A new approach for nonlinear distortion correction in endoscopic images based on least squares estimation

Abstract

Abstract-Images captured with a typical endoscope show spatial distortion, which necessitates distortion correction for subsequent analysis. In this paper, a new methodology based on least squares estimation is proposed to correct the nonlinear distortion in the endoscopic images. A mathematical model based on polynomial mapping is used to map the images from distorted image space onto the corrected image space. The model parameters include the polynomial coefficients, distortion center, and corrected center. The proposed method utilizes a line search approach of global convergence for the iterative procedure to obtain the optimum expansion coefficients. A new technique to find the distortion center of the image based on curvature criterion is presented. A dual-step approach comprising token matching and integrated neighborhood search is also proposed for accurate extraction of the centers of the dots contained in a rectangular grid, used for the model parameter estimation. The model parameters were verified with different grid patterns. The distortion-correction model is applied to several gastrointestinal images and the results are presented. The proposed technique provides high-speed response and forms a key step toward online camera calibration, which is required for accurate quantitative analysis of the images.

Fast Barrel Distortion Correction for Wide-Angle Cameras

“…To obtain the pixel intensity at (x , y ), the DIS has to be resampled since either x or y may not be an integer, for which the bilinear interpolation can be employed [1]- [4]. This process is known as backward mapping, as it describes a mapping from a CIS pixel to a DIS pixel.…”

“…where c i is the distortion coefficient that can be estimated by applying a least-square method as presented in [1]. In (1), N represents the accuracy of the distortion model, which consequently affects the quality of the correction if it is based on the backward mapping.…”

Foveated endoscopic lens

“…One can then use least squares analysis to estimate the mapping parameters for performing image correction. [23][24][25][26][27][28] Since the mapping of object to image is in principle a purely radial function, the mapping parameters are the image coordinates of the optical axis ðx 0 c ; y 0 c Þ together with the a i coefficients used to express the radial form of the mapping from image plane ðx 0 ; y 0 Þ to object plane ðx; yÞ:…”

Computational Tasks in Bronchoscope Navigation During Computer-Assisted Transbronchial Biopsy

“…The methodology presented in [12], [13] was used for correction of bronchoscope Olympus BF-160 camera lens distortions. As a test image black dotes lying on straight lines have been chosen.…”