Patent Description:
Conventionally, an image capturing technique for authenticating a document for document security is known. Such a technique embeds invisible information that cannot be seen by human eyes in a document, and reads the invisible information by using invisible light to authenticate the document.

<CIT> discloses a technique for extracting only a visible wavelength component by removing an infrared component from a visible image including the infrared component. According to the technique, a document image is illuminated by a lamp having an infrared wavelength component, and an infrared image including an infrared component is acquired by an infrared image sensor. At the same time, a visible image including a visible component and an infrared component is acquired by a visible image sensor. The infrared image and the visible image are used, so that the infrared component is removed from the visible image including the infrared component to extract only a visible wavelength component.

However, the technique disclosed in <CIT> has an issue since calculation for removal of the infrared component from the visible image including the infrared component causes an increase in noise in the visible image from which the infrared component has been removed. Such an increase in noise degrades image quality.

<CIT> discloses a video signal processing apparatus including an image sensor and an infrared component remover. The image sensor receives light through a color filter, the color filter including long-pass filters only or a combination of a long-pass filter and an all-transmissive filter. The long-pass filters in the color filter a visible-light transmissive long-pass filter for permitting a visible-light component and an infrared-light component to pass therethrough and an infrared-light transmissive long-pass filter for permitting an infrared-light component to pass selectively therethrough. The infrared-light component remover removes an infrared-light component contained in a signal having passed through the visible-light transmissive long-pass filter, with transmittance data of an infrared-light region of the visible-light transmissive long-pass filter and the infrared-light transmissive long-pass filter applied.

The invention is defined by the set of appended claims.

The aspects, features, and advantages of the present disclosure are better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:.

The accompanying drawings are intended to depict embodiments of the present disclosure.

However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have the same function, operate in a similar manner and achieve similar results.

An image processing apparatus, an image processing method, and a carrier medium are hereinafter described in detail with reference to the drawings.

<FIG> is a diagram illustrating one example of a configuration of an image processing apparatus <NUM> according to a first embodiment. The image processing apparatus <NUM> is an image forming apparatus generally called a multifunctional peripheral having at least two of a copy function, a print function, a scanner function, and a facsimile function.

The image processing apparatus <NUM> includes an image reading device <NUM> as a reading apparats or an image reading apparatus, an automatic document feeder (ADF) <NUM>, and an image forming device <NUM>. The image forming device <NUM> is disposed in a lower portion of the image processing apparatus <NUM>. In <FIG>, the image forming device <NUM> without an external cover is illustrated to describe an internal configuration of the image forming device <NUM>.

The ADF <NUM> is a document supporting device that feeds a document the image of which is to be read to a reading position. The ADF <NUM> automatically conveys the document placed on a tray to the reading position. The image reading device <NUM> reads the document conveyed by the ADF <NUM> in a predetermined reading position. On an upper surface of the image reading device <NUM>, an exposure glass <NUM> as a document supporter on which a document is to be placed is disposed. The image reading device <NUM> reads the document on the exposure glass <NUM> in the reading position. Particularly, the image reading device <NUM> is a scanner including a light source, an optical system, and an image sensor such as a charge-coupled device (CCD) to read reflected light from a document illuminated by the light source by using the image sensor via the optical system.

The image forming device <NUM> prints the document image read by the image reading device <NUM>. The image forming device <NUM> includes a bypass roller <NUM> that is used if a recording sheet is manually fed, and a recording sheet supplier <NUM> that supplies a recording sheet. The recording sheet supplier <NUM> has a mechanism for supplying recording sheets from a plurality of sheet cassettes 107a. The supplied recording sheet is fed to a secondary transfer belt <NUM> via a registration roller <NUM>.

A transfer device <NUM> transfers a toner image on an intermediate transfer belt <NUM> to the recording sheet to be conveyed on the secondary transfer belt <NUM>.

The image forming device <NUM> includes an optical writing device <NUM>, a tandem image formation device <NUM> (for yellow (Y), magenta (M), cyan (C), and black (K)), the intermediate transfer belt <NUM>, and the secondary transfer belt <NUM>. An image written by the optical writing device <NUM> is formed as a toner image on the intermediate transfer belt <NUM> by an image forming process performed by the image formation device <NUM>.

