JP2007150884A - Original reading device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an original reading device capable of performing proper output correction to a CCD drive frequency. <P>SOLUTION: In the original reading device using a photoelectric conversion element array 10 having a plurality of output terminals by a several drive frequencies, there is provided a multiple correction table 21 in which a correction table for correcting the level differences among the output terminals being set on a basis of each drive frequency. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an original reading apparatus using a CCD image sensor having a plurality of output terminals (Odd, Even, or First, Last) for each line.

A conventional document reading apparatus will be described with reference to FIGS. FIG. 5 is a configuration diagram of a general document reading apparatus. Below the contact glass 1 is a scanning optical system 2. The scanning optical system 2 includes a first carriage 5 on which an optical lamp 3 and a first mirror 4 are mounted, a second mirror 6, a second carriage 8 on which a third mirror 7 is mounted, a lens 9, and a CCD 10. Further, downstream of the CCD 10 is a substrate on which an image processing block shown in FIG. 6 is mounted.
FIG. 6 is a circuit block diagram of an image reading apparatus according to a conventional example. A CCD 10 having a terminal that outputs pixels in the first half (F side, First) sequentially from the first pixel and a terminal that outputs pixels in the second half (L side, Last) sequentially from the last pixel is used. The CCD 10 is further divided into a terminal for outputting odd-numbered pixels O (Odd) and a terminal for outputting even-numbered pixels E (Even) on each of the F side and L side, and has four outputs in total.
O and E of F and L are connected to the analog signal processing circuit 11, respectively. Here, an appropriate analog signal is generated by combining gain adjustment and the outputs of O and E. Furthermore, an A / D converter 12, a one-line circuit (composed of a memory such as a FIFO) 13 for synthesizing image data divided into F and L, and shading for correcting the illuminance distribution and the CCD pixel sensitivity difference. There is a correction circuit (consisting of a memory and an arithmetic element) 14. The numerical value 8 represents the number of bits.
The F-side and L-side digital image output obtained in this way may have a difference in output value even after shading correction (FL difference). That is, even when a document having a uniform density is read, a step appears at the boundary between F and L in the center. For this reason, for example, a correction table (lookup table) 15 is provided in the L side circuit to correct the FL difference.
The correction table 15 has input / output characteristics such as the graph shown in FIG. 7, for example, which is such that L is input and F is output. Since the characteristics differ for each CCD, for example, the correction table 15 is obtained in the process of the production line of the document reading apparatus.
Specifically, a plurality of gray charts having different densities are read, and the relationship is such that the digital output values on the L side of each gray chart coincide with those on the F side. Get the correction table. Here, the case where L is corrected based on F is shown, but the reverse is also possible.
As a technique for correcting the left and right steps using the correction table 15, for example, a technique described in Patent Document 1 is known.
JP 2002-218186 A

In the above conventional example, the left and right steps are corrected using a correction table for one frequency. Here, when the CCD is used at a plurality of driving frequencies, a correction table corresponding to each frequency is required, and if the same correction table is used for a plurality of driving frequencies, improper correction may occur. .
The case where frequency switching is necessary is a case where the user reselects, for example, a copy mode / scanner mode or a monochrome mode / color mode. In the scanner mode or in the color mode, the copy speed required by the system may be slower, so the scanner reading speed may be slower, and therefore the frequency may be slower. It will be better.
The present invention has been made in view of such a background, and an object of the present invention is to provide a document reading apparatus capable of performing appropriate image output correction with respect to a CCD driving frequency.

In order to achieve the above object, the invention described in claim 1 corrects an output level difference between the plurality of output terminals in a document reading apparatus that drives a photoelectric conversion element array having a plurality of output terminals at a plurality of drive frequencies. The document reading apparatus includes a multiple correction table set for each driving frequency as a correction table to be used.
According to a second aspect of the present invention, in a document reading apparatus that drives a photoelectric conversion element array having a plurality of output terminals at a plurality of drive frequencies, a correction table that corrects an output level difference between the plurality of output terminals, and the correction table The document reading apparatus is provided with a correction value calculation circuit that calculates and rewrites the content of the above for each drive frequency.

