# Evaluation Model of Holographic Communication Experience in the 6G Era Based on Light Field Display
## 3 Method
### Data Set  
First, in terms of image data, the light field images used for testing in this article came from the public database MPI-LFA (Max Planck Institut Informatik Light Field Archive) database [31]. The display device used in this article's experiments is a Lookingglass, as shown on the left side of Figure 2. The images in MPI-LFA need to be cropped and spliced into a quilt array form that can be used by the Lookingglass. One of the quilt array images is shown on the right side of Figure 2.  
In terms of image content, this article selected 6 types of scene content, including 3 types of real scenes and 3 types of virtual content scenes, covering scene semantic elements such as real/virtual, distant view/close-up view, indoor/outdoor, texture, light and shadow, people/objects. Representative diagrams of the six types of scenarios are shown in Figure 3.  
Figure 1: Main flow of method. Figure 3: Six types of scene content. Figure 2: Lookingglass device (**left**), quilt array image (**right**). In order to meet the testing requirements, we need to perform different types and levels of distortion/degradation processing on the original image. Referring to relevant research, we selected seven treatment methods, each of which contains five treatment levels, as shown in Table 1.  
So far, we have produced a total of 6 types of scenes, with 100 light field images for each type of scene. Each light field image has been processed in 7 ways, and each process is divided into 5 levels and comes with an original image. A total of 21,600 light field images were used as experimental data. It is worth mentioning that each light field image is an array composed of 9 \(\times\) 11 2D images with a resolution of 1536 \(\times\) 2048. Next comes the test-scoring part. According to ITU standards, the rating scale for the subjective indicator system in the experiment refers to the five-level quality damage scale in the \"ITU-R BT.2021-1 [32] Recommendation on subjective evaluation methods for stereoscopic three-dimensional television systems\". The display method of holographic visual materials in the experiment refers to the double excitation damage scale method (EBU method) in the \"ITU-R BT.500-14 [33] Recommendation on subjective evaluation methods of television image quality\". The scale (left) and demonstration method (right) are shown in Figure 4.  
The requirements for the subjects are shown in Table 2. \begin{table}
\begin{tabular}{c c} \hline \hline
**Distortion Type** & **Adjustment Parameter** \\ \hline Smooth filtering & Smooth kernel size \\ Gaussian filter & Gaussian kernel size, standard deviation \\ RGB color saturation & Channel coefficient \\ JPEG compression & Compression ratio \\ PNG compression & Compression ratio \\ Gaussian noise & Mean and variance \\ Brightness range & Luminance value \\ \hline \end{tabular}
\end{table} 
Table 1: Distortion processing methods, parameters, and levels. Figure 4: 5-levels scale (**left**) and presentation rules (**right**). \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{Five-level scale} \\ \hline Quality & \multicolumn{2}{c}{Injure} \\ \hline
5 Optimal & 5 & Imperceptible \\
4 Good & 4 & Perceptible but not obnoxious \\
3 Intermediate & 3 & Slight dislike \\
2 Poor & 2 & Odious \\
1 Bad & 1 & Nasty \\ \hline \end{tabular}
\end{table} 
Table 2: Requirements for the subjects. Based on the conclusions of existing studies [34], at least 16 subjects can achieve a statistical detection power of 0.95, so a total of 20 subjects were recruited for this experiment, and after screening, a total of 1000 pieces of valid scoring data were collected. For the same image, the mode of different subjects is used as the final classification label. At this point, the production of the experimental data set has been completed, with a total of 21,600 light field images, including 1000 labeled images and 20,600 unlabeled images. The labeled images have three category labels in the three dimensions of realism, comfort, and space, with discrete integers ranging from 1 to 5.