Facsimile and static presentation processing – Natural color facsimile – Scanning
Reexamination Certificate
1999-07-12
2004-05-11
Wallerson, Mark (Department: 2626)
Facsimile and static presentation processing
Natural color facsimile
Scanning
C358S475000, C358S513000, C358S482000
Reexamination Certificate
active
06735000
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image reading apparatus and method, and in particular, to an image reading apparatus and method, which form image information of an original illuminated with light coming from a light source on a solid-state image sensing element via an optical imaging system, and read the image.
2. Description of the Related Art
Conventionally, various image reading apparatuses, each of which forms image information of, e.g., an original, on a plurality of line sensors including solid-state image sensing elements such as CCDs, via an optical imaging system, and digitally reads monochrome or color image information on the basis of the output signals from the line sensors, have been proposed.
FIG. 5
is a schematic view of an optical system of a conventional color image reading apparatus.
Referring to
FIG. 5
, reference numeral
100
denotes a platen glass on which an original to be read is placed;
101
, a linear light source for illuminating an original; and
102
, a reflector for improving the irradiation efficiency.
Light reflected by an original (not shown) illuminated with light emitted from the linear light source
101
and reflected by the reflector
102
is guided to an optical imaging system
104
via mirrors
103
-
a
,
103
-
b
, and
103
-
c
, and the optical imaging system
104
forms image information of the original on a solid-state image sensing element
105
.
The mirror
103
-
a
moves at a scanning speed of v in a sub-scanning direction A of image information of the original, and the mirrors
103
-
b
and
103
-
c
move at a speed of v/2 in synchronism with the movement of the mirror
103
-
a
, thus reading the image information in two dimensions in combination with the line-up direction (main scanning direction) of line sensors in the solid-state image sensing element
105
.
In this arrangement, the image information formed on the solid-state image sensing element
105
is converted into an electrical signal and output. The electrical signal is sent to an output device (not shown) to output image information as a printout, or is sent to a storage device or the like to store the image information. Thus, the image reading apparatus is used for various purposes.
As a light source for an image reading apparatus of this type, a halogen lamp is generally used. Since the halogen lamp has high luminance but causes considerable temperature rise in the apparatus resulting from heat it produces and consumes electric power of 200 to 300 W, power consumption required for the entire apparatus increases.
In recent years, to avoid such problems, a high-luminance fluorescent and xenon lamps have been developed, and are used as the light sources of image reading apparatuses.
In most of fluorescent and xenon lamps, a small quantity of mercury grains and several Torr of Ar, Kr, Xe gas, or the like are sealed in a linear hollow tube, which has a structure in which the inner wall of the tube is coated with various fluorescent materials, and electrodes are placed at the two ends of the tube to tightly seal the tube.
The fluorescent material coated on the inner wall of the tube is excited by ultraviolet rays radiated from mercury or various kinds of gases due to discharge from the electrodes, and visible light is emitted in accordance with the emission characteristics of the fluorescent material. An appropriate fluorescent material is selected in accordance with the spectral energy characteristics required for the intended light source.
Especially, a color image reading apparatus requires a light source having a broad wavelength range corresponding to, e.g., RGB. When a light source having especially high luminance is required, a plurality of colors of fluorescent materials are mixed and applied to the inner wall of the tube.
The quantity of light (emission intensity) emitted from the fluorescent or xenon lamp is normally controlled by pulse-width modulation that controls the ON period using a constant current value, in place of a method of controlling the starting voltage unlike the halogen lamp. This is because of the emission characteristics of the fluorescent or xenon lamp, i.e., the lamp emits light when a given current value is exceeded, and the method of controlling the emitted quantity of light by controlling the current value cannot assure a broad control range of the emitted quantity of light.
On the other hand, the following technique has also been proposed. That is, in some image reading apparatuses using a fluorescent or xenon lamp, the aforementioned light quantity control is omitted, and the gain of, e.g., an amplifier for electrically amplifying the output signal from a solid-state image sensing element in accordance with a decrease in quantity of light due to aging is variably set to obtain an appropriate signal output by changing the gain in correspondence with the decrease in light quantity. In such technique, however, the S/N ratio of the read signal may vary depending on the gain value.
The aforementioned prior art suffers the following problems.
An image reading apparatus using a light source such as a fluorescent or xenon lamp, which has a fluorescent material as an emission source, as described in the above prior art, normally uses the technique of controlling the emitted quantity of light by controlling the pulse width corresponding to the ON period while maintaining a constant current value to be supplied to the lamp.
FIG. 6
shows the control waveform for controlling the emitted light quantity from the light source. The abscissa in
FIG. 6
plots time, and the ordinate plots the current value that controls the emitted light quantity from the light source.
An Hsync period along the abscissa indicates the time corresponding to one accumulation period of a solid-state image sensing element, i.e., a charge accumulation period in accordance with the quantity of light that hits a light-receiving section of the solid-state image sensing element, as normally used.
Upon executing normal pulse-width control, a control signal is output once per accumulation period in synchronism with the leading or trailing edge position of a trigger signal indicating the start of this accumulation period. In this fashion, the light quantity control is performed in synchronism with a signal corresponding to a trigger signal for one accumulation period, thereby removing noise in an image signal arising from beat produced by interference between the pulse-width control that controls the quantity of light and the accumulation period.
On the other hand, in relation to the fluorescent or xenon lamps that use a fluorescent material as an emission source, a white light source having emission characteristics over the broad wavelength range that covers the entire visible light range obtained by mixing and applying some different color fluorescent materials is normally used in an image reading apparatus for reading color image.
When such white light source is used, a problem is raised due to different afterglow or persistence characteristics unique to the individual color fluorescent materials. The afterglow characteristics are determined by the time of the fluorescent material excited by ultraviolet rays stays at high energy level, and normally diminish exponentially.
This phenomenon suggests that emission remains even after a current that controls emission of the light source is cut off instantaneously and, depending on the characteristics of the fluorescent material used, it is given by:
T=e
(&tgr;−1)
where &tgr; is the characteristics determined by the fluorescent material. When fluorescent materials corresponding to RGB are mixed and used like in the white light source used in the color image reading apparatus, the afterglow characteristics of the respective colors are different from each other.
In general, materials used as fluorescent materials are determined in terms of the emission wavelength characteristics and emission efficiency of the materials in the respective wavelength ranges, service life
Kurita Mitsuru
Sato Hiroshi
Satomura Seiichiro
Shimomura Hidekazu
Canon Kabushiki Kaisha
Morgan & Finnegan , LLP
Wallerson Mark
Worku Negussie
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