Camera focal length from distances in a single image

Abstract

Camera focal length estimation from a single image is of great importance for many computer vision tasks. Unfortunately, previous methods cannot achieve satisfactory accuracy yet. This paper proposes a focal length estimation approach based on distances among four points in the scene of a single image. The issue is cast into a nonlinear optimization by adapting a standard pinhole camera model under the constraints of distance information. Multiple algorithms are employed to solve the optimization, and the best solution is then regarded as the final solution. Experimental results show that our method is able to obtain a more accurate focal length than some state of the art in a single image setting. In addition, we provide some simple application examples and show the intuitive effects of focal length estimation errors. We also demonstrate experimentally that distance information has an improved meaning for the solution of the focal length.