Particularly, the image formation device <NUM> (for Y, M, C, and K) includes four rotatable photoconductor drums (Y, M, C, and K). An image formation element <NUM> including a charging roller, a developing device, a primary transfer roller, a cleaner, and a discharger is disposed around each of the photoconductor drums. The image formation elements <NUM> function at the respective photoconductor drums, so that images on the photoconductor drums are transferred to the intermediate transfer belt <NUM> by the respective primary transfer rollers.

The intermediate transfer belt <NUM> is disposed in nips between the photoconductor drums and the respective primary transfer rollers and extends across a drive roller and a driven roller. With movement of the intermediate transfer belt <NUM>, a toner image primarily transferred to the intermediate transfer belt <NUM> is secondarily transferred to a recording sheet on the secondary transfer belt <NUM> by a secondary transfer device. Such a recording sheet is conveyed to a fixing device <NUM> by movement of the secondary transfer belt <NUM>, and the toner image is fixed as a color image on the recording sheet. Subsequently, the recording sheet is ejected to an ejection tray disposed outside the image forming device <NUM>. If duplex printing is performed, a front surface and a back surface of the recording sheet are reversed by a reverse device <NUM> and the reversed recording sheet is fed to the secondary transfer belt <NUM>.

The invention has been described using a case in which the image forming device <NUM> employing the electrophotographic method forms an image as described above. However, the present embodiment is not limited to the electrophotographic image forming device. An image forming device employing an inkjet method can form an image.

Next, the image reading device <NUM> is described.

<FIG> is a sectional view illustrating an example of a structure of the image reading device <NUM>. As illustrated in <FIG>, the image reading device <NUM> includes a sensor board <NUM> with an image sensor <NUM> as an image capturing element, a lens device <NUM>, a first carriage <NUM>, and a second carriage <NUM> that are arranged in a body <NUM>. The image sensor <NUM> is, for example, a CCD image sensor or a complementary metal-oxide-semiconductor (CMOS) image sensor. The first carriage <NUM> includes a light source <NUM> that is a light emitting diode (LED), and a mirror <NUM>. The light source <NUM> includes mirrors <NUM> and <NUM>. In addition, the exposure glass <NUM> and a reference white board <NUM> are arranged on the upper surface of the image reading device <NUM>.

In a reading operation, the image reading device <NUM> emits light upward from the light source <NUM> while moving the first carriage <NUM> and the second carriage <NUM> in a sub-scanning direction (a direction indicated by an arrow A shown in <FIG>) from standby positions (home positions). Then, the first carriage <NUM> and the second carriage <NUM> cause reflected light from a document <NUM> to form an image on the image sensor <NUM> via the lens device <NUM>.

Moreover, the image reading device <NUM> reads reflected light from the reference white board <NUM> to set a reference, for example, when the power is turned on. That is, the image reading device <NUM> moves the first carriage <NUM> to a location immediately below the reference white board <NUM>, and turns on the light source <NUM> to cause reflected light from the reference white board <NUM> to form an image on the image sensor <NUM>, thereby performing gain adjustment.

<FIG> is a block diagram illustrating an electric connection of each component of the image reading device <NUM>. As illustrated in <FIG>, the image reading device <NUM> includes a reader <NUM>, an image processor <NUM>, a controller <NUM> as control circuitry, and a light source driver <NUM>.

The reader <NUM> includes the image sensor <NUM> and the light source <NUM> including visible component light and NIR component light that is invisible component light. The reader <NUM> irradiates a document with the visible component light and the NIR component light.

The light source driver <NUM> drives the light source <NUM>.

The image sensor <NUM> acquires a visible invisible mixture image (a visible NIR mixture image) including a visible component and a NIR component (an invisible component), and a NIR image (an invisible image) including a NIR component based on reflected light from the document, and outputs the acquired images to the image processor <NUM> disposed in the following stage. In visible image reading, the image sensor <NUM> outputs red, green, and blue (RGB) signals. In invisible image reading, the image sensor <NUM> outputs a NIR signal. A general image sensor includes a color filter characterized in that NIR light is transmitted through the color filter. Hence, in invisible image reading, the NIR signal appears in each of RGB outputs (NIRr, NIRg, and NIRb).

In the present embodiment, an example in which a NIR image is used as an invisible image is described. However, an ultraviolet image can be used as an invisible image, and a wavelength region to be used for the invisible image is not particularly limited to any one region.

The controller <NUM> controls each of the light source driver <NUM>, the image sensor <NUM>, and the image processor <NUM>.

