Optical scanner having a variable resolution

Facsimile and static presentation processing – Facsimile – Picture signal generator

Reissue Patent

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Details

C358S443000, C358S451000, C358S483000, C348S312000, C250S208100

Reissue Patent

active

RE037282

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention generally concerns optical scanning systems, including systems having a high resolving power for scanning documents and the like to generate digital, binary data which represent the scanned information. The scanned information can then be stored electronically for later computer processing. There is a great need for a facility for the scanning of documents, drawings and similar materials, thereby saving storage space and facilitating corrections of drawings, etc.
2. Background of the Invention
Since scanning systems of this type are designed to scan very broad documents, the optical system in front of the actual scanning unit or the CCD camera will be utilized to the utmost. Thus, use is made of very expensive lens beams which are either mounted mechanically very stably or are stitched together, as shown in U.S. Pat. No. 5,117,295. The optical system is arranged stationarily in front of the CCD cameras, and the scanning unit is therefore borne with a constant resolution which depends upon the configuration of the documents, the lens system and the CCD cameras as well as the density of the photosensitive cells on the CCD camera.
If a variable resolution of the document of the scanned data is desired, such is provided by the subsequent data processing of the written data internally in the optical scanner. U.S. Pat. No. 4,631,598, U.S. Pat. No. 4,972,273 and U.S. Pat. No. 5,218,457 provide examples of such subsequent data processing. The analog signals from the CCD cameras are converted into digital signals, which takes place controlled by a periodic clock signal. If the resolution is to be enhanced, new grey level values are then estimated between already existing grey level values which are determined by sampling. According to the method disclosed in these documents it is not possible to select an arbitrary position of these estimated grey level values, because of the limitations imposed by the algorithms on which the method is based. Thus, it is not possible to choose an arbitrary resolution of the written data, which is generally desirable in many cases.
The object of the invention is therefore to provide an optical scanning system in which the resolution can be selected freely.
Another object of the invention is to provide an optical scanning system wherein the variable resolution enables compensation for imaging errors in the optical system of the scanner.
SUMMARY OF THE INVENTION
The present invention overcomes the drawbacks and limitations of the prior art in connection with the selection of resolution. The invention provides an optical scanner having a variable resolution and comprising a detecting unit which, controlled by a pixel clock signal, applies a discrete signal representing pixels scanned in a region, a filter for filtration of the discrete signal, clock-controlled analog-to-digital converter means which convert the signal received on their input to a digital representation having a preselected resolution, said resolution being controlled by a sample clock generator, said sample clock generator comprising a counter means, a store as well as a first register, said counter means receiving the pixel clock signal on the input and applying a multibit signal on the output, said store containing binary data words, said multibit signal from the counter means serving as an address signal, an addressed, binary data word being read from the store, said first register receiving the read, binary data word from the store and being coupled to a further periodic clock generator which controls reading from the register so as to provide a clock signal having clock pulses when the individual bits of the data word assume a first binary state, and having no clock pulses when the bits of the data word assume a second binary state, said clock signal being applied to the analog-to-digital converter means as a sample clock signal.
It may be said here that the objects of the invention are achieved in that the written information is clocked out of the CCD camera by the inherent pixel clock signal of the system, and that the data signal thus clocked is sampled or resampled subsequently with a new clock signal which possesses precisely the desired clock frequency, thereby achieving the desired resolution. The essential feature of the invention is precisely this clock signal which is provided in a special manner in terms of clock signals, because the signal is stored as sequences in a RAM store, which are read successively and are transferred to a register. This register is read bit by bit under the control of a further clock generator having a clock frequency which is higher than the desired clock frequency. The clock signal generated by the register is thus synchronous with the clock signal from the further clock frequency generator, but some of the clock pulses will be missing.
In the preferred embodiment a bit in the register corresponding to a binary 1 involves the presence of a clock pulse, while a binary 0 involves non-presence of a clock pulse. The clock signal from the register is thus not periodic. Prior to scanning, a controller calculates how the clock pulses in the clock signal from the register are to be distributed in response to the desired resolution, and the sequences necessary for achieving this clock signal are stored as data words in the RAM store. A counter successively addresses these data words, which are read and transferred to the register, where the further clock frequency generator clocks the contents of the clock register to provide the desired clock signal. The further frequency generator typically supplies an integer multiple of the pixel clock frequency when a fine resolution is desired, and equal to the clock frequency or less when a coarse resolution is desired.
Since the clock signal of the register is synchronous with the pixel clock signal, but is not periodic, it is possible to determine the clock signal of the register in a manner such that the clock pulses are as close to being periodic as possible, while compensating for imaging errors in the optical system of the scanner.
These and other objects and advantages are achieved in the embodiments illustrated herein.


REFERENCES:
patent: 4631598 (1986-12-01), Burkhardt et al.
patent: 4934821 (1990-06-01), Morton
patent: 4972273 (1990-11-01), Burkhardt et al.
patent: 5218457 (1993-06-01), Burkhardt et al.
patent: 5303064 (1994-04-01), Johnson et al.
patent: 5402234 (1995-03-01), Deck
patent: 5452109 (1995-09-01), Compton

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