WO2020039954A1

WO2020039954A1 - Display device

Info

Publication number: WO2020039954A1
Application number: PCT/JP2019/031307
Authority: WO
Inventors: 真一郎田尻
Original assignee: ソニー株式会社
Priority date: 2018-08-20
Filing date: 2019-08-08
Publication date: 2020-02-27

Abstract

A display device according to the present invention is provided with: a light source for outputting light which becomes a source of illumination light; an optical modulation element that modulates the illumination light on the basis of bit plane data for each gradation bit within a display period allocated to each of the gradation bits; a period control unit that variably controls the display period for each of the gradation bits in the optical modulation element so as to achieve T2≥T1>T2·1/2, where T1 denotes a display period for a lowest-order gradation bit among the gradation bits, and T2 denotes a display period for a gradation bit higher by one order than the lowest-order gradation bit; and a light source output control unit that variably controls an output from the light source at least in the display period of the lowest-order gradation bit.

Description

Display device

The present disclosure relates to a display device that displays an image using a light modulation element.

In a display device using a mirror array device such as a micro mirror array (MMA) as a light modulation element, gradation control is performed by a PWM (Pulse Width Modulation) method. In a general PWM method, the brightness of the light source is kept constant and the width of the light emission time of the light source is changed according to the brightness, thereby enabling a multi-step gradation expression. Further, in the PWM method, a technique has been proposed in which one frame is divided into a plurality of subframes, and the luminance of the light source is variably controlled in subframe units (see Patent Document 1). In gradation control by the PWM method, image data for each gradation is transferred to the light modulation element prior to a display period for each gradation.

JP 2007-78866 A

When higher resolution (higher pixels) and higher gradations are required, the data transfer speed of image data to the light modulation element needs to be increased, while the circuit configuration makes it difficult to increase the data transfer speed. There is.

ことが It is desirable to provide a display device capable of increasing the frame rate and the number of pixels.

A display device according to an embodiment of the present disclosure includes a light source that outputs light that is a source of illumination light and a bit plane for each gradation bit within a display period allocated to each of the plurality of gradation bits. A light modulation element for modulating the illumination light based on the data; a display period of the lowest gradation bit of the plurality of gradation bits as T1; and a display period of the gradation bit one stage higher than the lowest as T2. Then, a period control unit that variably controls a display period for each gradation bit in the light modulation element so that T2 ≧ T1> T2 ・ 1/2, and a light source at least in a display period of the lowest gradation bit. A light source output controller for variably controlling the output.

In the display device according to an embodiment of the present disclosure, the display period of the lowest gradation bit of the plurality of gradation bits is T1, and the display period of the gradation bit one step higher than the lowest is T2. At this time, the display period for each gradation bit in the light modulation element is variably controlled so that T2 ≧ T1> T2 ・ 1/2, and at least the output of the light source in the display period of the least significant gradation bit is variably controlled. You.

FIG. 9 is an explanatory diagram illustrating an example of light emission control of a light source in a display device according to a comparative example. 1 is a configuration diagram schematically illustrating a configuration example of a projector as a display device according to a first embodiment of the present disclosure. FIG. 3 is an explanatory diagram schematically illustrating an example of a frame configuration of an image in the display device according to the first embodiment. FIG. 2 is a block diagram schematically illustrating a configuration example of a control system of the display device according to the first embodiment. 9 is a timing chart illustrating an example of light emission control of a light source in a display device according to a comparative example. 5 is a timing chart illustrating an example of light emission control of a light source in the display device according to the first embodiment. 9 is a timing chart illustrating an example of a transfer timing of data transfer for each gradation bit in a display device according to a comparative example. 5 is a timing chart illustrating an example of a transfer timing of data transfer for each gradation bit in the display device according to the first embodiment. FIG. 9 is an explanatory diagram illustrating an example of light emission control of a light source in a display device according to a first modification of the first embodiment. FIG. 11 is an explanatory diagram illustrating an example of light emission control of a light source in a display device according to a second modification of the first embodiment. FIG. 3 is an explanatory diagram illustrating an example of an ideal output waveform and an actual output waveform of a light source in the display device according to the first embodiment. 9 is a timing chart illustrating an example of light emission control of a light source in a display device according to a second embodiment. FIG. 9 is an explanatory diagram illustrating an example of an output waveform of a light source in the display device according to the first embodiment and an output waveform of a light source in the display device according to the second embodiment.

