JP2998971B2 - Image reading device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus used for an apparatus such as a digital copy and a facsimile machine.

2. Description of the Related Art Various types of image reading devices are used in digital copying and facsimile machines. Generally, an optical scanning device in which a light source such as a fluorescent lamp and a line sensor are arranged in parallel is a document support plate. The sub-scanning movement is performed below the glass plate.

Here, in the image reading apparatus as described above, the illuminance of the light source of the optical scanning device such as a fluorescent lamp fluctuates depending on the use period or the ambient temperature. It is necessary to correct. Therefore,
A reference white plate is arranged at a position facing the optical scanning device and outside the reading scanning area, illuminating the reference white plate with a light source of the optical scanning device, measuring the lightness with a line sensor or the like, and reading the original reading threshold value according to the measured value. The one which corrects is developed.

Since the image reading apparatus as described above corrects a change in the illuminance of the light source of the optical scanning apparatus according to the brightness of the reference white plate, it is necessary to read and scan the image information of the document with a good white balance as needed. Can be.

Here, the reference white plate is disposed between the upper surface of the reading opening of the frame and the lower surface of the glass plate, or mounted on the glass plate. In this case, the reference white plate and the surface to be scanned of the document are optically scanned. Since the distance to the device is different, the illuminance difference due to this is electrically corrected.

However, in practice, even if the above-mentioned correction is performed, a white balance defect tends to occur at the end in the main scanning direction.
That is, the reference white plate and the surface to be scanned of the document face the light source of the optical scanning device via the reading opening of the frame. The rate of light shielding by the frame is different.
For this reason, the brightness of the reference white plate is measured relatively high or low at the end in the main scanning direction, and when the image information read from the document is reproduced, the end in the main scanning direction becomes black or white. It will fly.

Means for Solving the Problems In an image reading apparatus for reading an original, a light receiving element is provided to face the line sensor and the light source by using a line sensor having a light receiving element connected in the main scanning direction and a light source long in the main scanning direction. A reference white plate formed such that the surface brightness at least at one end in the main scanning direction is different from the surface brightness at the center, the distance between the document and the line sensor, the reference white plate, the line sensor, The error of the white balance of the line sensor caused by the difference in the distance is corrected.

Since the surface brightness of at least one end of the reference white plate in the main scanning direction is different from the surface brightness of the central portion, the image information at the end in the main scanning direction can be read with good white balance.

Embodiment An embodiment of the present invention will be described with reference to FIGS. First, in the image reading device 1, an optical scanning device 4 in which a line sensor 2 having a series of light receiving elements and a straight tube-type fluorescent lamp 3 as a light source are supported side by side on a rail (not shown). A glass plate 7 serving as a document support plate is placed on a frame 8 on which a reading opening 5 is formed at a position facing the optical scanning device 4 which moves in the sub-scanning direction. Mounted through. In the image reading apparatus 1, a reference white plate 10 fixed by a bracket 9 at a position corresponding to an end of the reading opening 5 in the sub-scanning direction between the members 6, 7 as shown in FIG. The surface at the end in the main scanning direction adjacent to the edge of the reading opening 5 is painted dark.

In such a configuration, the image reading device 1 also measures the illuminance of the fluorescent lamp 3 of the optical scanning device 4 with the brightness of the reference white plate 10, corrects the reading threshold of the line sensor 2 according to the measured value, and The image information is read and scanned with a good white balance. That is, as illustrated in FIGS. 2 (a) and 3 (a), the original is placed on the glass plate 7.
When the paper size and the magnification are set in the apparatus after the document 11 is placed, the optical scanning device 4 operates the document 11 in accordance with the set values.
Before scanning, the reference white plate 10 is read and scanned. At this time, as illustrated in FIG.
Since the position adjacent to the edge of the reading opening 5 is dark, the reading brightness is low at the end and high at the center. Therefore,
After such a correction has been made, FIG.
As illustrated in FIG. 2B, the image information of the document 11 is read and scanned by the optical scanning device 4 that moves in the sub-scanning direction below the glass plate 7. At this time, in the image reading device 1, the white balance of the line sensor 2 of the optical scanning device 4 is corrected in accordance with the read brightness of the reference white plate 10, so that the image information of the document 11 is smaller than the actual one at the end in the main scanning direction. It is read brightly.

