In the image-reader, a first reading unit generates the first surface worth of first image data by reading a first surface of an document sheet. The second reading unit generates the second surface worth of second image data by reading a second surface. The process surface determining unit determines which of the first surface and the second surface is a process surface. The parameter storing unit stores a first parameter that corresponds to the first surface and a second parameter that corresponds to the second surface. The selecting unit selects one of the first parameter and the second parameter as a process parameter that corresponds to the process surface. The selecting unit outputs the process parameter. The image process executing unit executes an image process on the one of the first image data and the second image data by using the process parameter.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2010-022233 filed Feb. 3, 2010. The entire content of the priority application is incorporated herein by reference.

TECHNICAL FIELD

The invention relates to an image-reader having two image-reading sensors for simultaneously reading both sides of a document sheet.

BACKGROUND

A conventional image-reader known in the art is provided with two image-reading sensors disposed on a path along which a document sheet is conveyed. One image-reading sensor is provided for the front surface of the document sheet, and the other for the back surface of the document sheet, whereby the two image-reading sensors can simultaneously read both surfaces of a document sheet conveyed along the conveying path.

Japanese patent application publication No. H8-265576 describes an information processor having two image-reading sensors corresponding to both surfaces of a document sheet, and a single signal processing circuit. One image-reading sensor is provided for the front surface of the document sheet, and the other is provided for the back surface of the document sheet. Each of two image-reading sensors reads the document sheet in units of lines along a main scanning direction. Based on the parameters individually set for the two image-reading sensors, the signal processing circuit performs image processes on image signals received from the image-reading sensors, while alternating between the two image signals.

SUMMARY

In view of the foregoing, it is an object of the invention to provide an image-reader capable of quickly reading images from both surfaces of a plurality of document sheets using to two image-reading sensors and one image processor.

In order to attain the above and other objects, the invention provides an image-reader. The image-reader includes a conveyance unit, a first reading unit, a second reading unit, a storing unit, a process surface determining unit, an acquiring unit, a parameter storing unit, a selecting unit, and an image process executing unit. The conveyance unit is configured to sequentially convey a plurality of document sheets at a predetermined interval along a conveying path, each document sheet including a first surface and a second surface. The first reading unit is configured to generate the first surface worth of first image data by reading a first surface of a document sheet on the conveying path. The second reading unit is configured to generate the second surface worth of second image data by reading a second surface of a document sheet on the conveying path. The storing unit is configured to store the first image data and the second image data. The process surface determining unit is configured to determine which of the first surface and the second surface is a process surface. The acquiring unit is configured to acquire one of at lest part of the first image data and at least part of the second image data corresponding to the process surface from the storing unit. The parameter storing unit is configured to store a first parameter that corresponds to the first surface and a second parameter that corresponds to the second surface. The selecting unit is configured to select one of the first parameter and the second parameter as a process parameter that corresponds to the process surface. The selecting unit outputs the process parameter. The image process executing unit is configured to execute an image process on the one of at least part of the first image data and at least part of the second image data by using the process parameter.

DETAILED DESCRIPTION

An image-reader10according to an embodiment of the invention will be described while referring to the accompanying drawings.

Structural Descriptions

(1) Overall Structure of an Image-Reader

The image-reader10of the embodiment constitutes part of a scanner, and a copier.

FIG. 1is a block diagram showing the structure of the image-reader10. The image-reader10includes a conveying unit100, an image-reading unit200, document sheet sensors300, a RAM400, a ROM500, and a CPU600. All of these components are interconnected via an internal bus700.

The conveying unit100is integrally provided with a document sheet cover30(seeFIG. 2) of the image-reader10. The conveying unit100(the cover30) functions as an automatic document feeder (ADF) for conveying sheets of a document sheet placed in a feeding tray along a conveying path. The image-reading unit200is capable of reading images from both front and back surfaces of a document sheet conveyed along the conveying path. The document sheet sensors300detect the document sheet on the conveying path. The RAM400and the ROM500store various data and programs. The CPU600executes various processes based on the programs stored in the ROM500to control overall operations of the image-reader10. The back surface corresponds to a first surface and the front surface corresponds to a second surface.

