JPH1078550A - Method and system to emphasize strong white display region in sequential digital-mirror-display(dmd) video system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the method and the system in which a strong white display region in a sequential DMD video system is emphasized. SOLUTION: The system includes the steps and the means in which specific signals are generated for the pixels that indicate whether the luminance of all color pixels is increased or not. Moreover, the system includes the steps in which a DMD 19 having a mirror receives the different mixtures of color light beams that are combined together to generate strong white and the mirror is turned on within the time of color boundaries. The system includes degamma.look up.tables for each color. The tables are increased when a specific signal is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to digital mirror display (DMD) systems, and more particularly to enhancing the strong white display area in sequential DMD video systems.

[0002]

2. Description of the Related Art A video display on a CRT (Cathode Ray Tube) has the ability to overdrive its output intensity over a very bright small visible area with respect to the rest of the background. This feature has the effect of highlighting locally bright areas that are brighter than can be achieved over the entire background. This effect is desirable in many situations. A new projection display that utilizes reflections from hundreds of thousands of micromirrors, each mounted on a semiconductor memory cell, is a Texas Instruments, Inc.
IEEE Spectrum, Nov. 1993, vol.
30, no. The digital mirror device (DMD) has a specific light modulator. DM
D, a digital micromirror device, has each memory cell of a CMOS static RAM with a movable micromirror. Electrostatic force based on the data in this cell tilts the mirror ± a few degrees to modulate light incident on the surface. As an example, the slope is 10 °. Light reflected from any of the mirrors passes through a projection lens and forms an image on a large screen. Light from the remaining off-mirrors is reflected from the projection lens and trapped. The time portion of each video frame where the mirror remains on determines the shade of gray from black for 0 on-time to white for almost 100% of the time.

[0003] One of the coloring methods is by a color wheel. This type of system is a sequential DM
It is called D-video system. Sequential color DMD displays using a color wheel use pulse width modulation (PWM) to describe the brightness of each wheel color for each pixel. The individual mirrors are switched between an off state and an on state so that each is turned on for some portion of the time when the DMD is uniformly illuminated with a single color. The on-time for the mirror is proportional to the desired brightness in that color. Since all the time available in one color is used to draw full-scale brightness, DMD displays can use pixels of a particular color without reducing the amount of time available for proportional pulse width modulation. Can't "overdrive".

[0004]

SUMMARY OF THE INVENTION According to a preferred embodiment of the present invention, a method and system for enhancing a strong light display area in a sequential DMD video system comprises:
It is provided by generating a specific bit for each pixel that indicates whether to boost the brightness of the pixel in all colors. These bits are loaded into the DMD array at the beginning of every color transition period, so that each pixel is turned on during these times.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a digital micromirror device (DMD) display system 10 is shown.
Is shown. The light from the light source 11 is transmitted through the first condenser lens 13 to about 60 Hz, that is, about 6 Hz.
Light provided through the color wheel 15 rotating by 0 frames and passing through the color wheel
Passes through the second condenser lens 17. The DMD chip contains an array of small mirrored elements, ie, micromirrors. Here, each mirror element is
It is hinged by a torsion hinge and a support post on the memory cell of the CMOS static RAM shown in FIG. The movable micromirror is tilted on or off by an electrostatic force based on data in the cell. The mirror tilt can be either + or-, for example, 1
At 0 ° (off), it modulates light incident on the surface. As shown, light reflected from either mirror passes through a projection lens 20 to form an image on a large screen 21. As mentioned earlier, part of the time while the mirror is on determines the shade of gray. The time while a cell is in the positive direction, ie, on, is represented by 8 bits of data sent to that cell. The color wheel 15 is divided into, for example, red, green, and blue. In the example of a red, green, blue color wheel, maximum red is when red is reflecting for a maximum period of time. That is, the micromirror is in the on position when light has substantially passed through the entire time the wheel is in the red section. The same is true for the other two colors.

