JP6501125B2 - Image reading apparatus, image reading method, image forming apparatus, and image reading program - Google Patents

Description

  The present invention relates to an image reading apparatus, an image reading method, an image forming apparatus, and an image reading program.

  Equipped with an ACS (Auto Color Selection) function that automatically identifies when the document is read, even if the user does not specify whether the document is a color document or a monochrome document each time copying or scanning is performed Color MFPs are becoming popular. On the other hand, with the spread of automatic document feeders (ADFs), there are increasing cases in which a large number of documents are read at once by fixing the optical scanning system and transporting the document on the optical scanning system. However, the automatic document feeder (ADF) may adversely affect the correction of the gap between the lines of the CCD line sensor depending on the place (the place where the jitter occurs) where the paper feed speed becomes unstable. Therefore, the use of the ADF causes color misregistration between R, G, and B, and causes black pixels to be erroneously recognized as color pixels. Jitter generally occurs when a document enters a roller for transporting a document, or when a document leaves the roller.

  For such a problem, for example, Patent Document 1 focuses on the mechanism of the automatic document feeder, manages the sub-scanning direction position at which color shift occurs due to the occurrence of jitter in the document image, and determines the ACS function. Threshold is changed to suppress false positives. On the other hand, for example, according to Patent Document 2, the ACS function is not operated at a position in the sub-scanning direction in which color misregistration occurs due to the occurrence of jitter in the document image.

Unexamined-Japanese-Patent No. 2003-298859 gazette Unexamined-Japanese-Patent No. 2005-80101

  However, the technique of Patent Document 1 is not an essential solution for solving the decrease in the determination accuracy caused by the color misregistration, although the erroneous recognition can be reduced by the fluctuation of the threshold value of the ACS function. On the other hand, in the technique of Patent Document 2, when a color image is present at a position in the sub-scanning direction at which color misregistration occurs, erroneous recognition in which color misregistration occurs is inevitable.

  The present invention has been made in view of such a situation, and it is an object of the present invention to provide a technique for suppressing misrecognition due to color misregistration in the determination of the ACS function.

  The image reading apparatus according to the present invention has an automatic sheet feeding unit for feeding a document, and three detection units for respectively detecting three colors, and the document is scanned by the sheet feeding to scan the document on the document An image reading unit for obtaining an image as a combination of the three colors, a normal area in which color shift due to fluctuation of the scanning speed is relatively difficult to occur, and a color shift area relatively prone to the color shift When the area dividing unit for dividing the acquired image into a plurality of colored pixels and the number of chromatic color pixels larger than a first threshold value preset in the normal area are detected, the document is at least partially When it is determined that the document is a chromatic color document having a chromatic color area and a number of chromatic color pixels equal to or less than the first threshold value are detected in the normal area, a second preset in the color misregistration area Number of colors below the threshold And a document color determination unit that determines that the document is an achromatic document that does not have the chromatic color region, and the document color determination unit determines that the color difference region has more than the second threshold in the color shift region. When a large number of intrinsic color pixels are detected in the color misregistration area in the color misregistration area, it is determined that the document is a chromatic color original. When the number of true color pixels equal to or less than the third threshold is detected, it is determined that the document is the achromatic document, and the true color pixels are pixels of any of the three colors and the three colors. It is a pixel which excluded the pixel of the specific color containing the pixel of any color of the complementary color of the above from the pixel of the chromatic color.

