Patent Application
20080084369
For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
a and 1b are diagrams of a high level view of a prior art DMD-based display system and exemplary sequences of colors;
a through 2c are diagrams of a high level view of a prior art DMD-based display system, exemplary sequences of colors, and exemplary descriptions of sequences of colors, wherein the display system utilizes a rapidly switching light source;
a and 5b illustrate sequences of events in the displaying of a desired color sequence and a detailed view of an exemplary use of a reference color sequence to generate the desired color sequence, according to a preferred embodiment of the present invention; and
a and 6b are diagrams of exemplary timer enable circuits, according to a preferred embodiment of the present invention.
The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
The present invention will be described with respect to preferred embodiments in a specific context, namely a sequential color display system utilizing a DMD (digital micromirror device) as a spatial light modulator. The invention may also be applied, however, to other sequential color display systems, such as those using deformable mirror, reflective liquid crystal, liquid crystal on silicon, and so forth, display technologies.
With reference now to
A controller 320 can be responsible for the operation of the display system 300. The controller 320 can be a custom designed integrated circuit (also referred to as an application specific integrated circuit (ASIC)), a general purpose processor with customized software and firmware, a digital signal processor, and so forth. The controller 320 can contain circuitry such as a light controller circuit 325, which can be responsible for providing control signals to a light driver circuit 330. The control signals from the light controller circuit 325 can control a drive current to illuminate the light elements in the light source 310. Additionally, the light controller circuit 325 can also provide control signals and/or control instructions to turn on and off particular light elements in the light source 310 to produce light of desired color and intensity.
Also included in the controller 320 can be a sequence controller 335. The sequence controller 335 can be used to provide color sequences to the light controller 325. The color sequences provided by the sequence controller 335 can be based on image data that is to be loaded into the array of light modulators 305. For example, the bit weight of the image data (which specifies the significance of the image data) as well as the chromatic characteristics of the image data can have an effect on the color sequences provided to the light controller 325. According to a preferred embodiment of the present invention, the sequence controller 335 can provide a color sequence to the light controller 325, which can then compute clock drop factors for each color in a reference color sequence (which can be stored in a memory 340) based on the color sequence. Detailed descriptions of the clock dropping technique are provided in co-assigned U.S. Pat. No. 5,912,712, entitled “Time Expansion for Pulse Width Modulation Sequences by Clock Dropping,” issued Jun. 15, 1999, and U.S. Pat. No. 7,019,881, entitled “Display System with Clock Dropping,” issued Mar. 28, 2006, which U.S. patents are incorporated herein by reference.
The clock drop factors can either be stored back in the memory 340 for subsequent use or in dedicated memory (such as registers) located in the controller 320. Although shown in
A light sensor 345 can be used detect the light produced by the light source 310. The light detected by the light source 310 can be converted into electrical signals by the light sensor 345 that can be provided to the light controller 325. The light controller 325 can make use of the electrical signals provided by the light sensor 345 to help ensure that the light being produced by the light source 310 matches the color sequence provided by the sequence controller 335. If the light does not match the color sequence provided by the sequence controller 335 within a specified margin, the light controller 325 can make adjustments to the control signals and commands that it is providing to the light driver 330 to make changes to the light being produced by the light source 310.
In addition to providing the electrical signals to the light controller 325, the light sensor 345 can also provide the electrical signals to the sequence controller 335. The electrical signals provided to the sequence controller 335 can provide information about the light output of the light source 310. The sequence controller 335 can then derive information about the capabilities of the light source 310. For example, the sequence controller 335 can compare the light output of the light source 310 with the light that it expects the light source 310 to produce. Using this information, the sequence controller 335 can make adjustments to the color sequences that it is providing the light controller 325. For example, if the sequence controller 335 determines that the color output of the light source 310 is changing, due to aging, for example, then the sequence controller 335 can instruct the light controller 325 to make use of a different reference color sequence to compensate for changes in the light source 310, or the sequence controller 335 can attempt to adjust the color sequences directly to compensate for changes in the light source 310.
