Liquid crystal display and method of adjusting brightness for the same

• US 20070285379A1
• Filed: 01/19/2007
• Published: 12/13/2007
• Est. Priority Date: 06/09/2006
• Status: Abandoned Application

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Seong, Ki-bum, Park, Yung-jun, Jung, Jun-ho, Kim, Hyung-rae, Sung, Jun-ho, Hong, Chang-wan, Chen, Hanfeng, Choi, Hoon
• Application Number:
  US11/655,257
• Publication Number:
  US 20070285379A1
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• 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 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2360/16 Calculation or use of calculated indices related to luminance levels in display data
• 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 3/3611 Control of matrices with row and column drivers

Abstract

A liquid crystal display (LCD) and method of adjusting brightness for the LCD are provided. The LCD includes a light emitter including a plurality of luminescent bodies which are divided into a predetermined number of partial areas, a backlight driver connected to the light emitter to control the brightness of each of the partial areas of the light emitter, and a controller for calculating a representative value for adjusting the brightness of each of the partial areas of the light emitter in accordance with an input image signal and outputting the representative value as a brightness adjustment signal for adjusting the brightness of each of the partial areas to the backlight driver. Thus, the brightness of each of partial areas of a backlight can be adjusted in accordance with the input image signal to improve a contrast ratio. Also, a representative value to be used for adjusting the brightness of each of the partial areas can be lowered by a predetermined ratio to effectively reduce power needed for lighting the backlight. Also, light loss and light gain occurring between neighboring partial areas can be compensated to improve the contrast ratio, and image artifacts can be reduced.

Claims

1. An LCD (liquid crystal display), comprising:

a light emitter comprising a plurality of luminescent bodies divided into a predetermined number of partial areas;

a backlight driver connected to the light emitter for controlling a brightness of each of the partial areas of the light emitter; and

a controller for calculating a representative value for adjusting the brightness of each of the partial areas of the light emitter in accordance with an input image signal and outputting the representative value as a brightness adjustment signal for adjusting the brightness of each of the partial areas to the backlight driver.

2. The LCD of claim 1, wherein the controller is configured to filter and output the brightness adjustment signal.

3. The LCD of claim 2, wherein the controller is configured to filter and output the brightness adjustment signal using at least one of spatial filtering and temporal filtering.

4. The LCD of claim 1, wherein the controller is configured to:

classify pixels of each of the partial areas into a number of pixels according to each gray level in accordance with an input image signal; and

calculate the representative value to be used to adjust the brightness of each of the partial areas by using the number of pixels of each of sections which are made by dividing gray levels at predetermined intervals and a mean value of the gray levels of each section.

5. The LCD of claim 4, wherein the representative value is calculated using the equation:

$L=f<br><br>\left(\mathrm{L\_Thr}*\left({N_0<br><br>\left(\frac{M_0}{256}\right)}^2+{N_1<br><br>\left(\frac{M_1}{256}\right)}^2+{N_2<br><br>\left(\frac{M_2}{256}\right)}^2+{N_3<br><br>\left(\frac{M_3}{256}\right)}^2+{N_4<br><br>\left(\frac{M_4}{256}\right)}^2+{N_5<br><br>\left(\frac{M_5}{256}\right)}^2+{N_6<br><br>\left(\frac{M_6}{256}\right)}^2+{N_7<br><br>\left(\frac{M_7}{256}\right)}^2\right)\right)$

wherein L_Thr denotes a coefficient for compensating brightness of each of the partial areas, Mn(n=0, 1, 2, . . . ) denotes a mean value of the gray levels of a section n, and Nn(n=0, 1, 2, . . . ) denotes a number of pixels of the section n.

6. The LCD of claim 5, wherein if a mean brightness of the entire input image signal is lower than a predetermined threshold value, a partial area of which the representative value is greater than the mean brightness of the entire input image is applied with a new representative value L′

which has been compensated in order to adjust the brightness of the partial area using the equation;

L′

=L+BEN*(L−

mean)

wherein L′

denotes a new representative value of a partial area of which brightness loss has been compensated, L denotes a representative value before being compensated, BEN denotes a coefficient for compensating for the brightness, and mean denotes a mean brightness of an entire input image.

7. The LCD of claim 1, wherein the controller is configured to adjust the brightness of the light emitter at a speed substantially the same as a speed at which the input image signal is processed in synchronization with the input image signal.

