Oce-nederland B.v.

Etienne L Van Dorsselaer

Johannes P Oyen

An encoding method for digital image data comprising consecutive blocks of data groups having as content binary values always of an equal number of pixels of an image, utilizing a code which indicates that the encoded block is partly equal to the corresponding part of a reference block, the reference block preferably being the preceding block, and identifies the end point of that part of the reference block by reference to transitions in pixel value in the reference block. On decoding, that part of the reference block is taken over in the decoded block. This encoding method is, in practice, combined with run length encoding and encoding by copying an entire data group in the code.

Method and apparatus for encoding and decoding digital image data

Method of processing photoelectrically scanned image information representing different gray values, before such information is converted, by half-tone processing, into image information representing no more than two gray values, such that the scanned information is distinguished into different categories of information, each category being subjected to a filtering operation determined by the category, the information thus filtered for each category being suitable for subjecting to one type of half-tone processing.

Scan/print system for performing image processing and an image selection

Coding of digital data corresponding to a dithered image. The digital pixel values determined by comparison with a given threshold value of the dither matrix are combined to form a string. A string of this kind is formed for all the threshold values of the dither matrix. Strings found which are built up largely of a given pixel value are immediately converted into strings built up entirely of that pixel value, and are coded collectively. The other strings found are coded individually by comparing each of them with a set of standard strings and replacing them by the most similar standard string.

Method and apparatus for coding digital image information obtained from

The entire dithered image to be enlarged/reduced is divided into contiguous relatively small areas, called input areas, and the pixel pattern of each input area is represented by (i) an average gray level characterized by a standard pixel pattern and (ii) the pixels deviating from the standard pattern. Every input area is imaged onto an output area according to the enlargement/reduction factor, whereby the output area is filled with a standard pixel pattern yielding the average gray level of the input area and extra pixels are added to the standard pattern for the deviating pixels of the input area on locations determined by linear transformation.

Method of enlarging/reducing dithered images

The invention provides a method for reconstructing a dither matrix, used to transform a rastered gray-level image into an image of binary pixels, from the dithered image. The method includes the steps of determining the dimensions of the dither matrix from the spatial frequencies present in the dithered image and then determining the threshold values of the dither matrix from the distribution function of the pixels having a specific value.

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Sintjansteen, Netherlands

Etienne L Van Dorsselaer