SATURATION PROCESSING SPECIFICATION FOR DYNAMIC RANGE MAPPINGS

• US 20170223367A1
• Filed: 07/16/2015
• Published: 08/03/2017
• 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
• Granted Patent: US 10,313,687 B2
• Time in Patent Office: 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 in-put 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

1-2. -2. (canceled)

3. An image encoder for encoding at least one high dynamic range image for at least one time instant, and for the same time instant at least one image of a second dynamic range which is different from the dynamic range of

the high dynamic range image by at least a factor two and the lowest one of the dynamic ranges has a peak brightness of 100 nit, and arranged to encode a matrix of pixel colors for at least one of those two images, comprising a specification unit which comprises a color saturation modification apparatus arranged to determine three 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, characterized in that the apparatus is arranged to determine the gain from a saturation modification specification function depending on a difference value being defined as the value of the highest one of the linear color differences, and the apparatus being arranged to add the luminance to the result of the multiplication of the linear color differences by the gain, yielding an output color;

and the image encoder comprising a saturation specification unit arranged to specify a saturation modification specification function F which encodes gains as a function of the linear color difference value being defined as the value of the highest one of linear color differences of a pixel color which linear color differences are defined as the respective linear additive color component minus the luminance of the pixel color, the saturation modification specification function being usable to calculate a gain for any highest linear color difference of a pixel being color processed, for effecting a saturation change by multiplying the linear color differences by the gain, and the encoder further comprising a formatter arranged to output in an image signal an encoding of an image comprising the matrix of pixel colors, and as data the saturation modification specification function F.

4. An image decoder arranged to be able to decode at least two images of at least a factor two different luminance dynamic range for at least one time instant, at least one of the two images being a high dynamic range image and the other image having a peak brightness of 100 nit, the decoder comprising a color mapper arranged to derive one of the two images by applying a received luminance transformation function and a received saturation modification specification function to the other one of the two images which functions are received via an image input, characterized in that the color mapper comprises a color saturation modification apparatus arranged to determine three 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 determined as the result of applying a saturation modification specification function on a difference value being defined as the value of the highest one of the linear color differences, and being arranged to add the luminance to the result of the multiplication of the linear color differences by the gain, yielding an output color, and by applying these color transformations obtaining the derived one of the two images.

5. A display apparatus comprising an image decoder as claimed in claim 4.

6. (canceled)

7. A method of image encoding comprising:

receiving an input image of a first luminance dynamic range;

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

outputting an image signal comprising one of the input image and the obtained image of the second dynamic range, and metadata specifying the functions used in the color transformation, characterized in that the color transformation comprises applying a method of color saturation which determines three linear color differences defined as a linear additive primary color component of an input color minus a luminance of the input color, and multiplies the linear color differences by a gain, characterized in that the gain is determined as output of a saturation modification specification function depending on as input a difference value being defined as the value of the highest one of the linear color differences, and adds the luminance to the 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 gain values for various values of a difference value being defined as the value of the highest one of the linear color differences of a pixel color.

8. A method of image decoding comprising:

receiving an input image of a first luminance dynamic range;

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

applying a color transformation to the input image comprising determining three linear color differences defined as a linear additive primary color component of an input color minus a luminance of the input color, determining a gain corresponding to the highest one of the three linear color differences, and multiplying the three linear color differences by the corresponding gain to obtain an image of a second luminance dynamic range which is at least a factor of two different, wherein one of the input image and the image of second luminance dynamic range has a peak brightness of 100 nit; and

outputting the image of a different second luminance dynamic range (Im_LDR_out.

9. An image signal encoding at least two images of different dynamic range, at least one of the images being a high dynamic range image, and the image of the lowest dynamic range having a peak brightness of 100 nit and the dynamic range of the highest dynamic range image being at least two times higher than the dynamic range of the lowest dynamic range image, the image signal comprising an encoding of a set of pixels of one of the at least two images, and function metadata specifying the color transformation functions to be applied to derive the other one of the at least two images, characterized in that the function metadata comprises a saturation modification specification function specifying gains for various values of a difference value being defined as the value of the highest one of three linear color differences of a pixel color, which linear color differences are defined as the value of the respective linear additive primary color component of the pixel color minus the luminance of the pixel color.

10. A memory product comprising a memory for digital data bits, characterized in that the memory is filled with an image signal as claimed in claim 9.