JP2002297085A - Gradation display method and gradation display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gradation display method and a gradation display device, capable of realizing high picture quality and high gradation, without having to lower light use efficiency with consideration for controversial points of the conventional technology. SOLUTION: In the gradation display method which is to be conducted in the gradation display device provided at least with a spatial optical modulation element and a light source for illuminating the element, the intensity modulation of the light source is carried out, and in the spatial optical modulation element, one unit for performing gradation is constituted by a plurality of pixels and each pixel is made to individually twin on/off area modulation display.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gradation display method and a gradation display device used for a projector or a finder type display.

[0002]

2. Description of the Related Art Various methods of displaying gradation in a spatial light modulator have been reported and commercialized. The gradation is realized by modulating the amount of light transmitted or reflected by the pixel. Various modulation methods have been put to practical use. In response to the recent increase in pixel density and resolution, a spatial light modulator (light valve; hereinafter, referred to as LV) has a digital mirror device (DM) having good switching characteristics.
D), a ferroelectric liquid crystal or the like is used. Since these devices themselves do not have a halftone display, it is necessary to perform a grayscale display by contriving driving. 12 to 15
Fig. 2 shows a comparison of the conventional gray scale display. For comparison, each figure shows a state at the time of 64 gradation display. In the figure, the horizontal axis is the time axis, and basically indicates the period of one frame. The number of gradations (gradation 1, 2, 3, 10) shown in the figure is
Pixels that are turned ON to indicate this gradation are indicated by arrows. FIG. 12 shows an area modulation method as one gradation display method. FIG. 12 shows an area ratio of 1: 8. Each pixel having an area ratio of 1 and an area ratio of 8 is O
N / OFF is possible. In area modulation, one frame is 7
It is divided into subframes. As another method, a pulse width modulation method is used in which one frame is divided into a plurality of sub-frames, and pixels are turned on / off in each sub-frame, thereby modulating the amount of light in one frame.

[0003] FIG. 13 shows a display using only pulse width modulation. The frame is divided into 63 in order to simply express the gradation by the pulse width. Examples of the high frame frequency include a field sequential method in which RGB is driven in a time-division manner, and a driving method in which an image from an LV is moved in a time-division manner to increase the definition. Also, "Osamu Akimoto
et al, “Hight-resolution FLC Microdisplay”, Projec
According to the technology disclosed in “Exhibition Display 2000. Vol. 3954 (2000) pp. 104-110” (hereinafter referred to as “prior art 1”), light source modulation is performed at an early part of a frame, and most of the frame is modulated by pulse width modulation. The driving method has been announced. By combining light source modulation and PWM, it has become possible to lengthen a subframe. FIG. 14 shows a combination of light source modulation and pulse width modulation. 3 bits are displayed by light source modulation and 3 bits are displayed by pulse width modulation. The frame is divided into ten. In FIG. 14, the vertical axis indicates the light intensity, and the first 3 bits
Indicates light source modulation with an intensity ratio of 1: 2: 4. 4b
After the it-th time, the light source is not modulated and driven at 100% illuminance. LV takes time to rise or fall during driving. During the rise or fall time, an intermediate state of ON / OFF originally assumed for image display occurs, so that the lower the ratio of this portion to the whole, the better the display quality. That is, the longer the sub-frame, the better the display quality. Frame frequency 60
When the frequency is set to Hz, the sub-frame times in FIGS. 12 to 14 have the values shown in Table 7, respectively.

[Table 7] The invention disclosed in Japanese Patent Application Laid-Open No. 7-212686 (hereinafter referred to as "prior art 2") discloses a combination of pulse width modulation of a spatial light modulator and light intensity modulation of a light source.
By modulating the light source simultaneously with the LV by this method,
Compared with the conventional method, the number of subframe divisions can be reduced, and it is possible to deal with high gradation.