The image processor <NUM> includes a black subtracter <NUM>, a line-to-line corrector <NUM>, a NIR component remover <NUM>, and a shading corrector <NUM>.

The black subtracter <NUM> performs black level correction on a visible NIR mixture image and a NIR image output from the image sensor <NUM>.

The line-to-line corrector <NUM> performs a line-to-line correction process by which physical displacement of a line of the image sensor <NUM> is corrected.

The NIR component remover <NUM> functioning as an invisible component remover removes a NIR component (an invisible component) from a visible NIR mixture image (a visible invisible mixture image) to generate a visible image that does not include the NIR component. A detailed description of the NIR component remover <NUM> will be given below.

The shading corrector <NUM> functioning as an image corrector performs shading correction on each of the NIR image and the visible image with the NIR component removed. In the shading correction, a reading level of a white background plate is maintained for each main scanning pixel, and document read data is standardized at the reading level of the white background plate, so that fluctuations in reading level in a main scanning direction are removed.

The NIR component remover <NUM> is described in detail.

<FIG> is a block diagram illustrating a configuration of the NIR component remover <NUM>. As illustrated in <FIG>, the NIR component remover <NUM> receives the visible NIR mixture image and the NIR image acquired by the image sensor <NUM>. The NIR component remover <NUM> includes a noise reducer <NUM> and a removal calculator <NUM>.

The noise reducer <NUM> performs a noise reduction process on each of the visible NIR mixture image and the NIR image which have been input.

The removal calculator <NUM> uses the visible NIR mixture image and the NIR image which have undergone the noise reduction to remove a NIR component from the visible NIR mixture image.

Examples of removal calculation equations to be used by the removal calculator <NUM> are as follows. <MAT> <MAT> <MAT>.

In the equations, where Rin, Gin, and Bin are image signals that have been input to the removal calculator <NUM>.

The image signals (Rin, Gin, and Bin) represent images in which visible components and NIR components are mixed. The removal calculator <NUM> subtracts NIR signals from the input image signals (Rin, Gin, and Bin) to output images having only visible components. Moreover, the removal calculator <NUM> multiplies a NIR signal by different coefficients Kr, Kg, and Kb on a channel basis. Such multiplication corrects a difference of the NIR components for each channel due to characteristics of the color filter disposed in the image sensor <NUM>.

Generally, addition and subtraction of images each having noise superimposes noise. That is, a root-sum-square value of noise amount σ1 of a visible NIR mixture image to be input and a noise amount σ2 of a NIR image to be input is a noise amount σ3 of a visible image to be output.

The noise amount of the visible image to be output by such calculation is greater than a noise amount of a visible image including only a visible component optically acquired by an element such as an infrared cut filter.

In the present embodiment, the noise reducer <NUM> disposed in a stage preceding the removal calculator <NUM> reduces noise prior to removal of the NIR component. Such noise reduction lowers noise amounts σ1 and σ2 beforehand, and thus a noise amount σ3 of an output visible image can be lowered. Accordingly, the noise reduction process prior to the removal calculation enables the removal calculator <NUM> to perform NIR component removal calculation on the noise-reduced image. Therefore, noise influence can be reduced, and output image quality can be maintained.

Next, a noise reduction method performed by the noise reducer <NUM> is described.

First, an example in which a linear filter is used as a noise reduction method is described.

<FIG> are diagrams each illustrating a noise reduction process using a linear filter. The linear filter represents a filter such as an averaging filter as illustrated in <FIG> and a smoothing filter as illustrated in each of <FIG>. The linear filter assigns weights to peripheral pixel values with respect to a target pixel, and performs convolution calculation.

As for the smoothing filter, filter strength can vary depending on a coefficient setting. However, the filter coefficient does not vary depending on a pixel position or a pixel value, and the same weighting calculation is performed on the entire area. Since a complicated process is not necessary, the use of the smoothing filter enables a noise reduction process to be performed with small circuit scale.

Accordingly, the noise reducer <NUM> executes a filter process using a linear filter. Thus, noise can be reduced by a simple process and roughness degradation can be prevented.

Next, an example in which a non-linear filter is used as a noise reduction method is described.

<FIG> is a diagram illustrating a noise reduction process using a non-linear filter. Herein, an epsilon filter is described as an example. The epsilon filter is expressed by Equation <NUM>. An output y (n) is a value determined by adding a value determined from a coefficient ak and a non-linear function F to an input x (n).