FIG. 2is an explanatory diagram conceptually illustrating the image-reader10in a partial cross-sectional view. As shown inFIG. 2, the image-reader10has an original support base20, and the document sheet cover30. The original support base20functions as a flatbed scanner. The cover30is attached by hinges (not shown) to the original support base20. The cover30can be rotated open and closed on the original support base20via the hinges (not shown).

The conveying unit100is built inside the document sheet cover30. Here, the structure of the document sheet cover30will be described in greater detail with reference to the explanatory diagram ofFIG. 2.

The document sheet cover30includes a feeding tray110that holds a document sheet to be read, and a discharge tray130for receiving document sheets that have been read. The conveying unit100includes conveying rollers121-129for conveying the document sheets from the feeding tray110to the discharge tray130along a conveying path indicated by a bold dotted line inFIG. 2.

The document sheet cover30includes a first CIS (contact image sensor)710, a hack surface pressing piece220, a second CIS230, and a front surface of document pressing piece240. An upstream reading position P1and a downstream reading position P2are established on the conveying path. The first CIS210is for reading images from the back surface of a document sheet and is disposed at the upstream reading position P1. The back surface of document pressing piece220is provided for pressing the document sheet against the reading surface of the first CIS210as the document sheet is conveyed through the upstream reading position P1. The second CIS230is for reading images from the front surface of a document sheet and is movably disposed on the original support base20so as to be movable to the downstream reading position P2. The front surface pressing piece240is provided for pressing a document sheet against the reading surface of the second CIS230as the document sheet is conveyed through the downstream reading position P2.

An F sensor310, an RB sensor320, and an R sensor330are provided along the conveying path as the document sheet sensors300for detecting the presence of a document sheet being conveyed through the positions of the corresponding sensors.

(2) Structure of the Image-Reading Unit

Next, the structure of the image-reading unit200provided in the image-reader10will be described with reference to the block diagram inFIG. 3.

The image-reading unit200includes the first CIS210, a back-surface read controlling circuit250, the second CIS230, a front-surface read controlling circuit260, an image data memory unit270, and a digital image-processing circuit280.

The back-surface read controlling circuit250controls the first CIS210to scan images from the back surface of a document sheet passing through the upstream reading position P1and sequentially generates image data in units of lines (in a line basis) extending in a main scanning direction.

The front-surface read controlling circuit260controls the second CIS230to scan images from the front surface of a document sheet passing through the downstream reading position P2and sequentially generates image data in units of lines extending in a main scanning direction.

The image data memory unit270is configured of a back-surface memory area271and a front-surface memory area272, each of which is configured of a ring buffer. The back-surface memory area271stores image data (specifically, a line data set) sequentially generated and written by the back-surface read controlling circuit250, while the front-surface memory area272stores image data (specifically, a line data set) sequentially generated and written by the front-surface read controlling circuit260. Alternatively, the image data memory unit270may be configured as part of the RAM400and need not be included in the image-reading unit200.

The digital image-processing circuit280performs processes to read image data in units of lines from either the back-surface memory area271or the front-surface memory area272and to enlarge or reduce the size of the image represented by this image data. In addition, the digital image-processing circuit280performs filtration, gamma correction, color conversion, and other image processes on image data and sequentially outputs the processed image data.

The back-surface read controlling circuit250includes a scan data output circuit251for writing image data to the back-surface memory area271in units of lines after each line of image data (line data set) is generated. The scan data output circuit251outputs a count-up signal to a back-surface line counter282a(described later in greater detail) in the digital image-processing circuit280for every line of image data written to the back-surface memory area271.

Similarly, the front-surface read controlling circuit260includes a scan data output circuit261for writing image data to the front-surface memory area272in units of lines after each line of image data (line data set) is generated. The scan data output circuit261outputs a count-up signal to a front-surface line counter282b(described later in greater detail) in the digital image-processing circuit280for every line of image data written to the front-surface memory area272.

