1. An image digitizer comprising: (A) a preliminary thresholder for receiving signals representing the optical intensity of pixels of an image and producing a preliminary binary bitmap representation of the image suitable for discrimination between text and grey scale image; (B) a text thresholder for receiving signals representing the optical intensity of pixels of the image to be digitized and producing a binary bitmap representation of the imge according to a text thresholding algorithm; (C) a grey scale imge thresholder for receiving signals representing the optical intensity of pixels of the image and producing a binary bitmap representation of the image according to a grey scale image thresholding algorithm; and (D) thresholder selection means (a) for computing from the preliminary binary bitmap an average run length for each of a plurality of regions of the image, (b) for comparing the computed average run length of each region with a predetermined run length threshold to categorize each region as either a text type or a grey scale type image, (c) for causing the text thresholder to be applied to regions of the image determined to be of the text type, and (d) for causing the grey scale image thresholder to be applied to regions of the image determined to be of the grey scale type.