JP2015035668A - Image processing device and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a time required for the detection of blank paper with the prevention or reduction of incorrect blank paper detection.SOLUTION: A resolution converter unit 24, on receiving image data generated by scanning a manuscript according to scan resolution, converts the resolution of the image data to resolution lower than the scan resolution. From the image data after the resolution is converted, a blank paper detector unit 26 detects the number of pixels having a preset concentration or greater, to detect blank paper on the basis of the magnitude relationship between the detected number of pixels and the threshold of the number of pixels. The blank paper detector 26 changes the threshold of the number of pixels according to scan resolution, to detect blank paper.

Description

  The present invention relates to an image processing apparatus and a program.

  A technique is known in which image data is generated by scanning a document, and a blank document is detected based on the image data.

  Patent Document 1 discloses an apparatus that detects a blank sheet based on an information amount of a document read by scanning.

  Patent Document 2 discloses an apparatus that detects the amount of black pixels in image data generated by scanning a document and detects a document whose black pixel amount exceeds a threshold value as a blank sheet.

JP-A-4-68757 JP-A-2-123870

  By the way, as a method of performing blank sheet detection, there are a method using hardware and a method using software. By detecting the number of black pixels in the document using hardware and detecting a blank sheet based on the detection result, a blank sheet is detected at high speed, but a dedicated circuit must be used. On the other hand, by detecting the volume of image data by software processing and detecting a blank page based on the capacity, a blank page is detected at high speed even by software processing, but a blank page is detected by the data volume. Therefore, there is a problem that the accuracy of blank sheet detection is lowered. Also, by detecting a blank page based on the number of black pixels detected by software processing, a blank page can be detected more accurately than when data capacity is used. However, as the resolution of image data increases, blank page detection is performed. There is a problem that it takes a long time.

  An object of the present invention is to shorten the time required for blank sheet detection while preventing or reducing blank sheet false detection.

  According to a first aspect of the present invention, there is provided resolution conversion means for receiving image data generated by scanning an original according to a scan resolution and converting the resolution of the image data to a resolution lower than the scan resolution. Blank sheet detecting means for detecting a blank sheet based on the magnitude relationship between the number of pixels detected from the image data after resolution conversion based on the comparison result with the density value and the pixel number threshold corresponding to the scan resolution; And the blank sheet detecting means detects the blank sheet by changing the pixel number threshold according to the scan resolution.

  According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the blank sheet detecting unit detects the blank sheet by changing the pixel number threshold in accordance with a resolution conversion rate.

  The invention according to claim 3 is the image processing apparatus according to claim 2, wherein the blank sheet detecting unit detects the blank sheet by decreasing the pixel number threshold as the resolution before conversion is higher. is there.

  In the invention according to claim 4, the resolution conversion unit maintains the resolution of the image data as a blank sheet detection resolution without converting the resolution when the scan resolution is equal to or lower than a preset resolution threshold, When the scan resolution exceeds the resolution threshold, the resolution of the image data is converted to the blank detection resolution, and the pixel number threshold when the resolution is converted is smaller than the pixel number threshold when the resolution is not converted. The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus.

  The invention according to claim 5 further includes a non-blank sheet detecting unit that detects a non-blank sheet based on the information amount of the image data before resolution conversion, and the non-blank sheet detecting unit detects that the original is a non-blank sheet. 5. The image processing apparatus according to claim 1, wherein, if not, the resolution conversion unit performs resolution conversion, and the blank page detection unit performs blank page detection. 6. It is.

  According to a sixth aspect of the present invention, the blank sheet detecting means detects the number of pixels having a density equal to or higher than a preset density for each line, and detects a blank sheet based on a magnitude relationship between the number of pixels for each line and the pixel number threshold. The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus.

  According to a seventh aspect of the invention, a computer receives image data generated by scanning an original according to a scan resolution, and converts the resolution of the image data to a resolution lower than the scan resolution; and the scan A step of changing the pixel number threshold according to the resolution; the number of pixels detected from the image data after resolution conversion based on a comparison result with a preset density value; and the pixel number threshold according to the scan resolution; And a step of detecting a blank sheet on the basis of the magnitude relationship of.

