# Quality Assessment of HDR/WCG Images Using HDR Uniform Color Spaces
## 3 Methodology for the Quality Assessment Metrics Evaluation
### Databases Presentation
#### 3.1.2 Proposed Databases  
To deal with the limitations of existing databases, we propose two new databases (Available at www-percept.irisa.fr/software/). The first one is a database with BT.709 contents encapsulated in a BT.2020 gamut and the second one is composed with native BT.2020 content. We used the same display for both of them: the SONY BVM-X300. This is a professional HDR video monitor able to faithfully display the brightness of signals [42]. It has a peak brightness at 1000 cd/m\({}^{2}\) and a luminance of a black pixel that was too low to be measured by our equipment (\(<\)0.2 cd/m\({}^{2}\)). In this paper, we assume a luminance for the black pixel at 0.001 cd/m\({}^{2}\). This monitor also allows us to force the use of a chosen EOTF without having to consider the image metadata. To display the images on the screen, we used the b\(<\)com *Ultra Player* which allows to distribute uncompressed YUV content with a 10 bits quantization and 4:2:0 chroma sub-sampling.The connection to the screen was done using 3G-SDI cables. To create the distortions, we used HDRTools (v0.16) (Available at [[https://gitlab.com/standards/HDRTools/](https://gitlab.com/standards/HDRTools/)]([https://gitlab.com/standards/HDRTools/](https://gitlab.com/standards/HDRTools/))) to apply format conversion, chrominance sub-sampling or gamut conversion. For the compression and decompression of the images, we used the reference software of HEVC, the HEVC test Model (v16.17) (Available at [[https://hevc.hhi.fraunhofer.de/](https://hevc.hhi.fraunhofer.de/)]([https://hevc.hhi.fraunhofer.de/](https://hevc.hhi.fraunhofer.de/))). For both subjective tests, we used the same methodology: the Double-Stimulus Impairment Scale (DSIS) variant I methodology [43] with a side-by-side comparison. Pairs of images were presented to the viewers, one side being always the reference. 50% of the participant had the reference always on the right-hand side, 50% always on the left-hand side. To avoid a bias with the order of presentation, the pairs of images were randomized for each participant with the condition that the same content was never shown twice consecutively. Each image pair was shown 10 s and voting time was 5 s. The test  
Figure 5: Characteristics of the [PERSON] et al. [19] images: (**a**) The dynamic range, (**b**) key, (**c**) spatial Information, (**d**) Colorfulness. session lasts 35 min (including instructions and training time) with a 5 min pause in the middle of the test. To obtain realistic distortion we compress the images with the HEVC codec using the recommendation ITU-T H Suppl.15 [44], i.e., a 10 bits quantization for the images, the PQ EOTF and the \(Y^{\prime}CrCb\) color space. Moreover this recommendation proposes different processes for increasing the quality of the compression such as a 4:2:0 chroma subsampling using a luma-adjustment process and a chroma Qp adaptation. This last is of special interest for this study because it corrects errors due to the compression of the chrominances. In WCG, most of chroma values tend to be near their mean value (i.e., 512) while the \(Y^{\prime}\) component tends to use most of its range. This is even more significant for BT.709 content encapsulated in a BT.2020 gamut. This behaviour creates a shift in the bitrate allocation from the chrominance to the luminance. This can potentially create visible chrominance artifacts. The chroma Qp adaptation proposed in the recommendation is a method to counter this effect. Because we wanted to create realistic color artifacts, we distort the images using the compression with and without the chroma Qp adaptation to study the sensibility of the color metrics. The first database we propose was already presented in [45]. Eight images were selected from 3 collections: two are from the MPEG HDR sequences (FireEater and Market) [46], one is from the Stuttgart HDR Video Database [47] and the remaining five images are from the HDR photographic survey [48]. Note that these images also belong to [PERSON] et al. 's database [19].