LIQUID CRYSTAL DISPLAY

• US 20100165002A1
• Filed: 11/16/2009
• Published: 07/01/2010
• Est. Priority Date: 12/26/2008
• Status: Active Grant

• Current Assignee: LG Display Co., Ltd.
• Original Assignee: LG Display Co., Ltd.
• Inventors: AHN, Jiyoung
• Granted Patent: US 8,294,738 B2
• Time in Patent Office: Days
• US Class Current: 345/690
• 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 2330/028 Generation of voltages supplied to electrode drivers in a matrix display other than LCD
• CPC Class Codes: G09G 2340/06 Colour space transformation
• CPC Class Codes: G09G 2360/144 the light being ambient light
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers

Abstract

There is provided a liquid crystal display. A liquid crystal display panel displays an image. An external light sensor senses a color temperature of external light around the liquid crystal display panel. The output luminance of a backlight is controlled in response to an adjustment dimming signal which is varied according to an input image. A gamma curve adjustment circuit restores an original color of the display image irrespective of a change in the viewing environments by modulating input digital video data based on the color temperature of the external light or a relative maximum white luminance for the adjustment dimming signal.

Claims

1. A liquid crystal display, comprising:

a liquid crystal display panel displaying an image;

an external light sensor sensing a color temperature of external light around the liquid crystal display panel;

a backlight having an output luminance controlled in response to an adjustment dimming signal which is varied according to an input image; and

a gamma curve adjustment circuit restoring an original color of the display image irrespective of a change in viewing environments by modulating input digital video data based on the color temperature of the external light or a relative maximum white luminance for the adjustment dimming signal.

2. The liquid crystal display of claim 1, wherein the gamma curve adjustment circuit comprises:

a gamma curve setting unit selecting pieces of RGB gamma curve information corresponding to input color temperature information with reference to pieces of R gamma curve information, pieces of G gamma curve information, and pieces of B gamma curve information for every predetermined external light color temperature;

a storage unit comprising a number of look-up tables corresponding to the pieces of R gamma curve information, the pieces of G gamma curve information, and the pieces of B gamma curve information in a one-to-one manner; and

a gamma curve converter generating modulation digital video data by mapping the input digital video data to data which are registered with the respective look-up tables in a one-to-one manner using the look-up tables corresponding to the pieces of selected RGB gamma curve information.

3. The liquid crystal display of claim 1, wherein the gamma curve adjustment circuit comprises:

a gamma curve conversion controller determining whether color temperature information received from the external light sensor falls within a predetermined reference color temperature range and, if, as a result of the determination, the color temperature information is determined not to fall within the predetermined reference color temperature range, generating an operation signal;

a gamma curve setting unit, in response to the operation signal, calculating color coordinates of the input digital video data which have been distorted by the external light and color coordinates of white which has been distorted by the external light with respect to all gray scales, determining an RGB gray scale set which is a closest to color coordinates of an original white by the input digital video data, from among the color coordinates of the distorted white, as output RGB gray scales, and in real time determining R gamma curves, G gamma curves, and B gamma curves for compensating for the distorted color as an original state based on the determined RGB gray scales with respect to all the gray scales; and

a gamma curve converter generating modulation digital video data by mapping the input digital video data to the determined RGB gamma curves in a one-to-one manner.

4. The liquid crystal display of claim 3, wherein the gamma curve converter performs ‘

luminance equality mapping’

or ‘

brightness equality mapping with external light taken into consideration’

on gray scales which have not been mapped so that a gamma curve of each of the input digital video data has a predetermined curve.

5. The liquid crystal display of claim 1, wherein the gamma curve adjustment circuit comprises:

a gamma curve conversion controller determining whether color temperature information received from the external light sensor falls within a predetermined reference color temperature range and, if, as a result of the determination, the color temperature information is determined not to fall within the predetermined reference color temperature range, generating an operation signal;

a gamma curve setting unit, in response to the operation signal, calculating color coordinates of the input digital video data which have been distorted by the external light and color coordinates of white which has been distorted by the external light with respect to specific k gray scales comprising minimum gray scales and maximum gray scales, determining an RGB gray scale set which is a closest to color coordinates of an original white by the input digital video data, from among the color coordinates of the distorted white, as output RGB gray scales, and in real time determining R gamma curves, G gamma curves, and B gamma curves for compensating for the distorted color as an original state based on the determined RGB gray scales with respect to the specific k gray scales; and

a gamma curve converter generating modulation digital video data by mapping the input digital video data to the determined RGB gamma curves in a one-to-one manner.

6. The liquid crystal display of claim 5, wherein the gamma curve converter performs ‘

luminance equality mapping’

or ‘

brightness equality mapping with external light taken into consideration’

on gray scales which have not been mapped so that a gamma curve of each of the input digital video data has a predetermined curve.