In the non-linear function F illustrated in <FIG>, x (n - K) - x (n) is a difference between an input pixel value and a value of a pixel that is a certain distance away from an input pixel, and the difference is used as an input. If an absolute value of the difference is greater than the epsilon, a value "<NUM>" is set. If the absolute value of the difference is smaller than the epsilon, a value of such a difference is repeated in the function. That is, since a pixel having a large pixel value is excluded from a weighting calculation target, the epsilon filter can serve as a smoothing filter by which noise can be reduced without edge degradation.

The non-linear filter is not limited to the epsilon filter. A non-linear filter such as a bilateral filter can be used for noise reduction.

Accordingly, the noise reducer <NUM> performs a filter process using a non-linear filter to perform a noise reduction process in a state in which an edge is preserved, thereby preventing roughness degradation while reducing degradation in resolving power.

Next, an effect of noise reduction prior to removal calculation performed by the removal calculator <NUM> is described.

<FIG> and <FIG> are diagrams illustrating a noise reduction effect if noise reduction is performed prior to removal calculation. Each of <FIG> and <FIG> illustrates a change in a reading value acquired by reading an image having a certain pixel value.

<FIG> illustrates a reading value and a removal calculation result if only removal calculation is executed. In <FIG>, a thick line represents data having an average reading value of <NUM> on the assumption that visible NIR mixture reading is performed, and a thin line represents data having an average reading value of <NUM> on the assumption that NIR reading is performed. In <FIG>, a dotted line represents a result of removal calculation based on a visible NIR mixture image and a NIR image.

As illustrated in <FIG>, since read data has a noise component, a reading value is not constant and fluctuates depending on a position. As illustrated in the removal calculation result in such a state in which noise is added, a reading value can be zero or less depending on a position. In a state in which a bit width is held constant, since a reading value of zero or less is clipped, a reading value is greater on average than a pixel value to be originally used. Consequently, color reproduction is degraded.

<FIG> illustrates a reading value and a removal calculation result if noise reduction is performed prior to removal calculation. As illustrated in <FIG>, if noise is reduced prior to removal calculation, fluctuations in the reading values are reduced, and the number of pixels to be clipped is reduced. Hence, a NIR component can be removed with color reproduction having higher accuracy without addition of a bit of negative expression.

On the other hand, smoothing filters (linear filters) as illustrated in <FIG> may be used with different strength for a visible NIR mixture image and a NIR image, or an epsilon filter (a non-linear filter) in which a process is changed for each pixel as described in Equation <NUM> may be used. In such a case, since each of a NIR component in the visible NIR mixture image and a NIR component in the NIR image changes, removal calculation by coefficient calculation is not enough to remove an appropriate NIR component from the visible NIR mixture image. In such a case, thus, a process to be performed by the removal calculator <NUM> needs to be switched in a complicated manner such that a filter characteristic in the noise reducer <NUM> in a stage preceding the removal calculator <NUM> is absorbed.

Accordingly, in the present embodiment, the noise reducer <NUM> preferably uses linear filters having same strength for a visible NIR mixture image and a NIR image at noise reduction. The use of such filters enables a NIR component to be appropriately removed from the visible NIR mixture image even if a process to be performed by the removal calculator <NUM> is simplified.

Hence, the use of linear filters having the same strength for a visible NIR mixture image and a NIR image can prevent inconsistency of invisible components included in the visible NIR mixture image and the NIR image at removal calculation.

Next, determination of noise reduction strength in the noise reducer <NUM> is described.

<FIG> is a diagram illustrating determination of noise reduction strength based on a component ratio of visible components to NIR components. In <FIG>, a change in signal to noise (S/N) ratio of each image with respect to a mixture ratio of visible components to NIR components is illustrated. In <FIG>, a thin solid line indicates a change in S/N ratio of a NIR image, and a thick solid line indicates a change in S/N ratio of a visible image that is acquired by removing a NIR component from a visible NIR mixture image by using a NIR image. A dotted line indicates a change in S/N ratio of a visible image.

As illustrated in <FIG>, if a ratio of the NIR component is increased, a NIR signal level increases and the S/N ratio increases. If a ratio of the NIR component is increased, the S/N ratio decreases since visible components are reduced. In addition, removal of the NIR component degrades the S/N ratio (a larger decrease than a decreases in the S/N ratio if only visible components are acquired).

