Abstract: In a data processing system a large number of reduced images of documents are shown simultaneously on the screen of a visual display unit. The images are reduced in a two-step process. The first step includes performing a run-length algorithm on an original image to obtain an intermediate image with a predetermined linear reduction. In the second step, blocks of pixels of the intermediate image are replaced by single pixel of a reduced image to obtain further linear reduction. The pixels in the reduced image are assigned a grey level or color which depends on the distribution of pixels in the block of pixels in the intermediate image.

Abstract: A method and device for recognizing half-tone image information having a local frequency within predetermined limits such that an information area which may also contain other kinds of image information, is scanned line by line to generate a video signal or series of pixels which is subjected to a recognition process to determine, for each part of the signal, whether the same belongs to half-tone image information, wherein: the grey level maxima in the signal above a predetermined high threshold value are determined; the distance between each two successive grey level maxima is determined and compared with a predetermined fixed distance; and for the part of the signal between two successive maxima a positive decision is made that the information in that part of the signal is half-tone image information if the distance between two successive grey level maxima previously determined to be above a predetermined high threshold value and a predetermined fixed distance lies within predetermined limits.