Distance measurement based on a single defocused photograph

Abstract

Subject of Research. Westudied a method of estimating the object distance on the basis of its single defocused photograph. The method is based on the analysis of image defocus at the contour points corresponding to borders of photographed objects. It is supposed that the brightness drop in not defocused image of border can be simulated with an ideal step function – the Heaviside function. Method. The contours corresponding to local maxima of brightness gradient are detected in the initial image to be analyzed and recorded for further analysis. Then the initial image is subjected to additional defocusing by a Gaussian filter having the dispersion parameter of defined in advance value. The ratios of local gradient values for the initial and additionally defocused images are then calculated at the contour points, and the defocus values of initial image at the points of objects borders are estimated based on these ratios. A sparse map of relative remoteness is built on the basis of these estimations for the border points of photographed objects, and a dense depth map of relative distances is then calculated using a special interpolation technique. Main Results. The efficiency of described technique is illustrated with the results of distance estimation in the photographs of real environment. Practical Relevance. In contrast to the widely applied stereo-technique and distance measurement methods analyzing the sets of defocused images, the investigated approach enables dealing with a single photograph acquired in a standard way without setting any additional conditions and limitations. If the relative remoteness of objects may be estimated instead of their absolute distances, no special calibration is needed for the camera applied, and the pictures taken once previously in diversified situations can be analyzed using the considered technique.