[0004]

As a method of displaying a gray scale, a method of dividing the time during which one screen is displayed into a plurality of sub-frames and performing ON / OFF of each sub-frame is generally used. Is being done. In order to increase the number of gradations by this method, it is necessary to divide the frame into more subframes. However, since the LV has a response speed, if the shortest subframe is shorter than the LV response speed,
Sufficient display cannot be performed during the subframe, and the display quality deteriorates. On the other hand, as a gradation display method that does not degrade display quality, there is a method of expressing gradation by the number of pixels that are turned ON / OFF collectively by a plurality of existing pixels in the area modulation method. However, in this method, since the number of pixels required for gradation display needs to be grouped together, for example, to display 16 gradations, 4 × 4-1 = 15 pixels are treated as one unit of display, and By performing ON / OFF of the pixel, 0 to 15 (16 gradations) is displayed. in this case,
The resolution of the entire display panel is reduced to 1/15. Further, in the conventional method using only the pulse modulation, the liquid crystal takes a finite rise and fall time, so that the response may not be enough. If the response of the liquid crystal cannot be made in time, the light use efficiency is reduced throughout the gradation display, resulting in a dark display as a whole. Further, in the content of the technique disclosed in the prior art 1, the light source modulates both the pulse width and the intensity to modulate the light amount, and the light source is not modulated, and a spatial light modulator (such as a liquid crystal panel) is used. The gradation display is performed by combining the pulse width modulation. By using light source modulation for the lower order of gradation and performing pulse width gradation for the upper order, this is a driving method with high light utilization efficiency and a relatively small number of divisions. There is a problem that the efficiency is reduced.
Further, in the invention disclosed in the prior art 2, the light source intensity modulation is performed to compensate for the disadvantage of the simple pulse width modulation, and the light use efficiency is extremely reduced because the light source intensity modulation is performed over one frame. There was a problem of doing. The present invention has been made in view of the above-described problems of the related art, and provides a gradation display method and a gradation display device that realize high image quality and high gradation without lowering light efficiency.

[0005]

A gradation display according to claim 1.
The method includes at least a spatial light modulator and an
-Level display method performed in a gray-scale display device provided with a light source
Performing intensity modulation of the light source and performing spatial light modulation.
The element is composed of a plurality of pixels, one unit for performing gradation.
Each pixel individually displays ON / OFF and area modulation display
Do. In the gradation display method according to the second aspect, the first aspect is described.
Area modulation is composed of two pixels
The number of gradations displayed by one color constituting the color display is 2
ⁿWhen expressed as, at least one unit for display is changed in area.
The area ratio for adjusting is approximately 1: 2 when n is an even number.^{n / 2}
Where n is an odd number, approximately 1: 2^{( n-1) / 2}Noseki
Show the person in charge. In the gradation display method according to the third aspect,
Or, in the gradation display method described in 2, the one frame
When n is an even number, the number of divisions into subframes is n / 2.
When n is an odd number, a relationship of (n + 1) / 2 is shown.
For the light source modulation used, the sub-frame
Number of consecutive natural numbers to be divided into
Added to each frame, and the added number is set to m.
And the intensity of the light source in each subframe, that is, the subframe
(M-1) is approximately (maximum illuminance of the light source) x (1 /
2)^m-1Indicated by In the gradation display method according to the fourth aspect, the contract
The gradation display method according to claim 1, claim 2, or claim 3
In this case, as a method of modulating pixels for performing area modulation,
A pal whose value within the frame is multiplied by 100%
Use width modulation. The gradation display method according to claim 5,
Is a gradation display according to any one of claims 1 to 4.
In the method, the image is time-divided and divided in one frame.
The displayed image is displayed on the spatial light modulator. The gradation according to claim 6.
In the display device, at least the spatial light modulator and the light
Gradation display performed by a gradation display device having a light source
An apparatus according to any one of claims 1 to 5,
It is characterized in that gradation display is performed.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a gradation display method for a spatial light modulator (light valve, hereinafter referred to as LV). More specifically, the display time (hereinafter, referred to as a sub-frame time) divided for displaying a gray scale is lengthened, thereby alleviating the limitation on the number of gray scales displayed due to the response speed of the LV. The following shows specific examples of the present invention,
explain. As a method of displaying a gray scale, a method of dividing a time during which one screen is displayed into a plurality of subframes and performing ON / OFF of each subframe is generally performed. In order to increase the number of gradations by this method, it is necessary to divide the frame into more subframes.
However, since the LV has a response speed, if the shortest sub-frame is shorter than the LV response speed, sufficient display cannot be performed during the sub-frame, and the display quality deteriorates. The present invention
Light intensity modulation of a light source (hereinafter referred to as light source modulation) in a display device using a light source that illuminates a gradation display with at least LV.
And a duty ratio of LV (hereinafter, referred to as PWM), and a gradation display method in which the minimum unit for displaying is modulated by an area ratio of a plurality of pixels (hereinafter, referred to as area modulation).

