Lightning-Fast Dual-Layer Lossless Coding for Radiance Format High Dynamic Range Images

TL;DR

This paper introduces a rapid dual-layer lossless coding method for HDR images in Radiance format, achieving significant reductions in encoding time and modest bitrate savings without extra decoding complexity.

Contribution

The proposed method uniquely combines a dual-layer structure with linear regression modeling of mantissas to enhance coding speed and efficiency for HDR Radiance images.

Findings

Reduces encoding time by up to 99%

Decreases average bitrate by 1.57-6.68%

Maintains lossless HDR decoding without extra algorithms

Abstract

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 $87.13$-$98.96$ %.