Accordingly, an S/N ratio subsequent to visible image generation can be estimated from a mixture ratio of visible components to NIR components. Thus, a change in noise reduction strength based on the mixture ratio can simply adjust the S/N ratio to a target S/N ratio.

According to the present embodiment, when an invisible component included in a visible image is to be removed, an increase in noise to be generated at the removal of the invisible component can be prevented, and image quality degradation can be prevented or reduced.

According to the present embodiment, moreover, execution of a noise reduction process prior to a removal calculation process can prevent or reduce a computing error at the time of removal calculation.

The second embodiment differs from the first embodiment in that a noise reducer <NUM> is disposed in a stage following a removal calculator <NUM>. The first embodiment has been described using an example in which a noise reduction process is performed prior to the process performed by the removal calculator <NUM>. However, a noise reduction process can be performed on an output visible image from the removal calculator <NUM> to reduce a noise amount α3 of the output visible image. Hereinafter, components and configurations that differ from components and configurations of the first embodiment will be described, and description of like components will be omitted.

<FIG> is a block diagram illustrating an electric connection of each component of an image reading device <NUM> according to the second embodiment. As illustrated in <FIG>, the image reading device <NUM> includes a reader <NUM> and an image processor <NUM>.

Unlike the NIR component remover <NUM> described in the first embodiment, the NIR component remover <NUM> of the present embodiment includes the noise reducer <NUM> in a stage following the removal calculator <NUM>. That is, the NIR component remover <NUM> first performs removal calculation in the removal calculator <NUM> by using a NIR image and a visible NIR mixture image that are output from the line-to-line corrector <NUM> as inputs. Then, the NIR component remover <NUM> performs a noise reduction process in the noise reducer <NUM> on the visible image and the NIR image output from the removal calculator <NUM>. Such a configuration can enhance image quality of the NIR image originally having a small signal level while enhancing image quality of the visible image on which noise has been superimposed by the removal calculation.

In addition, a relation between a NIR component included in the visible NIR mixture image and a NIR component included in the NIR image needs to be clear (preferably match each other) to remove the NIR component from the visible NIR mixture image with good accuracy.

In a case where noise reduction is performed prior to the removal calculation as described in the first embodiment, a relation between the noise reduction and the removal calculation may be affected depending on a noise reduction method. However, if noise reduction is performed subsequent to removal calculation, any noise reduction method can be applied as the noise reduction is performed on an image that has undergone the removal calculation.

Moreover, since a non-linear filter as described in Equation <NUM> can be aggressively used so that the accuracy of the NIR component removal calculation is not affected by a noise reduction method, noise can be reduced while degradation in sharpness of characters and lines can be being prevented or reduced. Hence, image quality can be more enhanced.

According to the present embodiment, a noise reduction process is performed subsequent to the process performed by the removal calculator <NUM>, and thus various noise reduction methods can be applied without consideration of influence on the removal calculation process.

According to the present embodiment, moreover, the use of a non-linear filter in a process subsequent to the process performed by the removal calculator <NUM> can not only maintain resolving power but also prevent roughness degradation due to noise without consideration of influence on the removal calculation.

<FIG> is a block diagram illustrating a modification of the image reading device <NUM>. As illustrated in <FIG>, the NIR component remover <NUM> can limit noise reduction to be performed by the noise reducer <NUM> in a stage following the removal calculator <NUM> to a visible image. In a NIR image, since noise is not degraded by removal calculation, a noise reduction process may be unnecessary if the NIR image has adequate quality for a usage scene. Such a configuration can reduce circuit scale for the noise reduction process.

The third embodiment differs from the first and second embodiments in that an offsetter <NUM> that performs an offset process for providing an offset amount to a visible NIR mixture image is disposed. Hereinafter, components and configurations that differ from components and configurations of the first and second embodiments will be described, and description of like components will be omitted.

<FIG> is a block diagram illustrating a configuration of a NIR component remover <NUM> according to the third embodiment. As illustrated in <FIG>, the NIR component remover <NUM> receives a visible NIR mixture image and a NIR image acquired by an image sensor <NUM>.

As described in <FIG> and <FIG>, read data includes a noise component. If NIR removal calculation is performed on a visible NIR mixture image without noise reduction, a value of zero or less is clipped. Such a situation may degrade color reproduction.

In the present embodiment, the NIR component remover <NUM> includes the offsetter <NUM> and an offset remover <NUM> in addition to a noise reducer <NUM> and a removal calculator <NUM>.

