International Business Machines Corporation

Shigeki Asada

Hiroaki Yasuda

Hiroshi Yanagisawa

Masayuki Sohda

Megumi Hasegawa

A display system for converting N bit signals, each representing 2.sup.N gray levels, to M bit signals representing 2.sup.M gray levels, where N is an integer larger than or equal to 2 and M is an integer satisfying N&gt;M.gtoreq.1. Each of the N bit signals are separated into higher M bits and lower N-M bits. There are 2.sup.N-M tables, each of which stores a distinctive set of P.times.Q modification values satisfying P.times.Q.gtoreq.2.sup.N-M. One of the tables is selected using the N-M bits. Unequality between a first set of modification values and a second set of modification values of the selected table are detected. The first set of modification values and the second set of modification values are exchanged to generate a modified table of the selected table. The M bits of one N bit signal and each of the modification values of the selected table are added to generate a first set of P.times.Q M bit signals. The M bits of the next N bit signal and each of the modification values of the modified table are added to generate a second set of P.times.Q M bit signals. The first and second sets of M bit signals are provided to a display device of 2.sup.M gray levels.

Display system

A document scan apparatus in which the position of a document support table relative to an optical system is detected during the relative movement between the document support platen and the optical system. A reference position marker is mounted on the document support table which directly reflects a light from a document illumination light source into an optical sensor array or a CCD sensor array through a mirror and a lens for causing the CCD sensor array to operate in a saturated range to generate a higher output signal level than an expected highest signal level of the CCD sensor array in the document scan operation; and by setting a threshold level of a comparator circuit to a high level which is exceeded by the higher output signal level of the CCD sensor array. The reference position marker is positioned within the field of view of the CCD sensor array for sensing the image of the document, so that the CCD sensor array sensing the document image also senses the reference position marker.

Document scan apparatus with reflective reference position marker

The invention directly controls the start of application of clock pulses to a shift register of an image sensor unit in synchronism with read signals supplied from a processor unit, to transfer video data of successive scan lines of an image. Transfer time of video data of one scan line from the shift register to the processor unit is compared to a predetermined time period. If the transfer time exceeds the predetermined time period, transfer of video data of the next scan line to the shfit register is allowed after the video data of the one scan line in the shift register has been transferred to the processor unit, whereby electric charges for the next scan line accumulated in the photodiodes are vanished. And, the video data of the next scan line in the shift register is discarded. In addition, the invention is devised to provide a data disposing cycle in the operation mode of the shift register in addition to the data reading cycle, so that, even when interruption from others causes the operation of the processor fetching the video data from the shift register to exceed a predetermined scanning time before completion of the operation, the data disposing cycle is inserted right after completion of the operation to disposed high level data that has been sensed for a long period of time by a photosensor of the sensor unit, and normal level data or image information properly representing an image being scanned is obtained. Furthermore, the invention reduces significantly the processing load of the processor with a simple hardware constitution by adding the operation of a run length counter, etc., so as to enable high speed linear data compression.

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Yokohama, Japan

Shigeki Asada