Methods and apparatuses for encoding an hdr images, and methods and apparatuses for use of such encoded images

An image encoder comprising:

• a dynamic range conversion circuit, wherein the dynamic range conversion circuit is arranged to convert the high dynamic range image to an image of lower luminance dynamic range, wherein the dynamic range conversion circuit comprises:
• a normalizer circuit, wherein the normalizer circuit is arranged to normalize the high dynamic range image to a luma axis ranging over (0,1) and to output normalized luminances;
• a loggamma conversion circuit, wherein the loggamma conversion circuit is arranged to apply a loggamma function to the normalized luminances and to output loggamma-converted lumas;
• an arbitrary tone mapping circuit,
• wherein the arbitrary tone mapping circuit is arranged to apply an arbitrary strictly monotonically increasing function which maps the loggamma-converted lumas to output lumas of the lower dynamic range image,
• wherein the loggamma conversion circuit is connected to the normalizer circuit, and wherein the arbitrary tone mapping circuit is connected to the loggamma conversion circuit wherein the image encoder comprises an image compressor circuit,
• wherein the image compressor circuit is arranged to apply a data reduction transformation to the colors of the lower dynamic range image,
• wherein pixel colors are organized in component images,
• wherein the data reduction transformation involves at least applying a DCT transform to blocks of adjacent color component values, yielding a compressed codification of the pixel colors of the lower luminance dynamic range image;
• and wherein the image encoder comprises a formatter circuit,
• wherein the formatter circuit is arranged to output the compressed codification in an image signal data,
• wherein the formatter circuit is arranged to output in the image signal data values encoding the function shape of the arbitrary monotonically increasing function as metadata,
• wherein the metadata allows a receiver to reconstruct a high dynamic range image based upon the lower luminance dynamic range image.

A non-transitory medium comprising a high dynamic range image signal, the high dynamic range image signal comprising:

• a pixellized lower dynamic range image with encoded pixel colors;
• a senstivity value;
• a gamma value;
• a gain value;
• and
• a set of values specifying an arbitrary monotonically increasing tone mapping function shape.