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The description will be made in the following order.
0. Comparative example (FIG. 1)
1. First Embodiment (Technique for lowering the light source output so as to lengthen the display period of LSB)
1.1 Configuration of Display Device According to First Embodiment (FIGS. 2 to 4)
1.2 Control Operation of Display Device According to First Embodiment (FIGS. 5 to 8)
1.3 Effects 1.4 Modifications of First Embodiment (FIGS. 9 to 11)
2. 2. Second Embodiment (Technique for shortening light emission time of light source so as to lengthen display period of LSB) (FIGS. 12 to 13)
3. Other embodiments

<0. Comparative Example>
(Overview and Issues of PWM Display Device According to Comparative Example)
In a display device that performs gradation expression by a general PWM method, a light source continuously emits light having a constant luminance to a light modulation element. The light modulation element controls the modulation of light into two states of light and dark for each pixel according to the luminance of an image to be displayed. At this time, in the display device, as light modulation control, on (light emission) / (non-light emission) off control of light reaching the image display surface is performed in a pulsed manner. Then, the light modulation element changes the pulse width of light by changing the on / off switching timing for each pixel, and performs gradation expression. By irradiating the light modulated in this manner on the image display surface, an image is displayed in multiple gradations.

In the case of gradation representation by the PWM method, for example, an image of 16 gradations can be represented by combining at least four types of images having different luminances within a predetermined period (usually one frame). That is, when expressing 16 gradations, first, the luminance is quantized into, for example, four gradation bits for each pixel. Then, for example, one frame of image data is represented by a combination of four types of image data weighted by each gradation bit. At this time, a group of image data for each gradation bit is usually called a “bit plane”. The bit plane is an information surface of luminance for each gradation bit.

では In the above-described general PWM type display device, the output of the light source is controlled to be constant. On the other hand, a technique for variably controlling the output of a light source has been proposed in order to improve image quality and the like.

FIG. 1 illustrates an example of light emission control of a light source in a display device according to a comparative example.
For example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2007-78866), as shown in FIG. 1A, one frame is divided into a plurality of subframes SF1, SF2, SF3, and SF4 having different lengths. The display periods of R (red), G (green), and B (blue) are dispersed in one frame. In the example of FIG. 1A, the display period is shortened in the order of the plurality of subframes SF1, SF2, SF3, and SF4. A bit plane of gradation bits corresponding to the display period of each color is displayed for each subframe. At this time, as shown in FIGS. 1B and 1C, the emission intensity of each color is changed for each subframe in synchronization with the display period of each color. This makes it possible to express the gradation more precisely than in the case where the output of the light source is controlled to be constant, and particularly, the gradation expression on the dark side is improved.

In the technique of the comparative example, as shown in FIGS. 1B and 1C, the emission intensity of each color is changed for each subframe, but the display period of each gradation bit of each color and the emission The period is fixed. For example, in FIG. 1B and FIG. 1C, the light emission intensity of each color of the sub-frames SF2, SF3, and SF4 changes, but FIG. 1B and FIG. 1C. There is no change in the light emission period of each color.

On the other hand, generally, in gradation control by the PWM method, it is necessary to transfer bit plane data for each gradation to the light modulation element in advance before a display period for each gradation. For example, the data of the bit plane of the sub-frame SF4 in FIG. 1A needs to be transferred to the light modulation element within the display period of the sub-frame SF3 earlier than that. Therefore, the transfer period during which the data of the bit plane is transferred needs to be shorter than at least the display period of the least significant gradation bit (LSB). In the example of FIG. 1A, it is necessary to send the data of the bit plane for the next frame within the shortest sub-frame SF4.

