System and method for backlight and LCD adjustment

• US 9,692,946 B2
• Filed: 06/28/2010
• Issued: 06/27/2017
• Est. Priority Date: 06/29/2009
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Orlick, Christopher, Giaretta, Giorgio, Patel, Saagar, Smith, Jared, Wan, Chun Chi, Davies, Trevor
• Primary Examiner(s): Watko, Julie Anne
• Application Number:
  US12/824,457
• Publication Number:
  US 20100328537A1
• Time in Patent Office: 2,556 Days
• Field of Search: 345102, 345 88, 345 89, 345690
• 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 2320/0276 for the purpose of adaptation to the characteristics of a display device, i.e. gamma correction
• CPC Class Codes: G09G 2320/0646 Modulation of illumination source brightness and image signal correlated to each other
• CPC Class Codes: G09G 2320/0673 for control of gamma adjustment, e.g. selecting another gamma curve
• CPC Class Codes: G09G 3/3426 the different display panel areas being distributed in two dimensions, e.g. matrix
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: H04N 5/202 Gamma control circuits for controlling camera response irrespective of the scene brightness H04N23/82

Abstract

In one embodiment the present invention includes a display system for displaying video. The display system includes a backlight layer and an LCD layer. The display system controls the backlight layer and the LCD layer to emulate a cathode ray tube response. This emulation may be accomplished by applying a gamma function to a gamma corrected input signal. In this manner, the effects resulting from the “crushed blacks” phenomenon may be reduced.

Claims

1. An apparatus for reproducing the response of an emulated device including a circuit for generating video signals for a video display device that includes a liquid crystal display (LCD) layer and a backlight, said backlight comprising a set of light emitting diodes (LEDs) wherein each LED is configured to be individually modulated, the circuit comprising:

a backlight generation circuit that generates a backlight control signal based on an input video signal, said input video data comprising a non-linear signal produced by gamma correcting recorded linear light image data, the backlight control signal comprising an average of the gamma corrected input video signal in the area around each LED;

a backlight transfer function circuit that transforms the backlight control signal to a linear backlight control signal to drive each individual LED using pulse width modulation (PWM) signal calculated for each individual LED and further such that the backlight generates a low resolution image of the input video signal;

a emulated device gamma response function circuit that converts the input video signal to a modified input video signal using a transfer function that corresponds to a emulated device response;

a LCD correction circuit that generates a linear LCD transmissivity signal based on the modified input video signal and the light field simulation signal;

a LCD modification circuit that modifies the linear LCD transmissivity signal, applying an inverse characterization of the LCD layer to generate the LCD control signal; and

wherein the video display device according to the backlight control signal and the LCD control signal reproduces the response of the emulated device.

2. The apparatus of claim 1, further comprising:

a light field simulation circuit, coupled between the backlight generation circuit and the LCD correction circuit, that simulates a light field of the LCD layer according to light field simulation signal.

3. The apparatus of claim 1, wherein the emulated device gamma response function circuit implements a gamma function, wherein the gamma function operates on RGB components, and wherein the modified input video signal comprises a linear R, G, B signal.

4. The apparatus of claim 1, wherein the transfer function circuit implements a gamma function with a factor of between 2.2 and 3.0.

5. The apparatus of claim 1, wherein the transfer function circuit implements a gamma function with a factor that is selectable between 2.2 and 3.0.

6. The apparatus of claim 1, wherein the backlight generation circuit generates the backlight control signal to have a mean perceptual light level increased by a factor greater than 1.

7. The apparatus of claim 1, wherein the backlight generation circuit generates the backlight control signal to have a mean perceptual light level increased between 180% and 220%.

8. The apparatus of claim 1, wherein the backlight generation circuit generates the backlight control signal to have a mean perceptual light level increased between 150% and 250%.

