MARK CODE READING METHOD

PURPOSE:To read an optionally-shaped, constant-area mark added to a display medium at a prescribed position, by finding its presence by comparing an arithmetic numeral based upon a picture pattern with a reference numeral indicating an effective mark. CONSTITUTION:Marks 2 having constant area are provided to a sheet 1 at positions I-V and coded for information display, and they are scanned together with positioning check marks 3 to obtain a picture signal Av; and the signal Av as a time-series analog signal indicating the density of every picture element is clamped at a constant threshold level by an interface 9 corresponding to every picture element to be converted into a binary signal having level ''1'' and ''0'', which are stored in an RAM8. On the basis of the binary signal, a CPU6 calculates a numeral which corresponds to the area of a mark picture to make a comparison with a reference numeral Sref stored in an ROM7; when a numeral read out of the RAM8 is greater, the presence of the ''1'' is discriminated and when less, the nonpresence of the ''0'' is discriminated, thus reading the mark codes.