Three decision thresholding mode switch and method for mode selection

A three decision thresholding mode switching device for establishing an optimum operational mode from at least two available mode control algorithms for printing copies of mixed format documents in a system that includes a scanner for scanning the reflectance from that portion of the document then being copied to develop therefrom an analog output signal indicative thereof, and an analog-to-digital converter to convert the developed analog signal to a digital output signal that includes a plurality of pels, said mode switching device comprising:

• gradient constant establishing means for receiving said plurality of pels indicative of the reflectance sensed by said scanner and developing therefrom a gradient constant for each pel when thresholded, said gradient constant being indicative of the rate of change of reflectance of said pel then being thresholded with respect to the average rate of change of predetermined others of said plurality of pels, said gradient constant establishing means including means for establishing three different decision ranges of gradient constants and providing outputs indicative thereof;
• and
• selecting means for receiving said gradient constants from said gradient constant establishing means and responsive thereto providing a mode control output for establishing said optimum operational mode for printing that portion of the copy of said document then being scanned.

An electronic switching device for establishing the optimum operational mode with respect to a predetermined parameter of data from a plurality of available modes in a processing unit receiving said data in the form of a plurality of bytes indicative of a portion of said data, said device comprising:

• first means for receiving a plurality of bytes representing said received data and developing therefrom an output signal indicative of differences with respect to said predetermined parameter of said data between one of said received bytes and others of said bytes of said received plurality of bytes;
• second means connected with said first means and for establishing at least three ranges into which said differences sensed by said first means can fall and providing output signals indicative thereof;
• and
• third means for receiving said output signals from said second means and responsive thereto selecting one of three decisions as established by said second means to provide mode establishing signals that enable selection of the optimum operational mode for said processing unit.

A method for establishing an optimum operational mode for printing copies of mixed format documents by selection of a thresholding algorithm, from a plurality of algorithms, most suitable for each scanned segment of the document, said method comprising:

• scanning a document and producing a plurality of pels indicative of reflectance from different segments of the scanned document;
• developing an output indicative of the rate of change of reflectance of the pel from which a thresholding algorithm is then to be selected with respect to other pels of said plurality of pels;
• determining the value of said developed output with respect to the value ranges of at least three different rates of change of reflectance ranges;
• and
• utilizing said determination to cause the most suitable thresholding algorithm to be utilized to print copies of that portion of the document then being scanned.

A method for establishing an optimum operational mode for printing copies of mixed format documents by selection of one of a black-white thresholding algorithm and a gray-scale thresholding algorithm for each segment of the scanning document, said method comprising:

• scanning a document and producing a plurality of pels indicative of the reflectance as sensed from different segments of the document during scanning;
• determining the reflectance differences between adjacent pels of said plurality of pels and summing the determined differences;
• normalizing the summed differences by dividing the summed differences by the reflectance value of the pel for which a thresholding algorithm is then to be selected to establish a gradient constant with respect to said pel;
• selecting three ranges of gradient constants corresponding to three decisions one of which is to utilize said black-white thresholding algorithm, the second of which is to utilize said gray-scale thresholding algorithm, and the third of which is to utilize the last utilized thresholding algorithm;
• determining into which of the said three ranges said established gradient constant falls;
• and
• utilizing said determination to select the thresholding algorithm best suited for printing copies of that segment of the document then being scanned.