Method and apparatus for reading image information formed on material

• US 5,070,414 A
• Filed: 08/15/1989
• Issued: 12/03/1991
• Est. Priority Date: 09/20/1988
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Tsutsumi, Teruo
• Primary Examiner(s): Coles, Sr., Edward L.
• Application Number:
  US07/393,951
• Time in Patent Office: 840 Days
• Field of Search: 358/461, 358/482, 358/483, 358/465, 358/466
• US Class Current: 358/466
• CPC Class Codes: H04N 1/4076 dependent on references outside the picture
• CPC Class Codes: H04N 25/63 applied to dark current
• CPC Class Codes: H04N 25/701 Line sensors

Abstract

To read a document accurately and produce an image signal faithfully representing the document, an image reading method and apparatus adopts various means, of "latching an average light-shielded signal in a digital form", "using an average light-shielded signal resulting from averaging output signals of a plurality of light-shielded pixels as a black reference signal", "replacing that part of an image signal in which an average light-shielded signal is larger than an effective pixel signal in level with a signal of a zero level", "driving CCD sensors at such timing as to allow effective pixel signals output from the CCD sensors to be continuous in time" and "setting DC offset voltages of signals output from CCD sensors to a predetermined clamp potential."

Claims

1. An image reader comprising:

a line sensor comprising a one-dimensional array of a plurality of photoelectric conversion elements, said plurality of photoelectric conversion elements being selectively shaded to provide light-shielded pixels for outputting light-shielded signals and effective pixels which are not shaded for outputting effective pixel signals;

analog to digital conversion means for converting the light-shielded signals to digital light-shielded signals;

holding means for holding the digital light-shielded signals; and

image signal producing means for correcting a first signal corresponding to the effective pixel signals in accordance with a second signal corresponding to the digital light-shielded signals held by said holding means, and generating an image signal.

2. An image reader according to claim 1, wherein

said image signal producing means includes comparing means for making a comparison in level between the first signal and the second signal;

and

image signal correcting means for replacing produced image signal with a signal of a zero level when the second signal is larger than the first signal in level.

3. An image reader according to claim 1, wherein

said image signal producing means produces the image signal in digital form and includes digital to analog conversion means for converting the produced image signal to an analog signal.

4. An image reader comprising:

image reading means having an array of a plurality of line sensors for generating output signals having DC offset voltages, each of a said sensors has a one-dimensional array of a plurality of photoelectric conversion elements; and

a plurality of clamp means provided in correspondence with said line sensors, for clamping the DC offset voltages to a predetermined potential.

5. An image reader according to claim 4, wherein

each of said clamp means includes means for performing a charging operation during a time interval in which the corresponding one of said line sensors perform no reading operation.

6. An image reader comprising:

a line sensor having a one-dimensional array of a plurality of photoelectric conversion elements, said plurality of photoelectric conversion elements becoming selectively shaded to provide light-shielded pixels for outputting light-shielded signals and effective pixels which are not shaded for outputting effective pixel signals;

average signal producing means for averaging at least two of the light-shielded signals to produce an average signal;

holding means for holding the average signal produced by said average signal producing means; and

image signal producing means for correcting a first signal corresponding to the effective pixel signals in accordance with a second signal corresponding to the average signal held by said holding means.

7. An image reader according to claim 6, wherein

said image signal producing means includes comparing means for making a comparison in level between the average signal and the first signal;

and

image signal correcting means for replacing the produced image signal with a signal of a zero level when the average signal is larger than the first signal in level.

8. An image reader according to claim 6, wherein

said image signal producing means produces the image signal in digital form and includes digital to analog conversion means for converting the produced image signal to an analog signal.

9. An image reader comprising:

image reading means comprising an array of a plurality of line sensors each of which is a one-dimensional array of a plurality of photoelectric conversion elements, said plurality of photoelectric conversion elements being selectively shaded to provide light-shielded pixels for outputting light-shielded signals and effective pixels which are not shaded for outputting effective pixel signals;

drive controlling means for sequentially driving said line sensors at such timing as to allow the effective pixel signals output to be continuous in time; and

signal selecting means for selecting the effective pixel signals to output the selected signal as a serial signal.

