GAMMA-CORRECTION TECHNIQUE FOR VIDEO PLAYBACK

• US 20090002555A1
• Filed: 06/24/2008
• Published: 01/01/2009
• Est. Priority Date: 06/26/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Chen, Wei, Barnhoefer, Ulrich T., Allegrucci, Jean-Didier, Corlett, Barry J., Yao, Wei H.
• Granted Patent: US 8,692,755 B2
• Time in Patent Office: Days
• US Class Current: 348/554
• CPC Class Codes: G09G 2300/0452 Details of colour pixel setup, e.g. pixel composed of a red, a blue and two green components
• CPC Class Codes: G09G 2310/0232 Special driving of display border areas
• CPC Class Codes: G09G 2320/0242 Compensation of deficiencies in the appearance of colours
• CPC Class Codes: G09G 2320/0247 Flicker reduction other than flicker reduction circuits used for single beam cathode-ray tubes
• CPC Class Codes: G09G 2320/0646 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 2320/0666 for control of colour parameters, e.g. colour temperature
• 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 3/3406 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

Embodiments of a system that includes one or more integrated circuits are described. During operation, the system transforms the video image from an initial brightness domain to a linear brightness domain, which includes a range of brightness values corresponding to substantially equidistant adjacent radiant-power values in a displayed video image. In this linear brightness domain, the system may determine an intensity setting of the light source based on at least a portion of the transformed video image, such as the portion of the transformed video image that includes spatially varying visual information in the video image. Moreover, the system may modify the transformed video image so that a product of the intensity setting and a transmittance associated with the modified video image approximately equals a product of a previous intensity setting and a transmittance associated with the video image. For example, the modification may include changing brightness values in the transformed video image.

Claims

1. A system, comprising one or more integrated circuits, wherein the one or more integrated circuits are configured to:

transform a video image from an initial brightness domain to a linear brightness domain, the linear brightness domain characterized by a range of brightness values corresponding to substantially equidistant adjacent radiant-power values in a displayed video image;

determine an intensity setting of a light source based on at least a portion of the transformed video image, the light source configured to illuminate a display that is configured to display video images; and

modify the transformed video image so that a product of the intensity setting and a transmittance associated with the modified video image approximately equals a product of a previous intensity setting and a transmittance associated with the video image.

2. The system of claim 1, wherein the transformation compensates for gamma correction in the video image which is associated with an imaging device that captured the video image.

3. The system of claim 1, wherein the transformation is determined using a look-up table.

4. The system of claim 1, wherein the one or more integrated circuits are further configured to convert the modified video image to another brightness domain characterized by the range of brightness values corresponding to non-equidistant adjacent radiant-power values in a displayed video image.

9. The system of claim 1, wherein the modification of the video image is performed on a pixel-by-pixel basis.

10. The system of claim 1, wherein the video image includes a frame of video.

11. The system of claim 1, wherein at least the portion of the transformed video image includes spatially varying visual information in the video image.

12. The system of claim 1, wherein the intensity setting is determined based on a histogram of brightness values in at least the portion of the transformed video image.

13. The system of claim 1, wherein the light source comprises a light-emitting diode or a fluorescent lamp.

14. The system of claim 1, wherein the modification includes changing brightness values in the transformed video image.

5. The system of claim 5, wherein the other brightness domain is approximately the same as the initial brightness domain.

6. The system of claim 5, wherein the conversion applies a gamma correction to the modified video image.

7. The system of claim 6, wherein the gamma correction is associated with the display.

8. The system of claim 5, wherein the conversion is determined using a look-up table.

15. A system, comprising:

an input node configured to receive video signals associated with a video image;

a transform circuit electrically coupled to the input node, the transform circuit configured to transform the video image from an initial brightness domain to a linear brightness domain that is characterized by a range of brightness values corresponding to substantially equidistant adjacent radiant-power values in a displayed video image;

a computation circuit electrically coupled to the transform circuit, the computation circuit configured to determine an intensity setting of a light source, which is configured to illuminate a display that is configured to display video images, based on at least a portion of the transformed video image and configured to modify the transformed video image so that a product of the intensity setting and a transmittance associated with the modified video image approximately equals a product of a previous intensity setting and a transmittance associated with the video image; and

an output node electrically coupled to the computation circuit, the output node configured to output signals corresponding to the modified video signals.