  According to the image forming method of the present invention, the original is scanned by the sheet feeding using the automatic sheet feeding step of feeding the original and the three detection units respectively detecting three colors, and the original is scanned on the original An image reading process for acquiring an image as a combination of the three colors, a normal area in which color shift due to fluctuation of the scanning speed is relatively difficult to occur, and a color shift area relatively prone to the color shift And the document is at least partially formed when a region dividing step of dividing the acquired image into a plurality of pixels having a larger number of chromatic colors than the first threshold preset in the normal region is detected. When it is determined that the document is a chromatic color document having a chromatic color area and a number of chromatic color pixels equal to or less than the first threshold value are detected in the normal area, a second preset in the color misregistration area Below the threshold And a document color determination step of determining that the document is an achromatic document having no chromatic region, and the document color determination step includes the step of: If a large number of intrinsic color pixels are detected in the color misregistration area when a plurality of intrinsic color pixels are detected in the color misregistration area, the chromatic color original is detected. And determining the number of true color pixels equal to or less than the third threshold value, determining the achromatic document as the achromatic document, wherein the true color pixels are of any of the three colors. It is a pixel which excluded the pixel of the specific color containing a pixel and a pixel of a color of any of the three colors' complementary colors from the pixel of the chromatic color.

  The present invention provides an image forming program for controlling an image reading apparatus having an automatic sheet feeding unit for feeding a document. The image forming program includes three detection units that respectively detect three colors, and an image reading unit that scans the document by the paper feeding and acquires an image on the document as a combination of the three colors An area dividing unit for dividing the acquired image into a normal area in which color shift due to fluctuation of the scanning speed is relatively difficult to occur and a color shift area relatively susceptible to the color shift; When a large number of chromatic color pixels are detected in the normal area than the preset first threshold value, it is determined that the document is a chromatic color document having a chromatic color area at least in part. When chromatic pixels equal to or less than the first threshold value are detected in the normal area, chromatic pixels equal to or less than a second threshold value set in advance are detected in the color shift area: Said The image reading apparatus is caused to function as a document color determination unit that determines that the document is an achromatic document that does not have a colored region, and the document color determination unit determines that the number of color misregistration regions is greater than the second threshold. When a pixel of a color is detected, when the number of intrinsic color pixels is detected in the color misregistration area more than the third threshold value set in advance, it is determined that the document is the chromatic color document, and the third threshold value is detected. When the following number of true color pixels are detected, it is determined that the document is the achromatic document, and the true color pixels are pixels of any of the three colors and any of the complementary colors of the three colors. It is a pixel which excluded the pixel of the specific color including the pixel of a color from the pixel of the chromatic color.

  According to the present invention, there is provided a technique for suppressing erroneous recognition due to color shift in the determination of the ACS function.

FIG. 1 is a schematic configuration view showing an entire configuration of an image forming apparatus 1 according to an embodiment of the present invention. It is a flow chart which shows the contents of automatic color judging processing concerning one embodiment. FIG. 6 is an explanatory view showing a normal area and a color shift area of a document image according to an embodiment. It is a flow chart which shows the contents of the color gap analysis processing concerning one embodiment. It is explanatory drawing which shows the chromatic color which arises due to a color shift.

  Hereinafter, modes for carrying out the present invention (hereinafter, referred to as “embodiments”) will be described with reference to the drawings.

  FIG. 1 is a schematic configuration view showing an entire configuration of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 includes a control unit 10, an image analysis unit 20, an image forming unit 30, a storage unit 40, an operation display unit 50, and an image reading unit 100. The image reading unit 100 includes an automatic document feeder (ADF) 160 and a document table 170, reads an image from a document, and generates an image data ID which is digital data. The automatic document feeder 160 is also called an automatic sheet feeder.

  The image forming unit 30 forms and discharges an image on a print medium (not shown) based on the image data ID. When the image forming apparatus 1 is connected to an external terminal device, an image may be formed on a print medium (not shown) and discharged based on the image data ID sent from the external terminal device. it can. The operation display unit 50 receives a user's operation input from a display (not shown) functioning as a touch panel, various buttons and switches (not shown).

  The control unit 10 includes a main storage unit such as a RAM and a ROM, and a control unit such as an MPU (Micro Processing Unit) and a CPU (Central Processing Unit). The control unit 10 also has a controller function related to interfaces such as various I / O, USB (Universal Serial Bus), bus, and other hardware, and controls the entire image forming apparatus 1.

