Collimator artifacts may be present within the images produced by collimators whose septal width approaches the inherent resolution of the gamma-camera system. As the inherent resolution of the gamma-camera is improved, collimator artifacts become more prominent. The purpose of this study is to eliminate collimator artifacts from gamma-camera images. To eliminate the septum effect produced by high-energy parallel-hole collimators with thick septa, the following method was used: X and Y signals from the detector are made to ride on the triangular waves changing periodically, and resultant position signals obtained by this processing are applied to the corresponding deflection circuits in the CRT display. The oscillation amplitude of processed position signals can be regulated by the frequency and amplitude of the triangular waves. Regulation of the oscillation amplitude of position signals, which would produce maximum reduction of collimator artifacts, was to approach the spatial frequency responses of the overall processed line spread functions obtained experimentally to those of the Gaussian functions with FWHM equal to the geometric resolution calculated from the equation given by Gerber and Miller. In images of a pancreas phantom containing 131I, collimator artifacts were clearly seen in the unprocessed case, but were eliminated in the processed case.