Full-automatic self-calibration of color digital cameras using color targets

Abstract

In photogrammetric applications, camera calibration and orientation procedures are a prerequisite for the extraction of precise and reliable 3D metric information from images. This study presents a method for full automatic calibration of color digital cameras using color targets. Software developed using Borland C + + Builder programming language is used to apply the method. With this software, the calibration process is carried out in 3 stages: firstly, at least four of six color targets (whose 3D object coordinates are known) on each image of the overall test field are detected and the approximate exterior orientation parameters are computed. Then, the remaining target points are measured using the approximate image locations, determined using these parameters and the 3D object point coordinates parameters. Finally, calibration parameters are determined using a self-calibration bundle adjustment technique. The colored targets within the test field are assigned labels corresponding to their color. For the detection of color targets and computation of approximate exterior orientation elements, HSV color space was used together with space resection computation method for all the possible color labels of targets. To test the proposed method, full automatic calibration was carried out using six different digital cameras. The calibration accuracies achieved in object space were within the range 0.006 to 0.030 mm; the accuracies achieved in image space were within the range 0.14 to 0.51 µm.