Image processing apparatus and method for generating correction formula

An image processing apparatus includes a support member to support a sheet, a light source that extends in a main-scanning direction and is configured to move in a sub-scanning direction and irradiate light on the sheet as the light source moves in the sub-scanning direction, a conversion unit configured to generate multiple line image data based on light reflected by the sheet and incident thereon, as the light source moves in the sub-scanning direction, and a processing unit configured to carry out a correction process with respect to each of the line image data using a different correction formula for each of the line image data.

FIELD

Embodiments described herein relate generally to an image processing apparatus and a method for generating a correction formula with respect to each line image data obtained by an image processing apparatus.

BACKGROUND

An image processing apparatus, such as a scanner, has a light source that irradiates a sheet to be scanned and scans an image on the sheet based on the light reflected by the sheet. Specifically, the light reflected by the sheet is incident on a plurality of photoelectric transducers that is linearly arranged in a main-scanning direction, and an image data signal corresponding to intensity of the light is output from each of the photoelectric transducers.

Typically, the light source moves in a sub-scanning direction to irradiate a scanning region (scanning line) of the sheet. However, the light from the light source may not irradiate the scanning region in the same manner (e.g., same angle and same distance from the scanning region) as the light source moves in the sub-scanning direction. As a result, the obtained image data may not have the same brightness values in two different regions, even though the original sheet has the same brightness in the two regions.

DETAILED DESCRIPTION

In general, according to one embodiment, an image processing apparatus includes a support member to support a sheet, a light source that extends in a main-scanning direction and is configured to move in a sub-scanning direction and irradiate light on the sheet as the light source moves in the sub-scanning direction, a conversion unit configured to generate multiple line image data based on light reflected by the sheet and incident thereon, as the light source moves in the sub-scanning direction, and a processing unit configured to carry out a correction process with respect to each of the line image data using a different correction formula for each of the line image data.

Hereinafter, an image processing apparatus100of an embodiment will be described with reference to the accompanying drawings. The same configurations are given the same reference number in each drawing. The image processing apparatus100is one type of a paper-feeding apparatus.

FIG. 1illustrates configuration of the image processing apparatus100according to the embodiment.

As illustrated inFIG. 1, the image processing apparatus100includes a scanner unit2, a printer unit3, and a sheet storage unit4and is configured as an image forming apparatus. The image processing apparatus100, without being limited to the above configuration, may be configured to include the scanner unit2only.

The scanner unit2scans an image of a target to be copied based on intensity of light incident thereon. The scanner unit2outputs image information corresponding to the scanned image to the printer unit3.

The printer unit3transfers an output image (hereinafter, referred to as a “toner image”), which is visualized with developers such as toners, to a sheet S, which is a transfer medium, based on the image information output from the scanner unit2. Then, the printer unit3fixes the toner image on the sheet S by applying heat and pressure onto the sheet S to which the toner image is transferred.

The sheet storage unit4contains a plurality of the sheets S with respect to each predetermined size of the sheet S. The sheet storage unit4provides one sheet S at a time to the printer unit3at the timing of forming the toner image at the printer unit3.

A transport path5through which the sheet S is transported from the sheet storage unit4toward the printer unit3is disposed between the sheet storage unit4and the printer unit3. A transfer position5A is located at a middle portion of the transport path5. The transfer position5A is a position where the toner image formed at the printer unit3is transferred to the sheet S. Then, the sheet S is transported to a fixing device6via the transfer position5A.

In the embodiment, an upstream side of a sheet conveying direction along the transport path5is referred to as an upstream side of the transport path5. A downstream side of the sheet conveying direction along the transport path5is referred to as a downstream side of the transport path5.

An intermediate transfer belt11is disposed in the image processing apparatus100. For example, the intermediate transfer belt11is disposed on a lower side of the fixing device in the perpendicular direction. For example, the intermediate transfer belt11is an insulating film with a predetermined thickness and is formed into a belt shape. The intermediate transfer belt11may be a thin sheet-shaped metal of which the surfaces are protected by resin and the like.

A predetermined tensile force is applied to the intermediate transfer belt11by a transfer drive roller51, a first tension roller13, and a second tension roller14. A position on the intermediate transfer belt11moves in arrow A direction by the transfer drive roller51rotating. In other words, the belt surface of the intermediate transfer belt11circulates in one direction at the moving speed of the outer circumferential surface of the transfer drive roller51.

An image forming portion20is disposed along a section where the belt surface of the intermediate transfer belt11substantially moves like a flat surface in a state in which the predetermined tensile force is applied.

