Method and apparatus for image data transformation

• US 9,224,363 B2
• Filed: 03/15/2012
• Issued: 12/29/2015
• Est. Priority Date: 03/15/2011
• Status: Active Grant

• Current Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Original Assignee: Dolby Laboratories Licensing Corporation (Dolby Laboratories Incorporated)
• Inventors: Ballestad, Anders, Kostin, Andrey, Ward, Gregory John
• Primary Examiner(s): He, Yingchun
• Application Number:
  US13/984,903
• Publication Number:
  US 20140002478A1
• Time in Patent Office: 1,384 Days
• Field of Search: None
• US Class Current: 1/1
• CPC Class Codes: G06T 11/001 Texturing; Colouring; Generation of texture or colour inpainting G06T5/77
• 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 2320/066 for control of contrast
• CPC Class Codes: G09G 2320/0666 for control of colour parameters, e.g. colour temperature
• CPC Class Codes: G09G 5/02 characterised by the way in which colour is displayed details of colour display specific for CRTs G09G1/28; specific for flat matrix panels other than liquid crystal displays G09G3/2003; specific for liquid crystal displays G09G3/3607
• CPC Class Codes: H04N 1/6027 Correction or control of colour gradation or colour contrast H04N1/6058 takes precedence
• CPC Class Codes: H04N 1/6088 by viewing conditions, i.e. conditions at picture output
• CPC Class Codes: H04N 1/62 Retouching, i.e. modification of isolated colours only or in isolated picture areas only
• CPC Class Codes: H04N 9/67 for matrixing camera processing pipelines for matrixing of colour signals H04N23/85
• CPC Class Codes: H04N 9/68 for controlling the amplitude of colour signals, e.g. automatic chroma control circuits H04N9/71, H04N9/73 take precedence; camera processing pipelines for controlling the colour saturation of colour signals H04N23/86

Abstract

Image data is transformed for display on a target display. A sigmoidal transfer function provides a free parameter controlling min-tone contrast. The transfer function may be dynamically adjusted to accommodate changing ambient lighting conditions. The transformation may be selected so as to automatically adapt image data for display on a target display in a way that substantially preserves creative intent embodied in the image data. The image data may be video data.

Claims

1. An apparatus comprising one or more processors and at least one memory storing instructions that are executable by the one or more processors, the apparatus further comprising:

an image data input device, implemented at least partially in hardware, that receives image metadata for a color-timing display and image data comprising pixel values;

a pixel coordinate mapping device, implemented at least partially in hardware, that transforms the image data into transformed image data according to a parameterized transfer function characterized by a plurality of anchor points and a free parameter, the parameterized transfer function having a mid-range slope controlled by the free parameter, wherein transformations at the anchor points are not affected by the free parameter;

wherein the anchor points comprise black level and white level anchor points and a mid-tone anchor point, the black level anchor point corresponding to a transformation from a black level of the color-timing display used in color-timing or approving the image data to a black level of a target display used for display of the transformed image data, the white level anchor point corresponding to a transformation from a white level of the color-timing display to a white level of the target display;

wherein the mid-tone anchor point affects a target brightness of the image data on the target display;

wherein the black level of the color-timing display differs from the black level of the target display and/or wherein the white level of the color-timing display differs from the white level of the target display;

wherein at least one of the black level of the color-timing display or the white level of the color-timing display is a value specified by the image metadata;

an image data output device, implemented at least partially in hardware, that outputs the transformed image data.

2. The apparatus according to claim 1 wherein the image data comprises sets of pixel values for pixels in an image, the sets of pixel values comprising color values for each of a plurality of primary colors and the apparatus comprises a plurality of pixel coordinate mapping units each connected to transform a corresponding one of the color values.

3. The apparatus according to claim 2 comprising an electronic image display wherein the color values each corresponds to a primary color that is native to the electronic image display.

4. The apparatus according to claim 2 wherein the color values include values for red (R) green (G) and blue (B) primary colors.