Here, the display period of the lowest gradation bit of each color is arithmetically determined by the gradation displayed in one frame. For example, when one frame is displayed at 60 Hz and R, G, and B are switched evenly within one frame and the gradation is expressed in 256 levels, the display period of the lowest gradation bit of each color is as follows. .
(Display period of the lowest gradation bit) = (1/60) × (1/3) × (1/256) = 21.7 μs

(4) During the display period of the least significant gradation bit, display switching of all pixels of the light modulation element and data transfer of a bit plane to be displayed next must be performed. When the number of pixels of the light modulation element is, for example, 1920 × 1080, a transfer rate of about 100 Gbps is required. Since the data transfer speed that can be supported is limited by the circuit configuration of the light modulation element, the light modulation element designed for 60 fps, for example, cannot be driven at double speed to improve image quality. In order to increase the number of pixels, it is necessary to design a high-speed circuit correspondingly.

Therefore, it is desired to develop a display device capable of increasing the frame rate and the number of pixels.

Hereinafter, in the present embodiment, as compared with the display device according to the comparative example, by extending the display period of the lowest gradation bit, a longer data transfer period is ensured, and a higher frame rate and a higher pixel count are achieved. The technology to be realized will be described.

<1. First Embodiment>
[1.1 Configuration of Display Device According to First Embodiment]
(Overall configuration of display device)
FIG. 2 schematically illustrates a configuration example of the display device according to the first embodiment of the present disclosure. FIG. 2 illustrates a single-panel projector 10 as an example of the display device.

The projector 10 includes a plurality of light sources, a plurality of condensing optical systems, a color combining unit 13, an illumination optical system 14, a TIR (Total Internal Internal Reflection) prism 15, a display panel 16, and a projection optical system 17. Have.

光源 Each of the plurality of light sources outputs a color light which is a source of the illumination light. The plurality of light sources include a red light source 11R, a green light source 11G, and a blue light source 11B. Each of the plurality of light sources is composed of a solid-state light source such as a semiconductor laser (LD: Laser Diode) or an LED (Light Emitting Diode).

The plurality of light-collecting optical systems include a red light-collecting optical system 12R, a green light-collecting optical system 12G, and a blue light-collecting optical system 12B. Each of the red light collecting optical system 12R, the green light collecting optical system 12G, and the blue light collecting optical system 12B includes a light collecting lens and the like. The red light condensing optical system 12R is provided on the optical path of the red light emitted from the red light source 11R, and condenses the red light toward the color combining unit 13. The green light condensing optical system 12G is provided on the optical path of the green light emitted from the green light source 11G, and condenses the green light toward the color combining unit 13. The blue light condensing optical system 12B is provided on the optical path of the blue light emitted from the blue light source 11B, and condenses the blue light toward the color combining unit 13.

The color combining unit 13 has a first dichroic mirror 31 and a second dichroic mirror 32. The first dichroic mirror 31 is provided on an optical path of blue light and green light. The first dichroic mirror 31 has a property of transmitting blue light and reflecting green light, and combines the optical paths of blue light and green light. The second dichroic mirror 32 is provided on an optical path of the blue light, the green light, and the red light after being combined by the first dichroic mirror 31. The second dichroic mirror 32 has a property of transmitting blue light and green light and reflecting red light, and combines the optical paths of blue light and green light with the optical path of red light.

The illumination optical system 14 includes a light collecting optical system 41, a light pipe 42, and a light collecting optical system 43. Each color light from a plurality of light sources enters the illumination optical system 14 via the color synthesis unit 13. The condenser optical system 41 and the condenser optical system 43 include a condenser lens and the like. The condensing optical system 41 condenses each color light toward the light pipe 42. The light pipe 42 equalizes each color light to generate illumination light of each color. The condensing optical system 43 condenses the illumination light of each color from the light pipe 42 toward the TIR prism 15. The display panel 16 is illuminated at a desired angle by the illumination light of each color generated by the illumination optical system 14 via the TIR prism 15.

The TIR prism 15 has a pair of prisms having a triangular cross section. The TIR prism 15 deflects illumination light from the illumination optical system 14 toward the display panel 16 at a desired angle. Further, the TIR prism 15 emits a projection image from the display panel 16 toward the projection optical system 17.