The image forming portion20includes image forming units21,22,23, and24. The image forming units21,22,23, and24are disposed at a predetermined interval. The image forming units21,22,23, and24are disposed between the first tension roller13and the second tension roller14.

The image forming units21,22,23, and24include developing devices21A,22A,23A, and24A, respectively, and photoreceptors21B,22B,23B, and24B, respectively. Each of the developing devices21A,22A,23A, and24A accommodates a toner of a color. For example, the developing devices21A,22A,23A, and24A accommodate cyan (C), magenta (M), yellow (Y), and black (BK) toners, respectively.

An exposing device31is disposed at a position that faces the photoreceptors21B,22B,23B, and24B. The exposing device31forms electrostatic images that correspond to the colors to be developed with respect to the photoreceptors21B,22B,23B, and24B. The toners are selectively supplied to the photoreceptors21B,22B,23B, and24B by the developing devices21A,22A,23A, and24A, respectively. Accordingly, the electrostatic images on the surfaces of the photoreceptors21B,22B,23B, and24B are developed with the corresponding toners. As a consequence, toner images are formed on the surfaces of the photoreceptors21B,22B,23B, and24B.

Facing rollers41,42,43, and44are provided at positions that face the photoreceptors21B,22B,23B, and24B with the intermediate transfer belt11disposed between the facing rollers and the photoreceptors. The facing rollers41,42,43, and44presses the intermediate transfer belt11towards the photoreceptors21B,22B,23B, and24B, respectively. Accordingly, the toner images formed on the photoreceptors21B,22B,23B, and24B are transferred to the intermediate transfer belt11. The toner images on the surfaces of the photoreceptors21B,22B,23B, and24B are sequentially transferred to the intermediate transfer belt11at a predetermined timing. By transferring, the toner images of each color are formed on the intermediate transfer belt11. The toner images of each color are superimposed on each other at a predetermined position on the surface of the intermediate transfer belt11.

A transfer passive roller52that is in contact with the intermediate transfer belt11at a predetermined pressure is disposed at the transfer position5A, which is disposed on the middle portion of the transport path5. The transfer passive roller52is pressed towards the transfer drive roller51with the intermediate transfer belt11disposed therebetween.

A bias is applied between the transfer drive roller51and the transfer passive roller52. Accordingly, the charged toners move from the intermediate transfer belt11to the transfer passive roller52. The toner images of each color are transferred from the intermediate transfer belt11to the sheet S at the transfer position5A.

Meanwhile, when the toner images are not transferred to the sheet S, the transfer passive roller52is moved at a receding position by a roller release mechanism, which is not illustrated in the drawing. As the receding position, the transfer passive roller52is not in contact with the intermediate transfer belt11.

A pair of resist rollers7is disposed at a predetermined position along the transport path5from the sheet storage unit4to the transfer position5A. The sheet S transported from the sheet storage unit4passes through the pair of resist rollers7before entering the transfer position5A. The pair of the resist rollers7adjusts the transport direction of the sheet S that enters the transfer position5A.

The sheet S transported along the transport path5from the sheet storage unit4to the transfer position5A abuts the pair of resist rollers7and temporarily stops. This corrects inclination of the sheet S with respect to the transport direction.

The toner images on the intermediate transfer belt11are transported to the transfer position5A by the intermediate transfer belt11. The pair of resist rollers7rotates again at the timing of the toner images arriving at a place close to the transfer position5A. The toner images are transported by the intermediate transfer belt11and reach the transfer position5A. The sheet S arrives at the transfer position5A at the timing of the toner images reaching the transfer position5A. The sheet S passes through the transfer position5A. Consequently, the toner images are transferred to the sheet S.

The fixing device6applies heat and pressure to the toner images that are transferred to the sheet S. The toner images are fixed on the sheet S by the heat and the pressure applied thereto.

The sheet S where the toner images are fixed by the fixing device6is guided to a sheet discharging unit1aalong the transport path5. The sheet discharging unit1ais a part of an exterior cover that covers the printer unit3. The sheet discharging unit1ais located at a space between the scanner unit2and the sheet discharging unit1a.

A branch point8A that guides the sheet S in a direction which is different from a direction towards the sheet discharging unit1ais disposed further downstream of the transport path5with respect to the fixing device6. In case of double-sided printing on the sheet S, the sheet S is temporarily conveyed towards the sheet discharging unit1a. Subsequently, the sheet S is drawn into the printer unit3. Then, the sheet S is guided to an inverting unit8via the branch point8A.