The digital image-processing circuit280includes an image data reading unit281, a process surface determining circuit282, an image processing circuit283, selectors285a-285e, and process parameter storage units286a-286jstoring front-surface/back-surface process parameters or tables for each of various image processes performed by the image processing circuit283.

The digital-image processing circuit280performs image processes on image data of the front surface and image data of the back surface. As described above, the back surface is read by the first CIS210and the front surface is read by the second CIS230. The image quality of the image data of the back surface is generally different from the image quality of the image data of the front surface due to the difference of the sensors (that is, the difference between the first CIS210and the second CIS230). For example, because of difference in optical systems in the first CIS210and the second CIS230, the size of image in the image data of the front surface is different from the size of image in the image data of the back surface.

The image data reading unit281reads image data for one line unit (one line data set) from the memory area (either the back-surface memory area271or the front-surface memory area272) corresponding to a “process surface” of the document sheet. The process surface is indicated by a process surface flag outputted from the process surface determining circuit282. The process surface determining circuit282determines the process surface to be the surface of the document sheet corresponding to the next image data to be processed and outputs the process surface flag indicating this process surface.

When outputting one line of image data read from the specified memory area (either the back-surface memory area271or the front-surface memory area272), the image data reading unit281advances the line position for the next image data to be read. Specifically, the image data reading unit281outputs a count-down signal to the line counter (either a back-surface line counter282aor a front-surface line counter282bdescribed later) for the corresponding sheet surface.

The image processing circuit283performs a process to enlarge or reduce the image on each surface of the document sheet individually by outputting a line position to the image data reading unit281specifying the line of image data to be read from the back-surface memory area271or the front-surface memory area272. The image processing circuit283also performs various image processes on image data individually for each surface.

The process surface determining circuit282includes a back-surface line counter282a, a front-surface line counter282b, and a process surface counter283c. The back-surface line counter282acounts lines of the document sheet read by the back-surface read controlling circuit250. Similarly, the front surface line counter282bcounts lines of the document sheet read by the front-surface read controlling circuit260.

The process surface counter282cis used for determining the process surface based on the line number specified by the back-surface line counter282aand the front-surface line counter282b. Each time a new process surface is determined (the process surface is changed), the process surface counter283outputs the process surface flag to the image data reading unit281and the selectors described later, simultaneously.

Upon receiving a count-up signal outputted from the scan data output circuit251, the back-surface line counter282aincrements the line number. Further, after reading one line worth of image data from the back-surface memory area271and outputting this data, the image data reading unit281advances the line position for image data to be read next by outputting a count-down signal corresponding to the next line number to the back-surface line counter282a. Upon receiving this count-down signal, the back-surface line counter282acalculates the line number of the image data based on the signal. The front-surface line counter282bhas a similar configuration to the back-surface line counter282afor the front-surface memory area272.

The image processing circuit283includes an enlargement/reduction process unit283a, a filter process unit283b, a gamma correction process unit283c, and a color conversion process unit283d. The enlargement/reduction process unit283aperforms a process to enlarge or reduce the size of image data on the process surface. The filter process unit283bperforms noise filtration, edge detection, edge enhancement, smoothing, and other filtering processes on the image data. The gamma correction process unit283cperforms a well-known gamma correction process on the image data to set suitable densities. The color conversion process unit283dperforms a well-known color conversion process to change the method of color representation.

More specifically, the enlargement/reduction process unit283aacquires an enlargement or reduction parameter corresponding to the process surface from an enlargement/reduction process parameter storage unit (286aor286b) described later. Using this parameter, the enlargement/reduction process unit283acalculates position data indicating the line position for image data that the image data reading unit281will read from the memory unit corresponding to that process surface.

The filter process unit283bacquires a filter process parameter corresponding to the process surface from a filter process parameter storage unit (286cor286d) described later. Using this parameter, the filter process unit283bperforms the filter process for the image data of the process surface.

