  This paper proposes a fast dual-layer lossless coding for high dynamic range
images (HDRIs) in the Radiance format. The coding, which consists of a base
layer and a lossless enhancement layer, provides a standard dynamic range image
(SDRI) without requiring an additional algorithm at the decoder and can
losslessly decode the HDRI by adding the residual signals (residuals) between
the HDRI and SDRI to the SDRI, if desired. To suppress the dynamic range of the
residuals in the enhancement layer, the coding directly uses the mantissa and
exponent information from the Radiance format. To further reduce the residual
energy, each mantissa is modeled (estimated) as a linear function, i.e., a
simple linear regression, of the encoded-decoded SDRI in each region with the
same exponent. This is called simple linear regressive mantissa estimator.
Experimental results show that, compared with existing methods, our coding
reduces the average bitrate by approximately $1.57$-$6.68$ % and significantly
reduces the average encoder implementation time by approximately
$87.13$-$98.96$ %.