The inverting unit8transports the sheet S along a transport path81in the inverting unit8.

A pair of inverting unit resist rollers82is disposed in the inverting unit8.

The pair of inverting unit resist rollers82, similarly to the pair of resist rollers7, temporarily stops the sheet S that is transported through the transport path81. This corrects the inclination of the sheet S. In addition, the pair of inverting unit resist rollers82resumes transporting the sheet S at the timing when the toner images reaches a point close to the transfer position5A. The sheet S transported from the pair of inverting unit resist rollers82enters the transport path5.

A position where the sheet S discharged from the pair of inverting unit resist rollers82enters the transport path5exists on the transport path5. The sheet S is inserted from a manual feed tray83, from further upstream side of the transport path5with respect to the position where the sheet S joins the transport path5.

Next, the configuration of the scanner unit2will be described with reference toFIG. 2.FIG. 2illustrates configuration of the scanner unit2.

As illustrated inFIG. 2, the scanner unit2includes a light source201, a reflector202, a first mirror203, a second mirror204, a third mirror205, a first carriage206, a second carriage207, a condenser lens208, a charge coupled device (CCD) sensor209, a CCD substrate210, a scanner control substrate211, a document platen glass212, a shading plate213, a document scale214, and a through-read glass215. The scanner unit2may include an automatic document feed (ADF) unit.

Here, the direction in which the light source201moves is referred to as a sub-scanning direction y. A direction that is orthogonal to the sub-scanning direction y on the surface of the document platen glass212is referred to as a main-scanning direction x. The direction that is orthogonal to the main-scanning direction x and the sub-scanning direction y is referred to as z direction.

The document platen glass212includes a placement surface212aon which the sheet S is placed. The shading plate213is formed of a white member. The shading plate213is a white reference unit for performing shading correction on the image information obtained from the sheet S. The shading plate213has a long shape in the main-scanning direction x. The document scale214can be used to place the sheet S at a predetermined position on the document platen glass212. A tip end position214ais disposed at an end portion of the document scale214.

InFIG. 2, the sheet S is placed on the placement surface212aof the document platen glass212. The sheet S is placed at a predetermined scanning position on the placement surface212a. The tip end of the sheet S placed at the scanning position is in contact with the tip end position214aof the document scale214. Accordingly, the position of the sheet S on the document platen glass212is fixed. Although not described in detail, a position to which the corner of the tip end of the sheet S is aligned is set in advance on the placement surface212a. Aligning the corner of the tip end of the sheet S to the position set in advance determines the position of the sheet S in the main-scanning direction x and the sub-scanning direction y. The position used to align the corner of the tip end of the sheet S is set on the tip end position214a.

The light source201emits light. The reflector202reflects the light emitted from the light source201. The shading plate213and the sheet S are uniformly irradiated with the light reflected by the reflector202. This adjusts the light distribution characteristics in the main-scanning direction x at the reading position of the sheet S. The first mirror203receives the light reflected by the shading plate213and the sheet S. The first mirror203guides the light reflected by the shading plate213and the sheet S to the second mirror204.

The second mirror204receives the light reflected by the first mirror203. The second mirror204guides the light reflected by the first mirror203to the third mirror205. The third mirror205receives the light reflected by the second mirror204. The third mirror205guides the light reflected by the second mirror204to the condenser lens208. The condenser lens208condenses the light reflected by the third mirror205. An image is formed on an imaging surface (reading surface) of the CCD sensor209according to the light condensed by the condenser lens208.

The CCD sensor209is mounted on the CCD substrate210. For example, the CCD sensor209is a hybrid four-line sensor. The hybrid four-line sensor includes a three-line sensor that reads a color image and a one-line sensor that reads a monochrome image. The three-line sensor, which scans a color image, detects red (R), green (G), and blue (B) lights.

The CCD sensor209photoelectrically converts the light energy of an image formed with the condenser lens208into electric charge. Accordingly, the CCD sensor209converts the image formed with the condenser lens208into an electric signal. The CCD substrate210outputs the electric signal that the CCD sensor209photoelectrically converted to the scanner control substrate211.

The light source201, the reflector202, and the first mirror203are mounted on the first carriage206. The second mirror204and the third mirror205are mounted on the second carriage207. The first carriage206moves in the main-scanning direction x by a driving unit, which is not illustrated in the drawing. The second carriage207is driven to move in the same direction as that of the first carriage206at a half speed of the first carriage206. Therefore, the optical path length of the light guided to the imaging surface of the CCD sensor209does not change even when the first carriage206moves. That is, the optical path length from the placement surface212ato the imaging surface of the CCD sensor209is constant all the time in the optical system configured of the first mirror203, the second mirror204, and the third mirror205.