The offsetter <NUM> provides an offset amount to a visible NIR mixture image.

The offset remover <NUM> removes the offset amount provided by the offsetter <NUM> subsequent to removal calculation and noise reduction.

Next, a description is given of a noise reduction effect if an offset amount is proved prior to a process performed by the removal calculator <NUM>.

<FIG>, and <FIG> are diagrams illustrating a noise reduction effect if an offset amount is provided prior to removal calculation. Each of <FIG>, and <FIG> illustrates a change in a reading value acquired by reading an image having a certain pixel value.

<FIG> illustrates a reading value and a removal calculation result if only removal calculation is performed, and <FIG> is substantially the same as <FIG>. Since each of a visible NIR mixture image and a NIR image is data having noise, a pixel level has a positive value on average. However, a pixel having a value of zero or less is present subsequent to removal calculation. Each of such pixels is clipped to zero unless a bit with is expanded.

<FIG> illustrates a reading value and a removal calculation result if an offset value is provided prior to removal calculation. As illustrated in <FIG>, the offsetter <NUM> provides an offset amount to only a visible NIR mixture image to offset data to be a removal calculation source, so that a value subsequent to the removal calculation can be prevented from being zero or less.

<FIG> illustrates an example in which an offset amount is removed after noise reduction is performed on data subsequent to removal calculation. As illustrated in <FIG>, an offset amount is provided by the offsetter <NUM> and then removal calculation is performed. In addition, after noise reduction, the offset amount is removed by the offset remover <NUM>. Thus, a value of zero or less can be prevented.

Accordingly, even if the noise reducer <NUM> performs the noise reduction using a non-linear filter subsequent to the removal calculation, the number of pixels to be clipped at zero is reduced, and a NIR component can be removed with color reproduction having higher accuracy without addition of a bit of negative expression.

Next, determination of an offset amount by the offsetter <NUM> is described.

<FIG> are diagrams illustrating noise reduction effects that are respectively exerted if noise is high and noise is low. <FIG> illustrates a case where noise is high, and <FIG> is substantially the same as <FIG>. <FIG> illustrates a case where noise is low.

As illustrated in <FIG>, fluctuations in reading values of both the visible NIR mixture image and the NIR image are greater where noise is high in <FIG> than where noise is low in <FIG>. Moreover, since noise is higher in <FIG>, the number of values that are zero or less or the number of positions that are zero or less subsequent to the removal calculation is greater.

Accordingly, an offset amount to be provided in the visible NIR mixture image reading illustrated in <FIG> needs to be greater than an offset amount to be provided in the visible NIR mixture image reading illustrated in <FIG>. On the other hand, if noise is low as illustrated in <FIG>, an offset amount to be provided by the offsetter <NUM> is desirably small. A reading value that may be zero or less becomes color close to zero.

The greater the offset amount, the lower the possibility of zero clipping in a pixel having a reading value close to zero. However, an overflow may occur in a larger reading value. In the present embodiment, the offsetter <NUM> sets an offset amount to an appropriate value according to an amount of noise of the image reading device <NUM>, so that a suitable value can be set to the image reading device <NUM>.

According to the present embodiment, execution of an offset process can reduce a calculation error that occurs when the removal calculator <NUM> performs removal calculation. Moreover, the use of a suitable offset amount can prevent an overflow in a larger reading value.

The fourth embodiment differs from the first through third embodiments in that noise reduction is performed subsequent to image correction (e.g., subsequent to shading correction). Hereinafter, components and configurations that differ from components and configurations of the first thorough third embodiments will be described, and description of like components will be omitted.

<FIG> is a block diagram illustrating an electric connection of each component of an image reading device <NUM> according to the fourth embodiment. As illustrated in <FIG>, the image reading device <NUM> includes a reader <NUM> and an image processor <NUM>.

The image processor <NUM> includes a black subtracter <NUM>, a line-to-line corrector <NUM>, a NIR component remover <NUM>, and a shading corrector <NUM>. In the present embodiment, shading correction is described as image correction. However, the image correction is not limited to the shading correction.

Unlike the NIR component remover <NUM> described in each of the first through third embodiments, the NIR component remover <NUM> of the present embodiment includes a removal calculator <NUM> and a noise reducer <NUM> that are respectively arranged in stages preceding and following the shading corrector <NUM>.