16. A method for adjusting a video image, comprising:

compensating for gamma correction in a video image to produce a linear relationship between brightness values and an associated brightness of the video image when displayed;

calculating an intensity setting of a light source based on at least a portion of the compensated video image, the light source configured to illuminate a display that is configured to display video images; and

adjusting the compensated video image so that a product of the intensity setting and a transmittance associated with the adjusted video image approximately equals a product of a previous intensity setting and a transmittance associated with the video image.

17. A computer-program product for use in conjunction with a computer system, the computer-program product comprising a computer-readable storage medium and a computer-program mechanism embedded therein for adjusting a video image, the computer-program mechanism comprising:

instructions for compensating for gamma correction in a video image to produce a linear relationship between brightness values and an associated brightness of the video image when displayed;

instructions for calculating an intensity setting of a light source based on at least a portion of the compensated video image, the light source configured to illuminate a display that is configured to display video images; and

instructions for adjusting the compensated video image so that a product of the intensity setting and a transmittance associated with the adjusted video image approximately equals a product of a previous intensity setting and a transmittance associated with the video image.

18. A computer system to adjust a video image, comprising:

a processor;

memory;

a program module, wherein the program module is stored in the memory and configurable to be executed by the processor, the program module including;

instructions for compensating for gamma correction in a video image to produce a linear relationship between brightness values and an associated brightness of the video image when displayed;

instructions for calculating an intensity setting of a light source based on at least a portion of the compensated video image, the light source configured to illuminate a display that is configured to display video images; and

instructions for adjusting the compensated video image so that a product of the intensity setting and a transmittance associated with the adjusted video image approximately equals a product of a previous intensity setting and a transmittance associated with the video image.

19. A computer system configured to adjust a video image, comprising:

a processor;

a memory;

an instruction fetch unit within the processor configured to fetch;

instructions for compensating for gamma correction in a video image to produce a linear relationship between brightness values and an associated brightness of the video image when displayed;

instructions for calculating an intensity setting of a light source based on at least a portion of the compensated video image, the light source configured to illuminate a display that is configured to display video images; and

instructions for adjusting the compensated video image so that a product of the intensity setting and a transmittance associated with the adjusted video image approximately equals a product of a previous intensity setting and a transmittance associated with the video image.

20. An integrated circuit, comprising one or more sub-circuits, wherein the one or more sub-circuits are configured to:

transform a video image from an initial brightness domain to a linear brightness domain, the linear brightness domain characterized by a range of brightness values corresponding to substantially equidistant adjacent radiant-power values in a displayed video image;

determine an intensity setting of a light source based on at least a portion of the transformed video image, the light source configured to illuminate a display that is configured to display video images; and

modify the transformed video image so that a product of the intensity setting and a transmittance associated with the modified video image approximately equals a product of a previous intensity setting and a transmittance associated with the video image.

21. A portable device, comprising:

a display;

a light source configured to output light;

an attenuation mechanism configured to modulate the output light incident on the display, the display configured to display a video image; and

one or more integrated circuits, wherein the one or more integrated circuits are configured to;

transform the video image from an initial brightness domain to a linear brightness domain, the linear brightness domain characterized by a range of brightness values corresponding to substantially equidistant adjacent radiant-power values in a displayed video image;

determine an intensity setting of a light source based on at least a portion of the transformed video image, the light source configured to illuminate a display that is configured to display video images; and

modify the transformed video image so that a product of the intensity setting and a transmittance associated with the modified video image approximately equals a product of a previous intensity setting and a transmittance associated with the video image.