The display panel 16 is a light modulation element such as a mirror array device having a plurality of mirrors. The display panel 16 generates a projection image by modulating the illumination light for each color based on the image signal Vin. When the display panel 16 is formed of a mirror array device, the illumination light is deflected toward the projection optical system 17 via the TIR prism 15 by changing the tilt angle of each mirror based on the image signal Vin. The mirror array device is a micromirror array device such as a DMD (Digital Micromirror Device) in which a plurality of micromirrors corresponding to pixels are arranged in an array (matrix).

The projection optical system 17 includes, for example, a plurality of lenses, and projects a projection image generated by the display panel 16 onto a projection surface such as a screen 18.

FIG. 3 schematically shows an example of a frame configuration of an image in the projector 10.

The projector 10 uses a single display panel 16 and is a so-called single-panel type, and performs full-color display in a time-division manner. When performing color display, one frame is equally divided into R, G, and B sub-frames for display as shown in FIG. Light of each wavelength of R, G, and B is emitted from the plurality of light sources in a time division manner in synchronization with the period of the subframe. The display panel 16 is irradiated with illumination light of each color in a time-division manner. The display panel 16 generates a projection image of each color in a time-division manner with respect to the illumination light of each color in synchronization with the timing of irradiation of each color light.

(Configuration of display device control system)
FIG. 4 schematically illustrates a configuration example of a control system of the projector 10.

The projector 10 includes a sub-frame control unit 51, a PWM sequence control unit 52, a bit plane generation unit 53, and a light source output control unit 54.

The sub-frame control unit 51 controls the period of each color sub-frame in one frame of the input image signal Vin.

The PWM sequence control unit 52 is a period control unit that controls a display period for each gradation bit of each color within a period of a subframe of each color. As shown in FIGS. 6 and 8 described later, the PWM sequence control unit 52 sets the display period of the lowest gradation bit of the plurality of gradation bits in the subframe period of each color to T1 and the display period of the lowermost gradation bit to be lower than the lowest. Assuming that the display period of the gradation bit of one higher order is T2,
The display period of each gray scale bit on the display panel 16 is variably controlled so that T2 ≧ T1> T2 · 1/2. When the display period T1 of the lowermost grayscale bit exceeds the display period T2 of the uppermost grayscale bit, the grayscale relationship between the lowermost grayscale bit and the upper grayscale bit is reversed. Would. When the display period T1 of the lowermost grayscale bit is less than half of the display period T2 of the grayscale bit of the next higher level, the display period T1 of the lowermost grayscale bit becomes the same as that of a general PWM type display device. It becomes equal to or less than that, and as shown in FIG. 7 described later, there is no room in the transfer time of the data to be transferred next, and a failure occurs in the data transfer.

The bit plane generation unit 53 generates bit plane data for each gradation bit corresponding to each of the plurality of gradation bits and displayed during the sub-frame of each color based on the image signal Vin. The bit plane generation unit 53 transfers the generated bit plane data for each gradation bit to the display panel 16 for each gradation bit prior to the display period for each gradation bit.

As shown in FIGS. 6 and 8 described later, the light source output control unit 54 determines the light source output control unit 54 based on the display period for each gradation bit of each color within the subframe period of each color determined by the PWM sequence control unit 52. , The output (light emission timing and light emission intensity) of each light source of the red light source 11R, the green light source 11G, and the blue light source 11B. The light source output control unit variably controls the output of each light source in at least the display period of the lowest gradation bit. The light source output control unit 54 outputs the output of each light source during the display period of the lowest gradation bit to the light source of each light source during the display period of the other gradation bits other than the lowest gradation bit among the plurality of gradation bits. Vary to output. As shown in FIGS. 6 and 8 described below, the light source output control unit 54 lowers the output of each light source during the display period of the lowest gradation bit than the output of the light source during the display period of the other gradation bits. Let it.

The display panel 16 modulates the illumination light based on the data of the bit plane for each gradation bit within the display period allocated to each of the plurality of gradation bits.

[1.2 Control Operation of Display Device According to First Embodiment]
FIG. 5 is a timing chart illustrating an example of light emission control of a light source in a display device according to a comparative example. FIG. 6 is a timing chart illustrating an example of light emission control of the light source in the display device (projector 10) according to the first embodiment. FIG. 7 is a timing chart illustrating an example of a transfer timing of data transfer for each gradation bit in the display device according to the comparative example. FIG. 8 is a timing chart illustrating an example of a transfer timing of data transfer for each gradation bit in the display device according to the first embodiment.