As described above in the first embodiment, in the shading correction, a reading level of a white background plate is maintained for each main scanning pixel, and document read data is standardized at the reading level of the white background plate, so that fluctuations in the reading levels in a main scanning direction are removed. Consequently, in each main scanning position, in a case where a relation between the reading level of the white background plate and the reading level of the document surface collapses, the correction cannot be appropriately performed.

On the other hand, if noise reduction using a non-liner filer by the noise reducer <NUM> is used, a process to be performed changes (a pixel to be referred changes) depending on an image characteristic. Consequently, a relation between a reading level of a white background plate and a reading level of a document surface may change.

To prevent influence of such a change, in the present embodiment, shading correction is performed on data that has undergone removal calculation in the removal calculator <NUM>, and noise reduction is performed by the noise reducer <NUM> subsequent to the shading correction. With such a configuration, fluctuations in reading levels in a main scanning direction due to the shading correction can be appropriately corrected, and a high quality image without reading density unevenness can be provided.

According to the present embodiment, noise reduction is performed subsequent to image correction (e.g., shading correction). Therefore, an image change in a main scanning direction due to the noise reduction can prevented, and the image correction (e.g., shading correction) can be appropriately performed.

The fifth embodiment differs from the first through fourth embodiments in that a noise reducer <NUM> is disposed in each of stages preceding and following a removal calculator <NUM>. Hereinafter, components and configurations that differ from components and configurations of the first through fourth embodiments will be described, and description of like components will be omitted.

<FIG> is a block diagram illustrating a configuration of a NIR component remover <NUM> according to the fifth embodiment. As illustrated in <FIG>, the NIR component remover <NUM> receives a visible NIR mixture image and a NIR image acquired by an image sensor <NUM>.

The NIR component remover <NUM> of the present embodiment includes a first noise reducer 225a, a removal calculator <NUM>, and a second noise reducer 225b. That is, the NIR component remover <NUM> includes two noise reducers respectively disposed in stages preceding and following the removal calculator <NUM>.

The first noise reducer 225a uses a linear filter to perform a noise reduction process on the visible NIR mixture image and the NIR image, which have been received.

The removal calculator <NUM> uses the output data from the first noise reducer 225a to perform a removal calculation process by which a NIR component is removed from the visible NIR mixture image.

The second noise reducer 225b uses a non-linear filter to perform a noise reduction process on the data subsequent to the removal calculation process. The second noise reducer 225b may or may not perform a noise reduction process on a NIR image.

The NIR component remover <NUM> of the present embodiment removes a certain amount of noise by using a linear filter in the first noise reducer 225a prior to removal calculation. Accordingly, even if an offset process is not performed on a visible NIR mixture image, the NIR component remover <NUM> of the present embodiment can reduce degradation in color reproduction due to zero clipping at the removal calculation as described in <FIG>, <FIG>, and <FIG>.

Moreover, the NIR component remover <NUM> of the present embodiment performs a noise reduction process using a non-linear filter in the second noise reducer 225b subsequent to the removal calculation. Such noise reduction can further reduce noise while preventing resolution degradation, and thus quality of an image to be output in a following stage can be enhanced.

According to the present embodiment, therefore, even if an offset process is not performed, a noise reduction process in the first noise reducer 225a can reduce an error that occurs at removal calculation, and a noise reduction process in the second noise reducer 225b by using a filter that prevents resolving power degradation can reduce roughness degradation.

<FIG> is a block diagram illustrating a modification of the image reading device <NUM>. As illustrated in <FIG>, the NIR component remover <NUM> can include the second noise reducer 225b in a stage following the shading corrector <NUM>.

Accordingly, the noise reduction by the second noise reducer 225b is performed subsequent to the shading correction. Such a configuration enables the shading correction to be appropriately performed. More particularly, fluctuations in reading levels in a main scanning direction due to the shading correction can be appropriately corrected, and a high quality image without reading density unevenness can be provided.

The sixth embodiment differs from the first through fifth embodiments in that noise reduction is switched. Hereinafter, components and configurations that differ from components and configurations of the first through fifth embodiments will be described, and description of like components will be omitted.

<FIG> is a block diagram illustrating an electric connection of each component of an image reading device <NUM> according to the sixth embodiment. As illustrated in <FIG>, the image reading device <NUM> includes a reader <NUM>, an image processor <NUM>, a setting receiving unit <NUM>, and an operation control unit <NUM>. The setting receiving unit <NUM> and the operation control unit <NUM> are included in a controller <NUM>.