  The storage unit 40 is a storage device including a hard disk drive or a flash memory, which is a non-temporary recording medium, and stores control programs and data of processes executed by the control unit 10 and the image analysis unit 20.

  The image reading unit 100 includes a light source unit 110, a first reflecting mirror 131, a first carriage 120, a second reflecting mirror 135, a third reflecting mirror 136, a second carriage 137, and a condenser lens 138. And an image sensor 141. The first reflecting mirror 131 reflects the reflected light L from the document in the direction of the second reflecting mirror 135. The second reflecting mirror 135 reflects the reflected light L in the direction of the third reflecting mirror 136. The third reflecting mirror 136 reflects the reflected light L in the direction of the focusing lens 138. The condenser lens 138 focuses the reflected light L on the light receiving surface of the image sensor 141.

  The first carriage 120 mounts the light source unit 110 and the first reflecting mirror 131 and reciprocates in the sub scanning direction S. The second carriage 137 mounts the second reflecting mirror 135 and the third reflecting mirror 136 and reciprocates in the sub scanning direction S. The first carriage 120 and the second carriage 137 form a part of a scanning mechanism controlled by the control unit 10, and the light source unit 110 can scan an original in the sub-scanning direction. Thereby, the image sensor 141 outputs an analog electrical signal according to the two-dimensional image on the document placed on the document table 170, and the analog electrical signal is A / D converted to generate the image data ID. . The platen cover 171 is provided to be openable and closable with respect to the upper surface of the document table 170.

  The image sensor 141 has three CCD line sensors (not shown) as three detection units for detecting three colors of R, G, and B, respectively, and scans (sub-scans) the document to scan the document. The upper image is acquired as a combination of voltage values corresponding to R, G, B. In the three CCD line sensors, since there are gaps between the lines in the scanning direction, the timings are shifted to correct the gaps between the R, G, and B lines to match the respective pixels.

  The ADF 160 includes a platen roller 161, a document reading slit 162, a pickup roller 163, a registration roller 164, a sheet discharging roller 165, and a document placement tray 166. The ADF 160 can automatically feed a plurality of originals P set in the original placement tray 166 one sheet at a time.

  When the ADF 160 for automatically transporting a document is used, the first carriage 120 and the second carriage 137 are fixed at a preset sub-scanning position, and scanning (sub-scanning) is performed by automatic feeding of the document. To be done. In this case, since the first carriage 120 is fixed at a preset sub-scanning position, the light source unit 110 mounted on the first carriage 120 is also fixed at a predetermined position (see FIG. 1). ).

  Pickup roller 163 picks up a plurality of documents P set on document placement tray 166 one by one and carries them out to registration roller 164. The registration roller 164 conveys the document to the platen roller 161 at a predetermined timing. The platen roller 161 conveys the document to the discharge roller 165 via a predetermined document reading slit 162. The discharge roller 165 discharges the document P after completion of reading to the outside. As described above, in the ADF 160, reading of a document is performed via the document reading slit 162.

  FIG. 2 is a flowchart showing the contents of the automatic color determination process according to an embodiment. The automatic color determination process is a process of reading an image from a document P and automatically determining whether the image is a chromatic color document or an achromatic color document. The chromatic color original is also referred to as a color original, and is an original having an area of chromatic color at least in part. The achromatic document is also referred to as a monochrome document, and is a document having no chromatic region.

  In step S10, the user executes an original reading process. In the document reading process, the user places the document P on the document placement tray 166 and presses the start button (not shown) of the operation display unit 50. Thus, the control unit 10 activates the ADF 160 of the image reading unit 100 to start reading an image. The image reading unit 100 generates an image data ID and transmits the image data ID to the image analysis unit 20.