FIGS. 5 to 8 show timing charts in an arbitrary sub-frame period among the sub-frames of each color shown in FIG. In the display device according to the comparative example and the first embodiment, the same light emission control is performed for each color within the subframe period of each color.

5A and FIG. 6A show the state of the brightness (gradation) of the display image (bit plane). (B) shows the output state of the light source (red light source 11R, green light source 11G, or blue light source 11B) of a color corresponding to the color of the display image. (C) shows the state of an arbitrary pixel of the display panel 16. The display panel 16 controls the display state of each pixel to two states of ON / OFF (light emission (bright) / non-light emission (dark)). (D) shows the transfer timing of the bit plane data for each gradation bit transferred from the bit plane generation unit 53 to the display panel 16.

In the display device according to the comparative example and the first embodiment, as shown in FIGS. 5 and 6, (A) and (D), and FIGS. Bit plane data is transferred in the order of b4, b3, b2, and b1, and the bit plane of each gradation bit is displayed. Here, the least significant gradation bit is b1, the gradation bit one stage higher than the gradation bit b1 is b2, the gradation bit one stage higher than the gradation bit b2 is b3, and the gradation bit b3 is the same. The gradation bit one step higher is b4.

FIG. 7 shows a more specific state of brightness (gradation) of a display image (bit plane) and a transfer timing of bit plane data in the display device according to the comparative example. FIG. 7 shows, as a specific example, the state of the bit plane for each gray scale bit corresponding to the 16 gray scales, 15 gray scales, and 14 gray scales. FIG. 8 shows a comparison between the display period of each gradation bit in the display device according to the comparative example and the display period of each gradation bit in the display device (example) according to the first embodiment. FIG. 8 shows the output state of the light source and the transfer timing of bit plane data in the display device according to the first embodiment.

As shown in FIGS. 5A, 7 and 8, in the display device according to the comparative example, for example, the display period T3 of the gradation bit b3 is １／ of the display period T4 of the gradation bit b4, The display period T2 of the gradation bit b2 is １／ of the display period T3 of the gradation bit b3, and the display period T1 of the gradation bit b1 is の of the display period T2 of the gradation bit b2.

In the display device according to the comparative example, as shown in FIG. 5B, only the color switching is performed by switching the subframe, and the output of the light source is controlled to be constant during the subframe period of each color. You.

On the other hand, in the display device according to the first embodiment, as shown in FIGS. 6A and 6B and FIG. The output of the light source in the display period T1 of b1 is made lower than the output of the light source in the display period of another gradation bit. In the display device according to the first embodiment, in order to maintain the original brightness of the image by the reduction in the output of the light source, the PWM sequence control unit 52 is more compared to the display device according to the comparative example. The display period T1 of the lower gradation bit b1 is lengthened. Further, in the display device according to the first embodiment, as shown in FIG. 8, since the entire period of the subframe is the same as that of the comparative example, the display period T1 of the lowermost gradation bit b1 is made longer. As a result, the PWM sequence control unit 52 appropriately adjusts the display period of the other gradation bits. For example, in the example of FIG. 6B, the display periods T4 and T3 of the gradation bits b4 and b3 are adjusted to be shorter than in the display device according to the comparative example. In this case, in the example of FIG. 6B, the light source output control unit 54 is compared with the display device according to the comparative example in order to maintain the original brightness of the image by shortening the display periods T4 and T3. The output of the light source in the display periods T4 and T3 of the gradation bits b4 and b3 is increased. In the example of FIG. 8, the display period T4 of the gradation bit b4 is adjusted to be shorter than that of the display device according to the comparative example. In this case, in the example of FIG. 8, in order to maintain the original brightness of the image by the shortened display period T4, the light source output control unit 54 sets the gradation bit b4 to be smaller than that of the display device according to the comparative example. The output of the light source in the display period T4 is increased.

(About data transfer time)
Next, the relationship between the display period T1 of the lowest gradation bit b1 and the transfer time of bit plane data will be described.