The gamma correction process unit283cacquires a gamma correction process table corresponding to the process surface from a gamma correction process table storage unit (286eor286f). The gamma correction process table correlates input values and output values in order to correct densities of image. Using this parameter, the gamma correction process unit283cperforms the gamma correction process for the image data of the process surface.

The color conversion process unit283dacquires a color conversion process parameter corresponding to the process surface from a color conversion process parameter storage unit (286gor286h) and acquires a color conversion table from a color conversion table storage unit (286ior286j). The color conversion table correlates RGB values to CMYK values. The color conversion table may not have all of RGB values or CMYK values (0-255, for example). Intermediate values that are not included in the color conversion table are interpolated by calculation. The color conversion process parameter defines a number of intermediate values that is to be interpolated. Using this parameter and table, the color conversion process unit283dperforms the color conversion process for the image data of the process surface.

As mentioned earlier, the digital image-processing circuit280includes process parameter storage units286a-286j. More specifically, the digital image-processing circuit280has the front-surface enlargement/reduction process parameter storage unit286a, the back-surface enlargement/reduction process parameter storage unit286b, the front-surface filter process parameter storage unit286c, the back-surface filter process parameter storage unit286d, the front-surface gamma correction process table storage unit286e, the back-surface gamma correction process table storage unit286f, the front-surface color conversion process parameter storage unit286g, the back-surface color conversion process parameter storage unit286h, the front-surface color conversion table storage unit286i, and the back-surface color conversion table storage unit286j.

The front-surface gamma correction process table storage unit286estores a front-surface gamma correction process table used to perform the gamma correction process for the front surface, while the back-surface gamma correction process table storage unit286fstores a similar back-surface gamma correction process table for the back surface.

The front-surface color conversion process parameter storage unit286gstores a front-surface color conversion process parameter used to perform the color conversion process for the front surface, while the back-surface color conversion process parameter storage unit286hstores a similar back-surface color conversion process parameter for the back surface.

The front-surface color conversion table storage unit286istores a front-surface color conversion table used to perform the color conversion process for the front surface, while the back-surface color conversion table storage unit286jstores a similar back-surface color conversion table for the back surface.

As mentioned earlier, the digital image-processing circuit280further includes selectors285a-285erespectively corresponding to the enlargement/reduction process unit283a, the filter process unit283b, the gamma correction process unit283c, the color conversion process unit283d. Further, the selectors285a,285b, and285drespectively correspond to the enlargement/reduction process parameter storage units (286a,286b), the filter process parameter storage units (286c,286d), and color conversion process parameter storage unit (286g,286h). The selectors285cand285ealso correspond to the gamma correction process table storage unit (286e,2860and the color conversion table storage unit (286i,286j).

The selectors285a-285eselect the storage unit corresponding to the process surface indicated by the process surface flag and output a parameter or a table stored in the selected storage unit to the corresponding process unit.

The ROM500stores the above described parameters and tables, that is, the enlargement/reduction process parameters, the filter process parameters, the gamma correction process tables, the color conversion process parameters, and the color conversion tables. When starting reading process, the CPU600reads the above described parameters and tables and stores the parameters and tables in the corresponding storage units (286a-286j). The image-reading unit200may include a plurality of modes that having different reading settings each other. In this case, the ROM500stores parameters and tables for each mode. When performing the reading process, the CPU600reads the parameters and tables corresponding to the mode and stores the parameters and tables in the corresponding storage units (286a-286j).

(3) Structure of the Enlargement/Reduction Process Unit

Next, the structure of the enlargement/reduction process unit283aand the processes for enlarging and reducing an image performed by the enlargement/reduction process unit283awill be described. The enlargement/reduction process unit283aperforms a process to enlarge or reduce an image individually for each of the front and back surfaces of a document sheet. In this process, the enlargement/reduction process unit283aindividually calculates the position data at which the image data reading unit281is to read image data from memory.