If the micromirror is off throughout the entire time that the color wheel is in the color position,
Is the smallest. The luminance resolution in this pulse width modulation (PWM) is limited by the response time of the digital DMD mirror. The total time available to display the color frame and the minimum time required to rotate the mirror between the "on" and "off" states define the resolution of the system. In the arrangement for eight bits, the most significant bit is shown in FIG. 3 and is the seventh bit. The bit represents the longest "on" time, the sixth bit represents the next longest "on" time, and the fifth bit represents the third longest "on" time. The same applies hereinafter. The least significant, ie, “0”, bit represents the shortest time period. Sequential color D
For MD systems, 5 milliseconds (msec) are available for color frames. For an 8-bit binary PWM, the least significant bit (only 0 bits),
That is, the shortest period is about 19.6 microseconds (μ
Second). The mirror off / on time must be 19.6 microseconds or less to implement this design in the current method.

[0007] In the present design, all micromirrors of the DMD device 19 are rotated to the "off" state during the time period when the DMD illumination charges from one color to another.
During these times, the color boundaries traverse between the light source and the DMD with micromirrors that undergo various mixings of color light depending on the respective array position. According to the present invention, the solution providing a method of enhancing the strong white display area is to generate a specific bit for each pixel indicating whether to boost the luminance of the pixel in all colors. These bits are set at the beginning of the transition period for all colors so that individual pixels can be turned on during these times instead of always setting the mirror to the off state during the color transmission period.
Loaded into D array. In accordance with the present invention, although the various pixels undergo unequal color phases during any one transition, all transitions integrated together produce approximately the same color mixture across the array. Referring to FIG. 4, the transition of the color wheel on the split reset DMD is shown. In the example of FIG.
The change from color A to color B is shown. In the middle, this time period shown between the dotted middle lines, the time period of the transition of the color wheel between color A and color B when the system is normally off is shown. On the vertical axis, 16 reset groups 0-15 are represented. In the split reset DMD, the phase "on" to the phase "off" is represented by a staircase group 0-15 with group 0 being turned off at time X and turned on at time Y.

[0008] Group 1-15 starts at time X + 1 and ends at time X.
The phase is sequentially turned off to +15. X + 15 is the time when reset group 15 is turned "off". The time period during which group 0 is turned "on" is again at time Y
And the reset group from 1 to 15 is turned on sequentially from time Y + 1 to time Y + 15.
As shown in FIG. 4, in the split reset mode, the transition period of the color wheel is not only boosted by the system of light boost bits,
The period from phase "on" to phase "off" is represented by a group dependent number. For example, the period from X to Y for group 0 represents the entire period. The period from X + 15 to Y + 15 for the group 15 represents the light boost period for the group 15. FIG.
Referring to FIG. 3, the percentage of each color light during each transmission of the light spot for the pixels at points A and B is shown. As the light crosses the color boundary between the color wheel sections between red and green, for the pixel at point A at the edge of the DMD, the red section at point A is on for 1% of the time and green is the time Is on for 99% of the time. For the pixel at point B, at the right end of the DMD, red is
% For green, 1% for green and 0 for blue. If the color wheel changes from green to blue and the pixels are at points A and B, then for the pixel at point A it is 99% for blue and only 1% for green. For the pixel at point B, pixel B receives 99% of the green color and 1% of the blue color. For the transition between blue and red of the pixel located at points A and B, point A
Pixels receive 99% of red, 1% of blue and 0% of green. For the pixel at point B for the blue to red transition, there will be 1% red, 0% green and 99% blue. Over the entire cycle of the color wheel, the red, green and blue of each color for a pixel location receive 100% of the total light equally, giving white light.

A simple method is used to detect areas of the image that must be "peaked" as described below. The system detects peaks by comparing the red, green, and blue digital signals and boosts the boost bit for pixels having equal values of red, green, and blue above a predetermined threshold.
t) is set. Referring to FIG. 6, the red, green and blue outputs from the color converter 61 (block 50 in FIG. 1) are output to a white bit generator 63 and a red, green and blue degamma look-up table. (L
UT) 65, 66, 67 respectively. In the embodiment described here, 8 bits describe the luminance level for the red, green and blue signals. In an 8-bit system, the value of each pixel is divided into 32. The brightness level can also be represented by another number of bits, such as six. In this embodiment, 25 bits are:
Frame RAM if stored for each pixel
(Randam Access Memory) 69 stores a complete frame of pixels. 8 bits for each color, ie 2
There are four bits, and one bit from generator 63.

