# A Multi-Feature Automatic Evaluation of the Aesthetics of 3D Printed Surfaces
## 2 Materials and Methods  
To achieve the assumed goal of a relatively fast and accurate aesthetic quality assessment of 3D printed surfaces, a database of images and depth maps obtained for 107 planar samples was prepared. The dataset contains the photos and depth maps of planar samples (their dimensions are 35 mm \(\times\) 35 mm \(\times\) 4 mm) captured by a Sony DSC-HX100V camera (manufactured by Sony Corporation, Tokyo, Japan) in controlled illumination conditions and the GOM ATOS 3D scanner (manufactured by GOM GmbH, Braunschweig, Germany), respectively. All samples were produced with popular FDM 3D printers, such as Prusa i3, RepRap Ormerod 3, and da Vinci 1.0 Pro 3-in-1, from two popular types of filaments, namely PLA and ABS, using several colors of materials. The size of captured images obtained using the camera without flash for the exposure time 1/125 s and 5 mm focal length using an automatic white balance is 1600 \(\times\) 1600 pixels [21]. An illustration of some sample images and depth maps for various quality specimens is presented in Figure 1. The dataset is available on the corresponding author's website [[https://okarma.zut.edu.pl/?id=dataset&L=1](https://okarma.zut.edu.pl/?id=dataset&L=1)]([https://okarma.zut.edu.pl/?id=dataset&L=1](https://okarma.zut.edu.pl/?id=dataset&L=1)), (accessed on 16 April 2025).  
An integral part of the database is the set of expert assessments expressed on a 4-point scale (good, moderately good, moderately poor, and poor quality), as well as subjective assessment values (Mean Opinion Scores) obtained as a result of perceptual experiments conducted among a group of several dozen volunteers. These MOS values, verified as consistent with expert assessments, were used as a reference for the development and optimization of automatic quality-assessment metrics to achieve the highest possible correlation with subjective quality scores.  
The use of MOS values, similar to general-purpose image quality assessment [22], is the result of subjective experiments where the observers were asked about the perceived quality of the 3D printed surfaces. These opinions were related only to the aesthetic assessment in contrast to the assessment of mechanical parameters that may be measured, usually using destructive testing (e.g., using stress, squeezing, tearing, tensile, bending, twisting, etc.) [23]. The word \"aesthetic\" is used to emphasize this difference, as we do not assess any mechanical properties of the 3D printed samples.  
Figure 1: Illustration of some sample images and depth maps from the developed dataset for various quality specimens together with their MOS values.  
Since the quality evaluation of 3D printed surfaces differs from the general-purpose image quality assessment (IQA) due to the different nature and properties of the assessed images, a direct application of many well-known full-reference IQA metrics is often impossible. An important limitation is the typical lack of a reference image representing the perfect quality surface obtained using the same type and color of the filament, which might be used for comparison purposes. Therefore, several approaches were proposed during our earlier research, leading to some elementary quality metrics and features, which are fundamental for the hybrid approach discussed in the paper.