A SIMPLIFIED METHOD OF ENDOSCOPIC IMAGE DISTORTION CORRECTION BASED ON GREY LEVEL REGISTRATION (WP-P6)

Author(s) : Rosebet Miranda-Luna (CRAN-INPL, France) Walter Blondel (CRAN-INPL, France) Christian Daul (CRAN-INPL, France) Yahir Hernandez (CRAN-INPL, France) Ruben Posada (CRAN-INPL, France) Didier Wolf (CRAN-INPL, France)

Abstract : We present a new method of endoscopic camera calibration for non-linear radial distortion correction. The implemented algorithm computes projective (camera) and polynomial (distortion) transformations. The optimization process registrates the corrected distorted pattern image with the non-distorted one. Mutual information was used as measure of similarity and stochastic gradient descent method for optimization. The algorithm was tested with one grey level and two b/w (chessboard, concentric circles) patterns, for 3 angular positions of the endoscope (0°, 5° and 10° to perpendicular). Convergence time increased with the angle. Maximal mean correction error was less than 0.45 % with optimized distortion parameters calculated for the grey level pattern. Tested inclinations did not have significant effects on errors. Results obtained show the interest of the proposed method that requires only approximative perpendicular positioning of the endoscope and simple grey level calibration patterns without precise geometrical characteristics.

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