TEMPORAL FILTERING OF VIDEO SIGNALS

• US 20090201320A1
• Filed: 02/13/2008
• Published: 08/13/2009
• Est. Priority Date: 02/13/2008
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Damberg, Gerwin, Seetzen, Helge
• Granted Patent: US 8,493,313 B2
• Time in Patent Office: Days
• US Class Current: 345/694
• 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 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2320/0653 Controlling or limiting the speed of brightness adjustment of the illumination source
• CPC Class Codes: G09G 2320/066 for control of contrast
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix

Abstract

A process for reducing noise and temporal artifacts (e.g. walking LEDs) on a dual modulation display system by applying temporal filtering to rear modulation signals of a sequence of video frames. Flare and dimming rates are calculated for a current frame in the video. If a flare rate threshold is exceeded, an intensity of the backlight is limited to a predetermined flare rate. If a dimming rate threshold is exceeded, the backlight intensity is limited to a predetermined dimming rate. The limitations are applied, for example, on an element-by-element basis. In the event of a scene change, the limitations do not need to be applied. A forward modulation signal is calculated by taking into account any applied backlight limitations.

Claims

1. A method, comprising the steps of:

receiving a segment of a video;

calculating a rear modulation signal for the received segment;

calculating a difference in intensity between the rear modulation signal of the received segment and a rear modulation signal of a previous frame corresponding to the received segment; and

modifying the rear modulation signal for the received segment with a filtering limit R to obtain an actual rear modulation signal for the received segment.

2. The method according to claim 1, wherein the received segment comprises one of a full frame of the video, a fixed partial frame of the video, a variable partial frame of the video, and a scanned portion of the video.

3. The method according to claim 1, further comprising the step of determining the filtering limit R.

4. The method according to claim 1, wherein the filtering limit R is based on at least one of performance characteristics of a display on which the video is to be displayed and characteristics of the video signal.

5. The method according to claim 1, further comprising the steps of:

detecting when the current frame represents a scene change; and

if the current frame represents a scene change, then skipping the step of modifying the rear modulation signal.

6. The method according to claim 5, wherein the step of detecting a scene change comprises one of comparing at least one previous frame to the current frame, and testing meta data of the video.

7. The method according to claim 6, wherein said step of comparing comprises performing one of an average, weighted average, mean, or other mathematical function on each of the at least one previous frame and the current frame.

8. The method according to claim 1, further comprising the steps of:

comparing at least one previous modulation signal to at least one modulation signal subsequent to the at least one previous modulation signal and determining if a threshold T is exceeded; and

if the threshold T is exceeded, skipping the step of modifying the rear modulation signal.

9. The method according to claim 8, further comprising the step of determining the threshold T.

10. The method according to claim 8, wherein said step of comparing comprises comparing one of a previous rear modulation signal and a previous front modulation signal to one of a current and/or subsequent rear modulation signal and a current and/or subsequent front modulation signal.

11. The method according to claim 8, wherein said step of comparing comprises comparing a set of previous rear and/or front modulation signals to a set of rear and/or front modulation signals.

12. The method according to claim 10, wherein the method is embodied as a set of computer instructions stored on a computer readable media in a display device comprising a rear modulator configured to receive the rear modulation signal and a front modulator configured to receive the front modulation signal.

13. The method according to claim 12, wherein the display device comprises a high dynamic range display and the rear modulator comprises an array of LEDs.

14. The method according to claim 13, wherein the array of LEDs are controlled in groups within the array.

15. The method according to claim 1, wherein:

said method is embodied in a set of computer instructions stored on a computer readable media;

said computer instructions, when loaded into a computer, cause the computer to perform the steps of said method.

16. The method according to claim 15, wherein said computer instructions are compiled computer instructions stored as an executable program on said computer readable media.

17. An high dynamic range display, comprising:

a front modulator unit;

a rear modulation unit comprising an array of individually controllable backlights having a resolution lower than a resolution of the front modulation unit and configured to project modulated light onto the front modulation unit; and

a controller coupled to the rear modulation unit and configured to prepare a rear modulation signal and transmit it to the rear modulation unit, said rear modulation signal limited according to at least one of a flare rate and a dimming rate.

18. The high dynamic range display according to claim 17, wherein the controller is further configured to determine a scene change in a video to be displayed and prepare the rear modulation signal without limitations during the scene change.

19. The high dynamic range display according to claim 17, wherein the rear modulation signal is only modified for signals flaring or dimming at a rate exceeding the corresponding flare rate or dimming rate.

20. A controller configured to provide control signals to each individually controllable light element of a light element array, said control signals comprising an amount of light derived from a video signal and limited in intensity if at least one of a flare rate threshold and a dimming rate threshold are exceeded.

21. The controller according to claim 20, wherein the control signals received at an individual light element comprises light intensity from the video signal in an area of the video corresponding to a location of the individual light element.

22. The controller according to claim 20, wherein the controller determines if the thresholds are exceeded on a frame-by-frame basis by averaging light intensities across multiple previous frames.

23. The controller according to claim 22, wherein the limitation of intensity is performed in an area-by-area basis of a video image such that one area of the video image may be limited in intensity and another area is not limited.

24. The controller according to claim 23, wherein the areas are determined by one of a predetermined division of the video image and a dynamic division of the video image.

25. The controller according to claim 20, wherein at least one of the thresholds is determined dynamically.

26. A display comprising:

an LCD panel;

an array of backlight elements configured to project modulated light onto the LCD panel, wherein a resolution of the backlight elements is lower than a resolution of the LCD panel; and

a controller comprising a processing device configured to provide a light intensity to each backlight element, the light intensity of an individual backlight unit corresponding to an intensity in a portion of a video image to be displayed on the display and illuminated by the backlight element;

the controller further comprising means for reducing artifacts resulting from the difference in resolution between the backlight elements and the LCD panel, including,

means for detecting a flare rate in at least a segment of the video image compared to a corresponding segment of the video image previously displayed,

means for detecting a dimming rate in at least a segment of the video image compared to a corresponding segment of the video image previously displayed, and

means for limiting the light intensity of an individual backlight element if the light intensity of the individual backlight element per the video image exceeds at least one of the flare rate and the dimming rate.