Descriptions of the DMD, DMD fabrication, and DMD-based display systems can be found in greater detail in the following co-assigned U.S. patents: U.S. Pat. No. 4,566,935, issued Jan. 28, 1986, entitled “Spatial Light Modulator and Method,” U.S. Pat. No. 4,615,595, issued Oct. 7, 1986, entitled “Frame Addressed Spatial Light Modulator,” U.S. Pat. No. 4,662,746, issued May 5, 1987, entitled “Spatial Light Modulator and Method,” U.S. Pat. No. 5,061,049, issued Oct. 29, 1991, entitled “Spatial Light Modulator and Method,” U.S. Pat. No. 5,083,857, issued Jan. 28, 1992, entitled “Multi-Level Deformable Mirror Device,” U.S. Pat. No. 5,096,279, issued Mar. 17, 1992, entitled “Spatial Light Modulator and Method,” and U.S. Pat. No. 5,583,688, issued Dec. 10, 1996, entitled “Multi-Level Digital Micromirror Device,” which patents are hereby incorporated herein by reference.
With reference now to
The reference color sequence can be dependent on factors such as the chromatic characteristics of a light source, the usage history of the light source, the operating environment of the display system, and so forth. For example, a reference color sequence can describe the minimum display times for the colors in a color sequence that will produce a desired color temperature, given a specific light source, operating environment, and light source usage history. Different reference color sequences may be needed for producing different color temperatures, use with light sources, use in operating environments, different light source usage histories, and so forth. In an alternate preferred embodiment, the reference color sequence can describe a reference display time that specifies a nominal display time that is greater than the minimum display times for the colors in the color sequence. Then, utilizing scale factors between the minimum display time and the nominal display time, it is possible to effectively create color display times that are shorter in duration than the nominal times that are specified in the reference color sequence.
The diagram shown in
For example, the reference color sequence 405 can be used to produce a first color cycle 415, with the reference display time of the first color C1410 being scaled by a factor of 1.2 times to produce a scaled first color C1* 416, the reference display time of the second color C2411 being scaled by a factor of 1.8 times to produce a scaled second color C2* 417, and the reference display time of the third color C3412 being scaled by a factor of 1.0 times to produce a scaled third color C3* 418. Similarly, the reference color sequence 405 can be used to produce a second color cycle 420, with the reference display time of the first color C1410 being scaled by a factor of 2.0 times to produce a scaled first color C1** 421, the reference display time of the second color C2411 being scaled by a factor of 1.0 times to produce a scaled second color C2** 422, and the reference display time of the third color C3412 being scaled by a factor of 1.0 times to produce a scaled third color C3** 423.
Although the exemplary based color sequence descriptor 405 is a three-color color (RGB) sequence, the present invention can be applied to display systems utilizing other three-color sequences or more than three colors, i.e., multiprimary sequences. Additionally, the present invention can be applied to display systems using two colors. Therefore, the discussion of three-color color sequences should not be construed as being limiting to either the scope or the spirit of the present invention.
According to a preferred embodiment of the present invention, the scaling of the display times for each color provided by the reference color sequence 405 and the generation of the desired color sequence can have several constraints. For example, the desired color sequence should have an overall display time that is less than or equal to a color cycle period for the display system. Therefore, the display time of a red color, a blue color, and a green color should be less than or equal to the color cycle period. To simplify system design, the overall display time can further be restricted to being substantially equal to the color cycle period. Additionally, if the desired color sequence contains more than one color cycle, then the overall display time of the desired color sequence should be less than or equal to the frame time of the display system. Another potential constraint may be that the display times in the desired color sequence should be equal to or greater than the display times provided in the reference color sequence 305. This constraint may be relaxed by specifying nominal display time values in the reference color sequence 405 that are not the minimum display times for each color in the display system, which would permit the scaling of a color's display time to a value that is smaller than the specified display time in the reference color sequence 405.
With reference now to
According to a preferred embodiment of the present invention, the desired color sequence can be based upon factors such as the bit-weight of the image data being displayed, the relative distribution of colors in the image being displayed, the colors previously displayed, the colors to be displayed, the nature of the source of the images and the image data, and so forth. The sequence controller can, based on these factors, provide color sequences to the light controller circuit to have the light source produce colors of the color sequences and illuminate the array of light modulators.
