HDR IMAGE ENCODING AND DECODING METHODS AND DEVICES

• US 20150201222A1
• Filed: 07/01/2013
• Published: 07/16/2015
• Est. Priority Date: 07/13/2012
• Status: Active Grant

• Current Assignee: Koninklijke Philips N.V.
• Original Assignee: Koninklijke Philips N.V.
• Inventors: Mertens, Mark Jozef Willem
• Granted Patent: US 9,516,351 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04N 19/17 the unit being an image region, e.g. an object
• CPC Class Codes: H04N 19/182 the unit being a pixel
• CPC Class Codes: H04N 19/186 the unit being a colour or a chrominance component
• CPC Class Codes: H04N 19/196 being specially adapted for the computation of encoding parameters, e.g. by averaging previously computed encoding parameters processing of motion vectors H04N19/513
• CPC Class Codes: H04N 19/30 using hierarchical techniques, e.g. scalability H04N19/63 takes precedence
• CPC Class Codes: H04N 19/46 Embedding additional information in the video signal during the compression process H04N19/517, H04N19/68, H04N19/70 take precedence
• CPC Class Codes: H04N 19/98 Adaptive-dynamic-range coding [ADRC]

Abstract

To have a very efficient and in some embodiments also backwards compatible with legacy LDR display systems, apparatuses and methods relating to decoding an image encoding (LDR_CONT) corresponding to a first luminance dynamic range (R_oLDR) into a second luminance dynamic range (R_oHDR) output image (HDR_FIN), in which image encoding (LDR_CONT) are encoded pixels of an original image (HDR_ORIG) of a high dynamic range scene, the method comprising: tone mapping with a predetermined tone mapping strategy (FL2H) at least the lumas of pixels in the image encoding (LDR_CONT) onto lumas of pixels in an intermediate image (HDR_PRED) corresponding to the second luminance dynamic range (R_oHDR); and modifying the lumas of at least some of the pixels of the intermediate image (HDR_PRED) by multiplying them with predetermined multiplication factors, resulting in the output image (HDR_FIN) are taught.

Claims

1. A method of decoding an image encoding (LDR_CONT) corresponding to a first luminance dynamic range (R_oLDR) into a second luminance dynamic range (R_oHDR) output image (HDR_FIN), in which image encoding (LDR_CONT) are encoded pixels of an original image (HDR_ORIG) of a high dynamic range scene, the method comprising:

tone mapping with a predetermined tone mapping strategy (FL2H) at least the lumas of pixels in the image encoding (LDR_CONT) onto lumas of pixels in an intermediate image (HDR_PRED) corresponding to the second luminance dynamic range (R_oHDR); and

modifying the lumas of at least some of the pixels of the intermediate image (HDR_PRED) by multiplying them with predetermined multiplication factors, the predetermined multiplication factors representing a multiplicative correction to be applied to the lumas of the at least some of the pixels of the intermediate image for obtaining a correction of the tone mapping from the first luminance dynamic range to the second luminance dynamic range, resulting in the output image (HDR_FIN).

2. A method of decoding an image encoding as claimed in claim 1, in which the first luminance dynamic range is a low dynamic range, which typically corresponds to a peak brightness of the range of 500 nit or lower, and the second luminance dynamic range is a high dynamic range, having a peak brightness of at least 750 nit.

3. A method of decoding an image encoding as claimed in claim 1, in which the predetermined multiplication factors are stored in metadata associated with the image encoding (LDR_CONT), the method of decoding comprising reading in the metadata information defining a spatial region of the image encoding (LDR_CONT) for which at least one multiplication factor is encoded in the metadata, of which spatial region a geometric shape is encoded in the metadata.

4. A method of decoding an image encoding as claimed in claim 3, in which the predetermined multiplication factors are comprised in an array of multiplication factors comprising a multiplication factor per pixel or group of pixels, in which the array is defined in correspondence with the encoding of the spatial region geometric shape.

5. A method of decoding an image encoding as claimed in claim 4, in which the multiplication factors in the array of multiplication factors are encoded as indices into a definition table, which contains actual multiplication factors for the indices.

6. A method of decoding an image encoding as claimed in claim 5, in which the definition table is associated with a descriptor, which characterizes the definition table, and therewith in which cases of modifying the lumas it should be used, such as e.g. on a particular shot of images.

7. A method of decoding an image encoding as claimed in claim 6, in which the decoding further reads a window type, indicating that a spatial region associated with that window type has multiplication factors encoded by means of a definition table associated with a descriptor with corresponds with the window type.

8. A method of decoding an image encoding as claimed in claim 1, in which the modifying the lumas of at least some of the pixels of the intermediate image (HDR_PRED) is performed in a manner which constrains the multiplying to a multiplying strategy in which a local average luminance of the output image (HDR_FIN) is within a predetermined percentual deviation from a local average luminance of the intermediate image (HDR_PRED).

