# Quality Assessment of 2.5D Prints Using 2D Image Quality Metrics
## 4 Results and Discussion
### Which Set-Up Is More Appropriate for 2.5D Prints Capture Based on IQMs' Performance?  
We compare the correlation between (mean) quality maps of the tested IQMs from the MS and the SS captures to find which tested IQMs have more differences between the two set-ups and/or are more imperceptive to the set-up. For example, Figure 13 shows a boxplot of the correlation between the MS and the SS of height set images (i.e., for nine prints). Although the tested IQMs' median correlations between the two set-ups are relatively high (roughly around 0.7 for the given IQMs), the ranges of the correlation values are spread. In other words, the correlations of some IQMs are more variable than others. In particular, iCID's lightness contrast map has more prints which have lower correlations than the median value between the two set-ups. The tested IQMs seem to be more towards being imperceptive to the set-up in this set of images, meaning that they detect (more) differences (although the scale might vary between the set-ups) on the same areas irrespective of the set-up. This is in line with our observations in the previous subsections.  
The impact of elevation on the appearance can be better revealed in the MS captures. For example, Figures 4 and 11 show that the differences are better detected by the IQMs in the MS captures compared to the SS ones, where the latter depends on the illumination direction while the former can provide better error capture due to the mean of several illumination angles. In other words, the SS's light source is on top inside the light booth cabinet and shadowing will be more on one side than in the other side regardless of how diffuse the light is inside the light booth. This is a clear limitation of the SS with imperfect diffuse illumination inside the light booth. In contrast, the MS can provide diffuse illumination distributed evenly via capturing prints with a directional set of illumination angles (even generating mean quality maps from set of illumination angles can provide the similar effect). More information on the selected IQMs' ability to better detect differences in the MS captures than in the SS ones can be found in Section 4.1. Moreover, the tested IQMs can find more differences mostly in the MS captures in comparison to captures from the SS (refer to Section 4.2). SSIM and MS-SSIM (both terms, scale 2) detected differences that are perceptually difficult to see mostly in the MS captures as opposed to the SS ones.  
Figure 13: The boxplot of correlation between two set-ups of height set images by the tested IQMs. iCID’s lightness contrast map has a very spread range among the IQMs.  
Thus, they can in combination with the MS be useful in applications which need to detect such differences.  
To summarize, both set-ups can be useful for 2.5D prints' QA. Nevertheless, there is a dominance by the MS based on our observations in terms of the tested IQMs' ability to capture more differences and that the captured differences are clearly visible by the examined IQMs' mean quality maps in the MS captures. Moreover, the MS (i.e., RTI) is relatively simple which needs a camera, a sample of interest, and a light source (which is movable to illuminate the sample from different illumination angles) [43].