Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Reexamination Certificate
1998-05-01
2001-09-11
Lee, Thomas D. (Department: 2724)
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
C358S475000
Reexamination Certificate
active
06288797
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an image density correction device for correcting an image density difference in an image read from an original document by a CCD (a photoelectric converting element), and the method thereof, and an image reading device using the CCD, and an image forming apparatus such as an electronic copying machine which forms an image by using the image reading apparatus.
In the conventional image forming apparatus such as an electronic copying machine and a facsimile machine, pixel data transfer frequency by the image data reading device such as a CCD which reads an image from an original document sheet is increased as image data reading speed is increased. Accordingly, the control of the signals output from the CCD will become difficult. In order to ease the signal control, the pixels of the conventional CCD have been divided into two groups: odd and even pixels. In recent years, a quadruplex CCD in which the number of the pixel groups is increased by dividing the odd and even pixel groups respectively into first and second half pixel groups, i.e., front and rear pixel groups in the main scanning direction has been proposed. According to this proposal, the pixel data transfer frequency is decreased into a quarter of that of the CCD which does not divide pixels, to ease the processing of the signal.
In outputting image signals of the divided four pixel groups, however, the outputs of the four pixel groups respectively pass through the corresponding buffer amplifiers which are independent from each other. If the offset voltage of the four buffer amplifiers are different from each other, the image density of the read image may be affected thereby. For example, in the case where an image having a neutral tint (e.g. a gray chart) is read to precisely obtain fine difference in gradation, the offset voltages of the buffer amplifiers are respectively added to the voltage level of the original image density of the four pixel regions, with a result that the read image has four image densities.
This difference in image density is also caused by the CCD dividing the image data into odd and even pixel groups, of course. However, the odd and even pixels are alternately arranged, and thus the image density difference between the odd and even pixels is not clearly seen since the pixels are dispersed in a formed image in a marbled manner. While, in the image read by the above-mentioned quadruplex CCD, each of the odd and even pixels are divided into the front and rear pixel groups, and thus the formed image seems to be different in the image density in the front and rear portions of the image, and thus the image density difference is clearly seen. In order to solve this problem, the offset voltage correction by a staggered arrangement of a plurality of CCDs such as in the adhesion type sensor can be applied. According to this correction method, however, a gradation (gray chart) correction needs to be performed in addition to the conventional white and black shading corrections, and thus the algorithm of the correction operation becomes so complicated.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to provide a correction device and a correction method which facilitate the correction of the difference in image density in the read image, and an image reading device, and image forming apparatus capable of improving the quality and the reliability of the read image.
The object of the present invention is attained by an image density correction device of the first aspect of the present invention, comprising: a photoelectric conversion element having first and second blocks, for photoelectrically converting received light; first means for obtaining an absolute value of an amplitude of an output signal output from the first block of the photoelectric conversion element; second means for comparing the absolute value with a predetermined reference value to obtain a difference thereof; first correction means for correcting the output signal on the basis of the difference obtained by the second means; and second correction means for correcting an output signal output from the second block on the basis of the difference obtained by the second means.
The object of the present invention is also attained by an image density correction method of the second aspect of the present invention, by which an output signal of a photoelectric conversion element receiving reflection light from an irradiated document is corrected, wherein the output signal of the photoelectric conversion element is divided into an image signal and a control signal, an amplitude voltage of the output signal is detected from the obtained control signal, an absolute value of an amplitude of the output signal is detected on the basis of the detected amplitude voltage, the obtained absolute value is compared with a predetermined reference value to obtain an error signal voltage, the obtained error signal voltage is held, the held voltage is converted into an electric current, and the image signal divided from the output signal of the photoelectric conversion element is corrected to have a predetermined voltage with use of the electric current converted from the held voltage.
The object of the present invention is also attained by an image reading device of the third aspect of the present invention, which irradiates a document and reads an image of the document with use of a photoelectric conversion element having first and second blocks and photoelectrically converting received light reflected from the document by correcting an output signal from the photoelectric conversion element, comprising: first means for obtaining an absolute value of an amplitude of an output signal output from the first block of the photoelectric conversion element; second means for comparing the absolute value with a predetermined reference value to obtain a difference thereof; first correction means for correcting the output signal on the basis of the difference obtained by the second means; second correction means for correcting an output signal output from the second block on the basis of the difference obtained by the second means; transfer means for transferring the output signal corrected by the first correction means and the output signal corrected by the second correction means, by which a pixel arrangements in the output signals are corrected to original one; and processing means for processing the output signals which are transferred from the transfer means and have the original pixel arrangement.
The object of the present invention is also attained by an image reading device of the fourth aspect of the present invention, which irradiates a document and reads an image of the document with use of a quadruplex photoelectric conversion element for dividing image data into four groups and photoelectrically converting received light reflected from the document by correcting first, second, third, and fourth output signals from the qudruplex photoelectric conversion element, comprising: first correction means for dividing the first output signal output from the quadruplex photoelectric conversion element into an image signal and a control signal, comparing an absolute value of the control signal with a predetermined reference value, and correcting the divided image signal to have a predetermined voltage with use of an error signal obtained by the comparison; second correction means for dividing the second output signal output from the quadruplex photoelectric conversion element into an image signal and a control signal, comparing an absolute value of the control signal with the error signal obtained by the first correction means as a predetermined reference value, and correcting the image signal to have a predetermined voltage with use of an error signal voltage obtained by the comparison of the absolute value and the error signal output as a reference value from the first correction means; third correction means for dividing the third output signal output from the quadruplex photoelectric conver
Brinich Stephen
Foley & Lardner
Kabushiki Kaisha Toshiba
Lee Thomas D.
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