# Quality Assessment of HDR/WCG Images Using HDR Uniform Color Spaces
## 3 Methodology for the Quality Assessment Metrics Evaluation
### Databases Presentation
#### 3.1.1 Existing Databases  
In this section, three databases available online are presented. They all include compression artifacts. Some of them use a backward compatible compression. This method allows the images to be displayable with SDR equipment while preserving the dynamic range for the display on HDR screens. A Tone Mapping Operator (TMO) is used to tone map the HDR images into SDR range. These tone-mapped images are then compressed using different codecs. After the decoding process, they are tone expanded to recover their HDR characteristics. These three databases use the same HDR SIM2 display (HDR47 ES4 MB) which has a measured dynamic range going from 0.03 to 4250 cd/m\({}^{2}\). * [PERSON] et al. [34]'s database (Available at [[http://ivc.univ-nantes.fr/en/databases/JPEG_HDR_Images/](http://ivc.univ-nantes.fr/en/databases/JPEG_HDR_Images/)]([http://ivc.univ-nantes.fr/en/databases/JPEG_HDR_Images/](http://ivc.univ-nantes.fr/en/databases/JPEG_HDR_Images/))) is composed of 10 source images, which have been distorted by a backward compatible compression with the JPEG codec and the iCam TMO [36]. This database was used along with others to tune HDR-VDP2. The angular resolution used during the subjective test was 60 pix/degree and the surround luminance was 130 cd/m\({}^{2}\). For this database due to its surround luminance above 100 cd/m\({}^{2}\), we consider a surround luminance of 20 cd/m\({}^{2}\) to obtain the color space \(HDR\)-\(Lab_{100}\). The characteristics of each reference image are reported on Figure 3. \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline
**Name** & **\#Obs** & **\#Img** & **Protocol** & **Distortion** & **Display** & **Gamut** & **Size** \\ \hline [PERSON] et al. [34] & 27 & 140 & ACR-HR & JPEG & SIM2 HDR47 ES4 MB & BT.709 & 1920 \(\times\) 1080 \\ \hline [PERSON] et al. [35] & 24 & 240 & \begin{tabular}{c} DSIS \\ (side by side) \\ \end{tabular} & JPEG-XT & SIM2 HDR47 ES4 MB & BT.709 & 944 \(\times\) 1080 \\ \hline [PERSON] et al. [19] & 15 & 100 & DSIS & JPEG, JPEG-XT & SIM2 HDR47 ES4 MB & BT.709 & 1920 \(\times\) 1080 \\ \hline Proposed HDdth & 15 & 96 & \begin{tabular}{c} DSIS \\ (side by side) \\ \end{tabular} & \begin{tabular}{c} HEVC, Gaussian \\ noise, Gamut mismatch \\ \end{tabular} & Sony BVM-X300 & BT.2020 & 944 \(\times\) 1080 \\ \hline Proposed 4 Kdtb & 13 & 96 & \
\begin{tabular}{c} DSIS \\ (side by side) \\ \end{tabular} &
\begin{tabular}{c} HEVC, \\ Quantization \\ \end{tabular} & Sony BVM-X300 & BT.2020 & 1890 \(\times\) 2160 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Number of observers, number of images, subjective test protocol, kind of distortion and used display for the 3 existing HDR image quality databases and the two databases proposed in this paper. Figure 3: Characteristics of the [PERSON] et al. [34] images: (**a**) The dynamic range, (**b**) key, (**c**) spatial Information, (**d**) Colorfulness. * [PERSON] et al. [35]'s database (Available at [[http://mmspg.epfl.ch/jpegxt-hdr](http://mmspg.epfl.ch/jpegxt-hdr)]([http://mmspg.epfl.ch/jpegxt-hdr](http://mmspg.epfl.ch/jpegxt-hdr))) consists in images distorted with a backward-compatible compression scheme using the JPEG-XT standard and either the [PERSON] et al. [37] or the [PERSON] et al. [38] TMO. The angular resolution used during the subjective test was 60 pix/degree and the surround luminance was 20 cd/m\({}^{2}\). The characteristics of each reference images are reported on Figure 4.
* [PERSON] et al. [19]'s database (Available at [[http://webpages.l2s.centralesupelec.fr/perso/giuseppe.valenzise/](http://webpages.l2s.centralesupelec.fr/perso/giuseppe.valenzise/)]([http://webpages.l2s.centralesupelec.fr/perso/giuseppe.valenzise/](http://webpages.l2s.centralesupelec.fr/perso/giuseppe.valenzise/))) is partially composed of images from [39]. The distorted images are generated by using both backward-compatible compression using the TMO proposed by [PERSON] et al. [40] and using a non backward-compatible compression with the use of the PQ function for the EOTF.