Mechanism to Mitigate Color Breakup Artifacts in Field Sequential Color Display Systems

• US 20080192065A1
• Filed: 08/01/2006
• Published: 08/14/2008
• Est. Priority Date: 08/02/2005
• Status: Active Grant

• Current Assignee: Rambus Delaware
• Original Assignee: Uni-Pixel Displays Incorporated (Uni-Pixel Incorporated)
• Inventors: Selbrede, Martin G., Zemen, Rick
• Granted Patent: US 8,115,776 B2
• Time in Patent Office: Days
• US Class Current: 345/589
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/0261 in the context of movement of objects on the screen or movement of the observer relative to the screen
• CPC Class Codes: G09G 2320/0266 Reduction of sub-frame artefacts
• CPC Class Codes: G09G 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/2014 by modulation of the duration of a single pulse during which the logic level remains constant
• CPC Class Codes: G09G 3/3413 Details of control of colour illumination sources
• CPC Class Codes: G09G 3/3473 based on light coupled out of a light guide, e.g. due to scattering, by contracting the light guide with external means

Abstract

A mechanism for mitigating undesired color image breakup artifacts arising in display systems that exploit the principle of field sequential color generation. By suitably reducing the time interval during which image information strikes the moving retina, such that the differential position for the respective red, green, and blue components of the image falling upon the moving retina does not exceed the diameter of a retinal cone or rod, the cause of the breakup is negated and the image becomes unitary as expected: the eye sees the image as if all the components arrived at the same time. The truncation of light emission into shorter time frames necessitates a compensatory increase in imaging light intensity, such that the net amount of photonic flux striking the retina, averaged over time, remains unchanged. The mechanism can be applied to systems with discrete red, green, and blue sources as well as to color-wheel-based systems.

Claims

1. A field sequential color artifact suppression mechanism comprising:

a direct view field sequential color-based display system further comprising;

a mechanism for sequentially cycling between respective primary color illumination sources being applied to the display to supply primary light to the individual pixels comprising the controllable array of light modulating devices on the active display surface, the controlled activation of which generate the desired image by means of light modulation; and

means for controllably and selectively providing gray scale generation at each defined pixel on the display surface whereby any given primary color available in the display is appropriately modulated through each pixel as it activates and deactivates in synchronization with the respective primary being modulated.

2. The field sequential color artifact suppression mechanism as recited in claim 1, wherein said gray scale generation comprises a method of pulse width modulation at each pixel.

3. The field sequential color artifact suppression mechanism as recited in claim 1, wherein said gray scale generation comprises a method of amplitude modulation at each pixel.

4. The field sequential color artifact suppression mechanism as recited in claim 1, wherein said primary colors are the industry standard tristimulus colors red, green, and blue, in any arbitrary or specific cycling sequence.

5. The field sequential color artifact suppression mechanism as recited in claim 1, wherein said primary colors are cycled synchronously at fixed intervals during the illumination sequence regardless of program content being displayed.

6. The field sequential color artifact suppression mechanism as recited in claim 2, wherein said primary colors are cycled synchronously at fixed intervals during the illumination sequence regardless of program content being displayed.

7. The field sequential color artifact suppression mechanism as recited in claim 3, wherein said primary colors are cycled synchronously at fixed intervals during the illumination sequence regardless of program content being displayed.

8. The field sequential color artifact suppression mechanism as recited in claim 2, wherein said primary colors are cycled asynchronously during the illumination sequence, the respective intervals for each primary being determined by the requirements of program content for each displayed frame, such that the duration for each individual primary is shortened to match the longest corresponding pulse width for that primary color required in the frame of image data being displayed, which system further comprises:

means to re-encode each frame to enable said asynchronous sequencing of primary colors being supplied via the illumination means for the displays,

means to adjust the on and off times for the primary light sources that provide said illumination for each consecutive frame in real-time;

means to resynchronize pixel operation to an illumination cycling sequence that is no longer fixed but variable in respect to the length of time each primary color is being supplied to the display for the pixels to modulate via pulse width modulation; and

means to retain a uniform duration between the start point of each respective frame, such that global frame rate remains unchanged while image generation is compressed into the leading edge of each frame as required to suppress color image breakup and its associated artifacts.

