Display apparatus

• US 20050104838A1
• Filed: 12/26/2002
• Published: 05/19/2005
• Est. Priority Date: 03/07/2002
• 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: Sasaki, Takashi
• Granted Patent: US 7,136,044 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2320/0626 for control of overall brightness
• CPC Class Codes: G09G 2320/0633 by amplitude modulation of the brightness of the illumination source
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• 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 3/2011 by amplitude modulation
• CPC Class Codes: G09G 3/2077 by a combination of two or more gradation control methods
• CPC Class Codes: G09G 3/3406 Control of illumination source illumination devices structurally associated with liquid crystal cells G02F1/1336
• CPC Class Codes: G09G 3/3611 Control of matrices with row and column drivers

Abstract

The invention provides a display panel 9; a gain variable liquid crystal driving circuit 10 for driving the display panel 9 with an amplified video signal that is obtained by multiplying an input video signal by a variable coefficient; a backlight operating circuit 6 for operating, based on a lamp control signal, a backlight 8 for illuminating the display panel 9; a level extension signal calculating circuit 11 for outputting an optical output level extension signal Lout by extending a predetermined output level used to operate the backlight 8, wherein the predetermined output level is extended based on an optical output gain obtained from the input video signal, and an output peak value of the backlight 8; and a white peak improving circuit 5 for receiving the optical output level extension signal, and for outputting a lamp control signal, whose white peak level has been adjusted according to a change in brightness of a scene, to the backlight operating circuit 6, and for calculating and outputting a video amplitude gain, which adjusts an amplitude of a video signal, as a coefficient to a gain variable driving amplifier circuit 3, wherein the lamp control signal is outputted when the brightness of a scene is above normal level, and the video amplitude gain is outputted when the brightness is at normal level. As a result, there is provided a display apparatus that improves peak luminance in a bright scene and suppresses pale black display in a dark scene and thereby provide a wide dynamic range without increasing power consumption.

Claims

1. A display apparatus comprising:

a display panel;

coefficient variable driving means for driving the display panel with an amplified video signal that is obtained by multiplying an input video signal by a variable coefficient;

operating means for operating, based on a lamp control signal, a lamp for illuminating the display panel;

level extension signal calculating means for outputting an optical output level extension signal by extending a predetermined output level used to operate the lamp, wherein the predetermined output level is extended based on an optical output gain obtained from the input video signal, and an output peak value of the lamp; and

white peak improving means for receiving the optical output level extension signal, and for outputting a lamp control signal, whose white peak level has been adjusted according to a change in brightness of a scene, to the operating means, and for calculating and outputting a video amplitude gain, which adjusts an amplitude of a video signal, as a coefficient to the gain variable driving means, wherein the lamp control signal is outputted when the brightness of a scene is above normal level, and the video amplitude gain is outputted when the brightness is at normal level.

2. The display apparatus as set forth in claim 1, wherein the coefficient variable driving means includes:

gain variable amplifying means for amplifying a video amplitude by obtaining a product of the video coefficient gain, which is a coefficient calculated by the white peak improving means, and the input video signal, and outputting the amplified video amplitude to driving means; and

driving means for driving the display panel according to the amplified video amplitude.

3. The display apparatus as set forth in claim 1, wherein the level extension signal calculating means includes:

peak level detecting means for detecting a peak level of the input video signal during certain intervals of time;

optical output gain calculating means for producing an optical output gain by calculation from the peak level detected by the peak level detecting means; and

optical output control means for outputting the optical output level extension signal such that a maximum value of products obtained by multiplying the optical output gain of the optical output gain calculating means by a predetermined optical output level for operating the lamp coincides with a peak value of the lamp.

4. The display apparatus as set forth in claim 1, wherein the white peak improving means includes:

a varied component detecting block for detecting a varied component of brightness, and calculating a correction signal for the lamp control signal so as to facilitate a change in brightness;

a reference signal/video amplitude gain calculating block for calculating a reference signal for the lamp control signal, and the video amplitude gain; and

adding means for adding the output of the varied component detecting block and the reference signal for the lamp control signal, and outputting a result of calculation as the lamp control signal.

5. The display apparatus as set forth in claim 4, wherein the varied component detecting block includes:

a level converting circuit for subtracting a predetermined threshold from the optical output level extension signal outputted from the optical output control means, so as to output a positive component of a subtraction result;

a differentiating circuit for differentiating an output signal of the level converting circuit with a certain time constant;

a luminance adaptive converting circuit for multiplying the output of the differentiating circuit by a predetermined coefficient which is set for each of a positive component and a negative component of the output of the differentiating circuit, so as to calculate a signal for controlling a light quantity of the operating means; and

a clip circuit for clipping an upper limit of the output of the luminance adaptive converting circuit, so as to prevent the lamp control signal from being outputted above the peak of the lamp.

6. The display apparatus as set forth in claim 4, wherein the reference signal/video amplitude gain calculating block includes:

a waveform restricting circuit for clipping, at a predetermined threshold, the optical output level extension signal outputted from the optical output control means, so as to output the clipped optical output level extension signal as the reference signal for the lamp control signal; and

a video amplitude gain calculating circuit for calculating the video amplitude gain by normalizing and taking an inverse of the output signal of the waveform restricting circuit.

7. The display apparatus as set forth in claim 6, wherein the waveform restricting circuit clips the optical output level extension signal by the threshold used by the level converting circuit.

8. The display apparatus as set forth in claim 4, wherein the varied component detecting block includes:

a level converting circuit for subtracting a predetermined threshold from the optical output level extension signal outputted from the optical output control means, so as to output a positive component of a subtraction result;

a differentiating circuit for differentiating an output signal of the level converting circuit with a certain time constant;

a luminance adaptive converting circuit for multiplying a positive component of the output of the differentiating circuit by a predetermined coefficient and clipping a negative component, so as to calculate a signal for controlling a light quantity of the operating means; and

a clip circuit for clipping an upper limit of the output of the luminance adaptive converting circuit, so as to prevent the lamp control signal from being outputted above the peak of the lamp.

9. The display apparatus as set forth in claim 5, wherein the reference signal/video amplitude gain calculating block includes:

a waveform restricting circuit for clipping, with a predetermined threshold, the optical output level extension signal outputted from the optical output control means, so as to output the clipped optical output level extension signal as the reference signal for the lamp control signal; and

a video amplitude gain calculating circuit for calculating the video amplitude gain by normalizing and taking an inverse of a result of addition to a negative component of the output of the luminance adaptive converting circuit.

10. The display apparatus as set forth in claim 1, wherein the brightness is a parameter that is calculated from pixel information of a video and that indicates brightness of a video frame, irrespective of a signal type.

11. The display apparatus as set forth in claim 10, wherein the brightness is based on a parameter indicative of brightness, including a maximum value, mean value, or minimum value of yellow (Y) in a video frame.

12. The display apparatus as set forth in claim 10, wherein the brightness is based on a combination of RGB values, which are parameters indicative of brightness, and that the brightness of a brightest pixel in a video frame is used as the brightness of the video frame.

13. The display apparatus as set forth in claim 10, wherein the brightness is an upper predetermined percent of pixel brightness obtained from a histogram of parameters that indicate the brightness of a video frame.

14. The display apparatus as set forth in claim 10, wherein the brightness is determined not from information of a single video frame, but is determined by taking into account information of a previous video frame.

15. The display apparatus as set forth in claim 10, wherein a scene of normal brightness and a scene brighter than normal brightness be separated from each other by a threshold.