FIG. 1 shows a structural diagram of a monochromatic projector using an ND filter. The continuous light from the lamp 25 is divided into the respective intensities by the ND filter 22 whose transmittance is defined in the circumferential direction. One example is 1: 2: 4: 8. The polarization conversion and the optical axis are adjusted by the polarization conversion device 26, reflected by the PBS 24, and incident on the LV 23. LV2
Only the light whose polarization direction is modulated by 3 is transmitted through the PBS 24 and projected from the projection lens 27 onto the screen. By adding a rotating color filter to this configuration and rotating the ND filter 22 once for each of the RGB colors, colorization can be realized. Here, 21 is a perspective view of the ND filter 22. The controller 50 controls the LV 23 and the lamp 25 in a control method described later. As a method of realizing high resolution, a method of moving (shifting) pixels for each screen and displaying an image corresponding to the position can be used. (Hereinafter, this method is referred to as pixel shift.) Pixels are shifted by a piezo element or the like. FIG. 2 is an explanatory diagram around the LV23. The LV 23 is provided with piezo elements 32 and 33 for moving in two axial directions. LV23
Shifts the LV 23 in the direction described near the piezo element by the operation of each piezo element.

FIG. 3 shows a display device of the present invention. The LEDs 45 having the respective emission colors of RGB, which are light sources, sequentially emit RBG. The light from the LED 45 is transmitted to the polarization converter 4
The polarization conversion and the optical axis are adjusted in 6, and the light is reflected by the PBS 44 and enters the LV 43. Only the light whose polarization direction is modulated by the LV 43 passes through the PBS 44 and is projected from the projection lens 47 onto the screen. The drive is performed by setting the LED 45 to R, every 1/12 (= 1.39 msec) of 60 Hz per frame.
G and B are switched and turned on, and data corresponding to the LED emission color is displayed on the LV. RGB is 4.17mse
After the display of c, the piezo element 41 shifts to the right in the horizontal direction in the figure, and after displaying RGB again, the piezo element 4 is displayed.
1 is not changed, but is shifted upward in the figure by the piezo element 42. Table 1 below shows the operation of the piezo and the shift state of the LV.

[Table 1] The moving directions of the LVs in Table 1 are defined as upper, lower, left, and right with respect to FIG. 2, and indicate the moving directions from the previous position by the piezo operation. One configuration of the present invention clarifies the relationship between the number of gray scales to be displayed and the area ratio of dividing a pixel used for area modulation. For area modulation, processing accuracy is required when the minimum number of divisions for displaying gradation increases. In addition, the number of signal lines increases due to the necessity of individually controlling ON / OFF, and the LV interface becomes complicated and costs increase. The effect is high in ensuring the gradation, and the preferred number of divisions is 2. If the number of gradations of one color for performing color display forming an image is expressed as 2 ⁿ , the area ratio forming a pixel is approximately 1: (2 ^{n / 2} ) when n is an even number.
When n is an odd number, it is approximately 1: (2 ^{(n-1) / 2} ). Here, when n is an odd number, there are a method of summing up to an even number of n-1 of the present invention and a method of summing up to an even number of n + 1 of the present invention. In the method of grouping into n + 1, the area ratio for performing the area modulation becomes larger than that in the method of grouping with n−1, and a finer process is required to be eliminated at the time of manufacturing.
As a result, there is a possibility that the manufacturing cost will be increased and the yield will be reduced if the values are combined into n + 1. For the above reasons, in the present invention, when n is an odd number, the processing cost is reduced by combining the values into an even number of n-1. The range of the area is desirably suppressed to within ± 20% in consideration of the variation in the area after processing and the unevenness of illumination light. By emphasizing gradation and maintaining processing accuracy, ± 1
Within 0% is a more desirable range. The most preferable dimension is ± 5 in order to increase the reproducibility of gradation.
%.