9. A system for reproducing the response of an emulated device, comprising:

a backlight layer, said backlight layer comprising a set of light emitting diodes (LEDs) wherein each LED is configured to be individually modulated;

a liquid crystal display (LCD) layer; and

a dual control circuit that generates video signals for the backlight layer and the LCD layer, the dual control circuit including;

a backlight generation circuit that generates a backlight control signal based on an input video signal, said input video data comprising a non-linear signal produced by gamma correcting recorded linear light image data, the backlight control signal comprising an average of the gamma corrected input video signal in the area around each LED;

a backlight transfer function circuit that transforms the backlight control signal to a linear backlight control signal to drive each individual LED using pulse width modulation (PWM) signal calculated for each individual LED and further such that the backlight generates a low resolution image of the input video signal;

a emulated device gamma response function circuit that converts the input video signal to a modified input video signal using a transfer function that corresponds to a emulated device response;

a LCD correction circuit that generates a LCD control signal based on the modified input video signal and the light field simulation signal that generates the low resolution image wherein further the generated LCD control signal is a corrected signal in the linear domain based upon a function of the transmissivity of the LCD and the backlight illumination;

a LCD modification circuit that modifies the LCD control signal, using an inverse characterization of the LCD layer inputting the linearized LCD control signal, to generate a modified LCD control signal; and

a controller circuit that controls the backlight layer according to the backlight control signal and that controls the LCD layer according to the modified LCD control signal to display an output video signal, wherein the linear backlight control signal and the modified LCD control signal, in combination, control the backlight layer and the LCD layer to emulate the emulated device response.

10. A method of generating video signals for a video display device that reproduces the response of an emulated device that includes a liquid crystal display (LCD) layer and a backlight, said backlight comprising a set of light emitting diodes (LEDs) wherein each LED is configured to be individually modulated, comprising:

generating a backlight control signal based on an input video signal, said input video data comprising a non-linear signal produced by gamma correcting recorded linear light image data, the backlight control signal comprising an average of the gamma corrected input video signal in the area around each LED;

transforming the backlight control signal to a linear backlight control signal to drive each individual LED using pulse width modulation (PWM) signal calculated for each individual LED such that the backlight generates a low resolution image of the input video signal;

converting the input video signal to a modified input video signal using a transfer function that corresponds to a emulated device response;

generating a LCD control signal based on the modified input video signal and the light field simulation signal that generates the low resolution image wherein further the generated LCD control signal is a corrected signal in the linear domain based upon a function of the transmissivity of the LCD and the backlight illumination;

modifying the LCD control signal, using an inverse characterization of the LCD layer inputting the linearized LCD control signal; and

controlling the video display device according to the backlight control signal and the modified LCD control signal reproduces the response of the emulated device response.

11. The method of claim 10, wherein the input video signal comprises an input gamma corrected video signal, further comprising:

converting the input gamma corrected video signal, using a gamma function operating on RGB components, to generate the modified input video signal, wherein the modified input video signal comprises a linear R, G, B signal.

12. The method of claim 10, wherein generating the backlight control signal includes:

calculating an average signal level of the input video signal; and

generating the backlight control signal based on the average signal level.

13. The method of claim 10, wherein generating the backlight control signal includes:

increasing a mean perceptual light level of the backlight control signal by a factor.

14. The method of claim 10, wherein generating the backlight control signal includes:

increasing a mean perceptual light level of the backlight control signal by a factor of between 1.8 and 2.2.

15. The method of claim 10, wherein generating the backlight control signal includes:

increasing a mean perceptual light level of the backlight control signal by a factor of between 1.5 and 2.5.

16. The method of claim 10, wherein the transfer function is a gamma function.

17. The method of claim 10, wherein the transfer function is a gamma function calculated using an equation comprising Co=Ci^gamma when Ci represents gamma-corrected R, G, and B signals and wherein gamma is approximately 2.4.

18. The method of claim 10, wherein the transfer function is a gamma function calculated using a lookup table.