JPH09149350A - Space light modulation display with concentration filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To display an image where artifacts are reduced by executing an operation so as to use more bits per sample in the image displayed in a video display system using a space light modulator. SOLUTION: In the video display system adding the space light modulator, a tri-color wheel 30 adding a main color segment 32 and at least one segment 34 having a low strength area named a neutral density filter(NDF) or one transparent wheel is used. In exchange for if, the filter can be a liquid crystal controller for controlling one of light amplitude or color. The low strength area is used so that the quantity of time which can be used for processing the lowest- order bit (LSB) of a data sample is increased and, by this, limitation to the number of bits which can be used for displaying is removed.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to video display systems, and more particularly to video display systems that use spatial light modulators.

[0002]

Spatial light modulators used in video displays typically control a plurality of individual elements in the final image, one for each pixel, one for each pixel. To generate an image. These systems have some well-defined characteristics that require new research into handling input video data. Conventional cathode ray tube (CRT) systems have a non-linear response between the voltage of the signal and the brightness perceived by the viewer. One factor influencing this is the phosphorus used on the screens of most CRT systems, which phosphorus has a non-linear response but is necessary to produce color. With a spatial light modulator, color is controlled by the light that illuminates the screen surface of a CRT system. The light illuminating the individual elements is already tinged with a color, for example by using either a white light source and some type of color filter or a colored light source. With this, the conventional C
Eliminate the non-linear response of the RT system.

Because of the linearity of spatial light modulator systems,
It is necessary to "reverse gamma" the video data. C
Since RT systems are so prevalent, video signals have been subjected to a correction called gamma correction for the non-linearities of systems already built into this signal path. For linear systems, such as spatial light modulator systems, this correction must be removed.

Problems arise with the nature of most spatial light modulator systems. These systems typically operate by pulse width modulation (hereinafter referred to as PWM). The input data signal is digitized into samples with a predetermined number of bits for each pixel. The value for each bit of the sample depends on the perceived intensity for that pixel in that frame. The most significant bit (hereinafter referred to as MSB) is displayed for about 1/2 color segment time. The color segment time is equal to the frame time divided by 3, so each color, ie red, green, blue, has 1/3 of the frame time. The frame time is the time associated with each image frame of the incoming signal. For a 60 Hz system, the frame time is 16.67 ms. This is also called the display refresh rate because it is the rate at which a standard CRT system writes an image on its screen.

The operation of PWM is too fast for the eye to perceive changes so the eye perceives a full color image and the eye integrates brightness and color over a time frame.

The next MSB has 1/2 of the 1/2 color time segment of the previous MSB, ie, 1/4 of the color time segment, and so on, and finally the least significant bit (hereinafter , LSB) is displayed. The width of the LSB depends on the minimum achievable spacing. For example, if the modulator cannot switch and display the element in less than 40 μs, the LSB time is 40 μs.
It cannot be shorter than s.

However, to fully simulate the response of a CRT operating at a 60 Hz display refresh rate or frame time, the system requires more than 8 bits of data. 40μ
Spatial light modulators with an LSB time equal to s cannot achieve more than 7 bits per color segment. This results in some undesired artifacts in addition to low quality simulations of CRT systems. A few bits produce contouring artifacts in the low intensity regions of the image. In addition, dark areas appear “dirty” and data compression artifacts are enhanced. These problems could be eliminated if one method of operation were used to operate the system to use more bits per sample.

[0008]

SUMMARY OF THE INVENTION The present invention provides a system and method for improved display of video images. This system uses a color wheel or filter with a density filter (hereinafter NDF) for each color.
The NDF for each color allows the bits to be displayed during a longer time interval, overcoming a limitation that is some minimum amount of time for the display of the lower bits.

The advantage of this system is that it allows more bits per sample to be used in the displayed image, producing an image with reduced artifacts and more closely matching the image of conventional display systems. That is.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In a conventional PWM system, M
SB receives 1/2 of the color segment time. The color segment time is typically 1/3 of the frame time, i.e. 1/3 of each frame time for red, green and blue. 6
For a 0Hz system, the frame time is 1/60 second,
That is, it is 16.67 ms. This 60 Hz rate is also referred to as the display refresh rate, which is C
It comes from the writing time of the RT system. As a result, 0.
This gives a color segment time of 01667/3 ms, ie 5.56 ms and thus also 5,560 μs.