Next, a specific example will be described. · N is than 256 gradations = ²⁸ in the case of an even number (256-gradation display, a n = 8 At this time, the area ratio of pixels to be an area modulation, 1:. 2 ^{n / 2} from 1:16 Since n = 8 is an even number, the number of divisions into sub-frames is n / 2 = 4. When the intensity of the light source is 4, 3, 2, 1 for each divided frame, Assuming that the corresponding numerical value is m, the light source intensity of each sub-frame is sequentially represented by (maximum illuminance of the light source) × (）) ^{m -1} where m is the maximum value and the number of frame divisions. In the above example, m = 4, 3, 2, 1. In this example, assuming that the maximum illuminance of the light source is 1, each subframe is ８: １ ／: １ ／. : 1, the maximum illuminance of the light source is 8
Then, it becomes 1: 2: 4: 8. In the gradation method, the intensity of the light source is sequentially indicated as approximately (the maximum illuminance of the light source) × (１ ／) ^{m −1} . In this case, the division number m is 4, and the intensity ratio is 1: 2: 4: 8. FIG. 5 shows the state of division in this case. 1 to 4 pixels with an area ratio of 1 and an area ratio of 16
Are shown in 5-8. Table 2 shows the relationship between each pixel number in FIG. 5, the light source intensity by light source modulation, and the light intensity (hereinafter, referred to as LV intensity) obtained from the pixel.

[Table 2] As is clear from Table 2, the LV intensity was 2 between 1 and 128.
It takes all values of powers of. As a result, the combination of area ratios of 1 and 16 pixels turns off all.
In this case, since the LV intensity becomes 0, 25 from 0 to 255
Six gradations can be displayed. For reference, a simple P
In WM, one frame needs to be decomposed into 255.

An example in which n is an odd number will be described below. 1
From 28 gradations = 2 ⁷ , n = 7. In this case, the area ratio is 1: 8 from (1: 2 ^{( n-1) / 2} ). The number of divisions into subframes is divided into (n + 1) / 2, in this case four. The light source intensity of each sub-frame is sequentially (maximum illuminance of the light source) × (where m is a corresponding numerical value when 4, 3, 2, and 1 are sequentially associated with each divided frame). (）) ^{M −1} . Here, m is a natural number whose maximum value is the number of frame divisions.
In the above example, if m = 4, 3, 2, 1 and the maximum illuminance of the light source is 1, then each sub-frame is 1/8: 1/4:
1/2: 1, and the maximum illuminance of the light source is 8, 1: 2: 4:
It becomes 8. The intensity of the light source is sequentially (maximum illuminance of the light source) × (1
/ 2) The intensity is indicated by ^{m −1} . In this case, the division number m =
4, and the intensity ratio is 1: 2: 4: 8. In FIG. 6, a pixel having an area ratio of 1 has an unused subframe, but the total number of divisions is set to a necessary minimum.
In the present invention, 128 gradations can be displayed in four divisions. In addition, regarding the shape of each pixel forming one pixel,
The present invention is not limiting. Table 3 shows the relationship between each pixel number in FIG. 6, the light source intensity by light source modulation, and the light intensity (hereinafter, referred to as LV intensity) obtained from the pixel.

[Table 3] Here, in order to display 128 gradations by simple PWM,
One frame must be divided into 127 frames. (See FIG. 13) The range of light source modulation is approximately (the maximum illuminance of the light source) × (1
/ 2) For each illuminance indicated by ^{m- 1} , the range is ± 1
It is desirable to adjust within the range of 0%. From the viewpoint of the reproducibility of the gradation, it is more preferable to adjust within the range of ± 5%. In light source modulation, the value of the above equation becomes a theoretical value, but a natural display can be obtained by performing visibility correction or the like in the above range as necessary.

