  We propose an efficient two-layer near-lossless coding method using an
extended histogram packing technique with backward compatibility to the legacy
JPEG standard. The JPEG XT, which is the international standard to compress HDR
images, adopts a two-layer coding method for backward compatibility to the
legacy JPEG standard. However, there are two problems with this two-layer
coding method. One is that it does not exhibit better near-lossless performance
than other methods for HDR image compression with single-layer structure. The
other problem is that the determining the appropriate values of the coding
parameters may be required for each input image to achieve good compression
performance of near-lossless compression with the two-layer coding method of
the JPEG XT. To solve these problems, we focus on a histogram-packing technique
that takes into account the histogram sparseness of HDR images. We used
zero-skip quantization, which is an extension of the histogram-packing
technique proposed for lossless coding, for implementing the proposed
near-lossless coding method. The experimental results indicate that the
proposed method exhibits not only a better near-lossless compression
performance than that of the two-layer coding method of the JPEG XT, but also
there are no issue regarding the combination of parameter values without losing
backward compatibility to the JPEG standard.