9. A method of decoding an image encoding as claimed in claim 8, in which a type value is read, indicating that the multiplication factors are defined in relation to such a constrained multiplying.

10. A method of decoding an image encoding as claimed in claim 1 in which the multiplication factors are read from the metadata as a functional definition of multiplication factors over a running 1-dimensional or 2-dimensional position coordinate.

11. A method of encoding an original image (HDR_ORIG) of a high dynamic range scene as an image encoding (LDR_CONT) corresponding to a first luminance dynamic range (R_oLDR) the method comprising:

tone mapping with a predetermined tone mapping strategy (FL2H) at least the lumas of pixels in the image encoding (LDR_CONT) onto lumas of pixels in an intermediate image (HDR_PRED, GRAD_1LDR) corresponding to a second luminance dynamic range (R_oHDR);

determining multiplication factors for multiplying with the lumas of at least some of the pixels of the intermediate image (HDR_PRED, GRAD_1LDR), by analyzing the difference of pixel colors in the intermediate image (HDR_PRED, GRAD_1LDR) with those of a specified second image (HDR_ORIG, or GRAD_FINLDR);

the predetermined multiplication factors representing a multiplicative correction to be applied to the lumas of the at least some of the pixels of the intermediate image for obtaining a correction of the tone mapping from the first luminance dynamic range to the second luminance dynamic range, and

encoding in an image signal (S_im) the image encoding (LDR_CONT), data specifying the tone mapping strategy (FL2H) and the multiplication factors.

12. A method of encoding an original image (HDR_ORIG) of a high dynamic range scene as in claim 11, in which the first luminance dynamic range (R_oLDR) is a low dynamic range, which typically corresponds to a peak brightness of the range of 500 nit or lower, and the second luminance dynamic range (R_oHDR) is a high dynamic range, having a peak brightness of at least 750 nit.

13. A HDR image decoding apparatus (401) comprising:

a decoder arranged to obtain an image encoding (LDR_CONT) corresponding to a first luminance dynamic range (R_oLDR);

a tone mapper arranged to obtain a specification of a tone mapping strategy (FL2H), and to apply the tone mapping strategy to the image encoding (LDR_CONT) yielding an intermediate image (HDR_PRED) corresponding to a second luminance dynamic range (R_oHDR); and

a pixel color modifier arranged to obtain multiplication factor data (A_MUL) comprising at least one multiplication factor, and arranged to multiply the at least one multiplication factor with the luma of at least one pixel in the intermediate image (HDR_PRED), the at least one multiplication factor representing a multiplicative correction to be applied to the luma of the at least one pixel of the intermediate image for obtaining a correction of the tone mapping from the first luminance dynamic range to the second luminance dynamic range, yielding as output an output image (HDR_FIN).

14. A HDR image encoding apparatus comprising:

an input for obtaining an original encoding (HDR_ORIG) of a high dynamic range scene,

a grading manager arranged to convert that original encoding (HDR_ORIG) into an image encoding (LDR_CONT) corresponding to a first luminance dynamic range (R_oLDR), and arranged to determine an intermediate image (HDR_PRED) corresponding to a second luminance dynamic range (R_oHDR) by tone mapping the image encoding (LDR_CONT) with a tone mapping strategy encoded in tone mapping data (FL2H);

a grading difference comparator arranged to compare the intermediate image (HDR_PRED) with a specified second image (HDR_ORIG, or GRAD_FINLDR), and to derive on the basis of a difference between these images multiplication factor data (A_MUL) comprising at least one multiplicative factor representing a multiplicative correction which when multiplied with the luma of at least one pixel of the intermediate image (HDR_PRED) yields a final pixel color of an output image (HDR_FIN) which is closer to the color of a corresponding pixel in the second image than the color of the pixel in the intermediate image (HDR_PRED); and

an encoding unit arranged to encode the image encoding (LDR_CONT), the tone mapping data (FL2H) and the multiplication factor data (A_MUL) in an output image signal (S_im).

15. A HDR image encoding apparatus as claimed in claim 14, comprising a user interface unit arranged to allow a human color grader to determine at least the image encoding (LDR_CONT), and the tone mapping strategy.

16. An HDR image signal comprising:

an image encoding (LDR_CONT) corresponding to a first luminance dynamic range (R_oLDR);

tone mapping data (FL2H) to be used for tone mapping the image encoding (LDR_CONT) into an intermediate image (HDR_PRED) corresponding to a second luminance dynamic range (R_oHDR); and

multiplication factor data (A_MUL), comprising at least one multiplication factor to be used for multiplying with the luma of at least one pixel in the intermediate image (HDR_PRED), the at least one multiplication factor representing a multiplicative correction to be applied to the luma of the at least one pixel of the intermediate image for obtaining a correction of the tone mapping from the first luminance dynamic range to the second luminance dynamic range which results in an output image.

17. A portable data device arranged to be able to store data, such as e.g. a blu-ray disk, comprising an HDR image signal as claimed in claim 16.