Radiant energy – Photocells; circuits and apparatus – Photocell controlled circuit
Reexamination Certificate
1999-04-16
2002-04-23
Evans, F L (Department: 2877)
Radiant energy
Photocells; circuits and apparatus
Photocell controlled circuit
C358S515000
Reexamination Certificate
active
06376821
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus for reading a color manuscript (original) particularly.
For a manuscript reading apparatus such as a scanner, high resolving power, a high quality of image and others are demanded and for a manuscript reading apparatus such as a copying machine, high speed, correspondence to large width (A3 size) and the lifting of a manuscript in the binding margin of a book is demanded in addition to the above. Describing them in physical and optical terms, a high Nyquist frequency, a high modulation transfer function (MTF), the high sensitivity of a sensor, a large angle of view and the large depth of a focus are demanded. Of them, it is MTF and the depth of a focus that are related to the specifications of an imaging optical system after a sensor and conjugate length are determined.
Further, in the case of a color copying machine, in addition to the above conditions, there is also a problem related to the chromatic aberration of a lens. The chromatic aberration is classified into axial chromatic aberration equivalent to displacement in the direction of an optical axis and lateral chromatic aberration equivalent to displacement in the longitudinal direction of a charge-coupled (CCD) line sensor and have a different bad effect in the evaluation of an imaging optical system. Concretely, axial chromatic aberration displaces the peak of MTF of each color in an imaging optical system in a defocused direction, MTF is deteriorated as a result because balance is required to be kept and the quality of an image is deteriorated. In the meantime, as lateral chromatic aberration displaces the imaging position of each color in the longitudinal direction of a CCD sensor, chromatic displacement shown in
FIG. 12B
is caused through each color is to be overlapped as shown in FIG.
12
A.
As for MTF characteristics, as aberration in monochrome except chromatic aberration also deteriorates MTF, its mechanism is very complicated. For evaluation items related to MTF, there are the height of MTF at a level of a CCD sensor, tolerance (the depth of a focus) in case a manuscript is lifted and color balance (&Dgr;MTF) in each angle of view.
Of the MTF evaluation items, the increase of &Dgr;MTF and the increase of lateral chromatic aberration are different in a physical (optical) behavior, however, from the viewpoint of output from a CCD sensor, they produce similar effect. That is, as shown in
FIG. 12C
, there occurs a phenomenon that signal values (levels) of three colors to be output from a pixel in the same position in the longitudinal direction vary and as a result, chromatic information acquired by synthesizing them also varies from an original value. The variation of chromatic information means that the color reproducibility based upon a manuscript of an output image is deteriorated in the case of a color copying machine. In the case of a color copying machine, processing for converting the read information of BGR to yellow (Y), magenta (M), cyan (C) and black (K) which are respectively the color of toner is required, however, if the read chromatic information of original data includes displacement in unspecified quantity, correction is very difficult.
There is also a problem intrinsic to lateral chromatic aberration. It is pigmentation at an edge in the same chromatic area. If an image the contours of which are often obscure such as a photograph is copied and output, slight displacement of colors is often not an eyesore. However, if only an edge of a character and a graphic form in a vertical scanning direction has different color due to lateral chromatic aberration in a manuscript composed of a combination of characters and graphic forms such as a business document, it is very conspicuous and makes a bad impression on a user. In the meantime, in the case of &Dgr;MTF, color is different as a whole, however, it is never caused that only an edge has different color. At this point, lateral chromatic aberration has a worse effect upon the quality of an image than &Dgr;MTF.
Further, in a digital color copying machine, generally, different image processing is applied depending upon whether a manuscript is a text or an image such as a photograph. That is, if contrast between a text and a background is clear in case a manuscript is a text, visibility is satisfactory. Therefore, processing such as an edge part in a text is highlighted is executed. In the meantime, a case of an image manuscript is contrastive and if the gradation of color is smooth, visibility is satisfactory. As described above, the image processing section of a copying machine is often provided with a picture/character separating processing function to differentiate processing depending upon the type of a manuscript.
Also, in a digital color copying machine, if read color is black, a black judgment function is also provided in addition to the above picture/character separating processing function because more beautiful output can be acquired in a case that printout is acquired using black toner than in a case that black is acquired by overlapping Y, M and C. Therefore, if output from CCD is off from black due to the above aberration particularly in case a black character is separated from image information, an error of picture/character separating processing and an error of black judgment are simultaneously caused, a black character in a manuscript is colored and output in an obscure state and reducibility is very deteriorated. Particularly, recently, because of the development and popularization of a personal computer and a presentation document preparation tool, a full color manuscript including high definition character information overflows and the frequency of copying them is also increased. Therefore, the above problem becomes important.
Heretofore, as measures for these problems, generally, the balance of characteristics has been kept by determining parameters of a lens in the design of the lens so that aberration is as small as possible in addition to image processing. However, in the design of a lens, the characteristics of MTF have a tendency to be deteriorated when the correction of lateral chromatic aberration is tried. Then, anomalous dispersion glass effective as a countermeasure of chromatic aberration is considered to be used, however, there is a limit in improvement by improving the characteristics of only a lens. Anomalus dispersion glass requires three to five times as high costs as normal glass material.
In the design of a lens, a method of reducing an aperture or an angle of view is adopted to decrease aberration, however, an angle of view cannot be greatly varied because of constraints of manuscript size and space in a copying machine. Then, a method of reducing an aperture (darkening a lens) to decrease aberration is adopted, however, because of the signal-to-noise ratio (S/N) of a sensor, if a lens is darkened maintaining high speed and high resolving power, the luminous energy of a lamp is required to be increased to secure required luminous energy and power consumption is increased.
Normally, power acquired from the outlet of an office is 1.5 kVA, however, in the case of an electrophotographic copying machine, heat is utilized for fixing toner and a heater for generating heat requires very large power. Currently, a color electrophotographic copying machine requires power close to 1.5 kVA to read a manuscript at 400 dpi. Therefore, the reduction of power consumed to read a manuscript is desired. Further, as the area of a sensor pixel becomes smaller when resolving power is enhanced up to 600 dpi maintaining copying speed, the relative quantity of light received by a sensor becomes a half or less. As the quantity of data is increased, a video rate is also increased and as a result, as power is also increased, it is currently impossible to darken a lens in addition and increase the power of a lamp. Rather, to compensate the received quantity of light made a half or less, a lens is required to be lightened.
There are many reasons for designi
Imoto Yoshiya
Kikuchi Michio
Evans F L
Fuji 'Xerox Co., Ltd.
Smith Zandra V.
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