Signal-to-noise ratio and maximum information content of images displayed by a CRT

Hans Roehrig; Tinglan Ji; Michael P. Browne; William J. Dallas; Hartwig R. Blume

doi:10.1117/12.18847

1 July 1990 Signal-to-noise ratio and maximum information content of images displayed by a CRT

Hans Roehrig, Tinglan Ji, Michael P. Browne, William J. Dallas, Hartwig R. Blume

Proceedings Volume 1232, Medical Imaging IV: Image Capture and Display; (1990) https://doi.org/10.1117/12.18847
Event: Medical Imaging '90, 1990, Newport Beach, CA, United States

Abstract

This paper describes the results of measurements which permit determination of the maximum information content of images displayed with a high resolution CRT of a nominal pixel matrix of 2000 x 2000 adressable pixels. These measurements are based on the precise determination of signal, noise and spatial resolution. Noise is measured both as temporal noise and as spatial noise, using both temporal and spatial sampling techniques. The dynamic range as given by the maximum and minimum values of luminance can be as high as 1900, however for practical settings of brightness and contrast it is about 424. The dynamic range is reduced from 424 to 1 38 as a result of veiling glare when the SMPTE pattern is displayed. The spatial noise was significantly larger than the temporal noise: For a command level of GL = 255, a single pixel and a single CRT frame, the temporal signal-to-noise Eatio was 59, while the spatial signal-to-noise ratio was only 7. The RMS noise (both spatial and temporal) was proportional to the squareroot of the respective bandwidths. Both temporal and spatial noise power spectra were independent of their respective frequencies (white noises). In the average, the size of a pixel was much larger than the size of an addressable pixel, indicating, that the total number of usable pixels was smaller than the number of addressable pixels: Instead of the addressable pixelmatrix of 2000 x 2000 pixels, we estimated only 532 x 548 "Noise-Equivalent" pixels. It was estimated, that for spatial integration over a single pixel and temporal integration over a single CRT frame, the maximum information content of images produced by this monitor, is 1.72 x 10⁶ bits, based on temporal noise; however due to spatial noise that number is reduced to 1.28 x 10⁶ bits. This contrasts sharply with the nominal information content of 3.2 x 10⁷ bits as determined from the nominal raster of 2000 x 2000 pixels and the 8 bits digitization at the display buffer.

Citation Download Citation

Hans Roehrig, Tinglan Ji, Michael P. Browne, William J. Dallas, and Hartwig R. Blume "Signal-to-noise ratio and maximum information content of images displayed by a CRT", Proc. SPIE 1232, Medical Imaging IV: Image Capture and Display, (1 July 1990); https://doi.org/10.1117/12.18847

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