In the display device according to the comparative example, assuming that the display period T1 (PWM width) of the least significant gradation bit b1 is T_b1, as shown in FIGS. 5A and 5D, FIGS. The data transfer time T_d of the bit plane for each gradation bit can be secured at most only up to T_d = T_b1. In the display period T1 of the lowest gradation bit b1, the data of the bit plane of the first gradation bit (b4) in the next subframe is transferred. For this reason, if the display period T1 of the least significant gradation bit b1 is too short, as shown in FIG. 7, there is no room in the transfer time of the next data to be transferred, and a failure occurs in the data transfer.

In the display device according to the comparative example, the actual gradation (brightness) is an integral of the brightness due to the PWM control. Therefore, if the output of the light source of the lowest gradation bit b1 is P_b1,
P_b1 × T_b1.

On the other hand, in the display device according to the first embodiment, the output (P_b1_new) of the light source of the lowest gradation bit b1 is changed by the light source output control unit 54 to the output (P_b1) of the display device according to the comparative example. ) Is controlled (P_b1> P_b1_new). In this case, if the same gradation (brightness) as that of the display device according to the comparative example is to be displayed for the least significant gradation bit b1, the following relationship is established. Note that the display period T1 (PWM width) of the least significant gradation bit b1 in the display device according to the first embodiment is T_b1_new.
P_b1 × T_b1 = P_b1_new × T_b1_new

Here, from the relationship P_b1> P_b1_new, the relationship becomes T_b1 <T_b1_new. Therefore, in the display device according to the first embodiment, with respect to the data transfer time T_d, T_b1_new> T_d, and as shown in FIG. 5D and FIG. 6D and at the bottom of FIG. 7 and FIG. As compared with the display device according to the example, a large margin is provided for the data transfer time.

[1.3 Effects]
As described above, according to the display device according to the first embodiment, at least the display period of the lowest gradation bit and the output of the light source are optimized. Can be performed.

According to the display device according to the first embodiment, it is possible to extend the display period of the least significant gradation bit as compared with a general PWM type display device. It is possible to secure a long data transfer time. That is, high frame rate and high resolution data can be transferred within the display period of the lowest gradation bit without increasing the data transfer speed. As a result, it is possible to increase the frame rate and increase the number of pixels while maintaining a circuit configuration with a low data transfer speed.

効果 Note that the effects described in this specification are merely examples, and the present invention is not limited thereto. Other effects may be provided. The same applies to the effects of the other embodiments described below.

[1.4 Modification of First Embodiment]
(First Modification)
FIG. 9 illustrates an example of light emission control of a light source in a display device according to a first modification of the first embodiment.

In the display device according to the first embodiment, the light source output control unit 54 decreases the output stepwise as the output of the light source at the start of the subframe period is high and the end of the subframe period is approaching. Although an example in which such control is performed has been described, light emission control as illustrated in FIG. 9 may be performed in response thereto. That is, the light source output control unit 54 sets the plurality of light source outputs so that the output of the light source at the start of the sub-frame period and the output of the light source at the end of the sub-frame period are close to each other (to be substantially the same). The output of the light source in each display period of the gray scale bit may be changed.

By controlling the output of the light source at the start of the sub-frame period and the output of the light source at the end of the sub-frame period to be substantially equal to each other, at the time of display transition between two adjacent sub-frames (For example, at the time of transition from the red sub-frame to the green sub-frame shown in FIG. 3), the change in luminance is small, so that flicker and other flickers are suppressed, and the image quality is improved.

Other configurations, operations, and effects may be substantially the same as those of the display device according to the first embodiment.

(Second Modification)
FIG. 10 illustrates an example of light emission control of a light source in a display device according to a second modification of the first embodiment. FIG. 11 illustrates an example of an ideal output waveform and an actual output waveform of the light source in the display device according to the first embodiment.

In the display device according to the first embodiment and the display device according to the first modification, the light source output control unit 54 discretely changes the output control of the light source. In consideration of the light emission rising characteristic of FIG. 10, continuous light emission control as shown in FIG. 10 may be performed. That is, the light source output control unit 54 may continuously change the output of the light source in each display period of the plurality of gradation bits.

