Directional coding of backward compatible high dynamic range (HDR) image coding residues

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2018
Feyiz, Kutan
High dynamic range (HDR) image and video formats are proposed to overcome limitations of widely accepted standard 8-bit low dynamic range (LDR) image and video representations. The main aim of these formats is to encode the whole luminance range of real world scenes which changes from extreme darkness ( 10 − 6 cd/ m 2 ) to bright sunshine ( 10 8 cd/ m 2 ), and to generate and store such scenes independent from the display technology. To achieve a successful transition from LDR to HDR technology, backward compatible image and video representation formats are proposed so that both LDR and HDR displays can use the same representation to show LDR and HDR versions of the same content. This is typically achieved by including in the representation an LDR base layer, and an HDR enhancement layer that includes a method to predict HDR content from the LDR content in the base layer and possibly residue data to correct the HDR prediction. The main focus of this thesis is to implement a more efficient coding method for backward compatible HDR image coding residues, which are defined as the differences between original HDR images and their predictions from the corresponding base layer LDR images. As the first stage, analyses of similarities between spatial characteristics of backward compatible HDR image coding residues and LDR motion-compensated (MC) prediction residuals, for which directional coding methods were proposed, are performed. These analyses are followed by an implementation of suitable directional transforms which model spatial v characteristics of backward compatible HDR image coding residues more efficiently. Ratedistortion performance of the proposed method for coding of backward compatible HDR image coding residues are evaluated with objective and perceptual quality metrics. Results indicate that the proposed coding method can perform better than the standard coding methods for the coding of backward compatible HDR image coding residues.