## 3 Digital Image Acquisition, Processing and Modelling Reconstruction
### Digital Image Acquisition Devices  
Early digital imaging devices, usually relatively inexpensive microcomputers and digitizers collected the required data to analyze and measure the shape, surface area, and roughness of the aggregates and edited the data in combination with AutoCAD and Basicprograms to present them in the form of graphs, tables, and histograms [72]. This type of device can only measure the shape of the aggregate, and its accuracy is relatively low. It is clear that due to the limited technology and equipment available in the early days, it was impossible to characterize the angularity and texture of the aggregates. Among dynamic digital imaging methods, the VDG-40 particle classification video system from EMACO, Canada [73], can detect aggregates ranging in size from 1.18 mm to at least 37.5 mm, and capture 2D images of aggregates by calculating their length and width with a line-scan charge-coupled device (CCD) camera. However, the identification results can be heavily biased when the shape of the aggregate varies considerably. The computerized Particle Analyzer (CPA), which can be used in the laboratory and industrial production, applies dimensional and shape-based methods to analyze and process aggregate images [74]. The Micrometric Optisizer Particle Size Distribution Analyzer (PSDA) is used to analyze the aggregate shape by spherical and cubic methods [74]. PSDA is slow to image and captures only a fraction of the aggregates to analyze the particle size gradation. In the Video Image System (VIS), a sample holder is used to hold and move a large number of aggregates to a vibrating chute, and images of aggregates falling are captured by a CCD camera, which was further analyzed in the VIS system to generate a report. PSSDA is also able to provide information on the shape of the aggregates. The difference is that there are two systems for measuring the properties of coarse aggregates and fine aggregates, respectively. The Camsizer system captures digital images with two cameras, one taking images of coarse aggregates and the other one detecting fine particles. The Camsizer generally performs well in terms of analysis speed and accuracy, but its repeatability is relatively poor. The WipShape system, generally used for coarse aggregate analysis, has the ability to quickly analyze many aggregates. Size distribution curves and shape measurements are output by size category. Angles can be output through the minimum average curve radius method. Camsizer and WipShape acquired images of aggregates using two CCD cameras. However, these two techniques differ from each other in terms of instrumentation setup. 2D data is generated by Camsizer to determine the shape, whereas WipShape can capture images from two orthogonal views through two cameras separately, thus generating 3D shape information. The different methods presented above all use line scan CCD cameras to measure aggregates under backlight, while the difference between them lies in the physical configuration and software packages. The imaging techniques for analyzing morphological features are described in Table 4, including early digital, dynamic, and static imaging techniques. The range of aggregate sizes applicable to each technology is presented. The morphological calculation methods corresponding to these techniques are also collected. Obviously, with the development of image technology, aggregates have been extensively studied. The camera setup in different techniques also varies greatly. Therefore, the advantages and disadvantages of these imaging techniques are summarized in Table 5.