Another object of the present invention is to reduce the burden of fine processing of the pixel area in order to realize a display device of high gradation display. Specifically, a particularly problem in processing is to manufacture a pixel having a small area. Therefore, in the present invention, by adjusting the duty ratio of the smaller pixel in the sub-frame, the same effect as that of performing further fine processing is realized. An example will be described. As explained above, 25
Six gradations can be realized by dividing one unit pixel of the LV at an area ratio of 1:16 and dividing a frame into four. In the present invention, the 256 gradations are realized with an area ratio lower than 1:16. By using an LV having an area ratio of 1: 8, pixels having an area ratio of 1 are driven at a duty ratio of 中 during each subframe, and the number of divisions per frame is set to 4, so that 256 gradations can be displayed. It becomes possible. FIG. 7 shows a timing chart. Pixels with an area ratio of 1: 8,
7, pixels having an area ratio of 1 are driven at 1/2 duty in a subframe. The ratio of the element area itself is as follows: 1 to 4 pixels is 1 to 5 to 8 pixels.
Although it has an area ratio of 8, the result of driving is a ratio of 1:16.

Table 4 shows details of each item. The LV intensity (relative value) takes all values of powers of 2 between 1 and 128. Thus, when all of the pixels are OFF, the LV intensity = 0 when a combination of the area ratios is 1: 8 pixels, so that 256 gradations from 0 to 255 can be displayed.

[Table 4] Further, it is possible to correct the pixel area variation by adjusting the period (duty ratio) of performing PWM in the sub-frame using this method. This makes it possible to reduce gradation display unevenness due to variations in processing accuracy. For image data originally larger than the number of pixels of LV, LV
There is a driving method (hereinafter, referred to as pixel shift) for achieving high resolution by displaying video information from one pixel at different positions on a screen in a time-division manner. Since the pixel shift displays a plurality of screens, in addition to the normal driving method, the sub-frame time is shortened. The present invention realizes a longer sub-frame for gradation display than the conventional method, and reduces the limit of the response speed to the higher resolution.

An example will be described. At a frame frequency of 60 Hz, 2
A description will be given of a case where field sequential is used for 56 gradations and colorization, and four pixels are shifted as pixel shift. FIG. 8 illustrates the pixel shift. FIG. 8 shows a case where four pixels are shifted. The LV sequentially displays data corresponding to four pixels on the screen in a time-division manner. The number of pixels to be displayed becomes four times the number of LV pixels by moving the LV itself or an optical means such as a lens, which is an optical element, at high speed. In the driving according to the present invention, (the area ratio is divided into 1:16, and the light source modulation is set to 4 levels (when the maximum illuminance is set to 8,
When the intensity ratio is 1: 2: 4: 8), the subframe period is calculated to be 347 μsec. In this time, not only a digital mirror device (hereinafter referred to as DMD) but also a ferroelectric liquid crystal can be driven at a response speed of about 80 μsec. On the other hand, in the case of displaying gray scales using the conventional PWM alone, the subframe is 11 μsec, and the DMD element (response speed: about 10 μsec) barely rises in the subframe, so that the original image quality cannot be obtained. The light source used in the present invention is not limited except that intensity modulation can be realized, and a laser beam modulated by an LED, an inorganic / organic EL, an electro-optic element (EOM) or modulated by an acousto-optic element (AOM) is used. Can be used. In particular, in view of miniaturization, illuminance, field sequential, and the like, LEDs are promising. As a method of realizing color display, field sequential is effective in reducing LV cost. In this method, one LV is irradiated with red, green, and blue light in a time-division manner (a set of red, green, and blue is used at a frequency of about 120 Hz that does not cause flicker to be detected by human eyes. Red, green, and blue). Is considered as a single frame (360 Hz), and display data corresponding to the irradiated light is displayed on the LV, thereby reducing the number of LVs and reducing cost. Since the field sequential has a high frame frequency in principle as described above, in the conventional gradation display method, the response speed is currently commercialized only with a high-speed response device such as a 10 μsec DMD. It is. By using the gradation display method of the present invention, a projection device having excellent gradation display characteristics can be realized.

