Methods and Systems for Backlight Modulation with Scene-Cut Detection

• US 20090141178A1
• Filed: 11/30/2007
• Published: 06/04/2009
• Est. Priority Date: 11/30/2007
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Zhou, Jin, Kerofsky, Louis J.
• Granted Patent: US 9,177,509 B2
• Time in Patent Office: Days
• US Class Current: 348/700
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• 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 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 2320/0673 for control of gamma adjustment, e.g. selecting another gamma curve
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/144 the light being ambient light
• 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
• CPC Class Codes: H04N 21/42202 environmental sensors, e.g. for detecting temperature, luminosity, pressure, earthquakes
• CPC Class Codes: H04N 21/44008 involving operations for analysing video streams, e.g. detecting features or characteristics in the video stream arrangements characterised by components specially adapted for monitoring, identification or recognition of video in broadcast systems H04H60/59
• CPC Class Codes: H04N 21/4402 involving reformatting operations of video signals for household redistribution, storage or real-time display details of conversion of video standards at pixel level H04N7/01; video transcoding H04N19/40; adapting incoming signals to the display format of the display terminal G09G5/005; media handling at the source in data packet switching networks H04L65/764
• CPC Class Codes: H04N 5/147 Scene change detection
• CPC Class Codes: H04N 5/57 Control of contrast or brightness

Abstract

Elements of the present invention relate to systems and methods for filtering a display source light illumination level with an adaptive filter based on the presence of a scene cut proximate to the current frame.

Claims

1. A method for selectively filtering a source light illumination level signal based on scene cut detection, said method comprising:

a) detecting the presence of a scene cut in a video sequence;

b) determining a source light illumination level value for a current frame of said video sequence based on image characteristics of said current frame;

c) filtering said source light illumination level value with a first filter when a scene cut is detected proximate to said current frame; and

d) filtering said source light illumination level value with a second filter when a scene cut is not detected proximate to said current frame.

2. A method as described in claim 1 wherein said detecting comprises comparing a histogram of said current frame with the histogram of a frame proximate to said current frame.

3. A method as described in claim 1 wherein said detecting comprises measuring a histogram distance between said current frame and a frame proximate to said current frame.

4. A method as described in claim 3 wherein said histogram distance is measured with the following equations:

$D_{\mathrm{cor}}<br><br>\left(H_1,H_2\right)=\sqrt{\frac{1}{W}<br><br>\underset{i=1}{\overset{N}{\sum <br><br>}}<br><br>\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>a_{\mathrm{ij}}<br><br><br><br>H_1<br><br>\left(i\right)-H_2<br><br>\left(i\right)<br><br><br><br><br><br>H_1<br><br>\left(j\right)-H_2<br><br>\left(j\right)<br><br>}$ $W=\underset{i=1}{\overset{N}{\sum <br><br>}}<br><br>\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>a_{\mathrm{ij}}$ $a_{\mathrm{ij}}={\left(i-j\right)}^2,$

wherein i and j are bin indices, N is the number of bins and H₁(i) is the value of the i-th bin of the histogram of said frame proximate to said current frame and H₂(i) is the i-th bin of the histogram of said current frame, and a_ij is the correlation weight which is equal to the square of the distance between bin indices.

5. A method as described in claim 3 wherein said detecting comprises comparing said histogram distance to a threshold value.

6. A method as described in claim 1 wherein said first filter is less aggressive than said second filter.

7. A method as described in claim 1 wherein said first filter and said second filter are infinite impulse response filters with different poles.

8. A method as described in claim 1 wherein said first filter and said second filter are described with the following equation:

S(i)=α

·

S(i−

1)+(1−

α

)·

BL(i) 0≦

≦

1

where BL(i) is the backlight value based on image content, S(i) is a smoothed backlight value based on a current value and history and a defines the location of the filter pole.

9. A method as described in claim 8 wherein said value of a is approximately between ½

and 1 for said second filter.

10. A method as described in claim 8 wherein said value of a is approximately between 0 and ½

for said first filter.

11. A method for selectively filtering a source light illumination level signal based on scene cut detection, said method comprising:

a) generating a histogram for a previous frame;

b) generating a histogram for a current frame;

c) detecting the presence of a scene cut in a video sequence by comparing said previous frame histogram to said current frame histogram;

d) determining a source light illumination level value for said current frame of said video sequence based on image characteristics of said current frame;

e) filtering said source light illumination level value with a first filter when a scene cut is detected proximate to said current frame; and

f) filtering said source light illumination level value with a second filter when a scene cut is not detected proximate to said current frame.

12. A method as described in claim 11 wherein said detecting comprises measuring a histogram distance between said current frame and said previous frame.

13. A method as described in claim 12 wherein said histogram distance is measured with the following equations:

$D_{\mathrm{cor}}<br><br>\left(H_1,H_2\right)=\sqrt{\frac{1}{W}<br><br>\underset{i=1}{\overset{N}{\sum <br><br>}}<br><br>\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>a_{\mathrm{ij}}<br><br><br><br>H_1<br><br>\left(i\right)-H_2<br><br>\left(i\right)<br><br><br><br><br><br>H_1<br><br>\left(j\right)-H_2<br><br>\left(j\right)<br><br>}$ $W=\underset{i=1}{\overset{N}{\sum <br><br>}}<br><br>\underset{j=1}{\overset{N}{\sum <br><br>}}<br><br>a_{\mathrm{ij}}$ $a_{\mathrm{ij}}={\left(i-j\right)}^2,$

wherein i and j are bin indices, N is the number of bins and H₁(i) is the value of the i-th bin of the histogram of said frame proximate to said current frame and H₂(i) is the i-th bin of the histogram of said current frame, and a_ij is the correlation weight which is equal to the square of the distance between bin indices.

14. A method as described in claim 12 wherein said detecting comprises comparing said histogram distance to a threshold value.

15. A method as described in claim 11 wherein said first filter is less aggressive than said second filter.

16. A method as described in claim 11 wherein said first filter and said second filter are infinite impulse response filters with different pole values.

17. A method as described in claim 11 wherein said first filter and said second filter are described with the following equation:

S(i)=α

·

S(i−

1)+(1−

α

)·

BL(i) 0≦

α

≦

1

where BL(i) is the backlight value based on image content, S(i) is a smoothed backlight value based on a current value and history and α

defines the location of the filter pole.

18. A method as described in claim 17 wherein said value of α

is approximately 1000/1024 for said second filter.

19. A method as described in claim 17 wherein said value of α

is approximately 128/1024 for said first filter.

20. A method for selectively filtering a source light illumination level signal based on scene cut detection, said method comprising:

a) generating a histogram for a previous frame;

b) generating a histogram for a current frame;

c) measuring a histogram distance between said current frame histogram and said second frame histogram;

d) detecting the presence of a scene cut in a video sequence comprising said previous frame and said current frame by comparing said histogram distance to a threshold value;

e) determining a source light illumination level value for said current frame of said video sequence based on image characteristics of said current frame;

f) filtering said source light illumination level value with an infinite impulse response (IIR) filter with a first pole value when a scene cut is detected proximate to said current frame; and

g) filtering said source light illumination level value with said infinite impulse response (IIR) filter with a second pole value when a scene cut is not detected proximate to said current frame.