Image analysis for 3D micro-features: A new hybrid measurement method

Measuring 3D micro-features is a challenging task that is usually performed using high-cost systems generally based on technologies with narrow working ranges and very accurate control of the sensor positions. Well-known image analysis methods, such as Photogrammetry, would likely lower the costs of 3D inspection of micro-features and add texture information to the 3D models; however, the behaviour of Photogrammetry is strongly affected by the scaling method because it retrieves a model that must be scaled after its computation. In this paper, an experimental study of the validity of a hybrid 3D image processing method for measuring micro-features is presented. This method exploits the Depth-from-Focus method to retrieve the correct scale for a photogrammetric model. The measurement of properly-designed and manufactured specimens was performed by following and adapting the German guideline VDI/VDE 2634, Part 3 to validate the method using calibrated specimens. The proposed system has been demonstrated to be very promising can achieve an error of less than 10 μm.