As the light source, any light source that can modulate the light source can be used. As examples, the above-described LEDs, lasers, and lamp light sources that perform intensity modulation can be used. As an example of using a lamp light source,
Lamp light can be modulated by disposing a rotating filter and an ND filter whose transmittance is defined in the circumferential direction as shown in FIG. FIG. 11 shows a case where the light source is modulated into four levels. By rotating the filter shown in the figure, the light source intensity modulation is realized without directly modulating the intensity of the lamp by the transmittance of the filter. As an example, it can be used by setting the transmittance ratio of each filter to 1: 2: 4: 8 (8 is the highest illuminance). The LV is not particularly limited. The gray scale display for each pixel can be used even if the pixel itself can display the gray scale, and if only the binary display is used, the gray scale can be displayed by modulation of the ON / OFF time. Since the present invention aims to cope with a high frame rate, a ferroelectric liquid crystal combined with a switching element or a DMD is preferable. The display device according to the present invention can be a projection type such as a front projection type, a rear projection type, or a direct-view type having illumination on a back or a front, and the like.
It can be realized without being limited to the format.

(First Embodiment) Assuming field sequential, a display device having 64 gradations was manufactured and compared. Prototype 1: According to the present invention, one pixel was composed of two pixels having an area ratio of 1: 8. Use LED for lighting, 1, 2, 4
... (the power ratio was adjusted to the power of 2). In the present invention, one frame is divided into three at the timing shown in FIG.
By setting the ratio to 2: 4, 64 gradations could be displayed. Table 5 shows the relationship between the operation of each pixel and the LV intensity. At 60 Hz per frame, the sub-frame for displaying the gradation was 1.9 msec.

[Table 5] Prototype 2: For comparison, one unit to be displayed is divided by area ratio 1:
In the case of using four 2 pixels, an apparatus for displaying 64 gradations as in the case of the prototype 1 was prototyped. The light source modulation was performed at an intensity ratio of 1: 2: 4 as in the case of the prototype 1. As a result, the gray scale display shown in FIG. 10 (Table 6 shows the relationship between the sub-frame and the gray scale display) became possible, and the frame was divided into 5 sub-frames to realize 64 gray scales or more. At one frame of 60 Hz, the subframe was 1.11 msec.

[Table 6] As a result of the comparison, the sub-frame period could be lengthened by the area modulation (specifying the area ratio) of the present invention. Table 6 shows the number of gradations that can be displayed up to the number in the table.

(Second Embodiment) Assuming field sequential, a display device having 256 gradations was manufactured and compared. Prototype 3: According to the present invention, one pixel is composed of two pixels having an area ratio of 1:16.
It was composed of pixels. Using LED for lighting, 1, 2,
The intensity ratio was adjusted to 4 (power of 2). As a result, in the present invention, 256 gradations are displayed by dividing one frame into four at the timing shown in FIG. 5 and setting the LED illuminance in each frame to 1: 2: 4: 8 when the maximum illuminance is 8. We were able to. At one frame of 60 Hz, the sub-frame for displaying the gradation was 1.4 msec. Prototype 4: For comparison, the same as prototype 1 except that one pixel was composed of two pixels of 1: 4. An apparatus having the same configuration was prototyped, and a method for realizing 256 gradations was studied. As a result, if the light source modulation is 1: 2: 4: 8, which is the same as that of the prototype 3, one frame is divided into nine, and at 60 Hz per frame, the sub-frame for displaying the gradation is 617 μsec.
1: 2: 4: 8: When the light source modulation is 16 in lighting daylight
If 16 is set, one frame is divided into seven, and at 60 Hz per frame, the number of sub-frames for displaying gradation is seven.
It becomes 94 μsec. As a result of the comparison, the sub-frame period could be lengthened by the area modulation (area ratio) of the present invention. From the result of the prototype 4 of the comparative example, it is understood that the number of subframes can be reduced by increasing the number of light source modulations. However, switching the light source intensity at a high speed causes an increase in cost. As a realistic modulation number of the light source, 5 gradations or less are desirable. Most preferably, there are four gradations. (In the configuration of the present invention, by using four gradations of light source modulation, 16.77 million colors (256 gradations for each color), which are high-quality computer images, can be realized.)

