Abstract: A method for contrast-enhancing in a multi-dimensional image in image locally detects a contrast quantity. This quantity is determined to be either in a low range or in a high range. When in the high range, the contrast is locally enhanced with an enhancement factor that is a monotonic non-increasing function of the local contrast. After enhancing, the contrast itself is a monotonically increasing function of the contrast before enhancing.

Abstract: For noise reduction in a two-dimensional image it is sampled according to a regular array of window sampling positions. The image function is then subjected to multiplication by a window function and conversion to a weighted sum of polynomials according to ascending order. If the next-m-lowest order coefficient signals a sufficient intensity variation in the window, all coefficients are used for subsequent inverse polynomial transform. Otherwise, predominantly only the lowest order coefficient is used therefore. In a cascaded organization, the lowest order coefficient is viewed as itself representing the image information and likewise processed in a forward-inverse polynomial transform organization with respect to an upscaled-size window. The result is then used in a next lower cascade level in lieu of the unprocessed lowest order coefficient itself.

Abstract: In a television transmission system for digital picture signals each picture is partitioned into sub-pictures of N.sub.1 .times.N.sub.2 pixels for limiting the bit rate. Each sub-picture is subjected to a forward picture transform for generating basic picture weighting factors. To this end each sub-picture is multiplied by a reference picture which has different values for different pixels (for example, as described by a Gauss function). This multiplied sub-picture is subsequently multiplied by a number of kernel pictures so that the said basic picture weighting factors are obtained. Each kernel picture is equal to the product of the reference picture and a basic picture. Of the collection of basic pictures each basic picture is an orthogonal polynomial associated with the square value of the reference picture. For regaining the original sub-pictures each weighting factor is multiplied by the original kernel picture from which the weighting factor is obtained.

Abstract: In a television transmission system each picture is subjected to a number of picture transforms for limiting the bit rate. In each picture transform the picture is partitioned into sub-pictures of a given size. The sub-picture size is different for the different picture transforms. Each sub-picture is converted into a limited number of predetermined coefficients by use of a sub-picture transform. This number is related to the sub-picture size. With the matrix of coefficients thus obtained for each picture an approximation of the original picture is made by use of an inverse transform and this approximation is subjected to one of the said forward transforms. The matrix of coefficients now obtained is subtracted from this matrix of coefficients which is obtained by subjecting the original picture to the same forward transform.

Abstract: A pyramidal coding circuit comprises a decimation circuit (14.1) which receives the picture consisting of M.times.N pixels to be transmitted and converts it into K+1 auxiliary pictures B.sub.k, the numbers of horizontal and vertical pixels of B.sub.k being smaller by respective factors A.sub.H and A.sub.V than those of the auxiliary picture B.sub.k-1 (k=0, 1, 2, . . . K) preceding in ordinal number. Each auxiliary picture B.sub.k is expanded in an expansion channel 14.4(.) to an expanded auxiliary picture B'.sub.k having the same number of horizontal and vertical pixels as the auxiliary picture B.sub.k-1. In a difference picture former 14.7 (.) the auxiliary picture B.sub.k-1 and the expanded auxiliary picture B'.sub.k having the same number of horizontal and vertical pixels as B.sub.k-1 are subtracted from each other for generating a difference picture D.sub.k-1. The expansion channel has not only a two-dimensional interpolating low-pass filtering function 14.5(.) but also a picture prediction function 14.