The light controller circuit can then generate the control information necessary to generate the desired color sequence using the reference color sequence (block 510). The control information generated by the light controller circuit, when provided to the light source, will result in the light source producing the desired color sequence. A detailed description of the generation of the control information necessary to generate the desired color sequence is provided below. Alternatively, the light controller circuit can directly produce the drive signals for the light source needed to produce the desired color sequence from the reference color sequence. Finally, using the control information produced by the light controller circuit, the light source can display the desired color sequence (block 515).
The sequence of events shown in
Once the desired color sequence has been adjusted or if the desired color sequence as provided by the sequence controller is a valid color sequence, then a scaling factor can be computed for each color in the desired color sequence (block 565). The scaling factor can be computed based on the display time for each color as specified in the reference color sequence. For example, if the display time specified for a color in the reference color sequence is ten (10) milliseconds and a desired display time for the color is 14 milliseconds, then the scaling factor can be 1.4. The computed scaling factor for each color in the desired color sequence can be stored in a memory and then used sequentially to produce drive signals for driving the light source. For example, if the scaling factors for a RGB display system are RSF, GSF, and BSF, then each of the three scaling factors can be used by the light controller circuit to produce drive signals for use in having the light source produce the desired red, green, and blue colors in the desired order with the desired chromatic characteristics.
According to a preferred embodiment of the present invention, a desired display time for a color can be generated from a specified display time for the color in the reference color sequence by using a technique referred to as clock dropping. In clock dropping, a pulse width modulated sequence of a particular duration may be expanded by utilizing a cycle drop counter that counts cycles of a reference clock and causes a drop of a cycle of the reference clock whenever the counter resets or reaches a specified value. It is also possible to drop more than one cycle of the reference clock whenever the counter resets or reaches a specified value. The dropping of the clock cycles causes the pulse width modulated sequence duration to be expanded. The more clock cycles dropped, the greater the expansion of the pulse width modulated sequence. Detailed descriptions of the clock dropping technique are provided in co-assigned U.S. Pat. No. 5,912,712, entitled “Time Expansion for Pulse Width Modulation Sequences by Clock Dropping,” issued Jun. 15, 1999, and U.S. Pat. No. 7,019,881, entitled “Display System with Clock Dropping,” issued Mar. 28, 2006.
In a situation when a desired display time for a color is shorter than a reference display time for the color in the reference color sequence, it can be possible to scale the reference display time down to be substantially equal to the desired display time. This can occur when the reference display time for the color in the reference color sequence is a nominal display time and not the minimum display time for the color, since the minimum display time for a color is the shortest display time duration for the color in a display system. In order to shorten the display time when the minimum display time is specified, techniques other than simply modifying the display time must be employed to effectively reduce the amount of light produced by the display system, such as the use of neutral density filters, changing a diameter of an aperture positioned between the light source and the array of light modulators, and so forth. The nominal display time for a color can be longer in duration than the minimum display time, enabling the generation of a wide range of display times.
For example, if a nominal display time for each color in a three-color color sequence is specified as 50 time units, a minimum display time for the color is 30 time units, and a color cycle time is 150 time units, it can be possible to generate display times for a single color in the color sequence ranging from a minimum of about 30 time units to a maximum of about 90 time units, with the remaining 60 time units of the color cycle time being reserved to display the two remaining colors in the color sequence.
When clock dropping is used, the scaling factors for each color in the desired color sequence, calculated in block 565, can be referred to as clock drop factors, specifying the value in the cycle drop counter. The clock drop factor for each color in the desired color sequence can be stored in a memory after calculation and then recalled when the time to generate the particular color arises.
With reference now to
The output of the multiplexer 605 (a clock drop value for the selected color) can be provided to a clock drop circuit 620. The clock drop circuit 620 can include an adder 625 and a register 630. The register 630, preferably implemented using D-type flip-flops, can store the current value of the clock drop count. The adder 625 can adjust the value stored in the register 630 by a specified value, preferably the selected clock drop factor plus one. The combination of the register 630 and the adder 625 can be used as the clock drop counter discussed previously. An overflow bit of the register 630 can be an output of the clock drop circuit 620 and can be used as a timer enable. As another example, the diagram shown in
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.
Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
