Grey level linearising circuit for computer-interfaced display devices

An earlier paper by the authors on the linearisation of computer-interfaced display devices has described a radiometric procedure for quantifying device non-linearity and a software technique for using the data to linearise screen luminance with respect to display grey level. As the display non-linearity varies with the particular settings of the brightness and contrast controls, any change in these settings requires that the data used with the software also be modified. While it is possible to store data for a number of selected control settings, it would be more convenient if linearisation could be performed using hardware for all relevant settings of these controls. The electronic circuit described in this paper makes use of the same non-linearity data to achieve device linearity with the added advantage of increased flexibility of use. The circuit is suitable for connection immediately following the digital-to-analogue converter or video processor and provides two useful new controls. One of these determines the amount of non-linearity correction to be applied to the video signal, while the second enables screen contrast to be varied without affecting the linearity achieved. The standard brightness and contrast controls of the display device are left as initially preset and require no subsequent adjustment.