Image display device with reduced flickering and blur

• US 8,115,728 B2
• Filed: 06/20/2005
• Issued: 02/14/2012
• Est. Priority Date: 03/09/2005
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Laboratories of America Incorporated (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Feng, Xiao-fan
• Primary Examiner(s): Mengistu, Amare
• Assistant Examiner(s): LAM, VINH TANG
• Application Number:
  US11/157,231
• Publication Number:
  US 20060202945A1
• Time in Patent Office: 2,430 Days
• Field of Search: 345/87, 345/102, 349/62
• US Class Current: 345/102
• CPC Class Codes: G09G 2310/0237 Switching ON and OFF the backlight within one frame
• CPC Class Codes: G09G 2310/024 Scrolling of light from the illumination source over the display in combination with the scanning of the display screen
• CPC Class Codes: G09G 2310/08 Details of timing specific for flat panels, other than clock recovery
• CPC Class Codes: G09G 2320/0252 Improving the response speed
• CPC Class Codes: G09G 2320/0257 Reduction of after-image effects
• 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 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2320/103 Detection of image changes, e.g. determination of an index representative of the image change
• CPC Class Codes: G09G 2340/16 Determination of a pixel data signal depending on the signal applied in the previous frame
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix
• CPC Class Codes: G09G 3/3666 with the matrix divided into sections

Abstract

A backlit display with improved display characteristics.

Claims

1. A method for displaying an image having a first resolution on a liquid crystal display having a second resolution less than said first resolution, said liquid crystal display including a backlight that illuminates an array of at least one light valve, said array having a first surface illuminated by said backlight and a second surface parallel to said first surface, and from which transmitted light emanates away from said array based on respective transmittance states of respective light valves in said array, said backlight comprising a plurality of backlight regions, each backlight region capable of achieving a selected one of a plurality of illumination levels, independent of the respective illumination levels produced by other ones of said plurality of backlight regions, said method comprising:

(a) receiving an image signal representative of at least one frame of said image;

(b) processing said signal by dividing said at least one frame into a plurality of image blocks each associated with a respective one of said plurality of backlight regions, and providing light at a first said illumination level to impinge upon said first surface from a first region of said backlight based upon a first determination that an image block associated with said first region is likely to include motion greater than a threshold, said first determination being made from a motion map constructed based upon said image blocks;

(c) providing light at a second said illumination level to impinge upon said first surface from a second region of said backlight based upon a determination that an image block associated with said second region is not likely to include motion greater than a threshold, said second determination being made from said motion map;

where

(d) said first and second illumination levels are each provided over a respective temporal flashing period divided between a first interval when a backlight from a respectively associated said region is on and a second interval when a backlight from a respectively associated said region is off, said first and second intervals calculated based on comparison of the provided illumination level to a screen function having the form;

S(t)=A(1−

n*t+floor(n*t)) where t is a continuous float variable of time expressed in frames, A is the backlight screen amplitude, n is an integer value, and floor(t) is an operation that takes the integer portion of its argument.

2. The method of claim 1 where more than one said image block is associated with a single one of said plurality of backlight regions.

3. The method of claim 2 where said motion map is constructed by:

(a) determining, for each said image block, the difference between the average luminance of said image block during two consecutive frames; and

(b) comparing said difference to a luminance threshold.

4. The method of claim 3 where said luminance threshold is 5% of the total range of luminance of said backlight.

5. The method of claim 1 including the step of performing a logical “

or”

operation on respective modified motion maps of two consecutive frames.

6. The method of claim 1 where n is 1.

7. The method of claim 1 where n is 2.

8. The method of claim 1 where the value of n for a first region is different than that for a second region.

9. The method of claim 8 where n is selected for a region based on the motion for said region indicated by said motion map.

10. The method of claim 8 where n has a first value for a region during a first frame and a second value for a region during a second frame.

11. The method of claim 10 where said first and second levels are calculated for at least one transition frame, between said first frame and said second frame, based upon

S_t=A[1−

(t−

floor(t))/0.5(1+(i/(N+1)))] for 0<

=t−

floor(t)<

0.5[1−

i/(N+1)]

and

S_t=A[1−

(t−

0.5−

floor(t−

0.5))/0.5(1+(i/(N+1)))] for 0.5[1−

i/(N+1)]<

=t−

floor(t)<

1

where N is the total number of transition frames and i is the i^th transition frame.

12. A method for displaying an image having a first resolution on a liquid crystal display having a second resolution less than said first resolution, said liquid crystal display including a backlight that illuminates at least one light valve, said backlight comprising a plurality of backlight regions, each backlight region capable of achieving a selected one of a plurality of illumination levels, independent of the respective illumination levels produced by other ones of said plurality of backlight regions, said method comprising:

(a) receiving an image signal representative of at least one frame of said image and analyzing said signal to determine respective amounts of motion in areas of said image, each area associated with each said plurality of backlight regions; and

(b) providing light to a first pixel of said light valve having an illumination characteristic within a respective frame interval that is different from that of another pixel of said display during said respective frame interval, said respective frame interval divided between a first period when the said first pixel and said another pixel are each illuminated by respectively different ones of said plurality of backlight regions and a second period when the said first pixel and said another pixel are respectively not illuminated, said illumination characteristic selected based on the respectively determined amount of motion in the respective area associated with said backlight region illuminating said first pixel, where said first period and said second period have respective durations determined based on comparing the selected illumination level for said associated backlight region to a screen function having the form S(t)=A(1−

c₁*t+c₂*floor(t−

c₃)−

c₄), where t is a continuous float variable of time expressed in frames, A is the backlight screen amplitude, c₁ c₂, c₃, and c₄ are constants, and floor(t−

c₃) is an operation that takes the integer portion of its argument.

13. The method of claim 12 where n is 1.

14. The method of claim 12 where n is 2.

15. The method of claim 12 where the value of n for a first region is different than that for a second region.

16. The method of claim 12 where n is selected for a region based on the motion determined for said region.

17. The method of claim 12 where n has a first value for a region during a first frame and a second value for a region during a second frame.

18. The method of claim 17 where said first and second levels are calculated for at least one transition frame, between said first frame and said second frame, based upon

S_t=A[1−

(t−

floor(t))/0.5(1+(i/(N+1)))] for 0<

=t−

floor(t)<

0.5[1−

i/(N+1)]

and

S_t=A[1−

(t−

0.5−

floor(t−

0.5))/0.5(1+(i/(N+1)))] for 0.5[1−

i/(N+1)]<

=t−

floor(t)<

1

where N is the total number of transition frames and i is the i^th transition frame.

19. The method of claim 18 where overdrive is used to accelerate the transition between said first frame and said second frame.