For a color wheel system using a color wheel with three equal segments of red, green and blue, this time must include the spoke time.
Spoke time is the time it takes for the spokes of the wheel between colors to pass in front of the light source. This time must include the time it takes to load the modulator's addressing electronics with data and the response time of the individual elements of the modulator.

As an estimate, a 5,560 μs system can be used to create Table 1, which shows bit 7 as M
The time allocated to each effective bit is shown for an 8-bit system using the conventional PWM with SB and bit 0 as the LSB.

[0013]

[Table 1]

Therefore, for a modulator having a minimum time of 40 μs, it is not possible to display more than 7 bits of data. 21 μs cannot give the device sufficient time to reset to new data, receive the next data, and reset to this new data. An example of a modulator having such a limit is shown in FIG.

FIG. 1 shows a side view of a modulator 10 known as a digital mirror device (hereinafter referred to as DMD). The mirror 20 is stable in the horizontal position and is supported by the beam 16. When the mirror 20 is addressed by the address electrode 12b,
The mirror 20 is seated on one side on the landing electrode 14b and tilted until it assumes position 22a. After the time the bits for the mirror 20 of data have passed, the mirror 20 is reset, i.e., given a signal that causes the mirror 20 to respond to new data. For this discussion,
If the data is at position 2 on mirror 20, as discussed above.
If 2a can be taken, assume that mirror 20 is on. The light from the mirror 20 reflects to the surface of the scoop or image forming surface.

After the reset signal, if the new data is an ON signal, this causes mirror 20 to return to position 22a, or if the new signal is OFF, then mirror 2
Have position 22b at 0. Position 22b is achieved by addressing address electrode 12a to seat mirror 20 on landing electrode 14a. In the off position, it is desirable for the mirror 20 to assume an opposite position rather than remain horizontal, which prevents the hinge from being permanently tilted toward the on position and which causes the optics to rotate. This is because there is a large gap between the on-path and the off-path in the system.

However, there is a mirror 20 response time associated with the movement of the mirror 20. This response time requires a certain time interval, typically about 10 μs, which is called the mirror flight time, for the mirror 20 to take a new position. This response time is the time that limits the minimum amount of time that must be allowed within the LSB time. Other modulators besides DMDs impose similar limitations on their response times. Actuated mirror device, i.e.
AMA is subject to similar limitations on its mirror movement. The liquid crystal cell must be allowed to twist to turn the cell on and off.

However, there are methods and systems that allow more bits to be processed in the color segment time. The extra bits per sample available to the system help remove low intensity contouring artifacts, "dirty" dark areas, and help better simulate continuous intensity responses.

The limit imposed on the system is the minimum amount of time available to properly display the LSB. Therefore, if there were a way to lengthen the LSB time, the limit would not apply. However, if a standard density color wheel is used, the LSB
Increasing the time will change the image.

The inclusion of the low density segment within each color segment allows the color wheel to extend the LSB time, allowing more bits to be used for each data sample. An example of this color wheel is shown in FIG.

The color wheel 30 has three segments, each of these segments having an arc length θ _{CS of} 120 °. Each arc length θ _CS includes an NDF with a short arc length θ _NDF . For example, one arc length θ _{CS includes} a main color segment 32 which is blue and a low density blue segment of the length θ _NDF obtained by adding NDF to blue, that is, an NDF segment 34. To enable an NDF segment 34, the time for its lower bits must be lengthened in inverse proportion to the density of that NDF segment 34. The upper bits are modulated by conventional PWM.

PWM using NDF (hereinafter NDF.P
An example of a timing diagram for a system referred to as WM) is shown in FIG. For a standard PWM system,
The timing diagram begins at time t ₀ , which is the beginning of the MSB. The MSB keeps its conventional value of about 2,7 until time t _1.
It is displayed for a time width of 80 μs. PWM is at time t ₆
Standard PWM system up to the end of bit 0 in ND
Almost the same between the two diagrams for the F-PWM system respectively.