  According to the inventions according to claims 1 and 7, false detection of blank paper is prevented or reduced compared with the case where the pixel number threshold is not changed according to the scan resolution, and compared with the case where the resolution is not converted, Time required for blank sheet detection is shortened.

  According to the second aspect of the present invention, compared with the case where the pixel number threshold is not changed according to the resolution conversion rate, erroneous detection of blank paper is prevented or reduced.

  According to the third aspect of the present invention, even when the number of pixels having a density equal to or higher than a preset value changes according to the resolution conversion rate, erroneous detection of blank paper is prevented or reduced.

  According to the fourth aspect of the present invention, compared to the case where the pixel number threshold is not changed between the case where the resolution is converted and the case where the resolution is not converted, erroneous detection of blank paper is prevented or reduced.

  According to the fifth aspect of the present invention, the time required for blank page detection is shortened compared to a case where non-blank pages are not detected based on the information amount of the image data.

  According to the sixth aspect of the present invention, compared with the case where the number of pixels is not detected for each line, the time required for blank sheet detection is shortened.

1 is a block diagram illustrating an example of an image forming system according to an embodiment. It is a flowchart which shows an example of a primary detection process. It is a flowchart which shows an example of a secondary detection process.

  FIG. 1 shows an example of an image forming system according to an embodiment of the present invention. The image forming system according to the embodiment includes an image forming apparatus 10 and an image processing apparatus 20.

  The image forming apparatus 10 includes an image reading unit 12. The image reading unit 12 generates electronic image data by scanning an image on a document according to a preset scan resolution. As the scan resolution, for example, a resolution of 200 dpi, 300 dpi, 400 dpi, 600 dpi, or the like can be selected. However, the present invention is not limited to this example, and a resolution higher than 600 dpi may be selected as the scan resolution. Further, the image reading unit 12 may convert the format of the image data into an arbitrary format such as JPEG format.

  In addition to the function of the image reading unit 12, the image forming apparatus 10 has a function of transferring image data obtained by scanning to an external device via a communication path such as a network, a print function of printing received data, At least one of an image forming function such as a copy function for copying the image on a sheet and a facsimile function for facsimile transmission of the image. However, the present invention is not limited to these, and a scanner or the like that does not have a print function is also included in the category of the image forming apparatus 10.

  The image processing apparatus 20 includes a non-blank sheet detection unit 22, a resolution conversion unit 24, a blank sheet detection unit 26, a threshold value determination unit 28, and an output unit 30, and forms image data generated by scanning. A blank document is detected based on the image data acquired from the apparatus 10.

  The non-blank sheet detection unit 22 detects a non-blank document that is not a blank sheet, based on the data capacity of the image data generated by scanning. For example, the non-blank sheet detection unit 22 detects a document having image data whose data volume exceeds a preset data capacity threshold as a non-blank sheet.

  The resolution conversion unit 24 receives image data of a document that has not been detected by the non-blank sheet detection unit 22 (image data of a document that has not been determined to be non-blank), and changes the resolution (scan resolution) of the image data to another value. Convert to resolution. For example, if the scan resolution of the image data exceeds a preset resolution threshold, the resolution conversion unit 24 converts the resolution of the image data to a resolution lower than the scan resolution. On the other hand, when the scan resolution of the image data is equal to or less than the resolution threshold, the resolution conversion unit 24 maintains the scan resolution of the image data without performing resolution conversion. Any known technique may be employed as a method for converting the resolution. As an example, the resolution conversion unit 24 reduces the resolution of the image data by thinning out the pixels of the image data according to a preset condition.

  For example, the resolution conversion unit 24 converts the scan resolution to a preset resolution (blank paper detection resolution: internal processing resolution). Specifically, when the resolution threshold and the blank paper detection resolution are set to 200 dpi, the resolution conversion unit 24 sets the resolution of the image data with the scan resolution of 300 dpi, 400 dpi, and 600 dpi to 200 dpi (blank paper detection resolution). Convert. On the other hand, the resolution conversion unit 24 maintains 200 dpi (blank blank detection resolution) without converting the resolution of image data with a scan resolution of 200 dpi. Note that the resolution threshold and the blank page detection resolution may be changed to arbitrary values by the user or the like. For example, a value such as 300 dpi may be used as the resolution threshold or the blank page detection resolution, or the resolution threshold and the blank page detection resolution may be set to different values.

