1. A machine process for thinning an image, comprising the steps of: defining an image in terms of a plurality of discrete picture elements (pixels); convolving each horizontal string of pixels of the image with itself shifted a predetermined number of pixels; weighting each shifted position of each horizontal string; selecting certain of the pixels of the weighted horizontally convolved pixel strings which correspond to predetermined descriptors; convolving each vertical string of pixels of the image with itself shifted a predetermined number of pixels; weighting each shifted position of each vertical string; selecting certain of the pixels of the weighted vertically convolved pixel strings which correspond to predetermined descriptors; adding the selected pixels from the horizontal and vertical weighted convolutions and the pixels of the original image; retaining those pixels which are common to the original image and the selected pixels of both the horizontal and vertical weighted convolutions; discarding those pixels which are absent from the original image; filtering those pixels which are common to the original image and to the original image and only one of the selected pixels of the horizontal and vertical weighted convolutions; further retaining certain of the filtered pixels and discarding others in accordance with a predetermined filter matrix; and providing an output signal of the retained pixels which represents a thinned image.