{For example, as shown by a dotted line in FIG. 11, ideally, it is desirable that the light source emits light discretely in accordance with the display period of each gradation bit. However, there is actually an emission characteristic of a solid light source. For this reason, as shown by the solid line in FIG. 11, an output change that deviates from the ideal value occurs, and the display characteristics (gamma curve) of the gradation deviate from the assumption. On the other hand, by performing the light emission control such that the output changes continuously as shown in FIG. 10, the portion where the output changes suddenly is reduced, so that a more accurate gamma curve can be displayed.

Other configurations, operations, and effects may be substantially the same as those of the display device according to the first embodiment or the display device according to the first modification.

<2. Second Embodiment>
Next, a display device according to a second embodiment of the present disclosure will be described. In the following, portions that are substantially the same as the components of the display device according to the first embodiment are given the same reference numerals, and descriptions thereof will be omitted as appropriate.

FIG. 12 is a timing chart illustrating an example of light emission control of the light source in the display device according to the second embodiment. FIG. 13 shows the output waveform of the light source in the display device according to the first embodiment (FIG. 13A) and the output waveform of the light source in the display device according to the second embodiment (FIG. 13B). ) Is shown.

In FIG. 12, (A) shows the state of the brightness (gradation) of the display image (bit plane). (B) shows the output state of the light source (red light source 11R, green light source 11G, or blue light source 11B) of a color corresponding to the color of the display image. (C) shows the state of an arbitrary pixel of the display panel 16. (D) shows the transfer timing of the bit plane data for each gradation bit transferred from the bit plane generation unit 53 to the display panel 16.

In the display device according to the second embodiment, the light source output control unit 54 controls the sub-color of each color similarly to the display device according to the comparative example (FIG. 5) except for the display period T1 of the lowest gradation bit b1. Light emission control is performed so that the output of the light source is constant during the frame period. However, in the display device according to the second embodiment, the light source output control unit 54 partially controls the output of the light source during the display period T1 of the lowest gradation bit b1 to display another gradation bit. The output of the light source during the period. The display period T1 of the lowermost gradation bit b1 is set to a period of switching between subframes of each color.

In the example of FIGS. 12 and 13B, as in the display device according to the first embodiment, as compared with the display device according to the comparative example, the PWM sequence control unit 52 has the lowermost gradation bit. The display period T1 of b1 is extended from T_b1 to T_b1_new. In the display device according to the second embodiment, the light source output control unit 54 according to the comparative example uses the light source output control unit 54 according to the comparative example in order to maintain the original brightness of the image by the length of the display period T1 of the lowest gradation bit b1. Compared with the display device, the output of the light source in the display period T1 of the lowest gradation bit b1 is reduced in the middle of the display period T1. In the examples of FIGS. 12 and 13B, the display period T_b1_new of the lowest gradation bit b1 in the display device according to the second embodiment is set to the lowest gradation bit in the display device according to the comparative example. It is about twice as long as the display period T_b1 of b1. For this reason, the light source output control unit 54 controls the output of the light source to be turned off when about half of the display period T1 has elapsed.

According to the display device according to the second embodiment, the light emission time of the light source is shortened only within the display period T1 of the lowest gradation bit b1, so that the display device is compared with a general PWM type display device. Thus, the display period T1 of the lowest gradation bit b1 can be lengthened. In the display device according to the second embodiment, as compared with a general PWM type display device, light emission adjustment is performed only in the display period T1 of the lowest gradation bit b1, and light emission in other display periods is performed. No adjustments need to be made.

<3. Other Embodiments>
The technology according to the present disclosure is not limited to the description of the above embodiments, and various modifications can be made.

For example, in the first embodiment, a case has been described in which the display device of the present disclosure is applied to a projector, but the display device of the present disclosure can be applied to devices other than the projector.

For example, the present technology can also have the following configurations.
According to the present technology having the following configuration, at least the display period of the lowest gradation bit and the output of the light source are optimized, so that it is possible to increase the frame rate and increase the number of pixels.

