# 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
The characteristics of the images are not exactly the same as in [PERSON] et al. [19] because we used only half of the images (\(944\times 1080\)) to be able to display simultaneously both the reference image and the distorted image on the same screen. The characteristics of the images can be found on Figure 6.  
Fifteen naive subjects participated in this test (11 males, 4 females) with an average age of 25.8. All declared normal or corrected-to-normal vision. One participant was removed from the analysis using the methodology described in [43]. Because we used the display in HD mode, we choose to call this database HDdtb in this paper. Four kinds of distortions have been chosen:  
* HEVC compression using the recommendation ITU-T H Suppl.15 [44]. Four different quantization parameters (\(Qp\)) were selected for each image for this distortion. * HEVC compression without the chroma \(Qp\) adaptation leading to more chrominance distortions. Three \(Qp\) were selected for each image. * Gaussian noise on the chroma components: 3 levels of noise were selected. * Gamut mismatch: two kinds of distortion were created: on one hand, the BT.709 images were considered as if they had been already encapsulated in a BT.2020 gamut leading to more saturated images. On the other hand, we took images already encapsulated in a BT.2020 gamut and considered them as BT.709 images and re-encapsulated them in a BT.2020 gamut. This creates less saturated images. For the second database, we used eight 4K images produced by Harmonic Inc. The characteristics of the images are given in Figure 7. We used only part of these images so the reference and the distorted image could fit on our display (1890 \(\times\) 2160) with a band of 60 black pixels. We called this new database 4 Kdtb. We used the same visualization distance as in the previous database. Thirteen experts or sensitized subjects participated in this test (11 males, 2 females) with an average age of 40. All declared normal or corrected-to-normal vision. With this database we aim to create more visible color artifacts induced by compression than in the HDdtb database. We compressed the images with four different \(Qp\) with three different options for the compression:  
* HEVC compression using the recommendation ITU-T H Suppl.15 [44]. * HEVC compression without the chroma \(Qp\) offset algorithm. * HEVC compression with 8 bits quantization for the chroma instead of 10 during the compression. The chroma were re-sampled to 10 bits before displaying images on screen. Because we have a higher resolution, the angular resolution increases as well and become 120 pix/degree. Because most quality metrics are not adapted to this kind of resolution, we choose to downsample the images to obtain a 60 pix/degree resolution before testing the different quality metrics. Using a downsampled image can improve the performances of some metrics such as MS-SSIM or HDR-VDP2, which were tuned for lower resolution. Figure 6: Characteristics of the HDdtb images: (**a**) The dynamic range, (**b**) key, (**c**) spatial Information, (**d**) Colorfulness.