A method for in-field evaluation of the modulation transfer function of electronic display devices
Electronic medical display devices require routine monitoring of their resolution characteristics. This paper introduces a methodology for the assessment of resolution (MTF) characteristics of display devices using a photographic-grade CCD camera, and reports initial MTF measurements on a 5 megapixel medical CRT display device at three display resolution settings. The intrinsic performance of the camera was first evaluated. The camera was placed at a 2 cm distance from the display's faceplate and focused on the image plane. For each MTF assessment, the images of two test patterns were captured without moving the camera, each containing a single-pixel-wide, low-modulation (20% positive contrast) horizontal or vertical line within a uniform background. The captured CCD images were then transferred to a computer, where the orthogonal MTFs were deduced by 1) linearizing the data, 2) identifying the angle of the line transition within the images, 3) reprojecting the 2D data along that direction to determine the line spread function (LSF), and 4) Fourier transforming of the LSF. The results demonstrate that the methodology produces reproducible results in the orthogonal directions and is sensitive to the resolution setting of the display device. The instrumentation needed for the method is portable and can easily be utilized in a clinical setting.
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