10. An image reader comprising:

image reading means comprising an array of a plurality of line sensors each of which is a one-dimensional array of a plurality of photoelectric conversion elements for outputting photoelectric conversion signals, said plurality of photoelectric conversion elements being selectively shaded to provide light-shielded pixels for outputting light-shielded signals and effective pixels which are not shaded for outputting effective pixel signals;

drive controlling means for sequentially driving said line sensors in a predetermined order at a predetermined timing so that the effective pixel signals are continuously outputted;

group-serializing means for driving the photoelectric conversion signals output from said line sensor into a plurality of groups each having the photoelectric conversion signals which are not neighbored to one another and which are selectively extracted from the photoelectric conversion signals output from said line sensors, and serializing the selectively extracted signals for each group to produce a serialized photoelectric conversion signal;

analog to digital conversion means for converting the serialized photoelectric conversion signals to digital serialized photoelectric conversion signals;

holding means for holding light-shielded signals in the digital serialized photoelectric conversion signals;

black reference signal producing means for serializing the light-shielded signals held by said holding means for separate groups to produce a black reference signal;

effective signal producing means for serializing the effective pixel signals in the digital serialized photoelectric conversion signals to produce a serial effective pixel signal; and

image signal producing means for correcting the serial effective pixel signal in accordance with the black reference signal and for generating an image signal.

11. An image reader according to claim 10, wherein

said image signal producing means produces the image signal in digital form and includes digital to analog conversion means for converting the produced image signal to an analog signal.

12. An image reader according to claim 10, wherein

said image signal producing means includes comparing means for making a comparison in level between the first signal and the second signal;

and

image signal correcting means for replacing the produced image signal with a signal of a zero level when the second signal is larger than the first signal in level.

13. A method of reading an image comprising the steps of:

converting reflected light from a document into a photoelectric conversion signal by the use of a line sensor of a one-dimensional array of a plurality of photoelectric conversion elements, said plurality of photoelectric conversion elements being selectively shaded to provide light-shielded pixels for outputting light-shielded signals and effective pixels which are not shaded for outputting effective pixel signals;

converting the light-shielded signals into digital light-shielded signals;

holding the digital light-shielded signals; and

correcting a first signal corresponding to the effective pixel signals in accordance with a second signal corresponding to the held light-shielded signals.

14. A method of reading an image comprising the steps of:

converting reflected light from a document into a photoelectric conversion signal having DC offset voltages, by the use of image reading means comprising an array of a plurality of line sensors each of which includes a one-dimensional array of a plurality of photoelectric conversion elements; and

setting the DC offset voltages to a predetermined potential.

15. A method of reading an image comprising the steps of:

converting reflected light from a document into a photoelectric conversion signal by the use of a line sensor having a one-dimensional array of a plurality of photoelectric conversion elements, said plurality of photoelectric conversion elements being selectively shaded to provide lightshielded pixels for outputting light-shielded signals and effective pixels which are not shaded for outputting effective pixel signals;

averaging at least two of the light-shielded signals to produce an average signal;

holding the average signal; and

correcting a first signal corresponding to the effective pixel signals in accordance with a second signal corresponding to the held average signal.

16. A method of reading an image comprising the steps of:

sequentially driving a plurality of line sensors for producing photoelectric conversion signals, each of said line sensors having effective pixels for producing effective pixel signals and light-shielded pixels for producing light-shielded signals, at such timing as to allow the effective pixels signals to be continuous in time;

converting reflected light from document in a photoelectric conversion signals by means of the line sensors; and

selecting the effective pixel signals to output the selected signal as a serial signal.

17. A method of reading an image comprising the steps of:

sequentially driving a plurality of line sensors for producing photoelectric conversion signals, each of said line sensors having effective pixels for producing effective pixel signals and light-shielded pixels for producing light-shielded signals, in a predetermined order at a predetermined timing so that the effective pixel signals are continuously outputted;

converting reflected light from a document into a photoelectric conversion signal by means of said line sensors;

dividing the photoelectric conversion signals output from said line sensor into a plurality of groups each having the photoelectric conversion signals which are not neighbored to one another and which are selectively extracted from the photoelectric conversion signals output from said line sensors, and serializing the selectively extracted signals for each group to produce a serialized photoelectric conversion signal;

digitizing the serialized photoelectric conversion signals for each of groups;

holding light-shielded signal in the digitized photoelectric conversion signals for each of groups for a predetermined time interval;

serializing the light-shielded signals held for the respective groups to produce a black reference signal;

serializing the effective pixel signals in digitized photoelectric conversion signals for the respective groups to produce a serial effective pixel signal; and

correcting the serial effective pixel signal in accordance with the black reference signal to produce an image signal.