This is because the height of the lower surface of the reference white plate 10 and the surface to be scanned of the document 11 are different from each other as illustrated in FIG.
In the vicinity of the reading aperture 5, the surface to be scanned of the original 11 is a measure against the fact that the rate of light shielding by the frame 6 is larger than that of the reference white plate 10. Thus, the main scanning direction of the reference white plate 10 having a relatively large amount of received light. By making the edge dark, the image information of the document 11 is read and scanned with a white balance suitable for the amount of received light.

Here, when the present applicant actually manufactured an apparatus having the above-described structure and measured the illuminance distribution between the reference white plate 10 and the white document 11, as shown in FIG. It has been found that the difference in brightness read from the original 11 is smaller at the center in the main scanning direction and becomes larger as it approaches the end. Note that the curve illustrated in the figure indicates an error rate (%) calculated as {1− (lightness of white original / lightness of reference white board)} × 100 from each value of lightness as described above. It can also be seen that the white balance error is large at the end in the main scanning light direction.

Therefore, when the image reading apparatus 1 is implemented, the density of the dark paint formed on the surface of the reference white plate 10 is determined based on the above-described white balance error as shown in FIG. It will be higher at the end in the direction and lower at the center.

In this embodiment, the image reading apparatus 1 having a structure in which the lower surface of the reference white plate 10 is located below the surface to be scanned of the document 11 is exemplified. As a method for correcting the white balance, the end of the reference white plate 10 in the main scanning direction is used. Although the portion is dark, the present invention is not limited to the above structure. For example, in an image reading apparatus (not shown) having a structure in which the lower surface of the reference white plate 10 is located above the surface of the original 11 to be scanned. On the other hand, the reference white plate 10 is formed such that the end in the main scanning direction is white and the center is dark.

The image reading apparatus 1 is also assumed to be a one-side reference device in which, for example, a reference scale is provided at one edge of the glass plate 7 in the main scanning direction, and a document 11 of each size is placed in contact therewith. For example, the present invention is not applied to a center-based device that arranges each size original 11 at the center of the glass plate 7. When the one-side reference image reading apparatus 1 is implemented as described above, if the end in the main scanning direction on the non-reference side is a structure not used for reading scanning, the reference white plate 10 is used as the reference position of the document 11. If only the ends of the reference white plate 10 are dark and the scanning is performed using the entire area of the reading aperture 5, both ends of the reference white plate 10 in the main scanning direction are dark.
Further, the means for changing the brightness of the surface of the reference white plate 10 in this way is not limited to painting, but various surface processing, use of a filter, and the like can be performed.

Advantageous Effects of the Invention As described above, the present invention uses a line sensor in which light receiving elements are continuously provided in the main scanning direction and a light source that is long in the main scanning direction,
In an image reading apparatus for reading a document, a reference white plate is provided so as to face the line sensor and the light source, and is formed so that the surface brightness of at least one end in the main scanning direction is different from the surface brightness of the central portion. And correcting the white balance error of the line sensor caused by the difference between the distance between the document and the line sensor and the distance between the reference white plate and the line sensor. Information can also be read with good white balance.

[Brief description of the drawings]

The drawings show an embodiment of the present invention. FIG. 1 is a bottom view of a main part, FIG. 2 is a vertical front view, FIG. 3 is a vertical side view, and FIG.
FIG. 5 and FIG. 5 are characteristic diagrams. DESCRIPTION OF SYMBOLS 1 ... Image reading device, 2 ... Line sensor, 3 ... Light source, 4 ... Optical scanning device, 5 ... Reading aperture, 6 ... Frame, 7 ... Document support plate, 10 ... Reference white plate, 11 ... manuscript

Claims (1)

(57) [Claims] An image reading apparatus for reading an original by a line sensor having a light receiving element connected in the main scanning direction and a light source long in the main scanning direction, wherein the image reading apparatus is provided so as to face the line sensor and the light source. A reference white plate formed so that the surface brightness at one end in the main scanning direction is different from the surface brightness at the center, and the distance between the document and the line sensor and the distance between the reference white plate and the line sensor An image reading device configured to correct a white balance error of the line sensor due to a difference between the white balance and the white balance.