  As another example, the resolution conversion unit 24 may reduce the resolution of the image data according to a preset conversion rate. For example, the resolution conversion unit 24 may reduce the resolution of the image data to a resolution such as 1/2 or 1/4. Specifically, the resolution conversion unit 24 converts the resolution of image data with a scan resolution of 300 dpi to, for example, half of 150 dpi, converts the resolution of 400 dpi image data to 200 dpi, and converts the resolution of 600 dpi image data to 300 dpi. Convert to In this case, the resolution after the half conversion corresponds to the blank page detection resolution.

  The blank sheet detection unit 26 receives the image data from the resolution conversion unit 24, and the number of pixels that are greater than (or larger than) a preset density (tone value) from the image data, or a preset density. The number of pixels less than (or less than) (tone value) is detected, and a blank document is detected based on the number of pixels. For example, the blank sheet detection unit 26 binarizes the image data, counts the number of black pixels, determines that the document of the image data whose black pixel number is equal to or less than the black pixel number threshold Nth is a blank sheet, and the number of black pixels is black pixels A document having image data exceeding the threshold value Nth is determined as a non-blank sheet. Note that the blank page detection unit 26 counts the number of white pixels, determines an image data document in which the number of white pixels is equal to or greater than the white pixel number threshold as a blank page, and image data in which the number of white pixels is less than the white pixel number threshold. May be determined as non-blank paper.

  In the present embodiment, the blank page detection unit 26 performs blank page detection by changing the black pixel number threshold Nth in accordance with the scan resolution of the image data. That is, even if the resolutions after the resolution conversion are the same, if the scan resolutions are different, the blank page detection unit 26 performs blank page detection by changing the black pixel number threshold Nth. For example, the blank page detection unit 26 performs blank page detection by changing the black pixel number threshold Nth in accordance with the resolution conversion rate (thinning rate). As an example, the blank sheet detection unit 26 performs blank sheet detection by decreasing the black pixel number threshold Nth as the resolution before conversion is higher.

  The threshold value determination unit 28 determines the black pixel number threshold value Nth. In the present embodiment, the threshold value determination unit 28 changes the black pixel number threshold value Nth according to the scan resolution of the image data.

  For example, a black pixel number threshold Nth for each scan resolution for a predetermined image size is stored in a storage unit (not shown). The black pixel number threshold Nth for each scan resolution may be set for each color mode such as the black and white mode, the gray mode, and the full color mode. As an example, the black pixel number threshold Nth of each scan resolution such as 200 dpi, 300 dpi, 400 dpi, and 600 dpi for the A4 size is determined in advance for each color mode and stored in a storage unit (not shown). As an example, “500” is set as the black pixel number threshold Nth for A4 size 200 dpi in the full color mode.

  Here, the black pixel number threshold Nth for each scan resolution will be described. The reading parameters of the image reading unit 12 differ depending on the scanning resolution. For example, the image data obtained by scanning at 400 dpi may be thinner than the image data obtained by scanning at 200 dpi. Therefore, image data obtained by binarization by scanning an original at 400 dpi has four times as many black pixels as image data obtained by binarization by scanning the original at 200 dpi. The number of black pixels is less than four times. Therefore, when performing blank page detection after scanning at 400 dpi and converting to 200 dpi, blank page detection is performed using the same threshold value as the black pixel number threshold Nth used when scanning at 200 dpi and performing blank page detection. An error occurs in the blank sheet detection result of the document belonging to the boundary of blank sheet / non-blank sheet. In other words, if only the 200 dpi black pixel number threshold Nth is used as the black pixel number threshold Nth just because the scan resolution is converted to blank paper detection resolution (for example, 200 dpi), the scan resolution depends on the resolution at the time of scanning. Therefore, an error (variation) occurs in the blank sheet detection result of the document belonging to the boundary of blank sheet / non-blank sheet. Therefore, in the present embodiment, when blank page detection is performed on the same document, blank page detection is performed using a black pixel number threshold Nth that is different for each scan resolution so that the detection results match regardless of the scan resolution.

