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Geometrical reconstruction of images obtained with electronic endoscopy

The authors use an electronic video endoscope (Fujinon EG7-HR2) to image the mitral valve in situ in an isolated pig heart preparation. From video recordings, images are digitized and analysed with a computer. A complication encountered during the study concerned the geometric wide angle distortion caused by the device. The paper describes a method developed to reconstruct the image, and to correct for this distortion. In order to quantify the relation between object and image, model equations were formulated based on mild assumptions. Points in object space are transformed through a non-linear relation to corresponding points in image space. Furthermore, an oblique camera view, and an aspect ratio correction factor, are accounted for. As a test object, a regular grid of points was recorded at several distances from the camera. The images of the grid points were digitized, and the model equations were fitted to these data.