A well-recognized problem with the echo-planar imaging (EPI) technique most commonly used for functional magnetic resonance imaging (fMRI) studies is geometric distortion caused by magnetic field inhomogeneity. This makes it difficult to achieve an accurate registration between a functional activation map calculated from an EPI time series and an undistorted, high resolution anatomical image. A...

Digital Image Watermarking has become a need of the hour in case of multimedia. But along with that comes the problem of dealing with the geometric distortions. This paper presents an overview of the various techniques used for eliminating geometric distortions. It summarises the advantages and disadvantages of one method over the other. As we are more dependent on multimedia for passing of the...

background and aims. panoramic radiographs are used for surgical planning of unerupted third molars. the major problems associated with panoramic radiography include unequal magnification and geometric distortion of the image. the purpose of this study was the clinical evaluation of the effect of radiographic distortion on the position and classification of unerpted mandibular third molars. mat...

Compensating for distortions in pushbroom satellite imagery has a bearing on subsequent earth observation applications. Traditional distortion correction methods usually depend on ground control points (GCPs) acquired from a high-accuracy geometric calibration field (GCF). Due to the high construction costs and site constraints of GCF, it is difficult to perform distortion detection regularly. ...

We have obtained a new geometric-distortion solution for the STIS NUV-MAMA using two fields in NGC 4214 and NGC 604 which were imaged using three filters (CN182, CN270, SrF2) for GO program 9096. (WF)PC2 images of the same objects in F170W and F336W were used as an astrometric reference. Different polynomial degrees and weighting mechanisms for the geometric distortion were tested until an adeq...

This paper presents a study on the human perception of geometric distortions in images. The first part of the study is the design and implementation of a user-test to measure human perception of geometric distortions in images. The result of this test is then used to evaluate the performance of the second part of the study, namely the objective quality measurement scheme. Our experiment shows t...

This paper describes a new method for removing geometric distortion in images of submerged objects observed from outside shallow water. We focus on the problem of analyzing video sequences when the water surface is disturbed by waves. The water waves will affect the appearance of the individual video frames such that no single frame is completely free of geometric distortion. This suggests that...

The work presented herein describes our methods and results for predicting, measuring and correcting geometric distortions in a 3 T clinical magnetic resonance (MR) scanner for the purpose of image guidance in radiation treatment planning. Geometric inaccuracies due to both inhomogeneities in the background field and nonlinearities in the applied gradients were easily visualized on the MR image...