  In step S20, the image analysis unit 20 determines the pixel color in the normal area. The normal area is an area in which color misregistration is relatively unlikely to occur. The color misregistration area is an area where color misregistration is relatively likely to occur. The color misregistration occurs in the present embodiment as the paper feed speed of the ADF 160 becomes unstable.

  FIG. 3 is an explanatory view showing a normal area and a color shift area of a document image according to an embodiment. In the color misregistration region R2, the conveyance speed changes when the rear end of the document P leaves the registration roller 164, and the change adversely affects the correction of the gap between the lines of the CCD line sensor (not shown). , R, G, and B are areas where color misregistration tends to occur. The color misregistration area R4 is an area where the transport speed fluctuates when the leading end of the document P rushes into the sheet discharge roller 165, and color misregistration tends to occur between R, G, and B.

  On the other hand, the three normal areas R1, R3 and R5 are areas stably transported by any of the platen roller 161, the registration roller 164 and the sheet discharge roller 165. Therefore, the normal areas R1, R3 and R5 are areas which are relatively less likely to cause color misregistration than the color misregistration areas R2 and R4. The image analysis unit 20 divides the acquired image into a normal area where color shift due to fluctuation of scanning speed (paper feed speed) is relatively hard to occur and a color shift area where color shift is relatively easy to occur. Function as an area division unit.

  In step S30, the image analysis unit 20 counts the number of color pixels in the normal regions R1, R3, and R5. In step S40, when the count number of color pixels is larger than the first threshold A set in advance, the image analysis unit 20 determines that the document is a color document (step S50). When the count number of color pixels is equal to or less than the first threshold A set in advance, the image analysis unit 20 determines that the normal regions R1, R3, and R5 are monochrome regions (step S60). Thus, the image analysis unit 20 also functions as a document color determination unit.

Thus, the image analysis unit 20 can perform the following determination by counting the number of color pixels in the normal regions R1, R3, and R5.
(1) Count number> first threshold A
The document P is a color document having a chromatic color area at least in part.
(2) Count number ≦ first threshold A
The normal areas R1, R3, and R5 of the document P are monochrome areas having no chromatic area.

  In step S70, the image analysis unit 20 determines the pixel color in the color misregistration areas R2 and R4. The color misregistration area is an area where color misregistration is relatively likely to occur as described above. As a result, color pixels are detected. In step S80, the image analysis unit 20 counts the number of color pixels in the color misregistration areas R2 and R4.

  In step S90, if the count number of color pixels is larger than the second threshold B set in advance, the image analysis unit 20 advances the process to the color shift analysis process (step S100). When the count number of color pixels is equal to or less than the second threshold B set in advance, the image analysis unit 20 determines that the color misregistration areas R2 and R4 are monochrome areas. Thereby, the image analysis unit 20 determines that the document P is a monochrome document having no chromatic region, together with the determination that the normal regions R1, R3, and R5 are monochrome regions (step S200).

  FIG. 4 is a flowchart showing the contents of color misregistration analysis processing according to an embodiment. In the color misregistration analysis process, the image analysis unit 20 analyzes whether the pixel determined as a color pixel is a color pixel reflecting the color of the document or a color pixel having a chromatic color due to color misregistration. The inventors of the present invention have found that the color of a pixel that becomes chromatic due to color shift is practically limited to the following specific colors.

  FIG. 5 is an explanatory view showing a chromatic color generated due to a color shift. FIG. 5A shows that the black dot Dk1 is reproduced as a chromatic color due to the color shift. The black dots Dk1 are reproduced by overlapping the red R dots Dr, the green G dots Dg, and the blue B dots Db having the same gradation if there is no color misregistration. In FIG. 5A, the black area K is reproduced in the central portion.

  However, the red R dots Dr and the green G dots Dg are shifted by the shift amount Srg in the paper feeding direction, and the green G dots Dg and the blue B dots Db are shifted by the shift amount Sgb in the paper feeding direction. Therefore, a red pure color area R, a green pure color area G, and a B pure color area B are generated. The pure color area is an area of the color with the highest saturation.

