Image Sharpness Control in Modern Television Systems

The article is devoted to establishing a connection between the subjective assessment of the TV images quality and the generalized criterion of definition in two dimensions. In modern practice in television definition is characterized by the number of active scan lines and the number of active picture elements per line. It should be taken into account that the achievable image definition is limited by diffraction distortions of the lens and blurring due to the finite dimensions of the "light-to-signal" and "signal-to-light" conversion elements of the matrix sensor camera and playback display screen. The question of what should be the MTF of an image processing system used to improve definition in two dimensions is relevant, based on the compromise between the attainable level of definition and the interfering effect of edging in the image arising as a result of excessive emphasis on image details. The article is devoted to answering this question, but the experimental data presented in it are focused on solving the more general problem of establishing the relationship between image quality and definition in two dimensions for the general case. In the experiments, to vary the resulting definition, a controlled two-dimensional corrector was used in the form of a digital filter with circular symmetry MTF. It was provided for the possibility of blurring the image by limiting the frequency band and correcting definition by using a corrector with a rise that varies according to the cosine-square law so that the maximum was achieved at a frequency equal to half the spatial Nyquist frequency, i.e. the number of scan lines per frame height. The relative volume under the two-dimensional MTF of the TV path "from light to light" was used as a generalized criterion for definition.