“A Companding Based Two-Layer codec for HDR images” by Siddiq, Ahmed and Khan

  • ©Asif Siddiq, Jameel Ahmed, and Ishtiaq Rasool Khan



Entry Number: 41


    A Companding Based Two-Layer codec for HDR images



    TIFF and OpenEXR formats store HDR images as floating-point data. Therefore, these raw data HDR image formats occupy large storage space and require very high bandwidth for transmission. RGBE format transforms three floating-point HDR channels to four 8-bit channels by extracting a common exponent from RGB values. However, the algorithm requires lossless encoding, and therefore reduction in file size is not significant. RGBE also encodes raw data and is not compatible with existing codecs and displays.
    To resolve the problem of backward compatibility, two-layer solutions were proposed. In these formats, the first layer is a tone-mapped version of the HDR image suitable for display and can be encoded with the existing codecs. The second layer, known as residue layer or enhancement layer, stores the information lost in the process. JPEG released an extended JPEG-XT standard, which implements some of these algorithms as various profiles. These two-layer structures are generally called backward compatible formats, as they allow HDR contents to be visualized on traditional LDR displays and encoded with existing codecs.


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