  Furthermore, while the red R dots Dr and the green G dots Dg overlap, as an area not overlapping with the blue pure color area B, a yellow pure color area Y as a complementary blue color is generated. In addition, while the green pure color area G and the blue pure color area B overlap, a cyan pure color area C as a complementary red color is generated as an area not overlapping with the red pure color area R.

  FIG. 5B shows that the black dots Dk2 are reproduced as chromatic colors due to the color misregistration in another order. In FIG. 5 (b), in addition to the chromatic color generated in FIG. 5 (a), a red pure color area R and a blue pure color area B overlap, but as a non-overlapping green color area G. And a magenta pure color area M as a complementary color of green is generated.

  FIG. 5C shows how the black dots Dk3 are reproduced as chromatic colors due to the color deviation in another order. In FIG. 5 (c), the colors reproduced in FIG. 5 (a) and FIG. 5 (b) are reproduced.

  Thus, the inventor of the present application newly finds that the chromatic color generated due to the color misregistration is the color of R, G, B, C, M, Y, and K (also referred to as a specific color), and performs the following analysis. Created a new way.

  In step S110, the image analysis unit 20 analyzes whether the color of the color-determined pixel is any one of R, G, B, C, M, Y, and K, that is, a specific color. The specific color is a pixel within a predetermined gradation value range, that is, the pixel values (R, G, B) are (255, 0, 0), (0, 255, 0), (0, 0, 255) , (0, 255, 255), (255, 0, 255), or (255, 255, 0) (including a preset neighborhood). Note that 255 is the maximum tone value, and 0 is the minimum tone value.

  In step S120, if the pixel value of the color-judged pixel is not within the designated color area (specific color), the image analysis unit 20 is a pixel that is highly likely to have reproduced the chromatic color of the document. It is determined that the pixel is an intrinsic color pixel (step S125). In this way, true color pixels are detected. On the other hand, when the pixel value of the color-judged pixel is within the designated color area (specific color), the image analysis unit 20 proceeds with the process to step S130.

  In step S130, the image analysis unit 20 performs color analysis of surrounding pixels. The peripheral pixels are pixels in the range of (N × M pixels) around the target pixel to be determined. N and M are two or more settable natural numbers. As can be seen from FIG. 5, when a red color pixel (R) is generated due to color misregistration, a complementary color (C) or another detection color (G or B) pixel is generated in the periphery. Become. Therefore, when the pixel of interest is a specific color, the image analysis unit 20 confirms that the pixel of the specific color is generated in a large number around the pixel of interest and that the pixel is a color pixel due to color shift. There is. The peripheral pixels of a specific color are also referred to as specific pixels.

  In step S140, when the count number of the specific pixels is larger than the specific threshold set in advance, the image analysis unit 20 determines that the target pixel is a color pixel due to color shift (step S150). If the count number of the specific pixels is equal to or less than the predetermined threshold value, the image analysis unit 20 determines that the target pixel is an intrinsic color pixel (step S145). In this way, true color pixels are detected.

  The image analysis unit 20 executes the processing of step S110 to step S150 for all of the pixels determined as color pixels in step S70.

  In step S160, the image analysis unit 20 calculates the number of true color pixels. The true color pixel number can be calculated as the sum of the number of pixels determined as true color pixels in step S125 and step S145. The true color pixel number can also be grasped as a value obtained by subtracting the number of color pixels due to color misregistration from the pixels determined to be color pixels in step S70 (see FIG. 2).

  In step S170, the image analysis unit 20 determines that the color misregistration areas R2 and R4 are color areas when the count number of color pixels after subtraction is larger than the third threshold C set in advance. (Step S172). When the count number of color pixels is less than or equal to the third threshold C set in advance, the image analysis unit 20 determines that the color shift areas R2 and R4 are monochrome areas (step S174).