However, in the diagram for the NDF PWM system, the extra bits are displayed for the duration of time t ₇ to t _8, which is the same length as bit 0 time, but the strength of the segment for this bit. Is only 50% of the intensity of the main color segment 32 of the color segments. Halving the intensity allows the bit to be displayed twice as long. Therefore, the time in the 8-bit NDF PWM system is increased by 43 μs. To use the extra 43 μs, this must be accommodated by other bits in the system.

The time for these lower bits is the ratio of the intensity of the main color segment 32 to the intensity of the NDF segment 34 times the conventional PWM time. For example, the time for the 8 bits listed above is 43/2 μs, or 21.5 μs. NDF of main color segment 32
The intensity ratio for segment 34 is 2: 1 (NDF
The intensity of the segment 34 is 1 of the intensity of the main color segment 32.
/ 2). This is 2 × 21.5 μs = 43 μs.
However, as mentioned above, lengthening the time by 43 μs reduces the amount of time available for other, conventionally modulated bits.

This may result in an overall reduction in the optical efficiency of the system, as shown in Table 2 below as a trend example. Table 2 shows the number of bits in the system, which means the number of bits per data sample for each pixel. N
The DF density is the density of the NDF segment 34 compared to the density of the main color segment 32 which is assumed to be 1. For example, a concentration of NDF segment 34 of 0.5 is NDF
It means that the density of the segment 34 is 1/2 of the density of the main color segment 32 of the color. For a system with a certain number of bits, it may display more LSBs than those displayed in the NDF segment of a 7-bit system, as indicated by "bits in NDF".

The LSB time is a limit to the system, that is, the system cannot have an LSB below some amount of time, so that amount of time is usually referred to as the LSB time, and the time for other bits is It is a multiple of the LSB time. For example, in a 7-bit system, the MSB time is 64 x LSB time. The amount of time used for the NDF segment of the color wheel is also compared in Table 2.

[0027]

[Table 2]

As can be seen from Table 2, more bits of data can be obtained to represent, but in this example the LSB time and overall light efficiency are shortened and degraded. The reduction in overall light efficiency reduces the perceived brightness of the image. The reduced LSB time shown in this example can result in a significant load on the data processing and memory functions of the addressing system. However,
The use of these trade-offs is the responsibility of the system engineer. The system described above allows a greater number of bits to be imaged within the time constraints of the spatial light modulator, allowing the system to project an image with reduced artifacts.

The timing used in these examples has been simplified for discussion purposes. These times include not only the reset allowance time, the extra reset time for split bits, the special clear time for short bits on devices with a global reset, and the spoke allowance time, but also other miscellaneous special needs for the operation of the modulator. You have to take time into account. The timing diagrams in Table 1 and FIG. 2 do not account for these times to explain the general concept of the invention. However, the time given in Table 2 is
These times are taken into account.

The above-described use of NDF can also be incorporated into other system architectures. A monochrome system would use a transparent wheel instead of the color wheel above. The NDF region will be some predetermined shade of gray. This allows more bits to be used within a monochrome system.

Yet another embodiment includes a two-chip system, where there are two spatial light modulators and two color wheels. One color wheel will have one color and the second color wheel will have two colors. Each color has its own N
Will have a DF region. In a three-chip system, each spatial light modulator may have its own color wheel with one color and one NDF region. Alternatively, the entire system may have one wheel,
The wheel is transparent with a gray NDF area, where each modulator will have its own colored light source.

In these multiple color wheel systems, or single wheel systems, not every color wheel must necessarily have an NDF segment. For reasons related to a particular color profile of the system, one color has an NDF segment, another color does not, and so on. Further, while the filters described above use color wheels, other types of filters can also be used. For example, liquid crystal variable NDF
Alternatively, a color controller can also be used to control the amplitude modulation.

Thus, although a system and method for increasing the number of bits in a display system has been described with respect to particular embodiments, such particular embodiments are beyond the scope of the following claims. However, it is not intended to be considered a limitation on the scope of the invention.