8. The LCD of claim 1, wherein the controller is configured to adjust the brightness of the light emitter at a speed different from a speed at which the input image signal is processed.

9. A method of adjusting the brightness for an LCD, comprising:

calculating a representative value for adjusting brightness of each of partial areas of a light emitter in accordance with an input image signal;

outputting the calculated representative value as a brightness adjustment signal; and

adjusting the brightness of each of the partial areas based on the brightness adjustment signal.

10. The method of claim 9, further comprising filtering and outputting the brightness adjustment signal.

11. The method of claim 9, wherein the calculating of the representative value for adjusting the brightness of each of the partial areas of the light emitter in accordance with the input image signal comprises:

classifying pixels of each of the partial areas into a number of pixels according to each gray level in accordance with the input image signal; and

calculating the representative value to be used to adjust the brightness of each of the partial areas by using the number of pixels of each of sections which are made by dividing the gray levels at predetermined intervals and a mean value of the gray levels of each section.

12. The method of claim 11, wherein the representative value is calculated using the equation:

$L=f<br><br>\left(\mathrm{L\_Thr}*\left({N_0<br><br>\left(\frac{M_0}{256}\right)}^2+{N_1<br><br>\left(\frac{M_1}{256}\right)}^2+{N_2<br><br>\left(\frac{M_2}{256}\right)}^2+{N_3<br><br>\left(\frac{M_3}{256}\right)}^2+{N_4<br><br>\left(\frac{M_4}{256}\right)}^2+{N_5<br><br>\left(\frac{M_5}{256}\right)}^2+{N_6<br><br>\left(\frac{M_6}{256}\right)}^2+{N_7<br><br>\left(\frac{M_7}{256}\right)}^2\right)\right)$

wherein L_Thr denotes a coefficient for compensating for brightness of each of the partial areas, Mn(n=0, 1, 2, . . . ) denotes a mean value of the gray levels of a section n, and Nn(n=0, 1, 2, . . . ) denotes a number of pixels of the section n.

13. The method of claim 12, further comprising:

if a mean brightness of the entire input image signal is lower than a predetermined threshold value, compensating for brightness loss of a partial area of which the representative value is greater than the mean brightness of the entire input image by using the equation;

L′

=L+BEN*(L−

mean)

wherein L′

denotes a new representative value of a partial area of which brightness loss has been compensated, L denotes a representative value before being compensated, BEN denotes a coefficient for compensating for the brightness, and mean denotes a mean brightness of an entire input image.

14. The method of claim 9, wherein the brightness of the light emitter is adjusted at a speed substantially the same as a speed at which the input image signal is processed in synchronization with the input image signal.

15. The method of claim 9, wherein the brightness of the light emitter is adjusted at a speed different from a speed at which the input image signal is processed.

16. An LCD, comprising:

a backlight unit comprising a light emitter divided into a predetermined number of partial areas which are configured so that the brightness of each of the partial areas can be adjusted;

an LCD unit comprising an LCD panel and an LCD driver; and

a controller for calculating a representative value to be used for adjusting the brightness of each of the partial areas in accordance with an input image signal, lowering the representative value by a predetermined ratio to reduce power consumption of the backlight unit, and outputting the lowered representative value to the backlight unit.

17. The LCD of claim 16, wherein the predetermined ratio is calculated using the equation:

R=A/(A+T_—

Thr*(255−

A))

wherein R denotes the predetermined ratio, A denotes a cut-off gray level, and T_Thr denotes a predetermined threshold value within a range between “

0” and

“

1.”

18. The LCD of claim 17, wherein the cut-off gray level A denotes a maximum gray level of image pixels corresponding to a partial area wherein white Gaussian noise is excluded.

19. The LCD of claim 17, wherein the cut-off gray level A satisfies the equation:

$\underset{g=0}{\overset{A}{\sum <br><br>}}<br><br>H<br><br>\left(g\right)\ge <br><br>\mathrm{Cut\_Thr},\mathrm{and}<br><br><br><br>\underset{g=0}{\overset{A-1}{\sum <br><br>}}<br><br>H<br><br>\left(g\right)<<br><br>\mathrm{Cut\_Thr}$

wherein g denotes a gray level, H(g) denotes a total number of pixels corresponding to “

0”

through “

g”

, and Cut_Thr denotes a predetermined threshold value allowing a large number of pixels to belong to gray levels “

0”

through “

A.”