  For example, when the blank paper detection resolution is set to 200 dpi, a smaller value is used for the black pixel number threshold Nth for the scan resolution of 400 dpi than for the black pixel number threshold Nth for the scan resolution of 200 dpi. As described above, when scanning at 400 dpi, the image may be thinner than when scanning at 200 dpi. Therefore, when the resolution of the image data obtained by 400 dpi scan is converted to 200 dpi and binarized, pixels classified as black pixels in 200 dpi scan are classified as white pixels in 400 dpi scan, and the same document However, the number of black pixels may be smaller in the 400 dpi scan than in the 200 dpi scan. Therefore, if the same black pixel count threshold Nth is used for 200 dpi scanning and 400 dpi scanning, even if it is determined to be non-blank in 200 dpi scanning, it is determined to be blank if the resolution is converted to 200 dpi by performing 400 dpi scanning. May be. Therefore, by making the black pixel count threshold Nth for 400 dpi scan smaller than the black pixel count threshold Nth for 200 dpi scan, even if an original that is determined to be non-blank in 200 dpi scan has a black pixel count reduced by 400 dpi scan, 400 dpi. In the scan, it is determined that the sheet is not blank and is not blank. The black pixel number threshold Nth for each scan resolution is determined according to the characteristics of the image reading unit 12 (characteristics of an optical device, an image sensor, etc.). For example, the black pixel number threshold value Nth may be determined through experiments or the like so that the blank paper detection results match even when the scan resolution is changed.

  Here, an example of the black pixel number threshold Nth will be described. As an example, the image size is A3 size. For example, the black pixel number threshold Nth for image data with a scan resolution of 200 dpi is set to “700”. Further, the black pixel number threshold Nth for the image data having the scan resolution of 300 dpi and the resolution converted to 150 dpi is set to “300”. Further, the black pixel number threshold Nth for the image data having the scan resolution of 400 dpi and the resolution converted to 200 dpi is set to “630”. Further, the black pixel number threshold Nth for the image data whose scan resolution is 600 dpi and whose resolution is converted to 300 dpi is set to “1330”. As described above, the black pixel number threshold Nth is set according to the conversion rate of the scan resolution. For example, comparing the black pixel number threshold Nth when the scan resolution is 200 dpi and the black pixel number threshold Nth when the scan resolution is 400 dpi, even if the converted resolution is the same (200 dpi), the scan resolution is The black pixel number threshold Nth “630” at 400 dpi is smaller than the black pixel number threshold Nth “700” when the scan resolution is 200 dpi.

  The output unit 30 outputs image data. The output unit 30 may output the image data to the image forming apparatus 10 or may output it to an external device via a communication path such as a network. For example, the output unit 30 associates blank page attribute information indicating blank paper with image data of a document determined to be blank. As an example, when a document composed of a plurality of pages is scanned by the image reading unit 12 and image data of each page is generated, blank page detection is performed for each page, and the output unit 30 is a blank page. The blank page attribute information is associated with the image data of the page determined to be.

  Next, detailed processing of the image processing apparatus 20 will be described with reference to the flowcharts shown in FIGS. In the present embodiment, as an example, the non-blank detection unit 22 performs primary detection processing (rough detection processing), and the blank paper detection unit 26 performs secondary detection processing (detail detection processing). First, the primary detection process by the non-blank sheet detection unit 22 will be described with reference to FIG. In the primary detection process, a non-blank document is detected based on the data capacity of the image data.

  First, the image reading unit 12 generates image data of the original by scanning an image on the original according to the set scan resolution. The non-blank sheet detection unit 22 acquires image data from the image forming apparatus 10 and obtains the data capacity of the image data (S01). Further, the non-blank sheet detection unit 22 acquires size information indicating the size (width and height) of the image data (S02), and acquires color mode information indicating the color mode (S03). For example, the non-blank sheet detection unit 22 may acquire the size information and the color mode information from the attribute information (meta information) of the image data or may be acquired from the image forming apparatus 10.

