Saturation processing specification for dynamic range mappings

• US 10,313,687 B2
• Filed: 07/16/2015
• Issued: 06/04/2019
• Est. Priority Date: 10/10/2014
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips N.V.
• Inventors: Stessen, Jeroen Hubert Christoffel Jacobus
• Primary Examiner(s): Youssef, Menatoallah
• Application Number:
  US15/515,156
• Publication Number:
  US 20170223367A1
• Time in Patent Office: 1,419 Days
• CPC Class Codes: G06T 2207/20208 High dynamic range [HDR] image processing
• CPC Class Codes: G06T 5/92 based on global image properties
• CPC Class Codes: H04N 1/6027 Correction or control of colour gradation or colour contrast H04N1/6058 takes precedence
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/85 using pre-processing or post-processing specially adapted for video compression
• CPC Class Codes: H04N 19/98 Adaptive-dynamic-range coding [ADRC]
• CPC Class Codes: H04N 23/86 for controlling the colour saturation of colour signals, e.g. automatic chroma control circuits
• 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

Because we needed a new color saturation processing in tune with dynamic range transformations necessary for handling the recently introduced high dynamic range image encoding, we describe a color saturation modification apparatus (101) arranged to determine linear color differences (R-Y,G-Y,B-Y) on the basis of an input color (R,G,B) and a luminance (Y) of the input color, and to do a multiplication of the linear color differences (R-Y,G-Y,B-Y) with a gain (g), characterized in that the apparatus is arranged to determine the gain as a function of a difference value (V_in-Y) being defined as the value of the highest one of the linear color differences (R-Y,G-Y,B-Y).

Claims

1. A display apparatus comprising a display and an image encoder for encoding two images for a time instant, and for encoding a matrix of pixel colors for the two images, the two images including a first image having a first dynamic range and a second image having a second dynamic range, the first dynamic range image being larger by at least a factor two than the second dynamic range, and the second image having a peak brightness of 100 nit, the image encoder comprising:

a specification unit which comprises a color saturation modification apparatus configured to determine linear color differences defined as a linear additive primary color component of an input color minus a luminance of the input color, and to do a multiplication of the linear color differences by a gain, wherein the color saturation modification apparatus is configured to determine the gain from a saturation modification specification function depending on a difference value being defined as a value of a highest one of the linear color differences, and to add the luminance to a result of the multiplication of the linear color differences by the gain, yielding an output color;

a saturation specification unit configured to specify a desired saturation modification specification function F which encodes gains as a function of the difference value, wherein the desired saturation modification specification function is used by the color saturation modification apparatus to calculate a pixel gain for a highest linear color difference of a pixel being color processed, for effecting a saturation change by multiplying the linear color differences by the pixel gain; and

a formatter configured to output in an image signal an encoding of an image comprising the matrix of pixel colors, and to output as data the desired saturation modification specification function for display of one of the first image and the second image on the display.

2. A display apparatus comprising a display and an image decoder for decoding two images of at least a factor two different luminance dynamic range for a time instant, a first image of the two images being a high dynamic range image having a dynamic range higher than a second image of the two images and the second image having a peak brightness of 100 nit, the decoder comprising:

a color mapper configured to derive the first image by applying functions received via an image input to the second image, the functions including a luminance transformation function and a saturation modification specification function,

wherein the color mapper comprises a color saturation modification apparatus configured to;

determine linear color differences defined as a linear additive primary color component of an input color minus a luminance of the input color,

do a multiplication of the linear color differences by a gain determined as the result of applying the saturation modification specification function on a difference value being defined as the value of a highest one of the linear color differences,

add the luminance to the result of the multiplication of the linear color differences by the gain, yielding an output color, and

obtain the first image of the two images by applying the functions to the second image for display of one of the first image and the second image on the display.

3. A method of image encoding comprising acts of:

receiving a first image of a first luminance dynamic range;

applying a color transformation to the first image to obtain a second image of a different second luminance dynamic range which is different from the first dynamic range by at least a factor two, and a peak brightness of the second image being 100 nit;

outputting an image signal comprising one of the first image and the second image of the second dynamic range, and metadata specifying functions used in the color transformation, wherein the color transformation comprises applying a method of color saturation including determining linear color differences defined as a linear additive primary color component of an input color minus a luminance of the input color, performing a multiplication of the linear color differences by a gain, wherein the gain is determined from a saturation modification specification function depending on a difference value being defined as a value of a highest one of the linear color differences, and adding the luminance to a result of the multiplication of the linear color differences by the gain, yielding an output color, and the metadata comprising a saturation modification specification function specifying a pixel gain for a highest linear color pixel of a pixel color; and

displaying one of the first image and the second image on a display.

4. A method of image decoding comprising acts of:

receiving a first image of a first luminance dynamic range;

receiving a saturation modification specification function including gain values defined as output of a function of a highest difference value being defined as a value of a highest one of linear color differences;

applying a color transformation to the first image, the color transformation comprising acts of;

determining the linear color differences defined as a linear additive primary color component of an input color minus a luminance of the first color,

determining a gain corresponding to the highest one of the linear color differences, and

multiplying the linear color differences by the gain to obtain second image of a second luminance dynamic range which is at least a factor of two different, wherein the second has a peak brightness of 100 nit;

outputting an image including one of the first image and the second image; and

displaying one of the first image and the second image on a display.