Correcting the Defects of the Default Tone Mapping Operators Implemented in the JPEGXT HDR Image Compression Standard

This short article reports two imperfections or implementation bugs of the default tone mapping operators (TMOs) of the JPEGXT HDR image compression standard. In JPEGXT, profiles A and C use the same default TMO, while profile B uses a different default TMO. The first imperfection is with the default TMO of profile A and profile C. Specifically, the default TMO leads to a reduced dynamic range of the tone-mapped LDR images. Very often, the reduction can be severe. The mechanism of causing the dynamic range reduction stems from an implementation bug. To resolve the issue, the correction of adding the missed final normalization step to linearly stretch the dynamic range needs to be made. The second imperfection is the highlights clipping in the LDR images from the default TMO of profile B. The clipping could lead to unusable LDR images. Our suggestion is to unify the default TMO within JPEGXT, i.e., to use the corrected TMO of profiles A and C for profile B.