A generator 63 is coupled to the three separate color outputs from the color converter 61 and their levels are compared, and if all levels from the video source exceed a threshold, a white bit ( For example, logic 1 level) is provided. In one preferred embodiment, this is when all three levels are equal. The threshold is when the three colors are combined, one of which gives the pixel a sufficiently bright white to be at the boost white level. This comparison is based on the three MSBs (most signif
icant bits) or equivalent. When a white bit is generated, it is also added to the DMD and DMDRAM controllers. The DMDRAM controller tells the frame RAM where to get the data, 25-bit data, etc. DMD control is sent directly to the DMD. The white bit is
The DMD array is loaded at the start of every color transition, so that during these times individual pixels are turned on. When a white bit, e.g., a logic one level, is generated, that bit is converted to three LUTs 65, 66, 67.
(The filter 64 of FIG. 1). The degamma LUT is described by Doherty et al. In "Error Diffusion Filter for DMD Displays.
No. 08 / 315,457 filed Sep. 30, 1994 under the name of “DMD Display)”. When the generated white bits are applied to the LUTs 65, 66, 67, the table calls higher order transfer functions, with higher luminance levels being provided from each LUT to provide a smooth slope function for higher light levels.

The following items are disclosed in connection with the above description. (1) In a method for enhancing a strong white display area in a sequential DMD video system, a step of generating a specific signal indicating a white luminance of a boost, and while the specific signal is present, a light source for a DMD mirror is mounted on a color wheel. A method comprising: allowing a DMD mirror to be in an on position for a time that crosses a color boundary. (2) In a method of enhancing a strong white display area in a sequential DMD video system, there is a step of generating a specific signal for each pixel indicating a white luminance of boost of pixels in all colors, and the specific signal. The DMD mirror of the DMD system such that during the time the light source crosses the color boundary of the color wheel, the DMD mirror receives various mixtures of color light that are integrated together to produce intense white. A step of allowing the device to be turned on.

(3) The method according to (2), further comprising, after the generating step, loading the specific signal into a DMD array at the start of every color transition period. (4) The particular signal first compares the red, green and blue digital signals and generates a boost signal when the pixels from red, green and blue all exceed a given threshold. The method according to (2) above, wherein (5) Increasing the original transfer function in the degamma look-up table for red, green and blue colors in response to the particular signal generated. ). (6) The method according to (5), wherein the specific signal is used to change a gain of a degamma look-up table to provide a smooth gradient function. (7) A system for enhancing a strong white display area in a sequential DMD video system having a plurality of mirrors illuminated from a light source through a color wheel, wherein the luminance is combined with an incoming color video signal and is above a given threshold. And a mirror for generating a particular signal representing the signal, the mirror being turned on while traversing a color boundary of the color wheel in response to the particular signal. System having a mirror control device for enabling

(8) The system according to (7), wherein the color video signal is a red, green and blue video signal. (9) including a separate degamma look-up table coupled to the incoming color video signal to provide a first transfer function, the degamma look-up table responsive to the particular signal; The system according to (7), wherein the number is increased. (10) A plurality of DMD mirrors illuminated from a light source through a color wheel, wherein a step-like group of pixels is sequentially turned off at a boundary of the color wheel, and the step-like group of pixels is sequentially turned on in the same order. A system for enhancing strong white display in a split reset DMD video system, comprising: at least three color video signal sources; and said video signal coupled to said color video signal and above a given threshold. A generator for generating a particular signal representing all of the luminance of the mirror; and a mirror coupled to the DMD mirror and responsive to the particular signal for keeping the DMD mirror turned on during the color wheel boundary. A system comprising: a controller.

