Tone-mapping-operators (TMOs) provide a useful means for converting high dynamic range (HDR) images to low dynamic range (LDR) images so that they can be viewed on standard displays, but this may influence the visual quality of experience (QoE) of the end-user. There is a need to understand the impact of TMOs to inform the choice of TMO algorithms for different displays, especially for small-screen-devices (SSDs) such as those used in mobile phones. This is important, as mobile devices are becoming the primary means of consuming multimedia contents. However, few studies have been undertaken to assess the impact of TMOs and viewing devices (especially SSDs) on the visual QoE of the user when using. In this chapter, we evaluate subjectively and objectively, the commonly used TMOs in different displays and resolutions for colour and grey-scale HDR images. Our results show that viewing devices have an influence on the TMOs performance, suggesting the need for a careful choice of TMO to enhance the viewing-QoE of the end-user. As expected, the higher resolution, the better HDR-image quality. Surprisingly, there was no significant difference between the Mean of Opinion Score (MOS) scores for colour and grey-scale images in SSDs. The device and TMOs affect QoE for colour and grey HDR-image equally. We found Shannon entropy (SE) to be a good objective measure of quality for colour and grey HDR images, suggesting that entropy may find use in automated HDR quality control assessment schemes, while; HDR-VDP-2 is a good objective measure for colour HDR image only.

Chapter Contents:

• 10.1 Introduction
• 10.2 Comparison of HDR images with traditional images (LDR)
• 10.3 Characteristics of SSDs
• 10.4 Methodology
• 10.4.1 Subjective assessment of the impact of TMOS and viewing devices
• 10.4.1.1 Experimental set-up
• 10.4.1.2 The TMOs used in the study
• 10.4.1.3 Participants
• 10.4.1.4 Devices used in the study
• 10.4.2 Objective assessment of the impact of TMOs and viewing devices
• 10.5 Results
• 10.5.1 Results from subjective assessments
• 10.5.2 Results from objective assessments
• 10.6 Comparison of subjective and objective assessments of HDR image quality
• 10.7 Discussion
• 10.8 Conclusions and future work
• References

Inspec keywords: computer displays; entropy; image colour analysis; quality of experience

Other keywords: automated HDR quality control assessment schemes; SSDs; grey-scale images; tone-mapping-operators; HDR-VDP-2; high dynamic range; tone-mapping operators; colour HDR image; viewing devices; visual QoE; small-screen-devices; visual quality; mobile devices; low dynamic range images; HDR-image quality

Subjects: Optical, image and video signal processing; Computer displays; Computer vision and image processing techniques; Display technology