1. A decoding method comprising: receiving a JPEG compressed file, the JPEG compressed file includes a low dynamic range (LDR) image and a ratio image, the ratio image separated as an application extension from the LDR image; and reconstructing a reconstructed HDR image, the reconstructed HDR image determined by the LDR image and the ratio image, wherein LDR image has a lower dynamic range than the reconstructed HDR image, and wherein a pixel value of the ratio image is from a logarithm of a ratio of a luminance of a pixel of an HDR image and a luminance of a corresponding pixel of the LDR image.