1. Field of the Invention
The present invention relates to an original reader that reads an image from an original that is conveyed, and a method of reading an original.
2. Description of the Related Art
A copying machine and a facsimile machine are provided with respective original readers. Original readers are also known which are each equipped with an automatic document feeder (ADF).
Many of such original readers have a function which requires detection of the size of an original (hereafter also referred to as an original size) before the start of reading an image therefrom. Examples of the function that requires detection of an original size before reading an image include an automatic sheet selection function, an automatic magnification selection function, and so forth.
The automatic sheet selection function is a function that automatically selects a sheet of a proper size according to an original size, a designated magnification, and whether or not to execute image rotation processing. Further, the automatic magnification selection function is a function that calculates a degree of magnification of an image in order to reduce or enlarge a read original image based on a designated sheet size, and automatically sets the calculated magnification. The above-described functions, such as the automatic sheet selection function and the automatic magnification selection function, are executed by a controller of an image processing apparatus.
In a case where the size of an original is detected before the start of reading the original image, an original reader that has a conveying path of which the length between an original feeding position and an image reading start position is short is configured such that reading of the original image is started, after the original is conveyed to an inversion path and is inverted to finalize the size of the original. However, such configuration causes an increase in the size of the original reader and reduction of reading productivity.
To cope with the above problem, there has been proposed an original reader which provisionally decides an original size before the start of reading an original image, reading of an original to be read is started using the provisionally decided original size, and when an actual size of the original to be read and the provisionally decided original size are different, the original to be read is inverted to thereby reread the original image (see e.g. Japanese Patent Laid-Open Publication No. 2011-24098).
Further, there has also been proposed an image forming apparatus which is configured such that for the automatic magnification selection function, a memory having a capacity large enough to store two pages of original images is provided in advance, and reading of a original image with a size yet to be finalized and scaling processing of an original image with a finalized size are performed in parallel (see e.g. Japanese Patent Laid-Open Publication No. 2001-186335).
On the other hand, at present, to read images on both sides of an original, an original reader of a so-called one-pass double-sided simultaneous reading type is predominantly used which has a back side-reading unit mounted on a conveying path, besides a usual front side-reading unit, such that images on both sides can be read only by a single conveyance of the original, to thereby dispense with an inversion path.
However, when an original bundle in which originals of various sizes are mixed is to be read using the original reader of the one-pass double-sided simultaneous reading type, to execute the automatic sheet selection function or the automatic magnification selection function, it is necessary to detect the size of each original. Further, to enable detection of the size of each original, it is necessary to lengthen the conveying path from the original feeding position to the image reading start position or additionally provide an inversion path. This causes an increase in the size of the original reader and an increase in manufacturing costs thereof.
Further, in the original reader of the one-pass double-sided simultaneous reading type, to buffer image data read from the back side of the original until completion of transfer of image data read from the front side of the original, an image memory is provided which stores one page of image data. If the configuration disclosed in Japanese Patent Laid-Open Publication No. 2001-186335 is applied to such an original reader, it is necessary to provide an image memory for storing one more page of image data, which causes an increase in manufacturing costs of the original reader.