For example, the first carriage206moves from the left to the right along the sub-scanning direction y inFIG. 1. Accordingly, the image on the sheet S placed on the placement surface212ais scanned. A scanning position P with respect to the sheet S also moves along with the first carriage206moving in the sub-scanning direction y. The scanning position P moves from the left to the right along the sub-scanning direction y. The scanning position P corresponds to one line extending in the main-scanning direction x. The image on the sheet S at the scanning position P is sequentially formed on the imaging surface of the CCD sensor209as the scanning position P moves in the sub-scanning direction y. The CCD sensor209photoelectrically converts the light energy of the image and outputs image data. The CCD sensor209outputs the image data at the scanning position P as one-line image data Dx in the main-scanning direction x. The CCD sensor209converts the image on the entire sheet S into image data DX based on the multiple-line image data Dx.

A plurality of photodiodes is arranged along the imaging surface of the CCD sensor209. The CCD sensor209scans the one-line image data Dx in the main-scanning direction x based on the output from the plurality of photodiodes that are arranged. The CCD sensor209generates the one-line image data Dx for each different position in the sub-scanning direction y when the light source201moves along the sub-scanning direction y. That is, the CCD sensor209outputs the multiple-line image data Dx corresponding to the number of lines in the sub-scanning direction y.

In the embodiment, a line number that indicates a position in the sub-scanning direction y is assigned to each of the one-line image data Dx. The image data that the scanner unit2initially generates is referred to as first line image data D1. Similarly, the image data that the scanner unit2secondarily generates is referred to as second image data D2. The one-line image data Dx includes data units corresponding to the number of pixels of the CCD sensor209. The one-line image data Dx includes 7500 data units in the embodiment.

Next, functional configuration of the image processing apparatus100will be described with reference toFIG. 3.FIG. 3is a block diagram of the image processing apparatus100.

The CCD sensor209outputs the photoelectrically-converted electric signal to an analog front end (AFE)220. The AFE220converts the input electric signal from an analog signal into a digital signal. The AFE220outputs the electric signal converted into the digital signal to an application-specific integrated circuit (ASIC)211for correction process. The AFE220is mounted on the CCD substrate210or the scanner control substrate211.

The ASIC for correction process211is connected to a scanner central processing unit (CPU)230, an image memory240, a system CPU250, and a control panel CPU260.

The scanner CPU230controls the entire operations of the scanner unit2.

The image memory240stores the image data generated by the scanner unit2. For example, the image memory240is a memory unit such as a semiconductor memory device, a magnetic memory device, and a hard disk drive (HDD).

The system CPU250controls the entire operations of the image processing apparatus100.

The control panel CPU260controls a control panel1.

The scanner CPU230is connected to the system CPU250. The ASIC for correction process211is connected to a printer ASIC310. The printer ASIC310is connected to the printer unit3and an engine CPU320.

The printer ASIC310controls the entire operations of the printer unit3.

The engine CPU320controls the operation of a drive unit and the like that rotate rollers.

Next, an example of the ASIC211will be described with reference toFIG. 4.FIG. 4is a block diagram of the ASIC211.

A correction formula generation unit231, a shading correction process unit232, and an in-plane non-uniformity correction process unit233are functional software units achieved by the ASIC211executing a program stored in a storage unit234. Alternatively, the correction formula generation unit231, the shading correction process unit232, and the in-plane non-uniformity correction process unit233may be achieved by hardware. A configuration of the correction formula generation unit231, the shading correction process unit232, and the in-plane non-uniformity correction process unit233is included in a correction unit221. A part or all of the correction formula generation unit231, the shading correction process unit232, and the in-plane non-uniformity correction process unit233may be functional hardware units such as CPUs and large scale integration (LSI). In addition, the storage unit234may be a read-only memory (ROM) or a random access memory (RAM).

The storage unit234includes a shading correction value storing area2341, a reference data storing area2342, a comparative data storing area2343, and an in-plane non-uniformity correction formula storing area2344.

Reference data is stored in the reference data storing area2342. The reference data is image data Dv that corresponds to a reference line V set in advance among the image data Dx of the entire lines that the CCD sensor209scans. The 500th line is set as the reference line V in the embodiment.