5. The apparatus according to claim 2, wherein transfer functions for the mapping units are different from one another.

6. The apparatus according to claim 1, wherein the instructions which, when executed by the one or more processors, further instruct the one or more processors to perform a transformation according to:

7. The apparatus according to claim 1, wherein the instructions which, when executed by the one or more processors, further instruct the one or more processors to re-saturate transformed image data pixels according to the amount of tonal compression of the transformed image data pixels.

8. The apparatus according to claim 7, wherein the instructions which, when executed by the one or more processors, further instruct the one or more processors to re-saturate the transformed image data pixels based on the slope of the transfer function at the transformed pixel values.

9. The apparatus according to claim 1, further comprising:

a user input configured to accept from a user a value for the free parameter; and

a display connected to display the transformed image data.

10. The apparatus according to claim 9, wherein the image data comprises a plurality of color channels, the apparatus comprises a plurality of pixel mapping units, one for each of the color channels and the user input is configured to accept from the user a separate value of the free parameter for each of the color channels.

11. The apparatus according to claim 9, wherein the user input is configured to accept, from a user, information specifying a location of at least one of the anchor points.

12. The apparatus according to claim 1, further comprising an ambient light sensor and a circuit connected to receive an ambient-lighting signal from the ambient light sensor and configured to control one or more of the free parameter and a coordinate of one of the anchor points based at least in part on the ambient-lighting signal.

13. The apparatus according to claim 1, wherein the mid-tone anchor point transforms a representative middle value of the image data to a middle value for the target display.

14. The apparatus according to claim 13, wherein the representative middle value comprises a geometric mean of the image data luminance and the apparatus includes a processor configured to compute the geometric mean of the image data luminance.

15. The apparatus according to claim 13, wherein the apparatus is configured to receive metadata corresponding to the image data and to set a location of the mid-tone anchor point based at least in part on the image data.

16. A method for mapping image data for display on a target display, the method comprising:

receiving image metadata for a color-timing display and image data comprising pixel values through an image data input device;

transforming pixel values of the image data to corresponding transformed pixel values according to a parameterized transfer function characterized by a plurality of anchor points and a free parameter, the parameterized transfer function having a mid-range slope controlled by the free parameter, wherein transformations of pixel values corresponding to the anchor points are not affected by the free parameter;

wherein the anchor points comprise black level and white level anchor points and a mid-tone anchor point, the black level anchor point corresponding to a transformation from a black level of a color-timing display used in color-timing or approving the image data to a black level of the target display, the white level anchor point corresponding to a transformation from a white level of the color-timing display to a white level of the target display;

wherein the mid-tone anchor point affects a target brightness of the image data on the target display;

wherein the black level of the color-timing display differs from the black level of the target display and/or wherein the white level of the color-timing display differs from the white level of the target display;

wherein at least one of the black level of the color-timing display or the white level of the color-timing display is a value specified by the image metadata; and

outputting the transformed image data through an image data output device.

17. A method according to claim 16 comprising controlling one or more of the free parameter and a coordinate of one of the anchor points based at least in part on a signal indicative of ambient-lighting.

18. A method according to claim 16 wherein the transfer function is given by:

19. The method of claim 16, wherein the pixel values of the image data are transformed to first globally tone-mapped pixel values;

and the method further comprising;

transforming the globally tone-mapped pixel values to locally tone-mapped pixel values according to a local multi-scale tone mapping method.

20. The method of claim 19, wherein the local multi-scale tone mapping method comprises:

generating a high-resolution luminance ratio image comprising luminance values based on the first globally tone-mapped pixel values;

generating, based at least in part on the high-resolution luminance ratio image, a local multiscale ratio image that comprises a weighted combination of at least two different ratio images, each being of a different spatial resolution level; and

using ratio values in the local multiscale ratio image with luminance values derived from the input data to generate a locally tone-mapped luminance image.

21. The method of claim 16, wherein the pixel values of the image data are transformed to first globally tone-mapped pixel values.