(11) There is one degamma table for each color coupled to the generator for increasing the transfer function of the look-up table in response to the generation of the particular signal. The system of claim 10, including a degamma look-up table. (12) including a plurality of DMD mirrors illuminated from a light source through a color wheel, wherein during a time period of an absolute color wheel boundary, all of the pixels are turned off;
During a first transition time period before the absolute color wheel boundary, the pixels are sequentially turned off in a group before the absolute color wheel boundary and a second transition time period following the absolute color boundary A system for enhancing a strong white display in a split reset DMD video system, wherein said step-like groups of pixels are sequentially turned on in a similar order;
At least three color video signal sources, a generator coupled to the color video signal for generating a particular signal representing a luminance above a given threshold, and the DMD
A mirror controller coupled to the mirror and responsive to the particular signal to cause the DMD mirror to be turned on during the absolute color boundary and during the first and second transition times. A system characterized in that:

(13) There is one degamma table for each color coupled to the generator for increasing the transfer function of the look-up table in response to the generation of the particular signal. The system of claim 12, including a degamma look-up table. (14) including a plurality of DMD mirrors that are illuminated from a light source through a color wheel, and during a time period of an absolute color wheel boundary, all of the pixels are turned off;
During a first transition time period before the absolute color wheel boundary, the pixels are sequentially turned off in a group before the absolute color wheel boundary and a second transition time period following the absolute color boundary A method for enhancing a strong white display in a split-reset DMD video system, wherein said step-like groups of pixels are turned on in a similar order, said method comprising providing at least three color video signal sources; Generating a specific signal coupled to the color video signal and representing a luminance above a given threshold; and providing the DMD during the absolute color boundaries and during the first and second transition times. Allowing the mirror to be turned on.

(15) Providing a degamma look-up table for each color, combining the particular signal with the table, and generating a boost response in response to the particular signal. The method according to (14), further comprising increasing a transfer function. (16) A plurality of DMD mirrors illuminated from a light source through a color wheel, wherein a step-like group of pixels is sequentially turned off at a boundary of the color wheel, and the step-like group of pixels is turned on in the same order. Providing enhanced white display in a split-reset DMD video system, the method comprising: providing at least three color video signal sources; and identifying all luminances of the video signal above a given threshold. And the step of: when the particular signal is generated, leaving the DMD mirror turned on during the color wheel boundary.

(17) providing a degamma look-up table for each color, combining the particular signal with the table, and increasing the gain of the table in response to the particular signal; The method according to the above (17), comprising: (18) A method and system for enhancing a strong white display area in a sequential DMD video system generates a specific signal for each pixel to indicate whether to increase the brightness of all color pixels. including. Further, the method uses a D with mirror.
MD includes the step of allowing the mirror to be turned on during the time of the color boundary of the color wheel to receive a different mix of color lights incorporated together to produce an intense white. The system includes a degamma look-up table for each color. This degamma look-up table is augmented when a particular signal is generated.

[Brief description of the drawings]

FIG. 1 is an overall view of a sequential color digital micromirror display system.

FIG. 2 is a sketch of the micromirror element of FIG.

FIG. 3 is a timing chart showing on-time of MSB and LSB.

FIG. 4 shows the optical integration time lost before and after the transition of the wheel, phase off and phase on of the reset group.

FIG. 5 shows the operation of the system when all colors on the wheel have the same number of segments and the proportion of light from each color is equal.

FIG. 6 is a block diagram of a system according to an embodiment of the present invention.

Claims (2)

[Claims] 1. A method for enhancing a strong white display area in a sequential DMD video system, comprising the steps of: generating a specific signal indicative of a boosted white luminance; and wherein the light source for the DMD mirror is colored while the specific signal is present. A method comprising the step of allowing a DMD mirror to be in an on position for a time that crosses a color boundary of a wheel. 2. A system for enhancing a strong white display area in a sequential DMD video system having a plurality of mirrors illuminated from a light source through a color wheel, said system being coupled to an incoming color video signal and having a threshold greater than a given threshold A generator for generating a specific signal representative of the luminance of the DMD video system; and in response to the specific signal, the mirror is turned on while crossing a color boundary of the color wheel. A mirror control device to allow