7. The liquid crystal display of claim 5, further comprising:

a bit number extension unit extending a bit number of the input digital video data and supplying the extended bit number to the gamma curve setting unit in response to the operation signal; and

a bit number restoration unit restoring a bit number of the input digital video data mapped by the gamma curve converter in a state in which the bit number of the input digital video data has been extended.

8. The liquid crystal display of claim 1, wherein the gamma curve adjustment circuit comprises:

a gamma curve conversion controller determining whether color temperature information received from the external light sensor falls within a predetermined reference color temperature range and, if, as a result of the determination, the color temperature information is determined not to fall within the predetermined reference color temperature range, generating an operation signal;

a gamma curve setting unit, in response to the operation signal, calculating color coordinates of the input digital video data which have been distorted by the external light and color coordinates of white which has been distorted by the external light with respect to only maximum gray scales, determining an RGB gray scale set which is a closest to color coordinates of an original white by the input digital video data, from among the color coordinates of the distorted white, as output RGB gray scales, and in real time determining R gamma curves, G gamma curves, and B gamma curves for compensating for the distorted color as an original state based on the determined RGB gray scales with respect to the maximum gray scales; and

a gamma curve converter generating modulation digital video data by mapping the input digital video data to the determined RGB gamma curves in a one-to-one manner.

9. The liquid crystal display of claim 8, wherein the gamma curve converter performs ‘

luminance equality mapping’

or ‘

brightness equality mapping with external light taken into consideration’

on gray scales which have not been mapped so that a gamma curve of each of the input digital video data has a predetermined curve.

10. The liquid crystal display of claim 8, further comprising:

an image signal determination unit determining whether image signal color temperature information is included in the input digital video data and generating a selection signal having a different logic level according to a result of the determination;

a first gamma curve setting unit differently setting the pieces of gamma curve information for every image signal color temperature information and outputting R gamma curve information, G gamma curve information, and B gamma curve information of a range to which the external light color temperature belongs; and

a multiplexer selecting any one of the output of the gamma curve setting unit and the output of the first gamma curve setting unit and supplying the selected output to the gamma curve converter in response to the selection signal.

11. The liquid crystal display of claim 1, wherein the gamma curve adjustment circuit comprises:

a gamma curve conversion controller determining whether color temperature information received from the external light sensor falls within a predetermined reference color temperature range and, if, as a result of the determination, the color temperature information is determined not to fall within the predetermined reference color temperature range, generating an operation signal;

a gamma curve setting unit, in response to the operation signal, calculating color coordinates of the input digital video data which have been distorted by the external light and color coordinates of white which has been distorted by the external light with respect to only gray scales exceeding a critical value, determining an RGB gray scale set which is a closest to color coordinates of an original white by the input digital video data, from among the color coordinates of the distorted white, as output RGB gray scales, and in real time determining R gamma curves, G gamma curves, and B gamma curves for compensating for the distorted color as an original state based on the determined RGB gray scales with respect to the gray scales exceeding the critical value; and

a gamma curve converter generating modulation digital video data by mapping the input digital video data to the determined RGB gamma curves in a one-to-one manner,

wherein the critical value gray scale is a gray scale having a greatest value, from among gray scales which are more sensitive to luminance distortion than to color distortion resulting from the external light, and

the critical value becomes small with a higher luminance of a maximum gray scale and becomes great with a lower luminance of the maximum gray scale.

12. The liquid crystal display of claim 11, wherein the gamma curve converter performs ‘

luminance equality mapping’

or ‘

brightness equality mapping with external light taken into consideration’

on gray scales which have not been mapped so that a gamma curve of each of the input digital video data has a predetermined curve.

13. The liquid crystal display of claim 11, further comprising:

an image signal analysis unit storing input digital video data for one frame and extracting data having maximum gray scales and data having minimum gray scales by analyzing the data for the one frame;

a dimming ratio adjustment unit generating the adjustment dimming signal with reference to the maximum gray scale data and the minimum gray scale data; and

a maximum luminance calculation unit calculating a maximum white luminance of the input image in response to the adjustment dimming signal and supplying the calculated maximum white luminance to the gamma curve setting unit.

14. A liquid crystal display, comprising:

a liquid crystal display panel displaying an image;

an external light sensor sensing a color temperature of external light around the liquid crystal display panel;

a backlight having an output luminance controlled in response to an adjustment dimming signal which is varied according to an input image; and

a gamma curve adjustment circuit restoring an original color of the display image irrespective of a change in viewing environments by varying resistance values of variable resistors constituting a gamma resistance string based on the luminous intensity of the external light or a relative maximum white luminance for the adjustment dimming signal.