Potentially Achievable Image Definition in Video Applications

Abstract

The paper gives an estimate of the potentially achievable level of definition for light-to-light video transmission path, which can be considered as ideal, i.e. such that a decrease in definition in it occurs only due to the diffraction limitations of the camera lens and the finite dimensions of the transforming elements of the camera matrix sensor and of the reproducing display without additional image processing. The assessment is based on the parameters of the spatial modulation transfer function (MTF) and the integral criterion of definition, estimated as the relative volume under the two-dimensional MTF. The authors proceeded from the fact that when describing the characteristics of digital video systems, the fundamental is the choice of the spatial sampling frequency, which is determined by the number of cycles of brightness variation per a given interval; the sampling rate, calculated for video applications by the number of half-cycles of brightness variation, is twice as high. Thus, the spatial sampling frequency of the image horizontally and vertically is equal to twice the number of active lines per frame height, and the spatial Nyquist frequency is correspondingly equal to the number of active lines. These considerations form the basis of the estimates made in the work, as well as the principle of development the proposed algorithm for MTF correction. For examples of combinations of lens parameters and geometric dimensions of matrix sensors of television, multimedia and other cameras, an assessment of the non-uniformity of the ideal camera MTF for SDTV, HDTV, UHDTV 4K and UHDTV 8K systems within the Nyquist frequency band is given. Examples of MTF of end-to-end paths for SDTV, HDTV, UHDTV 4K and UNDTV 8K systems for the specified parameters of the lens and camera sensor, taking into account the distortions introduced by the reproducing display, are presented. It is shown that for considered examples, integral criterion of definition can vary thereabout within 0.75–0.3.