(1)
A light source that outputs light that is a source of illumination light,
Within a display period allocated to each of the plurality of gradation bits, a light modulation element that modulates the illumination light based on bit plane data for each gradation bit,
T2 ≧ T1> T2 ・ 1/2, where T1 is the display period of the lowermost grayscale bit of the plurality of grayscale bits and T2 is the display period of the grayscale bit one level higher than the lowermost grayscale bit. A period control unit that variably controls a display period for each of the gradation bits in the light modulation element,
A light source output control unit that variably controls an output of the light source during a display period of at least the least significant gradation bit.
(2)
The light source output control unit outputs the output of the light source during the display period of the least significant grayscale bit during a display period of another grayscale bit other than the least significant grayscale bit of the plurality of grayscale bits. The display device according to (1), wherein the display device changes the output of the light source.
(3)
The display according to (2), wherein the light source output control unit lowers an output of the light source during a display period of the least significant gray scale bit than an output of the light source during a display period of the other gray scale bit. apparatus.
(4)
The period control unit controls a display period for each of the grayscale bits within a period of one subframe,
The light source output control unit, so that the output of the light source at the start of the period of the sub-frame and the output of the light source at the end of the period of the sub-frame approach each other, each of the plurality of gradation bits The display device according to (2) or (3), wherein an output of the light source is changed during a display period.
(5)
The display device according to any one of (2) to (4), wherein the light source output control unit continuously changes the output of the light source in each display period of the plurality of grayscale bits.
(6)
The light source output control unit partially lowers the output of the light source during the display period of the least significant gray scale bit than the output of the light source during the display period of the other gray scale bit. The display device according to (1).
(7)
A bit for generating bit plane data for each gradation bit based on an image signal and transferring the bit plane data to the light modulation element for each gradation bit prior to a display period for each gradation bit The display device according to any one of (1) to (6), further including a plane generation unit.
(8)
A projection optical system that projects an image generated by the light modulation element,
The display device according to any one of (1) to (7), configured as a projector.

This application claims priority based on Japanese Patent Application No. 2018-154407 filed on August 20, 2018 by the JPO, and hereby incorporated by reference in its entirety. Incorporated into application.

Various modifications, combinations, sub-combinations, and modifications may occur to those skilled in the art, depending on design requirements and other factors, which are within the scope of the appended claims and their equivalents. It is understood that it is.

Claims

A light source that outputs light that is a source of illumination light,
Within a display period allocated to each of the plurality of gradation bits, a light modulation element that modulates the illumination light based on bit plane data for each gradation bit,
T2 ≧ T1> T2 ・ 1/2, where T1 is the display period of the lowermost grayscale bit of the plurality of grayscale bits and T2 is the display period of the grayscale bit one level higher than the lowermost grayscale bit. A period control unit that variably controls a display period for each of the gradation bits in the light modulation element,
A light source output control unit that variably controls an output of the light source during a display period of at least the least significant gradation bit.
The light source output control unit outputs the output of the light source during the display period of the least significant grayscale bit during a display period of another grayscale bit other than the least significant grayscale bit of the plurality of grayscale bits. The display device according to claim 1, wherein the output is changed with respect to an output of the light source.
3. The display device according to claim 2, wherein the light source output control unit reduces an output of the light source during a display period of the least significant grayscale bit than an output of the light source during a display period of the other grayscale bit. 4. .
The period control unit controls a display period for each of the grayscale bits within a period of one subframe,
The light source output control unit, so that the output of the light source at the start of the period of the sub-frame and the output of the light source at the end of the period of the sub-frame approach each other, each of the plurality of gradation bits The display device according to claim 2, wherein an output of the light source is changed during a display period.
The display device according to claim 2, wherein the light source output control unit continuously changes the output of the light source in each display period of the plurality of gradation bits.
The light source output control unit partially reduces the output of the light source during the display period of the least significant gradation bit to be lower than the output of the light source during the display period of the other gradation bit. The display device according to claim 1.
A bit for generating bit plane data for each gradation bit based on an image signal, and transferring the bit plane data for each gradation bit to the light modulation element prior to a display period for each gradation bit. The display device according to claim 1, further comprising a plane generation unit.
A projection optical system that projects an image generated by the light modulation element,
The display device according to claim 1, wherein the display device is configured as a projector.