Comparative data is stored in the comparative data storing area2343. The comparative data is image data Dw that corresponds to a comparative line W set in advance among the image data Dx of the entire lines that the CCD sensor209reads. For example, every line from the 501st line to the last line is set as the comparative line W. In addition, a representative line between the 501st line and the last line may be the comparative line W. In the embodiment, the representative lines are the 2500th, the 4500th, the 6500th, and the 8500th lines.

The shading correction value storing area2341stores a shading correction value generated by the shading correction process unit232. The shading correction value storing area2341stores a correction value αywith respect to each pixel lined up in the main-scanning direction x. Each of the correction values is associated with a pixel number (x=1 to 7,500) that indicates a position in the main-scanning direction x.

The in-plane non-uniformity correction formula storing area2344stores a correction formula fythat is generated by the correction formula generation unit231. The in-plane non-uniformity correction formula storing area2344stores the correction formulas fyof which the number corresponds to the number of lines of a correction target. Each of the correction formulas fyis associated with a line number that indicates a position in the sub-scanning direction y.

The correction formula generation unit231generates the correction formula fybased on the image data of an image for correction obtained from a sheet for correction Sr. For example, the sheet for correction Sr is a white paper sheet. An example of the correction formula is illustrated in Expression 1.

Dx is the one-line image data Dx of the sheet, which is the correction target.

Dv is the one-line image data that corresponds to the reference line V.

Dw is the one-line image data that corresponds to the comparative line W.

For example, the correction formula fyin Expression 1 is stored in the in-plane non-uniformity correction formula storing area2344. Specific values for “Dv” and “Dw” in the correction formula fyare stored in the in-plane non-uniformity correction formula storing area2344. Specific values for “Dx” in the correction formula fyis not stored. The one-line image data Dx is input to “Dx” in the correction formula fywhen an image on the sheet S, which is the correction target, is scanned.

The correction formula generation unit231acquires the values of the reference data Dv from the reference data storing area2342. In addition, the correction formula generation unit231acquires the values of the comparative data Dw from the comparative data storing area2343. The correction formula generation unit231assigns the values of the reference data Dv and the comparative data Dw in the correction formula illustrated in Expression 1, and generates the correction formula fythat corresponds to the same line as that of the comparative data Dw. The correction formula generation unit231associates the generated correction formula fywith the line number of the comparative data Dw, and writes into the in-plane non-uniformity correction formula storing area2344.

The shading correction process unit232obtains the correction value αyfor each pixel based on the image data generated when the shading plate213is scanned. Specifically, the shading correction process unit232obtains the difference between the level of the image data obtained from the shading plate213and a predetermined target value, with respect to each pixel. The shading correction process unit232obtains the correction value αybased on the obtained difference. When the level of the image data obtained from the shading plate213is lower than the target value, the shading correction process unit232generates a correction value αythat corrects the level of the image data of the corresponding pixel so as to raise the level. When the level of the image data obtained from the shading plate213is higher than the target value, the shading correction process unit232generates a correction value αythat corrects the pixel level of the image data of the corresponding pixel so as to reduce the level.

Incidentally, there is some variation of values among pixels in the one-line image data. This variation may happen when the installed position and the like of the plurality of photodiodes that configures the CCD sensor209slightly differ. The shading correction process unit232obtains a correction value αythat makes variations in the values uniform.

Correction values generally used in shading correction are applicable to the correction value αy.

The shading correction process unit232associates the obtained correction value αywith the pixel number and writes into the shading correction value storing area2341.

When an image of the sheet S, which is the correction target, is scanned, the shading correction process unit232performs shading correction with respect to each one-line image data Dx. The shading correction is for correcting each value included in the one-line image data Dx based on the corresponding correction value αy. For example, the shading correction process unit232multiplies each value of pixels included in the one-line image data Dx by the corresponding correction value αy.

When the image of the sheet S is scanned, the in-plane non-uniformity correction process unit233performs in-plane non-uniformity correction on each one-line image data Dx. The in-plane non-uniformity correction means obtaining the calculation result of the correction formula fyby assigning the value of the one-line image data Dx in the correction formula fyillustrated in Expression 1. For example, the in-plane non-uniformity correction process unit233acquires a correction formula fythat is associated with the line number of the image data to be corrected from the in-plane non-uniformity correction formula storing area2344. The in-plane non-uniformity correction process unit233replaces the image data Dx in the read correction formula fywith the one-line image data Dx to be corrected. The in-plane non-uniformity correction process unit233performs the in-plane non-uniformity correction on the image data Dx with respect to each of the entire lines. The in-plane non-uniformity correction process unit233outputs the image data after the correction.