(Third Embodiment) Using the display device (prototype 1) prototyped in Example 1, a display device with 256 gradations according to the present invention was manufactured. Of the pixels having an area ratio of 1: 8 that constitute one pixel, the driving time of one pixel having an area ratio of 8
1/2 of the pixel. FIG. 7 shows a timing chart. With the driving method according to the present invention, 256 gradations could be displayed by dividing one frame into four and setting the LED illuminance to 1: 2: 4: 8 in each frame. At 60 Hz per frame, the sub-frame for displaying the gradation is:
It was 1.4 msec. For comparison, a comparison was made with the display devices of Example 5 and Prototype 3, which can display the same 256 gradations. The lighting timing of the LED and the number of divisions of one frame are the same, but the area ratio of two pixels constituting one pixel is different. According to the present invention, the area ratio is 1:
8 and 1:16 in the comparative example. As the definition of pixels increases, pixels with a small area are further reduced in size. According to the present invention, it has been found that the steps can be simplified and a high-definition display can be realized at low cost.

(Fourth Embodiment) In FIG. 8, data corresponding to 1 → 2 → 3 → 4 on the screen are sequentially displayed on the LV. In response, the image from the LV is projected onto the corresponding screen. Response speed (rise) is 80
A 64-gradation display device was manufactured using a ferroelectric liquid crystal of μsec and a driving method of performing a pixel shift for displaying an image of four pixels shown in FIG. 8 during a display time of one frame. The gradation display device uses RGB LED arrays as light sources, and realizes field sequential by individually lighting each color. The pixel shift was performed by shifting the LV using a piezo element in two axial directions. In the method according to the invention, an area ratio of 1: 8, LED
Illumination was achieved by driving at an intensity ratio of 1: 2: 4 at the timing shown in FIG. At 60 Hz per frame, the subframe for displaying the gradation was 460 μsec. From the response speed of the used ferroelectric liquid crystal of 80 μsec, it was possible to set an effective display time of 83% of the subframe period. For comparison, a display device was prepared in which the LV used was changed to one having an area ratio of 1: 4. In the display device manufactured for comparison, one frame 6
At 0 Hz, the subframe was 278 μsec.
From the response time of the ferroelectric liquid crystal, the effective display period of the sub-frame was 71%, indicating that the gradation method of the present invention can secure a longer sub-frame period and improve the display quality. .

(Fifth embodiment) Response speed (rise)
Using a ferroelectric liquid crystal of 80 μsec, a 256-gradation display device was manufactured by a driving method of performing a pixel shift for displaying an image of four pixels shown in FIG. 8 during a display time of one frame. The gradation display device uses RGB LED arrays as light sources, and realizes field sequential by individually lighting each color. Pixel shift includes
This was performed by shifting the LV using a piezo element in two axial directions. In the method according to the invention, the area ratio is 1: 1.
6. LED lighting is 1: 2: 4: at the timing shown in FIG.
It was realized by driving at an intensity ratio of 8. 1 frame 6
At 0 Hz, the sub-frame for displaying the gradation was about 340 μsec. From the response speed of the used ferroelectric liquid crystal of 80 μsec, during this sub-frame period, 76%
Can be set as an effective display time. For comparison, a display device was prepared in which the LV used was changed to one having an area ratio of 1: 4. The light source modulation was 1: 2: 4: 8 which is the same as that according to the present invention for comparison. In the display device manufactured for comparison, the subframe was 154 μsec at 60 Hz per frame. From the response time of the ferroelectric liquid crystal, the effective display period of the subframe was 48%, and a decrease in the contrast ratio was observed. In the gradation method of the present invention, no deterioration in image quality was observed. According to the present invention, it has been found that a longer subframe period can be secured, and display quality is improved.

[0020]

According to the first aspect of the present invention, light source modulation, P
By combining WM and area modulation, it was possible to secure a long subframe time for forming a gray scale. As a result, the number of gradations that cannot be displayed due to the limitation of the response speed in the existing LV, the time-division driving, and the driving method of high resolution are realized. According to the second aspect of the invention, by defining the area ratio of the area modulation, the number of divided frames can be reduced, and a long subframe time can be secured. According to the third aspect of the invention, by defining the number of subframe divisions, the number of frame divisions can be reduced, and a long subframe time can be secured. According to the fourth aspect of the present invention, the effect of the small area of the area modulation is realized by adjusting the ON / OFF time (duty ratio) of the pixel, and high gradation display can be performed without miniaturization during processing. Could be realized. Also, the manufacturing cost was able to be reduced. According to the fifth aspect of the present invention, by using the light source modulation, the area modulation, and the PWM, a long subframe time can be secured, and the field sequential and the pixel shift, which are difficult to realize with the conventional spatial light modulator, are used. And high gradation display could be realized. According to the sixth aspect of the present invention, by using light source modulation, area modulation, and PWM, a long subframe time can be secured, and a display device that achieves both high gradation display and high image quality can be realized. Was.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a gradation display device.