  Accordingly, when it is determined that the color misregistration areas R2 and R4 are color areas, the image analysis unit 20 determines that the document P is a color document (step S50, FIG. 2). On the other hand, when the image analysis unit 20 determines that the color shift regions R2 and R4 are monochrome regions, the document P is present together with the determination that the normal regions R1, R3 and R5 are monochrome regions. It is determined that the original is a monochrome original having no coloring area (step S200, FIG. 2).

  As described above, the image forming apparatus 1 according to the present embodiment can determine whether the document is a color document or a monochrome document by excluding (excludes) pixels caused by color misregistration among color pixels. . Thus, the image forming apparatus 1 can suppress erroneous recognition due to color misregistration in the determination of the ACS function.

  The present invention can be implemented not only in the above embodiment but also in the following modifications.

  Modification 1: The above embodiment analyzes not only the color of the pixel of interest but also the color of the peripheral pixels to determine whether the color pixel is caused by the color shift, but the analysis of the color of the peripheral pixels is not always necessary. Is not a required component. Specifically, in the present invention, for example, the processes of steps S130 to S150 may be omitted. In the present modification, a pixel determined to be an intrinsic color pixel in step S125 is an intrinsic color pixel.

  However, the above embodiment has an advantage that the determination accuracy of the ACS function can be improved in the processes of steps S130 to S150, and the process can be simplified if the processes of steps S130 to S150 are omitted. Has the advantage of being able to

  Modified Example 2 In the above embodiment, the third threshold C is different from the second threshold B, but may be a coincident threshold. The first to third threshold values A, B, and C may be configured to be adjustable for each model or for each individual.

  Variation 3: The above embodiment is described on the assumption of single-sided printing, but the output document may be double-sided printed. In the case of double-sided printing, the color misregistration area and the threshold are set in consideration of the instability of the paper feeding speed by the reversing mechanism.

  Modified Example 4 In the above-described embodiment, the present invention is applied to an image forming apparatus having an image reading function, but the present invention can also be applied to an image reading apparatus.

Reference Signs List 1 image forming apparatus 10 control unit 20 image analysis unit 30 image formation unit 40 storage unit 50 operation display unit 100 image reading unit 110 light source unit 141 image sensor 160 automatic document feeder (ADF)
162 Document reading slit 163 Pickup roller 164 Registration roller 165 Paper discharging roller 166 Document loading tray 170 Document holder 171 Platen cover 161 Platen roller 162 Document reading slit 170 Document holder

Claims (4)