As shown inFIG. 4(a), the enlargement/reduction process unit283aincludes a front-surface position data storage unit283a-1, a back-surface position data storage unit283a-2, selectors283a-3and283a-4, an updating unit283a-5, and an interpolation process unit283a-6. The front-surface position data storage unit283a-1stores front-surface position data indicating the reading position for the front surface. The back-surface position data storage unit283a-2stores back-surface position data indicating the reading position for the back surface. The selectors283a-3and283a-4function to select the position data storage unit (283a-1or283a-2) corresponding to the process surface indicated by the process surface flag outputted from the process surface counter282c. The updating unit283a-5updates position data stored in the position data storage unit (283a-1or283a-2) selected by the selector283a-4(i.e., the position data storage unit (283a-1or283a-2) corresponding to the process surface) using the enlargement/reduction process parameter corresponding to the process surface that was outputted from the enlargement/reduction process parameter storage unit (286aor286b). Subsequently, the updating unit283a-5outputs the updated position data to the image data reading unit281and stores the updated position data in the position data storage unit (283a-1or283a-2) selected by the selector283a-3. The image data reading unit281reads the image data corresponding to the position data from the image data memory unit270(specifically,271or272) and sends the read image data to the interpolation process unit286a-6.

Next, examples of enlargement and reduction processes executed by the enlargement/reduction process unit283awill be described.

First, a process to double the size of an original image will be described while referring to the explanatory diagram ofFIG. 4(b). When doubling the size of an original image, the enlargement/reduction process parameter is set to “0.5”. Thus the updating unit283a-5updates the position data by adding “0.5” to the line position indicated in the position data and outputs the updated position data to the image data reading unit281(in other words, position data is updated in the sequence 1, 1.5, 2, . . . ). Upon acquiring the position data, the image data reading unit281identifies the line position by ignoring any numbers to the right of the decimal in the position data (e.g., the image data reading unit281identifies the line position as the first line when the position data is either “1” or “1.5”) and reads image data for the line (line data set) specified by the line position from the identified line position. Accordingly, the image data reading unit281will read the same line twice, while outputting the image data to the interpolation unit286a-6. The image data reading unit281outputs a count-down signal when image data is outputted. Here, in the enlargement case where the same image data for the line specified by the line position is read a plurality of times (two times in this example), the image data reading unit281outputs a count-down signal only after the same image data for the line specified by the line position is read the plurality of times (two times), to maintain consistency with the value indicated by the line counter. The interpolation unit286a-6doubles the size of the original image in the acquired image data (that is, one line image) in the main scanning direction that is parallel to the line.

The interpolation unit286a-6also performs various image processes on image data for the same line acquired twice in this way, and sequentially outputs the resulting data. When combining the lines outputted above, the digital image-processing circuit280generates image data for an image enlarged to twice the size of the original.

Next, an example for a process to reduce the original image to one-third the original size will be described while referring to the explanatory diagram inFIG. 4(c). When reducing an original image to one-third the size, the enlargement/reduction process parameter is set to “3”. The updating unit283a-5then updates position data by adding “3” to the line position indicated in the position data and outputs the updated position data to the image data reading unit281(in other words, position data is updated in the sequence 1, 4, 7, . . . ). Upon acquiring the position data, the image data reading unit281reads image data for the line position indicated in the position data. Accordingly, the image data reading unit281reads image data for the indicated lines while skipping lines at a rate corresponding to the reduction ratio, and subsequently outputs the image data to the interpolation unit286a-6. When skipping lines in this process, the image data reading unit281outputs a count-down signal equivalent to the number of skipped lines in order to maintain consistency with the value indicated by the line counter. The interpolation unit286a-6reduces the original image in the acquired image data (that is, one line image) to one-third in the main scanning.

The interpolation unit286a-6also performs the various image processes on image data acquired for one line unit and sequentially outputs the processed data. When the lines of image data outputted in this way are combined, the digital image-processing circuit280generates image data for an image reduced to one-third the original size.

In the embodiment, an individual enlargement/reduction process parameter is provided for each surface of the document sheet, and position data corresponding to each surface of a sheet is updated individually based on the corresponding parameter. Hence, this process can set an individual magnification ratio for each surface.

