Statistical analysis and directional coding of layer-based HDR image coding residue

Abstract

Existing methods for layer-based backward compatible high dynamic range (HDR) image and video coding mostly focus on the rate-distortion optimization of base layer while neglecting the encoding of the residue signal in the enhancement layer. Although some recent studies handle residue coding by designing function based fixed global mapping curves for 8-bit conversion and exploiting standard codecs on the resulting 8-bit images, they do not take the local characteristics of residue blocks into account. Inspired by the local anisotropic characteristics of the residue signal and directional methods for motion compensated low dynamic range (LDR) video coding, in this paper we first investigate whether HDR image coding residue exhibits also local anisotropic characteristics. Specifically, we verify directional structures in residue blocks by means of auto-covariance analysis for different bitrates, spatial activities and dynamic ranges as the main variables in HDR image coding. Then, we compare the rate distortion performances of directional coding methods with the baseline residue coding methods in the literature along with different combinations of 8-bit conversion methods. The experiments indicate that content dependent 8-bit conversions and directional coding significantly outperforms the existing function based 8-bit conversions and typical coding for residue coding.

High dynamic range image compression based on visual saliency

“…As mentioned in Section II A), we do not take JPEG XT profile D into consideration, so we compare our method with profiles A, B, C. They are implemented by JPEG XT working group [25], and the recommended parameters are used in our experiments. Besides that, we compare our method with other state-of-the-art work, such as Choi et al [10], Wei et al [26], and Feyiz et al [27]. HDR-VDP-2 [24] and SSIM [28] are adopted as the evaluation metric of objective quality.…”

“…(On the left is the original image, top two rows on the right are non-salient regions of reconstructed image, and two bottom rows on the right are salient ones. From left to right, the first row is original image, official implementation of JPEG XT profile A,B,C, the second row is Choi's method [10], Wei's method [26], Feyiz's method [27], and our proposed method, respectively.) of quality range.…”