9. The field sequential color artifact suppression mechanism as recited in claim 1, wherein the re-encoding of color information allows for enhanced temporal truncation by:

analyzing each respective frame of video information;

determining the threshold minimum amount of image information in each frame that can be re-encoded using combinations of two temporally-adjacent primaries within the displays illumination cycling sequence;

re-encoding each respective frame of video information to maximize the availability and subsequent exploitation of temporally-adjacent primaries that can be overlapped rather than sequentially activated during the illumination cycling sequence;

displaying the re-encoded frame by using the appropriately overlapped primaries rather than the original sequentially-running primaries within the illumination sequence, thereby creating the same video information as would have been generated in the unmodified cycle except in a shorter aggregate time period due to temporal overlap of the respective illumination sources providing primary colors to the display pixels for modulation; and

retaining a uniform duration between the start point of each respective frame, such that global frame rate remains unchanged while image generation is compressed into the leading edge of each frame as required to suppress color image breakup and its associated artifacts.

20. A field sequential color artifact suppression mechanism as cited in claim 9, wherein temporal truncation is further enhanced by adding:

a white light source to said primary color sources;

a means for determining when said primary overlap includes all three primary colors (i.e. white) for some duration, over the entire field; and

a means within said re-encoding of each respective frame whereby said white source can be added to the three primaries, such that the duration of time when all three primaries are on and overlapping is shortened in accordance with the increased intensity said added white source provides.

21. A field sequential color artifact suppression mechanism as cited in claim 9, wherein temporal truncation is further enhanced by adding:

one or more extra sets of primary light sources to said primary color sources; and

a means within said re-encoding of each respective frame whereby said extra sets of primary light sources can be added to the first three primaries, such that the additional intensity they provide allows the duration of time when said primaries are on, whether individually or overlapping, to be shortened.

22. A field sequential color artifact suppression mechanism as cited in claim 9, wherein temporal truncation is further enhanced by adding:

one or more extra sets of secondary light sources to said primary color sources;

a means for determining when said primary overlap includes appropriate pairs of primary colors (i.e. red plus green making the secondary yellow) for some duration, over the entire field; and

a means within said re-encoding of each respective frame whereby said secondary source can be added to the pair of primaries, such that the duration of time when the pair of primaries are on and overlapping is shortened in accordance with the increased intensity said added secondary sources provide.

10. A field sequential color artifact suppression mechanism comprising:

a project-based field sequential color-based display system further comprising;

a mechanism for sequentially cycling between respective primary color illumination sources being applied to the display to supply primary light to the individual pixels comprising the controllable array of light modulating devices within the display projection system, the controlled activation of which generate the desired image by means of light modulation; and

means for controllably and selectively providing gray scale generation at each defined pixel within the display projection system whereby any given primary color available for projection is appropriately modulated by each pixel as it activates and deactivates in synchronization with the respective primary being modulated.

11. The field sequential color artifact suppression mechanism as recited in claim 10, wherein said primary colors are the industry standard tristimulus colors red, green, and blue, in any arbitrary or specific cycling sequence.

12. The field sequential color artifact suppression mechanism as recited in claim 10, wherein said primary colors are generated using discrete red, green, and blue light sources that are independently controlled to provide the requisite sequence of primary lights being modulated for projection.

13. The field sequential color artifact suppression mechanism as recited in claim 12, wherein said primary colors are cycled asynchronously during the illumination sequence, the respective intervals for each primary being determined by the requirements of program content for each projected frame, such that the duration for each individual primary is shortened to match the longest corresponding pulse width for that primary color required in the frame of image data being projected, which system further comprises:

means to re-encode each frame to enable said asynchronous sequencing of primary colors being supplied via the illumination means for the display projection system,

means to adjust the on and off times for the primary light sources that provide said illumination for each consecutively projected frame in real-time;

means to resynchronize pixel operation to an illumination cycling sequence that is no longer fixed but variable in respect to the length of time each primary color is being supplied to the display for the pixels to modulate via pulse width modulation; and

means to retain a uniform duration between the start point of each respective projected frame, such that global frame rate remains unchanged while image generation is compressed into the leading edge of each projected frame as required to suppress color image breakup and its associated artifacts.