Next, an illuminance stability area will be described with reference toFIGS. 5 to 7.FIG. 5illustrates a relationship between the position of an optical axis and the illuminance.

In the graph ofFIG. 5, the horizontal axis indicates a position of the placement surface212ain the sub-scanning direction y, and the vertical axis indicates a relative illuminance in the sub-scanning direction y. The graph indicates light distribution characteristics in the sub-scanning direction. The position of the placement surface212acorresponds to a position of the lens208through which the light passes.

When the position of the placement surface212aon the horizontal axis is 0 mm, the light from that point passes through an optical axis of the lens208. That is, the difference between the optical axis of the light that passes through the lens208and a position set to scan the image is 0 mm. The relative illuminance decreases as the difference between the optical axis of the light that passes through the lens208and the set position increases.

FIG. 6illustrates a state in which lights from the light source and the reflector form a wide illuminance stability area.FIG. 7illustrates a state in which lights from the light source and the reflector form a narrow illuminance stability area.

FIG. 6andFIG. 7show difference regarding light distribution of direct light from the light source201and light distribution of reflective light from the reflector202. The light distribution illustrated inFIG. 6is wide, as compared with the light distribution inFIG. 7.

The light distribution of the direct light and the reflective light is known to be different depending on the extent of assembling variations of mirrors and the light source201. That is, the assembling variation may cause a difference between the optical axis of the light that passes through the lens208and the position set for scanning. The illuminance stability area is wide as illustrated inFIG. 6when there is no difference between the optical axis of the light that passes through the lens208and the set position. The illuminance stability area is narrow as illustrated inFIG. 7when there is some difference between the optical axis of the light that passes through the lens208and the set position.

The illuminance decreases as the set position is apart from the illuminance stability area. In this case, the brightness indicated by the image data read from the sheet S, which is the reading target, becomes darker than the brightness of the actual reading target.

Next, a relationship between the relative illuminance in the sub-scanning direction y and the brightness of the image will be described with reference toFIG. 8.FIG. 8illustrates an example of the brightness of an image based on image data generated without the in-plane non-uniformity correction.

The brightness of the image based on the generated image data is not uniform in the sub-scanning direction y in the image illustrated inFIG. 8. The brightness becomes darker toward the right in the sub-scanning direction y. This is because the relative illuminance decreases as the scanning position with the light source201moves in the sub-scanning direction y.

For example, when the illuminance stability area is wide, the illuminance at the set position may not decrease significantly as the scanning position moves in the sub-scanning direction y decreases. However, when the illuminance stability area is narrow, the illuminance at the set position may decrease significantly as the scanning position moves in the sub-scanning direction y decreases. In the latter case, the image data with the different brightness in the sub-scanning direction y may be generated as illustrated inFIG. 8. As described above, the brightness of the image based on the image data obtained through the scanning is known to change because of the variations of the illuminance in the sub-scanning direction y.

Next, an example of the reference line V and the comparative line W will be described with reference toFIG. 9.FIG. 9illustrates the reference line V and the comparative lines W in the sheet S.

The sheet S is placed on the placement surface212ain a state in which a tip end Sa of the sheet S is in contact with the tip end position214a. The reference line V is set to be the 500th line from the tip end position214a. That is, the reference line V is the 500th line from the tip end Sa of the sheet S. The comparative lines W include a plurality of comparative lines W1to W4. The comparative lines W1, W2, W3, and W4are respectively set to be the 2500th, the 4500th, the 6500th, and the 8500th lines from the tip end position214a.

That is, the comparative line W1is the 2000th line from the reference line V. The comparative line W2is the 2000th line from the comparative line W1. The comparative line W3is the 2000th line from the comparative line W2. The comparative line W4is the 2000th line from the comparative line W3.

A center line Sc of the sheet S is a center line of the sheet S in the main-scanning direction x. The center line Sc is parallel to the sub-scanning direction y.

The comparative lines W include four lines in the drawing, but the number of the comparative lines W is not limited thereto. For example, the comparative line may be any line other than the reference line V among the entire lines scanned by the CCD sensor209. However, the first to 499th lines are preferably excluded from the comparative lines W.

Next, a relationship between an image level of the image data Dx and the scanning position will be described with reference toFIG. 10.FIG. 10illustrates the relationship between the image level of the image data Dx and the scanning position.

