Apparatus and method for dynamic range transforming of images
An image processing apparatus comprises a receiver ( 201 ) for receiving an image signal comprising an encoded image. Another receiver ( 1701 ) receives a data signal from a display ( 107 ) where the data signal comprises a data field that comprises a display dynamic range indication of the display ( 107 ). The display dynamic range indication comprises at least one luminance specification for the display. A dynamic range processor ( 203 ) is arranged to generate an output image by applying a dynamic range transform to the encoded image in response to the display dynamic range indication. An output ( 205 ) outputs an output image signal comprising the output image to the display. The transform may furthermore be performed in response to a target display reference indicative of a dynamic range of display for which the encoded image is encoded. The invention may be used to generate an improved High Dynamic Range (HDR) image from e.g. a Low Dynamic Range (LDR) image, or vice versa.
1 . An image processing apparatus, comprising:
a first receiver circuit,
wherein the first receiver circuit is arranged to receive an image signal,
wherein the image signal comprises at least one encoded image,
wherein the image signal is a high dynamic range image signal;
a second receiver circuit,
wherein the second receiver circuit is arranged to receive a data signal from a display,
wherein the data signal comprises a maximum display luminance;
wherein the image processing apparatus is arranged to establish a reference white point luminance for the encoded image,
wherein the reference white point luminance corresponds to a maximum luminance within the encoded image,
wherein the image processing apparatus is arranged to output an output image,
wherein the output image is for the display,
wherein the output image is dependent upon the reference white point luminance and the maximum display luminance.
2 . The image processing apparatus as claimed in claim 1 , wherein the defined maximum luminance is greater than or equal to 500 nit.
3 . The image processing apparatus as claimed in claim 1 ,
wherein the output image signal comprises drive values,
wherein the drive values are for instructing the display to display pixel colors according to the drive values,
wherein the drive values are determined based on the maximum display luminance.
4 . The image processing apparatus as claimed in claim 3 , wherein the drive values are defined as YCbCr values.
5 . The image processing apparatus of claim 1 ,
wherein the image signal comprises metadata,
wherein the metadata comprises a defined maximum luminance, and
wherein the reference white point luminance is less than the defined maximum luminance.
6 . A method, comprising:
receiving an image signal,
wherein the image signal comprises at least one encoded image,
wherein the image signal is a high dynamic range image signal;
receiving a data signal,
wherein the data signal comprises a maximum display luminance of a display;
establishing a reference white point luminance for the encoded image;
wherein the reference white point luminance corresponds to a maximum luminance within the encoded image,
providing an output image to the display,
wherein the output image is dependent upon the reference white point luminance and the maximum display luminance.
7 . The method of claim 6 , wherein the image signal comprises metadata,
wherein the metadata comprises a defined maximum luminance, and
wherein the reference white point luminance is less than the defined maximum luminance.
8 . The method of claim 7 , wherein the defined maximum luminance is greater than or equal to 500 nit.
9 . The image processing apparatus of claim 1 , comprising a memory,
wherein the memory is arranged to store a plurality of sets of transform parameters,
wherein the output image corresponds to a transform of the encoded image,
wherein the image processing apparatus is arranged to determine a difference between the reference white point luminance and the maximum display luminance,
wherein a set of parameters of the transform is selected from the plurality of sets of transform parameters based on the difference.
10 . The method of claim 6 , wherein the method comprises;
determining a difference between the reference white point luminance and the maximum display luminance, and
selecting a set of parameters of a transform from a plurality of sets of transform parameters based on the difference,
wherein the output image corresponds to the transform of the encoded image.
11 . A non-transitory computer-readable medium comprising a program that, when executed by a processing system, causes the processing system to perform the method of claim 6 .