14. The field sequential color artifact suppression mechanism as recited in claim 12, wherein the re-encoding of color information allows for enhanced temporal truncation by:

analyzing each respective frame of video information to be projected;

determining the threshold minimum amount of image information in each frame that can be re-encoded using combinations of two temporally-adjacent primaries within the displays illumination cycling sequence;

re-encoding each respective frame of video information to maximize the availability and subsequent exploitation of temporally-adjacent primaries that can be overlapped rather than sequentially activated during the illumination cycling sequence;

projecting the re-encoded frame by using the appropriately overlapped primaries rather than the original sequentially-running primaries within the illumination sequence, thereby creating the same video information as would have been projected in the unmodified cycle except in a shorter aggregate time period due to temporal overlap of the respective illumination sources providing primary colors to the display projection system'"'"'s pixels for modulation and projection; and

retaining a uniform duration between the start point of each respective frame, such that global frame rate remains unchanged while image projection is compressed into the leading edge of each frame as required to suppress color image breakup and its associated artifacts.

15. The field sequential color artifact suppression mechanism as recited in claim 10, wherein said primary colors are sequentially and cyclically generated by the display projection system by passing a white light through a rotating color wheel system, said color wheel system further comprising:

a white light illumination source that passes light through a color wheel, which light is then supplied to the pixel modulation system of the display projection system;

a color wheel that includes primary color filter zones and a black absorbing zone, geometrically configured such that;

each zone is a angular segment of the wheel proscribing a fixed radial angle;

the zones for each primary color filter are adjacent, or nearly adjacent, to one another;

the zone for the black absorbing zone occupies all geometric area on the color wheel not occupied by the color filter zones;

the rotational speed of the color wheel is set to match one revolution per frame;

the angle proscribed for each color filter zone is fixed at a value such that during each rotation of the color wheel, the time during which white light passes through the entire series of primary filter zones is short enough (e.g., one to four milliseconds) to provide satisfactory suppression of color image breakup; and

the intensity of the white light source is increased to compensate for the reduction in available illumination time occasioned by the reduced time during which the color wheel actually filters white light to colored light by virtue of its configuration (e.g., if the time duration is quartered due to the color wheel truncating the window of opportunity to filter light, the light intensity is quadrupled to compensate for this).

16. The field sequential color artifact suppression mechanism as recited in claim 15, wherein said primary colors used in the color filter zones of the rotating color wheel correspond to the industry standard tristimulus colors red, green, and blue, in any arbitrary or specific cycling sequence.

17. The field sequential color artifact suppression mechanism as recited in claim 15, wherein said white light source is turned off when it is shining on the black absorbing zone during color wheel rotation, and turned on when shining through any of the primary color filter zones, thereby enhancing the energy efficiency of the display projection system.

18. The field sequential color artifact suppression mechanism as recited in claim 17, wherein gray scale is generated using pulse width generation in the display projection system, and the efficiency-enhancing mechanism of claim 17 is further augmented by a mechanism comprising:

means to determine in real-time the maximum pulse width required for each respective frame of primary information to be projected;

means to synchronize the deactivation of the white illumination source that projects light through the rotating color wheel once the maximum pulse width required for a given primary color has transpired; and

means to prevent activation of the white light source if there is no image content required to be projected for a given primary for a given frame of video information.

19. The field sequential color artifact suppression mechanism as recited in claim 15, where a conventional color wheel is used instead of a modified color wheel, but truncation of the actual projection time is achieved by increasing the rotation rate of the wheel by a given fixed integral value and passing white light through the wheel only during the first complete revolution that begins the leading edge of consecutive frame based on the base frame rate of the display projection system, which further comprises:

means to turn controllably and selective turn the illumination source providing white light on and off in appropriate synchronization with the color wheel rotation as described above, and

means to compensate for decreased illumination time by increasing the intensity of the white light source while it is turned on, in order to secure equivalent image brightness between devices where the present invention is implemented and those where it is not.