Facsimile and static presentation processing – Natural color facsimile – Scanning
Reexamination Certificate
1999-08-19
2004-06-29
Lee, Cheukfan (Department: 2722)
Facsimile and static presentation processing
Natural color facsimile
Scanning
C358S504000
Reexamination Certificate
active
06757084
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus and method for forming an image of an original on solid-state image sensing devices via an image-forming optical system to read the image.
Various image reading apparatuses that form an image of an original on a plurality of line sensors (solid-state image sensing devices such as CCDs) via an image-forming optical system and that digitally read a black-and-white or colored image based on output signals from the line sensors have been proposed.
FIG. 21
is a schematic view of the integral part of an optical system in a conventional colored-image reading apparatus as seen from a lateral side.
In this figure,
100
is a platen glass on which an original to be read is placed,
101
is a bar-shaped light source for illuminating an original, and
102
is a reflector for improving the illumination efficiency.
An image of an original (not shown) illuminated by the bar-shaped light source
101
and the reflector
102
is guided to an image-forming optical system
104
via mirrors
103
-
a
,
103
-
b
, and
103
-
c
. The image-forming optical system
104
forms the image of the original on solid-state image sensing devices
105
.
Together with the light source
101
and the reflector
102
, the mirror
103
-
a
moves at a speed (v) in a sub-scanning direction A relative to the original, and in synchronization with the mirror
103
-
a
, the mirrors
103
-
b
and
103
-
c
also move in the sub-scanning direction A at a speed v/2. The line sensor of the solid-state image sensing devices
105
is arranged in a main scanning direction, so a combination of this arrangement with the relative shift of each of the above sections in the sub-scanning direction enables the image of the original to be two-dimensionally scanned and read.
In such a configuration, the image formed on the solid-state image sensing devices
105
is converted into an electric signal and used in various apparatuses. For example, it is sent to an output apparatus (not shown) for printout or to a storage apparatus where it is stored as input image information.
The light source for an image reading apparatus configured in this manner includes a halogen lamp, a fluorescent lamp, and a xenon lamp. Of these lamps, the halogen lamp has been typically used as the light source for such an image reading apparatus. Although the halogen lamp emits light of a high luminance, there are problems in which the temperature of the apparatus significantly increases with the increasing temperature of the lamp and this lamp requires 200- to 300-W power, thereby increasing the power consumption of the entire apparatus.
In order to avoid such problems, the recent trend is to develop fluorescent and xenon lamps of a high luminance as light sources for image reading apparatuses.
Most fluorescent and xenon lamps comprise a bar-shaped hollow tube with a small amount of mercury powders and several Torrs of argon (Ar), krypton (Kr), or xenon (Xe) sealed therein wherein various phosphors are coated on the inner wall of the tube and wherein electrodes are placed at the respective sides of the tube to seal it.
Ultraviolet rays emitted from mercury or various gases due to discharge from the electrodes excite the phosphors coated on the inside of the tube to radiate visible radiation depending on the emission property of the phosphors.
In addition, the phosphors are selected depending on a spectral distribution required for the light source.
In particular, a colored-image reading apparatus requires a light source radiating light of a wide wavelength range including red (R), green (G), and blue (B), and an approach for mixing phosphors of a plurality of colors together and coating the mixture on the inner wall of the tube is used if a light source of a particularly high luminance is required.
In addition, if the quantity of light from a fluorescent or xenon lamp is to be controlled, then instead of controlling the lighting voltage as in the halogen lamp, the pulse width modulation method for controlling the lighting time using a specified current is generally used to control the quantity of light. This is because the fluorescent or xenon lamp is characterized by lighting when current supplied to the lamp exceeds a fixed value and because the method for controlling the quantity of light by varying the magnitude of the current cannot provide a wide control range for the quantity of light.
On the other hand, for image reading apparatuses using a fluorescent or xenon lamp, an approach that omits the above light quantity control and that enables the variable setting of the gain of an amplifier for electrically amplifying output signals from the solid-state image sensing devices so as to correspond to a decrease in the quantity of light over time so that appropriate signal output levels can be obtained by varying the gain according to the decrease in the quantity of light has been proposed. In such a method, however, the gain value may vary the S/N ratio of read signals.
The above conventional examples, however, have the following disadvantages.
In an image reading apparatus using a light source with phosphors acting as a light emitting source as in the fluorescent or xenon lamp, a method of controlling the quantity of light by controlling the duration of a pulse signal corresponding to the lighting time while maintaining a current flowing through the lamp at a specified value.
FIG. 22
shows a waveform of a control signal for controlling the quantity of light from a light source. The horizontal axis in this figure represents time, and the vertical axis represents the value of a current for controlling the quantity of light from the light source and the intensity of light from a fluorescent lamp. In
FIG. 22
, calibration has been carried out so that the maximum current value and the corresponding intensity of light emitted from the fluorescent lamp are shown at the same point in the vertical-axis direction on the graph.
The Hsync interval on the horizontal axis indicates the time corresponding to one accumulation time period of the solid-state image sensing device, and during this time, charges corresponding to the quantity of light which incidents on a light receiving section of the solid-state image sensing device are accumulated.
For normal pulse width control, a control pulse signal having a predetermined-duration is output once per accumulation time period in synchronization with the leading or trailing edge of a trigger signal indicating the start of the accumulation time period. In this manner, by controlling the quantity of light in synchronization with the trigger signal indicating the start of an accumulation time period, noise in an image signal that results from beat caused by the interference between the accumulation time period and the pulse width control for controlling the quantity of light is conventionally removed.
On the other hand, in a fluorescent or xenon lamp using phosphors as a light source, by coating phosphors of a plurality of colors, it is often used as a white light source having a spectral distribution of a wide wavelength range covering the overall visible radiation range in an image reading apparatus for reading color information.
The use of such a white light source may pose a problem due to the difference in afterglow property among the phosphors. The afterglow property is generally an exponentially decreasing property that is determined by the time during which the phosphors excited by ultraviolet rays remain in a high energy state.
This phenomenon indicates that light emitted from the phosphors may remain despite the instantaneous interruption of a current controlling the emission of light from the light source. Attenuation time T that is the time from the start of attenuation of the intensity of light until it reaches 1/e of the intensity is expressed by the following Equation (1), which depends on the properties of the materials of the phosphor:
T=e
(&tgr;−1) (1)
where &tgr; is a property determined by the materia
Arai Koji
Ikeda Taro
Ishimoto Koichi
Kurita Mitsuru
Sato Hiroshi
Lee Cheukfan
Morgan & Finnegan L.L.P.
LandOfFree
Image reading apparatus and control method thereof does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image reading apparatus and control method thereof, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image reading apparatus and control method thereof will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3355213