The digital image-processing circuit280may be configured to execute one process cycle satisfying the following condition:
(time interval for one process cycle)×(maximum enragement ratio)×2=(time interval for reading lines by CIS).

Here, one process cycle includes the process for reading image data of a prescribed number of lines from a memory area (271or272), the image process, and the process outputting the result by the digital image-processing circuit280for the line data set. The “maximum enlargement ratio” is a maximum ratio that the image-reader10can set in the enlargement and reduction processes. The “time interval for reading lines by CIS” is a time interval for reading the image for one line by the read controlling circuit (250or260) with the CIS (210,230), for generating image data by the read controlling circuit (250or260), and for writing the image data in the memory area (271or272). In other words, the digital image-processing circuit280executes one process cycle, from reading image data of a line from a memory area to perform image processing and outputting the result, at a speed equivalent to twice the maximum enlargement ratio relative to the process in which each read controlling circuit reads an image for one line with the CIS, generates image data for one line, and writes the image data for one line to the image data memory unit270.

Further, in cases such as when the digital image-processing circuit280cannot achieve sufficient processing speed, delays in the process may generate an insufficient memory error, but the read controlling circuit may perform a process for preventing such errors from occurring. That is, when the line number indicated by the line counter (282aor282b) exceeds a prescribed number, the read controlling circuit (250or260) may temporarily halt the reading of image data while also stopping the conveying unit100from conveying the original. The read controlling circuit (250or260) can resume the reading of image data after processing by the digital image-processing circuit280has progressed and the line number indicated by the line counter (282aor282b) has sufficiently decreased. Further, when the line number indicated by the line counter (282aor282b) exceeds the prescribed number, the read controlling circuit (250or260) may reduce the speed at which the document sheet is conveyed and reduce the speed at which the image data is read. The read controlling circuit (250or260) may subsequently restore the conveying speed for the document sheet after processing by the digital image-processing circuit280has progressed and the line number indicated by the line counter (282aor282b) has decreased sufficiently.

Description of Operations

Next, a duplex reading process executed by the image-reader10will be described with reference to the flowchart inFIG. 5. The image-reader10begins the duplex reading process upon receiving a scan instruction from the user through input on an operating unit (not shown). Through this process, the image-reader10sequentially feeds the document sheets set in the feeding tray110and automatically conveys the document sheets while scanning both the front and back surfaces thereof.

In S805ofFIG. 5, the conveying unit100begins conveying a sheet of the original, after which the first CIS210begins scanning an image from the back surface of the document sheet as the document sheet passes through the upstream reading position on the conveying path. Next, the back-surface read controlling circuit250sequentially writes image data generated in units of lines to the back-surface memory area271. Similarly, the second CIS230begins scanning the front surface of the sheet as the sheet passes through the downstream reading position along the conveying path. Next, the front-surface read controlling circuit260sequentially writes image data generated in units of lines to the front-surface memory area272. Consequently, the image-reader10scans images from the back surface of the document sheet while the leading edge of the sheet is positioned between the upstream reading position P1and the downstream reading position P2, scans images in parallel from the front surface and back surface of the document sheet after the leading edge reaches the downstream reading position and until the trailing edge passes the upstream reading position, and scans images from the back surface of the document sheet after the trailing edge of the document sheet passes the upstream reading position P1and until the trailing edge reaches the downstream reading position P2. Further, when the conveying unit100begins conveying the document sheet, the process surface determining circuit282initializes the process surface counter282c, sets the process surface flag to the back surface, and initializes the back-surface line counter282aand the front-surface line counter282b. The enlargement/reduction process unit283ain the image processing circuit283also initializes the front-surface position data storage unit283a-1and the back-surface position data storage unit283a-2.

In S810the process surface determining circuit282determines whether to permit the image data reading unit281to read the image data of the process surface indicated by the process surface flag from the memory area (271or272). For example, the process surface determining circuit282may determine to read the image data of the process surface from the memory area (271or272) when the number of lines indicated by the line counter (282aor282b) corresponding to this process surface is at least a predetermined number, or when the number of lines indicated by the line counter (282aor282b) corresponding to the process surface is at least a predetermined number and is greater than or equal to the number of lines indicated by the other line counter. The process advances to S815when a positive determination is made (S810: YES). The process advances to S855when a negative determination is made (S810: NO).

