Image analysis – Image enhancement or restoration – Intensity – brightness – contrast – or shading correction
Reexamination Certificate
1998-03-23
2001-01-16
Lee, Thomas D. (Department: 2724)
Image analysis
Image enhancement or restoration
Intensity, brightness, contrast, or shading correction
C358S451000, C358S461000
Reexamination Certificate
active
06175660
ABSTRACT:
IMAGE READING APPARATUS
This application is based on Japanese Patent Application Nos. 9-071821, 9-071822 and 9-138515 filed in Japan, the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image reading apparatus and, more specifically, to an image reading apparatus used for a digital copying machine or the like.
2. Description of the Related Art
When a bound original such as a book (hereinafter referred to as a book original) is copied, sometimes there is a shade at a central portion. Therefore, in a conventional image reading apparatus, a method has been proposed in which a shade region at the central portion of the book original image is detected, and a threshold value for binarization is switched so as to eliminate fogging of the background.
The above described conventional method of switching the threshold value for binarization is effective when the original is a text original in which image data are dominantly white or black. However, an image data having halftone gradation such as in the case of a photo original cannot be reproduced clearly.
Various methods for zooming (changing magnification of) a read image have been proposed in conventional image reading apparatuses.
For example, Japanese Patent Laying-Open No. 7-273979 discloses a method of zooming a read image by changing speed of scanning. Japanese Patent Laying-Open No. 6-134451 discloses a method of zooming an image by approximation, by interpolating read data in equal magnification. Further, a method of zooming a read image by switching line period for reading and by correcting variation in sensor output derived from variation in time of storage by means of a circuit gain has been generally known.
However, of the conventional methods of zooming read image, the method of changing scanning speed leads to increased cost and complicated control, since the accuracy in scanning must be improved for switching the scanning speed. In the method of zooming an image by approximation by interpolation of read data in equal magnification, zooming is after all an approximation since data is interpolated by image processing, inevitably causing degradation in image quality. Further, in the method of switching line period for reading and correcting variation of sensor outputs derived from the variation in time of storage using a circuit gain, lowering of the sensor output when the time of storage reduces is corrected by circuit gain, resulting in degraded image quality.
In a conventional image reading apparatus, canceling in the number of bits in calculation occurs in image processing of a subsequent stage, and therefore, CCD outputs are A/D converted with the number of bits set larger than necessary, and after image processing, lower bits of the data are discarded.
However, in the conventional method of discarding lower bits of data after image processing, though rounding error in calculation (multiplication and division) can be canceled, quantization error between peak and other portions of light intensity occurs, due to difference in sensor outputs caused by light distribution variation of the light source, for example.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an image reading apparatus capable of accurately reproducing a read image by correcting variation of read data derived from variations in light distribution, sensitivity and so on, using reading means capable of logarithmic conversion. More specifically, an object of the present invention is to provide an image reading apparatus which can solve the above described problems and provide satisfactory image reproduction even when there is a shade in an original image having halftone gradation.
A still further object of the present invention is to provide an image reading apparatus which can solve the above described problems and prevent degradation of image quality even when electrical magnification is performed, by fixing scanning speed.
A still further object of the present invention is to provide an image reading apparatus which can solve the above described problems and perform A/D conversion with one same resolution even when output level varies because of variations in light distribution of a light source, sensitivity difference of sensors and so on.
According to one aspect of the present invention, an image reading apparatus is provided. The image reading apparatus includes means for correcting variation in read data caused by insufficient light intensity at a shade region of an original. More specifically, the present invention is directed to an image reading apparatus including:
image signal taking means for receiving as an input, light from an original, and outputting a logarithmically converted analog image signal;
an AD converter for converting the output analog image signal to a digital image signal;
shade region detecting means for detecting the shade region of said original, based on the digital image signal; and
image signal correcting means for correcting level of the digital image signal of the shade region, by comparing a digital image signal of a region other than the shade region and the digital image signal of the shade region.
In the image reading apparatus in accordance with this one aspect of the present invention, preferably, the image signal correcting means calculates difference between the digital image signal of the region other than the shade region and the digital image signal of the shade region, and shifts the level of the digital image signal of the shade region based on the calculated difference.
In the image reading apparatus in accordance with the aforementioned one aspect of the present invention, preferably, the image signal taking means includes an LOG CCD (logarithmic compression output image sensor).
In the image reading apparatus in accordance with the aforementioned one aspect, preferably, the AD converter performs AD conversion with the number of bits set to be wider than a necessary dynamic range.
The image reading apparatus in accordance with the above described one aspect may further include a bit converting means for converting the digital image signal corrected by the image signal correcting means to a signal of a necessary bit number, by discarding upper bits.
The image reading apparatus in accordance with the above described one aspect may further include shading correcting means for correcting the digital image signal based on a reference data obtained by reading a reference plate, and correction by the image signal correcting means is performed at the time of shading correction.
In the image reading apparatus in accordance with the above described one aspect, the shade region detecting means stores at least one line of monitor image data obtained by reading the original, and detects the shade region based on the monitor image data.
In the image reading apparatus in accordance with the above described one aspect, preferably, the shade region detecting means detects the shade region based on an image signal obtained by reading a portion inner by a prescribed distance from an edge of the original.
In accordance with another aspect, the present invention provides an image reading apparatus including:
image signal taking means for receiving as an input, light from an original and outputting a photoelectrically converted analog image signal;
an AD converter for converting the output analog image signal to a digital image signal;
shade region detecting means for detecting a shade region of the original based on the digital image signal, where light intensity received by the image taking means from the original is small;
shading reference data setting means for setting a first reference data for a region other than the shade region of the original, and setting a second reference data different from the first reference data for the shade region of the original; and
shading correction means for correcting the digital image signal of the region other than the shade region based on the first reference da
Murakami Hiroshi
Nabeshima Takayuki
Burns Doane , Swecker, Mathis LLP
Lee Thomas D.
Minolta Co. , Ltd.
LandOfFree
Image reading apparatus 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, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image reading apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2533281