An image reader,
Automatic sheet feeder for feeding the originals,
An image reading unit having three detection units that respectively detect three colors, and scanning the document by the paper feed to obtain an image on the document as a combination of the three colors;
An area dividing unit for dividing the acquired image into a normal area in which color shift due to fluctuation of the scanning speed is relatively hard to occur and a color shift area in which the color shift is relatively easy to occur;
When a large number of chromatic color pixels are detected in the normal area than the preset first threshold value, it is determined that the document is a chromatic color document having a chromatic color area at least in part. When chromatic pixels equal to or less than the first threshold are detected in the normal area, and chromatic pixels equal to or less than the second threshold set in advance are detected in the color shift area A document color determination unit that determines that the document is an achromatic document that does not have the chromatic color area;
Equipped with
When the document color determination unit detects a larger number of chromatic color pixels than the second threshold in the color misregistration area, the number of colors is greater than a third threshold preset in the color misregistration area. It is determined that the original is a chromatic color document when it detects an intrinsic color pixel, and it is determined that it is an achromatic document when it detects a number of intrinsic color pixels less than the third threshold value,
The intrinsic color pixel is a pixel excluding a pixel of a specific color including a pixel of any of the three colors and a pixel of a complementary color of the three colors from the pixels of the chromatic color Oh it is,
The document color determination unit determines whether all the gradation values of the pixel to be determined are in the range preset from the maximum tone value or in the range preset from the minimum tone value. Of pixels within a predetermined gradation value range, and among peripheral pixels that are pixels within a predetermined range around the pixel, the pixels of the predetermined gradation value range An image reading apparatus that determines that the number of pixels whose number is larger than a predetermined specific threshold is a pixel of the specific color . An image forming apparatus,
An image reading apparatus according to claim 1 ;
An image forming unit for forming an image read by the image reading apparatus on a print medium;
An image forming apparatus comprising: An image reading method,
An automatic sheet feeding process for feeding a document,
An image reading step of scanning the original by the paper feeding to obtain an image on the original as a combination of the three colors using three detection units that respectively detect three colors;
An area dividing step of dividing the acquired image into a normal area in which color shift due to fluctuation of the scanning speed is relatively difficult to occur and a color shift area in which the color shift is relatively easy to occur; When a large number of chromatic color pixels are detected in the normal area than the preset first threshold value, it is determined that the document is a chromatic color document having a chromatic color area at least in part. When chromatic pixels equal to or less than the first threshold value are detected in the normal area, chromatic pixels equal to or less than a second threshold value set in advance are detected in the color shift area: An original color determination step of determining that the achromatic original does not have the chromatic color area;
Equipped with
When the document color determination step detects a greater number of chromatic pixels than the second threshold in the color shift area, the number of colors is greater than a third threshold preset in the color shift area. Determining that the document is a chromatic color original when detecting an intrinsic color pixel of the pixel, and determining the achromatic document when detecting a number of the intrinsic color pixels less than the third threshold,
The intrinsic color pixel is a pixel excluding a pixel of a specific color including a pixel of any of the three colors and a pixel of a complementary color of the three colors from the pixels of the chromatic color Oh it is,
In the document color determination step, all of the tone values of the pixels to be determined are either in the range preset from the maximum tone value or in the range preset from the minimum tone value. Of pixels within a predetermined gradation value range, and among peripheral pixels that are pixels within a predetermined range around the pixel, the pixels of the predetermined gradation value range The image reading method which determines that the pixel whose number is larger than the preset specific threshold value is a pixel of the said specific color . An image reading program for controlling an image reading apparatus having an automatic sheet feeding unit for feeding a document .
Three colors comprises three detection unit for detecting each of the image reading unit for scanning the original document in the paper feed obtains the image on the document as a combination of the three colors,
An area dividing unit for dividing the acquired image into a normal area in which color shift due to fluctuation of the scanning speed is relatively difficult to occur and a color shift area in which the color shift is relatively easy to occur; When a large number of chromatic color pixels are detected in the normal area than the preset first threshold value, it is determined that the document is a chromatic color document having a chromatic color area at least in part. When chromatic pixels equal to or less than the first threshold value are detected in the normal area, chromatic pixels equal to or less than a second threshold value set in advance are detected in the color shift area: Causing the image reading apparatus to function as a document color determination unit that determines that the document is an achromatic document that does not have the chromatic color area;
When the document color determination unit detects a larger number of chromatic color pixels than the second threshold in the color misregistration area, the number of colors is greater than a third threshold preset in the color misregistration area. It is determined that the original is a chromatic color document when it detects an intrinsic color pixel, and it is determined that it is an achromatic document when it detects a number of intrinsic color pixels less than the third threshold value,
The intrinsic color pixel is a pixel excluding a pixel of a specific color including a pixel of any of the three colors and a pixel of a complementary color of the three colors from the pixels of the chromatic color Oh it is,
The document color determination unit determines whether all the gradation values of the pixel to be determined are in the range preset from the maximum tone value or in the range preset from the minimum tone value. Of pixels within a predetermined gradation value range, and among peripheral pixels that are pixels within a predetermined range around the pixel, the pixels of the predetermined gradation value range An image reading program that determines that a pixel whose number is greater than a preset specific threshold is a pixel of the specific color .