  According to the present invention, in a document reading apparatus that uses a photoelectric conversion element array having a plurality of output terminals at a plurality of drive frequencies, a multiple correction table set for each drive frequency as a correction table for correcting the output level difference of the output terminals. Or a correction value calculation circuit that calculates and rewrites the contents of the correction table for correcting the level difference of the output terminal for each drive frequency, so that an appropriate image output correction can be performed with respect to the drive frequency. .

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The same modules as those in the conventional example are denoted by the same reference numerals, and redundant description is omitted.
FIG. 1 is a circuit block diagram of an image reading apparatus according to the first embodiment of the present invention. In the first embodiment, a multiple correction table 21 is provided. That is, a correction table is prepared for each frequency (CCD driving frequency), and which correction table is used is determined by a table selection signal that becomes High / Low for each frequency switching.
Specifically, the highest address of the ROM address is used as a table selection signal, the address below that is an input value, and the data is an output value. If the capacity of the ROM is increased, the table selection signal can be made into a plurality of bits, so that more frequencies can be handled.

FIG. 2 is a circuit block diagram of an image reading apparatus according to the second embodiment of the present invention. The second embodiment has a correction value calculation circuit 22 in addition to the configuration of the conventional example shown in FIG. In a device having a large number of frequencies, if a correction table is prepared for each frequency, the capacity of the ROM becomes enormous and the work in the manufacturing process also increases. Therefore, only the representative frequency correction table 15 is acquired, and other than that, a correction table is created by calculation based on the table.
However, it is assumed that the correlation between the frequency and the correction value (that is, the FL difference) is known. For example, as shown in FIG. 3, all input data is proportional to the frequency. According to FIG. 2, first, a correction table 15 for a basic frequency (for example, 30 MHz) is created in the same manner as in the prior art, and in this case, stored in a ROM built in the correction value calculation circuit 22.
If the actual frequency of a certain mode is 30 MHz, for example, if the other mode is 20 MHz, for example, a value obtained by doubling the difference of the output data with respect to all the input data is written in the correction table 15 (see FIG. 4). If the frequency is two or three, the amount may be written in the correction table 15.
Furthermore, the contents of the correction table 15 can be rewritten every time the frequency is switched by using a RAM for the correction table 15. In this case, the capacity only needs to be for one table. In any case, as long as the correlation between the frequency and the correction value is known, it is possible to deal with any frequency by only obtaining the basic frequency correction table 15.

When a single type of CCD 10 is mounted on several models, there are a number of different frequencies for each model or mode, but by using the correction value calculation circuit 22, it is basic when the CCD 10 is delivered as a part. If the correction table 15 for the frequency to be obtained is obtained, the appropriate correction table 15 can be obtained regardless of the mode of which model the CCD 10 is used. Further, if a history is left for the CCD 10, a suitable correction table 15 can be acquired even if it will be mounted on another model in the future by parts recycling.
In the case of a color original reading apparatus also serving as monochrome reading, there are three types of image data, Red, Green, and Blue, but only green among these is used for monochrome reading. Therefore, even if the frequency is different between color reading and monochrome reading, only Green has two correction tables. Therefore, the correction table may be switched only for Green.

1 is a circuit block diagram of an image reading apparatus according to a first embodiment of the present invention. FIG. 5 is a circuit block diagram of an image reading apparatus according to a second embodiment of the present invention. It is a figure which shows an example of the relationship between a frequency and FL difference. It is a figure which shows an example of a correction table. 1 is a configuration diagram of a general document reading apparatus. It is a circuit block diagram of the image reading apparatus which concerns on a prior art example. It is a figure which shows an example of the input / output characteristic of a correction table.

Explanation of symbols

  10 CCD (Photoelectric Conversion Element Array), 15 Correction Table, 21 Multiple Correction Table, 22 Correction Value Calculation Circuit

Claims (2)

  In a document reading apparatus that drives a photoelectric conversion element array having a plurality of output terminals at a plurality of drive frequencies, a multiplex correction table set for each drive frequency is provided as a correction table for correcting the output level difference between the plurality of output terminals. An original reading apparatus characterized by the above.   In a document reading apparatus that drives a photoelectric conversion element array having a plurality of output terminals at a plurality of drive frequencies, a correction table for correcting the output level difference between the plurality of output terminals, and the contents of the correction table are calculated for each drive frequency. An original reading apparatus comprising: a correction value arithmetic circuit that rewrites the data.

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