The image level of the image data Dx ranges from 0 to 255. The image level being 0 indicates that the corresponding pixel is a black color. The image level being 255 indicates that the corresponding pixel is a white color. Other image levels therebetween indicate shades between black and white. The color of the pixel becomes darker as the image level becomes close to 0, and the color becomes lighter as the image level becomes close to 255.

The image level gradually decreases from the reference line V inFIG. 10. This may occur when there is variation in the light distribution of the illuminance in the sub-scanning direction y.

Specifically, the image level of the comparative line W1is 215. That is, the image level of the comparative line W1is five points lower than the image level of the reference line V.

The image level of the comparative line W2is 210. That is, the image level of the comparative line W2is 10 points lower than the image level of the reference line V.

The image level of the comparative line W3is 205. That is, the image level of the comparative line W3is 15 points lower than the image level of the reference line V.

The image level of the comparative line W4is 200. That is, the image level of the comparative line W4is 20 points lower than the image level of the reference line V.

Next, a procedure for setting a correction formula by the image processing apparatus100will be described with reference toFIG. 11.FIG. 11is a flow chart of the procedure for setting a correction formula by the image processing apparatus100.

The system CPU250receives an instruction from a user via the control panel1to start an adjustment mode (ACT101). A plurality of adjustment modes may be prepared besides the adjustment mode to set the in-plane non-uniformity correction formula.

Subsequently, the system. CPU250determines whether the adjustment mode to set the in-plane non-uniformity correction formula is chosen from the adjustment modes by the user (ACT102). When the adjustment mode to set the in-plane non-uniformity correction formula is not chosen (ACT102—NO), the system CPU250does not execute the adjustment mode to set an in-plane non-uniformity correction formula (ACT103).

Meanwhile, when the adjustment mode to set the in-plane non-uniformity correction formula is chosen by the user (ACT102—YES), the system CPU250receives the instruction from the user via the control panel1to start the adjustment mode to set the in-plane non-uniformity correction formula.

Next, the sheet for in-plane non-uniformity correction Sr is placed at a predetermined reading position on the placement surface212aby the user (ACT104). That is, the sheet for correction Sr is placed on the placement surface212awith the tip end Sa of the sheet for correction Sr aligned to the tip end position214a.

Subsequently, the user chooses whether to newly set an in-plane non-uniformity correction formula (ACT105). When a new in-plane non-uniformity correction formula is not set (ACT105—NO), the ASIC211uses the correction formula that has been already set (ACT106).

When a new in-plane non-uniformity correction formula is set (ACT105—YES), the ASIC process211generates the correction formula generation unit231. The correction formula generation unit231starts a process of generating an in-plane non-uniformity correction formula (ACT107).

For example, the user instructs to perform a scan process via the control panel1. The scanner unit2starts a process of scanning the sheet for correction Sr (ACT108).

The image data Dx that the CCD sensor209generates is input to the correction formula generation unit231. The correction formula generation unit231determines whether the input image data Dx is the reference data based on the line number of the input image data Dx (ACT109).

When the input image data Dx is determined to be the reference data, the correction formula generation unit231writes the image data Dx that is determined to be the reference data into the reference data storing area2342(ACT110). For example, the correction formula generation unit231writes image data D500that is determined to be the reference data into the reference data storing area2342. Here, when information has been already written in the reference data storing area2342, the correction formula generation unit231overwrites the information with the most recent image data D500.

Meanwhile, when the input image data Dx is determined not to be the reference data, the correction formula generation unit231determines whether the input image data Dx is the comparative data based on the line number of the input image data Dx (ACT111).

When the input image data Dx is determined not to be the comparative data, the correction formula generation unit231deletes the input image data Dx therefrom (ACT112).

Meanwhile, when the input image data Dx is determined to be the comparative data, the correction formula generation unit231writes the image data Dx that is determined to be the comparative data into the comparative data storing area2343(ACT113). For example, the correction formula generation unit231writes image data D2500that is determined to be the comparative data into the comparative data storing area2343.

The correction formula generation unit231generates a correction formula fybased on the value of the reference data Dv and the value of the comparative data Dw (ACT114). Specifically, the correction formula generation unit231reads the value of the image data D500from the reference data storing area2342and reads the value of the image data D2500from the comparative data storing area2343. The correction formula generation unit231assigns the values of the reference data Dv and the comparative data Dw in the correction formula fydescribed in Expression 1. Consequently, the correction formula generation unit231generates the correction formula fydescribed in Expression 2.

The correction formula generation unit231writes the generated correction formula fyinto the in-plane non-uniformity correction formula storing area2344(ACT115).

The correction formula generation unit231then deletes the information stored in the comparative data storing area2343(ACT116).