The setting receiving unit <NUM> outputs mode information that is set by a user via an operation device such as an operation panel to the operation control unit <NUM>.

The operation control unit <NUM> controls operations of the reader <NUM> and the image processor <NUM> according to the mode information which has been set in the setting receiving unit <NUM>. More particularly, the operation control unit <NUM> controls lighting of a light source <NUM> and/or the noise reducer <NUM> and the removal calculator <NUM> of the NIR component remover <NUM> to switch operations according to the mode information set in the setting receiving unit <NUM>.

<FIG> is a diagram illustrating examples of operation control based on mode settings. As illustrated in <FIG>, for example, if a user sets a scan operation for scanning a simple document (e.g., a character document or a photograph document), only a visible light source is operated to acquire an image of the document (the character document or the photograph document). In such a case, operation of the NIR component remover <NUM> is not necessary.

On the other hand, if the user sets a scan operation for scanning a character document and an invisible latent image included in the character document, the visible light source and a NIR light source are simultaneously operated to acquire both of visible and invisible images. In such a case, since removal of a NIR component is necessary, not only removal calculation is set to ON but also noise reduction is set to ON to reduce image quality degradation due to noise degradation at removal calculation.

Herein, an increase in noise reduction strength may lower resolution. In the character document scanning, resolving power is more concerned than image quality degradation due to roughness caused by noise. Thus, although the noise reduction is performed, strength of the noise reduction is desirably suppressed.

Moreover, if the user sets a scanning operation for scanning a photograph document and an invisible latent image included in the photograph document, the visible light source and the NIR light source are simultaneously operated to acquire both of visible and invisible images. In such a case, since removal of a NIR component is necessary, removal calculation is set to ON. In addition, noise reduction is set to ON to reduce image quality degradation caused by noise degradation in the removal calculation.

In the photograph document scanning, since image quality degradation due to roughness is more concerned than resolving power and prevention of the image quality degradation is necessary, strength of the noise reduction is desirably set to a certain extent.

Moreover, image quality can be affected by an infrared component excited from a visible light source or a very small amount of an infrared component in the visible light source depending on a specific target object such as a phosphor. In such a case, since the infrared component needs to be removed, only the visible light source is turned on and removal calculation and noise reduction are set to ON.

According to the present embodiment, the control is switched according to a setting made by a user, so that a suitable process can be performed on a document to output the document with image quality desired by the user.

The present embodiment can employ a combination of control methods other than the combination illustrated in <FIG>. For example, a related-art visible light source including a NIR component may be used. In such a case, even if only the visible light is turned on, NIR component removal can be set to ON, and thus image quality can be enhanced.

<FIG> is a diagram illustrating one example of a hardware configuration including a hard disk drive (HDD) <NUM>, a central processing unit (CPU) <NUM>, and a memory <NUM>. The HDD <NUM> as a carrier medium can store, for example, program code. The CPU <NUM> or a computer reads the program code stored in the HDD <NUM> to load the program code into the memory <NUM>, and controls the image processor <NUM> based on the program code.

Each of the above embodiments has been described using an example in which an image forming apparatus as an image processing apparatus is a multifunctional peripheral having at least two of a copy function, a printer function, a scanner function and a facsimile function. However, each of the above embodiments can be applied to any image forming apparatus such as a copier, a printer, a scanner, and a facsimile device.

Claim 1:
An image processing apparatus (<NUM>) being an electrophotographic or inkjet image forming apparatus having at least two of a copy function, a printer function, a scanner function and a facsimile function, comprising:
a light source (<NUM>) configured to emit visible component light and invisible component light to a target object;
an image sensor (<NUM>) configured to receive reflected light from the target object to detect a visible invisible mixture image including an invisible component and a visible component and an invisible image including an invisible component; and
an invisible component remover (<NUM>), based on the visible invisible mixture image and the invisible image which have been detected, configured to remove the invisible component from the visible invisible mixture image to generate a visible image,
the invisible component remover including:
a removal calculator (<NUM>) configured to perform a removal calculation process of an invisible component with respect to the visible invisible mixture image by subtracting near infrared signals from the visible invisible mixture image to output an image having only a visible component; and
a noise reducer (<NUM>) configured to perform a noise reduction process on at least one of an image to be input to the removal calculator and an image to be output from the removal calculator.