Encoding, Decoding, and Representing High Dynamic Range Images

1. A method to decode a high dynamic range (HDR) image with a processor, the method comprising: parsing an image file to generate a base image and HDR reconstruction data, wherein the HDR reconstruction data comprises a quantized luma ratio image and one or more sets of quantized residual chroma values; extracting quantization parameters from the HDR reconstruction data; generating a dequantized luma ratio image and one or more sets of dequantized residual chroma values based on the quantization parameters, the quantized luma ratio image, and the one or more sets of quantized residual chroma values; linearizing the dequantized luma ratio image to generate a linearized luma ratio image; and generating an output HDR image based on the one or more sets of dequantized residual chroma values, the linearized luma ratio image, and the base image.

2. The method of claim 1 , wherein generating the output HDR image further comprises: generating an intermediate image by adding the one or more sets of dequantized residual chroma values to the base image; and generating the output HDR image by multiplying the intermediate image with the linearized luma ratio image.

3. The method of claim 1 , wherein the base image is a tone-mapped image.

4. The method of claim 1 , wherein the base image in the image file comprises a JPEG image and the HDR reconstruction data is separated by the base image using at least one JPEG application segment marker.

5. The method of claim 1 , wherein the quantized luma ratio image comprises quantized log ratio pixel values.

6. The method of claim 1 , wherein the one or more sets of quantized residual chroma values comprise normalized and quantized residual chroma pixel values.

7. The method of claim 4 , wherein the base image is decoded using JPEG decoding.

8. The method of claim 5 , wherein the quantization parameters related to the quantized log ratio pixel values comprise a minimum log ratio pixel value (lr min ) and a maximum log ratio pixel value (lr max ), and given a quantized log ratio pixel value (H), a corresponding unquantized log ratio luma value lr is determined as lr = H ⁡ ( lr max - lr min 255 ) + lr min .

9. The method of claim 6 , wherein a first set of quantization parameters related to quantized residual chroma pixel values comprise a minimum residual chroma pixel value (Cb min ) and a maximum residual chroma pixel value (Cb max ), and given a quantized residual chroma pixel value (U), a corresponding intermediate residual chroma pixel value Cb is determined as Cb = U ⁡ ( Cb max - Cb min 255 ) + Cb min .

10. The method of claim 1 , wherein linearizing the dequantized luma ratio image comprises applying an inverse logarithm function to pixels of the dequantized luma ratio image.

11. A decoder for decoding a high dynamic range image (HDR), the decoder comprising: an input to receive an image file; a processor configured to execute instructions to: parse the image file to generate a base image and HDR reconstruction data, wherein the HDR reconstruction data comprises a quantized luma ratio image and one or more sets of quantized residual chroma values; extract quantization parameters from the HDR reconstruction data; generate a dequantized luma ratio image and one or more sets of dequantized residual chroma values based on the quantization parameters, the quantized luma ratio image, and the one or more sets of quantized residual chroma values; linearize the dequantized luma ratio image to generate a linearized luma ratio image; and generate an output HDR image based on the one or more sets of dequantized residual chroma values, the linearized luma ratio image, and the base image; and an output to output the generated output HDR image.

12. The decoder of claim 11 wherein to generate the output HDR image further comprises instructions to: generate an intermediate image by adding the one or more sets of dequantized residual chroma values to the base image; and generate the output HDR image by multiplying the intermediate image with the linearized luma ratio image.

13. A non-transitory computer-readable storage medium having stored thereon computer-executable instructions for executing a method in accordance with claim 1 .