Next, the correction formula generation unit231determines whether the processes from ACT109have been performed on the entire image data Dx that the CCD sensor209scanned (ACT117).

When it is determined that the entire image data Dx has not been processed (ACT117—NO), the correction formula generation unit231returns to ACT109and repeats the processes.

Meanwhile, when it is determined that the entire image data Dx has been processed (ACT117—YES), the correction formula generation unit231completes the process of generating the in-plane non-uniformity correction formula (ACT118).

The correction formula generation unit231then ends the adjustment mode (ACT119).

Next, a reading operation carried out by the image processing apparatus100will be described with reference toFIG. 12.FIG. 12is a flow chart of the reading operation carried out by the image processing apparatus100.

The system CPU250receives an instruction from the user via the control panel1to start scanning (ACT201).

The system CPU250outputs the received instruction to the scanner CPU230. The scanner CPU230moves the light source201under the shading plate213(ACT202). The scanner CPU230then obtains a correction value αyfor each pixel based on the image data read from the shading plate213(ACT203). The shading correction process unit232associates the obtained correction value αywith the pixel number and writes into the shading correction value storing area2341(ACT204).

The scanner CPU230moves the light source201in the sub-scanning direction y to scan the sheet S (ACT205). Consequently, the one-line image data Dx is sequentially input to the ASIC211.

The shading correction process unit232performs the shading correction on each one-line image data Dx (ACT206). That is, the shading correction process unit232corrects each pixel value included in the one-line image data Dx based on the corresponding correction value αy.

Next, the in-plane non-uniformity correction process unit233performs the in-plane non-uniformity correction on each one-line image data Dx on which the shading correction is performed (ACT207).

The shading correction process unit232and the in-plane non-uniformity correction process unit233repeatedly perform the processes in ACT206and ACT207on each one-line image data Dx.

As described above, the image processing apparatus100according to the embodiment performs the shading correction on the image data obtained from the sheet S. This corrects variations in pixel values in the main-scanning direction. In addition, the image processing apparatus100performs the in-plane non-uniformity correction on the image data obtained from the sheet S. This corrects variations in the pixel values in the sub-scanning direction y. Therefore, variations in the brightness of the image data that the image processing apparatus100scans may be decreased.

The image processing apparatus100according to the embodiment generates the correction formula based on the image data obtained from the sheet for correction Sr. The image processing apparatus100outputs the calculation result after assigning the image data of the sheet S that has been corrected based on the image data read from the shading plate213in the correction formula. According to this configuration, the shading correction and the in-plane non-uniformity correction may be simply performed on the image data that is obtained from the same sheet S.

The image processing apparatus100according to the embodiment generates the correction formula for each line of which position is different in the sub-scanning direction y. According to this configuration, the in-plane non-uniformity correction may be performed on the image data with respect to each of the lines in the sub-scanning direction y. Accordingly, variations in the brightness of the image data that the image processing apparatus100generates may be decreased.

The image processing apparatus100according to the embodiment corrects the image data read from the sheet S based on the difference between the reference data and the comparative data. According to this configuration, the image data that corresponds to the comparative line obtained from the sheet S may be corrected close to the level of the data that corresponds to the reference line.

The image processing apparatus100is described as fixing the toner image, but the image processing apparatus100may be an inkjet-type image processing apparatus.

The correction formula generation unit231generates the correction formulas that correspond to the comparative lines W1to W4of which positions are different in the sub-scanning direction y. In this case, the correction formula generation unit231may estimate correction formulas that correspond to lines other than the comparative lines W1to W4based on the correction formulas that correspond to the comparative lines W1to W4. For example, the correction formula generation unit231estimates the image levels of the lines other than the comparative lines W1to W4based on the image levels of the comparative lines W1to W4. The correction formula generation unit231may estimate the image levels of the lines other than the comparative lines W1to W4from graphs as illustrated inFIG. 10. The correction formula generation unit231may generate the correction formulas that correspond to each line other than the comparative lines W1to W4based on the estimated image levels. The correction formula generation unit231associates the generated correction formulas with the line numbers and writes into the in-plane non-uniformity correction formula storing area2344. According to this configuration, the number of comparative data to be obtained decreases. Therefore, a process load for obtaining the image level for each image data is reduced. In addition, the in-plane non-uniformity correction may be performed on the image data of the entire lines in the sub-scanning direction y because the correction values of the lines other than the comparative lines W1to W4are generated.

The size and the position of each roller may be arbitrarily designed and changed.