In S815the enlargement/reduction process unit283adetermines whether the process surface indicated by the process surface flag is a front surface. When a positive determination is made (S815: YES), the process advances to S820. When a negative determination is made (S815: NO), the process advances to S825.

In S820the updating unit283a-5of the enlargement/reduction process unit283aupdates the front-surface position data stored in the front-surface position data storage unit283a-1. More specifically, the updating unit283a-5adds the front-surface enlargement/reduction process parameter outputted from the front-surface enlargement/reduction process parameter storage unit286ato the front-surface position data and stores this updated front-surface position data in the front-surface position data storage unit283a-1. The updating unit283a-5also outputs the updated front-surface position data to the image data reading unit281. Subsequently, the process advances to S830.

In S825the updating unit283a-5updates the back surface position data stored in the back-surface position data storage unit283a-2, similarly to S820. The updating unit283a-5also outputs the updated back-surface position data to the image data reading unit281. Subsequently, the process advances to S830.

In S830the image data reading unit281reads one line worth of image data (a set of line data) from the memory area (271or272) corresponding to the process surface for the line indicated by the position data corresponding to the process surface and outputs this image data to the image processing circuit283.

In S835the line worth of image data received by the image processing circuit283is outputted after passing through the enlargement/reduction process unit283a, the filter process unit283b, the gamma correction process unit283c, and the color conversion process unit283d. At this time, the image data is subjected to a filtering process in the filter process unit283b, a gamma correction process in the gamma correction process unit283c, and a color conversion process in the color conversion process unit283d, and the resulting image data is outputted from the image processing circuit283.

In S840the process surface determining circuit282determines whether image processing has been completed for the entire process surface. Specifically, by a well-known method of detecting the size of the sheet conveyed on the conveying path using the F sensor310and the RB sensor320to determine the total number of lines to be read on the back or front surface of the sheet. Then, the process surface determining circuit282can determine whether image processing has been completed for the process surface based on whether the number of lines processed on the surface has reached the total number of lines determined above. The process advances to S845when the process surface determining circuit282reaches a positive determination (S840: YES) and advances to S855when the process surface determining circuit282reaches a negative determination (S840: NO).

In S845the process surface determining circuit282determines whether there is another document sheet to be scanned next to the currently scanned document sheet, by using the F sensor310and the RB sensor320. The process advances to S855when a positive determination is made (S845: YES). The process advances to S850when a negative determination is made (S845: NO).

In S850the digital image-processing circuit280reads the image for the remaining portion of the surface not set as the process surface and executes the read process and image processes on this image. Once these processes are completed, the current duplex reading process ofFIG. 5is completed.

In S855the process surface counter282cswitches the process surface indicated by the process surface flag to the opposite surface, and the process returns to S810. In other words, in S855, the process surface determining circuit282determines the candidate process surface, and subsequently in S810determines whether the candidate process surface is the true process surface whose image data is to be read by the image data reading unit281.

Effects of the Embodiment

With the image-reader10according to the embodiment, the digital image-processing circuit280, and not the CPU600, determines which surface of the document sheet is targeted for image processing and selects the image process parameter to be used in the image process for each surface. Accordingly, the single image-processing circuit280can be used to quickly process images on both surfaces of a sheet scanned in parallel by two CISs210and230.

Variations of the Embodiment

For example, in the embodiment described above, the image data reading unit281reads image data from the image data memory unit270one line at a time. However, the image data reading unit281may instead read image data for a plurality of lines, and the enlargement/reduction process unit283amay update the position data based on the number of lines that are read at one time. This method will obtain the same effects described in the embodiment.

At least one of the first CIS210and the second CIS230may be a CCD (charge coupled device) sensor.

At least one of the storage units286a-286jmay store a plurality of parameters or tables.