Correcting the adjacent pixel nonlinearity on video monitors

In raster-scan CRT display systems, the luminous flux of a given pixel is affected by the preceding pixel along the raster direction. This spatial or adjacent pixel nonlinearity can adversely affect image quality. High contrast, high spatial frequency regions of an image will have wrong luminances. A simple lookup table (standard gamma correction) can not correct this nonlinearity. We measured the spatial nonlinearity under a variety of luminance conditions in two CRT displays. A model proposed by Mulligan and Stone1 was used in a 5parameter nonlinear regression to fit the data. Results show that the model fit our data very well. We employed a twodimensional lookup table to compensate for the spatial nonlinearity. The new lookup table has two entries: the intended luminance of the current pixel and the actual voltage of the previous pixel. The output of the new lookup table is the adjusted voltage which compensates for the pixel interaction and gives the correct average luminance for that pixel. Psychophysical experiments show that at small pixel sizes (less than 0.8 mm), the compensation results in a sharp accurate image.