20. The LCD of claim 19, wherein the controller is configured to multiply gray levels of image pixels corresponding to each of the partial areas by at least one of values “

1/R” and

“

(1/R)^1/γ

”

to compensate for the reduction in the brightness of the backlight unit caused by the lowered representative value so that the brightness of an image to be displayed can be adjusted.

21. The LCD of claim 16, wherein the controller is configured to perform spatial filtering of the representative value to maintain the brightness of the partial area of which the brightness is the maximum among the partial areas.

22. The LCD of claim 16, wherein the controller performs temporal filtering of the representative value using the equation:

L_out⁽ⁿ⁾(k)=P′

·

L_ST⁽ⁿ⁾(k)+(1−

P′

)·

L_out^(n-1)(k)

wherein P′

denotes a predetermined threshold value for filtering and P′

=min(P+S,

     1), where P=|Mean_P−

Mean_C|/256 and S=|Mean_P−

Mean_C|/256, L_out⁽ⁿ⁾(k) denotes a final output brightness of a k^th partial area of a current frame after filtering, L_ST⁽ⁿ⁾(k) denotes a brightness of the k^th partial area of the current frame, L_out^(n-1)(k) denotes a final output brightness of a k^th partial area of a previous frame, P denotes frame brightness variation, S denotes a partial area'"'"'s brightness variation, Mean_P denotes a mean brightness of pixels of the previous frame, and Mean_C denotes a mean brightness of pixels of the current frame.

23. A method of adjusting the brightness for an LCD, comprising:

calculating a representative value for adjusting brightness of each of partial areas of a light emitter in accordance with an input image signal;

lowering the representative value by a predetermined ratio to reduce power consumption of a backlight unit; and

outputting the lowered representative value to the backlight unit to apply the lowered representative value to adjust the brightness of each of the partial areas.

24. The method of claim 23, wherein the predetermined ratio is calculated using the equation:

R=A/(A+T_—

Thr*(255−

A))

wherein R denotes a predetermined ratio, A denotes a cut-off gray level, and T_Thr denotes a predetermined threshold value within a range between “

0” and

“

1.”

25. The method of claim 24, wherein the cut-off gray level A is a maximum gray level of image pixels corresponding to a partial area wherein white Gaussian noise is excluded.

26. The method of claim 24, wherein the cut-off gray level A satisfies the equation:

$\underset{g=0}{\overset{A}{\sum <br><br>}}<br><br>H<br><br>\left(g\right)\ge <br><br>\mathrm{Cut\_Thr},\mathrm{and}<br><br><br><br>\underset{g=0}{\overset{A-1}{\sum <br><br>}}<br><br>H<br><br>\left(g\right)<<br><br>\mathrm{Cut\_Thr}$

wherein g denotes a gray level, H(g) denotes a total number of pixels corresponding to “

0”

through “

g”

, and Cut_Thr denotes a predetermined threshold value allowing a large number of pixels to belong to gray levels “

0”

through “

A.”

27. The method of claim 26, further comprising multiplying gray levels of image pixels corresponding to each of the partial areas by at least one of values “

1/R” and

“

(1/R)^1/γ

”

to adjust the brightness of an image to be displayed to compensate for the reduction in the brightness of the backlight unit caused by the lowered representative value.

28. The method of claim 23, further comprising spatial filtering the representative value to maintain the brightness of the partial area of which the brightness is the maximum among the partial areas.

29. The method of claim 23, further comprising temporal filtering the representative value using the equation:

L_out⁽ⁿ⁾(k)=P′

·

L_ST⁽ⁿ⁾(k)+(1−

P′

)·

L_out^(n-1)(k)

wherein P′

denotes a predetermined threshold value for filtering and P′

=min(P+S,

     1), where P=|Mean_P−

Mean_C|/256 and S=|Mean_P−

Mean_C|/256, L_out⁽ⁿ⁾(k) denotes a final output brightness of a k^th partial area of a current frame after filtering, L_ST⁽ⁿ⁾(k) denotes a brightness of the k^th partial area of the current frame, L_out^(n-1)(k) denotes a final output brightness of a k^th partial area of a previous frame, P denotes frame brightness variation, S denotes a partial area'"'"'s brightness variation, Mean_P denotes a mean brightness of pixels of the previous frame, and Mean_C denotes a mean brightness of pixels of the current frame.