With respect to the above description, the following items are further disclosed.

(1) A spatial light modulator, wherein said spatial light modulator, said spatial light modulator, produces an image by deflecting selected elements of an array of individual elements. A light source operative to illuminate the light source, and at least one filter through which light from the light source passes before illuminating the spatial light modulator, the video comprising the filter comprising a neutral density region. Display system.

(2) In the system according to item 1,
The system, wherein the spatial light modulator is a DMD.

(3) In the system according to item 1,
The system, wherein the spatial light modulator is AMA.

(4) In the system according to item 1,
The system, wherein the spatial light modulator is a liquid crystal device.

(5) In the system according to item 1,
The system, wherein the filter is a liquid crystal controller.

(6) In the system described in item 5,
The liquid crystal controller operates to control colors,
system.

(7) In the system described in item 5,
A system wherein the liquid crystal controller operates to control the value of NDF.

(8) The system according to item 1,
A system that includes three spatial light modulators and one color wheel.

(9) The system according to item 1,
A system that includes three spatial light modulators and three color wheels.

(10) The system according to item 1, which includes two spatial light modulators and two color wheels.

(11) A pulse width modulation method used to generate an image, the method comprising: displaying the high order bit of a predetermined number of bits per data sample having a conventional pulse width; The lower bit of the predetermined number of bits has the conventional pulse width for the lower bit, the filter strength and the NDF
Displaying the lower bits to have a pulse width equal to the ratio of the segment to a predetermined low intensity.

(12) In the method described in item 11,
The method, wherein the step of displaying the low order bit further comprises displaying the low order bit of one of an 8-bit system.

(13) In the method described in item 11,
The method, wherein the step of displaying the low order bits further comprises displaying the two low order bits of a 9-bit system.

(14) In the method described in item 11,
Displaying the least significant bits further comprises displaying the three least significant bits of a 10-bit system.
Method.

(15) In the method described in item 11,
Displaying the lower bits further comprises displaying the four lower bits of an 11-bit system.
Method.

(16) The method according to item 11,
A method applied to a 5-bit system.

(17) The method according to item 11,
A method applied to a 6-bit system.

(18) The method according to item 11,
A method applied to a 7-bit system.

(19) The method according to item 11,
A method applied to a 12-bit system.

(20) A filter wheel which operates as used in a video display system, comprising:
A filter wheel comprising at least one segment of the wheel having the NDF filter such that the NDF segment comprises a low intensity region of the segment.

(21) A system and method for increasing the number of bits available for use in a video display system including at least one spatial light modulator. The system has at least one low intensity region referred to as NDF
A three color wheel 30 including one segment 34 or one color wheel that is transparent is used. Alternatively, the filter may be a liquid crystal controller that controls either the light amplitude or the color. The use of low intensity regions increases the amount of time available to process the LSBs of a data sample, thereby removing the constraint on the number of bits available for display.

[Brief description of the drawings]

FIG. 1 is a side view of a spatial light modulator.

FIG. 2 is a front view of a color wheel including an NDF for each color according to an embodiment of the present invention.

FIG. 3 is a timing diagram comparing a conventional standard PWM and a PWM using an NDF according to an embodiment of the present invention.

[Explanation of symbols]

 10 DMD 12a, 12b Address electrode 14a, 14b Landing electrode 16 Beam 20 Mirror 30 Color wheel 32 Main color segment 34 NDF segment

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Claims (2)

[Claims] 1. A spatial light modulator, said spatial light modulator, wherein said spatial light modulator produces an image by deflection of a selected number of elements of an array of individual elements. A light source operative to illuminate, and at least one filter through which light from the light source passes before illuminating the spatial light modulator,
A video display system including the filter including a neutral density region. 2. A pulse width modulation method used to generate an image, the method comprising: displaying the high order bit of a predetermined number of bits per data sample having a conventional pulse width; So that the low order bit of the predetermined number of bits has a pulse width equal to the conventional pulse width for the low order bit times the ratio of the filter strength to the predetermined low strength of the neutral density segment of the filter; A method comprising displaying the low order bits.