteristics as shown in FIG. 7A, and causes the LEDs 6b and 6c to emit light with the light emission characteristics as shown in FIG. 7B. Therefore, the light emission characteristic of the illumination light emitted from the illumination light source 6 is the characteristic shown in FIG. 7C, which is a combination of the light emission characteristic of FIG. 7A and the light emission characteristic of FIG. The characteristics shown in FIG. 7C are the same as those described with reference to FIG. Here, the LEDs 6a and 6d emit light with the light emission characteristics as shown in FIG. 7A, and the LEDs 6b and 6c emit light with the light emission characteristics as shown in FIG. 7B. Grouping is arbitrary. The number of light emitting diodes is not limited to four.

  The illumination light shown in FIG. 7C emitted from the illumination light source 6 is made substantially parallel light by the collimator lens 101 and enters the integrator 102 as shown in FIG. In FIG. 8, the optical axis of substantially parallel light is shown for simplification. Light incident on each lens cell in one fly-eye lens located on the collimator lens 101 side of the integrator 102 is incident on a corresponding lens cell in the other fly-eye lens. The light emitted from each lens cell in the other fly-eye lens is emitted as an integrated combined light.

  Returning to FIG. 5, the light emitted from the integrator 102 is emitted through the polarization conversion optical element 103 and the lens 104. The parts from the collimator lens 101 to the lens 104 constitute an illumination optical system. A color separation / synthesis optical system that separates and synthesizes the illumination light emitted from the illumination optical system into respective colors is provided at the subsequent stage of the illumination optical system. A portion from the dichroic mirror 105 to the cross dichroic prism 111 at the front stage of the projection lens 8 constitutes a color separation / synthesis optical system.

  The dichroic mirror 105 decomposes the incident illumination light into blue light and yellow light. The optical path of blue light is bent by 90 ° by the folding mirror 106b, and the optical path of yellow light is bent by 90 ° by the folding mirror 106y. The dichroic mirror 107 decomposes the incident yellow light into green light and red light.

  The blue light is incident on the wire grid polarizer 7b through the lens 108b and the polarizer 109b. The green light is incident on the wire grid polarizer 7g via the lens 108g and the polarizer 109g. The red light is incident on the wire grid polarizer 7r via the lens 108r and the polarizer 109r. The linear polarization degree of polarized light is improved by the polarizing plates 109b, 109g, and 109r. The wire grid polarizers 7b, 7g, and 7r correspond to the polarizer 7 in FIG.

  As described above, one polarized light transmitted through the wire grid polarizers 7b, 7g, and 7r is incident on the reflective light modulation elements 4b, 4g, and 4r, and is modulated in accordance with display data. The light modulation elements 4b, 4g, and 4r correspond to the liquid crystal image display 4 in FIG. The light modulation elements 4b, 4g and 4r modulate one incident polarized light to convert it into the other polarized light and emit it. The other polarized light emitted from the light modulation elements 4b, 4g, and 4r is reflected by the wire grid polarizers 7b, 7g, and 7r, respectively.

  The other polarized light reflected by the wire grid polarizers 7b, 7g, and 7r is incident on the polarizers 110b, 110g, and 110r, and unnecessary polarization components are removed. The cross dichroic prism 111 combines the other polarized light emitted from the polarizing plates 110 b, 110 g, and 110 r and causes the combined light to enter the projection lens 8. The projection lens 8 projects the incident combined light onto a screen (not shown).

  In the present embodiment, the configuration shown in FIGS. 1 and 5 does not generate a moving image pseudo contour and can increase the number of gradations that are apparently expressed as much as possible, thereby realizing good gradation display characteristics and high image quality. be able to.

  The present invention is not limited to the embodiment described above, and various modifications can be made without departing from the scope of the present invention. Although FIG. 5 shows a configuration using three light modulation elements, a configuration using one light modulation element may be used.

2 Error diffusion processing unit 3 Subfield processing unit 4 Liquid crystal image display 5 Light source control signal generation unit 6 Illumination light source 6a to 6d Semiconductor type light source (light emitting diode)
7 Polarizing plate 8 Projection lens 100 Image display device

Claims (3)

Data having a predetermined lower number of bits in each pixel data constituting the first video data having the first number of bits is error-diffused to a plurality of peripheral pixels, and the second number smaller than the first number of bits An error diffusion processing unit that outputs the second video data having the number of bits;
A subfield processing unit for generating display data for subfield driving in which the pulse width monotonously increases or decreases according to the gradation of each pixel data constituting the second video data;
Within each frame period, the first emission intensity is used in the period for determining the gradation in the low gradation region and the period in which the gradation in the high gradation region is determined, and the gradation in the intermediate gradation region between them is set. An illumination light source that emits illumination light having a second light emission intensity lower than the first light emission intensity in the period to be determined;
A liquid crystal image display that modulates the illumination light according to the display data;
An image display device comprising: The illumination light source is composed of a plurality of light sources,
The first light emission characteristic of the first set of light sources in the plurality of light sources is different from the second light emission characteristic of the second set of light sources in the plurality of light sources,
The combined light of the light emission by the first light emission characteristic from the first light source and the light emission by the second light emission characteristic from the second light source is used as the illumination light. The image display device according to claim 1.   The image display apparatus according to claim 2, wherein the plurality of light sources are light emitting diodes.

Images