FIG. 2 is a configuration diagram around an LV.

FIG. 3 is another configuration diagram of a gradation display device.

FIG. 4 is a diagram showing an example of a pixel according to the present invention.

FIG. 5 is a time chart showing 256 gradations according to the present invention.

FIG. 6 is a time chart showing 256 gradations according to another embodiment of the present invention.

FIG. 7 is a time chart showing 256 gradations according to another embodiment of the present invention.

FIG. 8 is an explanatory diagram of a pixel shift.

FIG. 9 is a time chart showing 256 gradations according to another embodiment of the present invention.

FIG. 10 is a time chart showing 256 gradations according to another embodiment of the present invention.

FIG. 11 is a diagram showing an ND filter that is arranged in a circumferential direction and that defines transmittance.

FIG. 12 is a diagram showing an example of conventional area modulation, in which 64 gray scales are displayed in 7 divisions.

FIG. 13 is a diagram showing an example of gray scale display by conventional pulse width modulation.

FIG. 14 is a diagram showing an example of a conventional light source gradation and gradation display by pulse width modulation.

[Explanation of symbols]

 1-4 Pixel having an area ratio of 1-5 Pixel 8 having an area ratio of 8 21 ND filter perspective view 22 ND filter 23 LV 25 Lamp 26 Polarization conversion device 27 Projection lens 32, 33 Piezo element 50 Controller

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) G02F 1/133 575 G02F 1/133 575 G09G 3/34 G09G 3/34 JD 3/36 3/36 H04N 5/66 H04N 5/66 A (72) Inventor Hiroyuki Sugimoto 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Ricoh Co., Ltd. (72) Inventor Yasuyuki Takiguchi 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (reference) 2H093 NA54 NA55 NC42 ND04 ND06 NE06 5C006 AA12 AA15 AA17 AA22 AC02 AF44 BB11 BB29 EA01 EC11 FA56 5C058 BA08 BA25 BB03 EA01 EA02 EA14 EA23 EA26 EA51 A04 EA05 A03 EA51 5C080

Claims (6)

[Claims] In a gradation display method performed in a gradation display device including at least a spatial light modulator and a light source for illuminating the spatial light modulator, intensity modulation of the light source is performed, and the spatial light modulator modulates a gradation. A gradation display method, wherein one unit for performing the operation is constituted by a plurality of pixels, and each pixel individually performs ON / OFF and area modulation display. 2. The gradation display method according to claim 1, wherein
If the area modulation is composed of two pixels, and the number of gradations displayed by one color that constitutes a color display is expressed by 2 ⁿ , the area ratio for area-modulating at least one unit for display is as follows: When n is an even number A substantially 1: 2 ^{n / 2} relationship, and when n is an odd number, a roughly 1: 2 ^{( n-1) / 2} relationship. 3. A gradation display method according to claim 1, wherein the number of divisions of each frame into individual frames (hereinafter referred to as sub-frames) is n / 2 when n is an even number. When n is an odd number, the relation of (n + 1) / 2 is shown. The light source modulation to be used is a continuous natural number whose number from 1 to the maximum is the number of divisions into the subframes. Assuming that the added number is m, the intensity of the light source in each subframe, that is, the subframe (m
(1) The intensity of (1) is approximately represented by (maximum illuminance of light source) × (１ ／) ^{m -1} . 4. The gradation display method according to claim 1, wherein a value obtained by multiplying a time in a sub-frame by a coefficient is 1 as a modulation method of a pixel for performing area modulation.
A gradation display method using a pulse width modulation of 00%. 5. The gradation display method according to claim 1, wherein the image is time-divided within one frame, and the divided image is displayed on a spatial light modulator. Key display method. 6. A gradation display device comprising at least a spatial light modulation element and a gradation display apparatus provided with a light source for illuminating the spatial light modulation element, wherein the gradation display method according to claim 1 is controlled. A gray scale display device comprising: