Abstract: An apparatus is provided for generating a pulse train, the apparatus comprising a member having a plurality of spaced marks disposed thereon with at least one of the spaced marks being a reference mark. The member is in communication with means for generating the pulse train as the plurality of spaced marks move. Additionally, the pulse train has a periodicity defined by the same edge of two successive pulses and the plurality of spaced marks are configured so that the periodicity of the pulse train remains constant.

Abstract: A scanned raster is divided into halftone cells that are, for example, four by four picture elements (pixels) in size, i.e., it takes sixteen picture elements to make one halftone cell. The tone is determined by summing a different and predetermined threshold value for each of the picture elements that comprise a halftone cell. Each of these signals is then sliced at a predetermined value; if the sum of the threshold and the video value is higher than the slicing level, the picture element is transmitted as a "1", and if below the slicing level, it is sent as a "0".