  The non-blank paper detection unit 22 calculates the unit data capacity S by dividing the data capacity of the image data by the size (width × height) (S04). When the unit data capacity S exceeds the preset unit data capacity threshold value Sth (S05, Yes), the non-blank sheet detection unit 22 detects the document of the unit data capacity S as a non-blank sheet (S06). On the other hand, when the unit data capacity S is equal to or less than the data capacity threshold value Sth (S05, No), the processing shifts to secondary detection processing by the blank paper detection unit 26 (S07). For example, the unit data capacity threshold Sth is set in the non-blank sheet detection unit 22 for each scan mode, and the non-blank sheet detection unit 22 detects the non-blank sheet by changing the unit data capacity threshold Sth for each scan mode. The unit data capacity threshold Sth is a value for detecting a document that is clearly non-blank. Therefore, a value sufficiently larger than the value assumed as the unit data capacity of blank image data is used as the unit data capacity threshold Sth so that a document that is clearly non-blank is detected. As an example, the unit data capacity threshold Sth in the full color mode is a value such as 0.5. As a result, the non-blank document detecting unit 22 detects a non-blank document original that is not a blank document that belongs to the blank / non-blank boundary and is not known whether or not it is blank. Since the unit data capacity threshold value Sth is set as described above, an image data document whose unit data capacity S is equal to or less than the unit data capacity threshold value Sth is an original document with an unknown whether or not it is a blank sheet, and may be a blank sheet. For example, it may be non-blank. Therefore, a blank sheet is detected by the secondary detection process by the blank sheet detection unit 26. The unit data capacity threshold Sth may be changed to an arbitrary value by the user or the like.

  As another example, the non-blank detection unit 22 may detect a document whose image data capacity exceeds the data capacity threshold as non-blank, without obtaining the unit data capacity S. The data capacity threshold used at this time is a value for detecting a document with a clear non-blank sheet. Therefore, a value sufficiently larger than the value assumed as the data capacity of blank image data is used as the data capacity threshold so that a document that is clearly non-blank is detected. To explain with a specific example, when a JPEG format image data is generated by scanning an A3 size document at a scanning resolution of 600 dpi, the data capacity of the image data is about 1 MB if the document is a blank sheet. Assuming that, a value sufficiently larger than 1 Mbytes (for example, about 3 Mbytes) is used as the data capacity threshold, so that an original document that is clearly non-white paper is not an original that is unclear whether it is blank or not. It is detected by the non-blank paper detection unit 22. Specifically, a document with image data having a data capacity exceeding 3 Mbytes is determined to be non-blank, and a document with image data having a data capacity of 3 Mbytes or less is not determined to be non-blank. Since the document of the image data whose data capacity is equal to or less than the data capacity threshold is a document with unknown whether or not it is blank, the blank sheet is detected by the secondary detection process by the blank sheet detection unit 26. The data capacity threshold may be changed to an arbitrary value by the user or the like.

  As described above, when image data of a document that is clearly non-blank is detected by the non-blank paper detection unit 22, the image data of the document is excluded from the target of the secondary detection process.

  Next, with reference to FIG. 3, the secondary detection process (detailed detection process) by the blank paper detection unit 26 will be described. In the secondary detection process, image data of a document that has not been detected as non-blank in the primary detection process is targeted, and a blank sheet is detected based on the number of black pixels in the image data.

  First, the resolution conversion unit 24 receives image data of a document that has not been determined as non-blank by the non-blank detection unit 22 from the non-blank detection unit 22, and specifies the scan resolution when the document is scanned (S10). ). For example, the resolution conversion unit 24 specifies the scan resolution by referring to the attribute information of the image data.

  If the scan resolution exceeds the resolution threshold (S11, No), the resolution conversion unit 24 converts the resolution of the image data to a resolution lower than the scan resolution (blank blank detection resolution) (S12). On the other hand, when the scan resolution is equal to or lower than the resolution threshold (S11, Yes), the resolution conversion unit 24 maintains the scan resolution of the image data without performing resolution conversion (S13). In this case, the maintained resolution corresponds to the blank sheet detection resolution. As an example, it is assumed that the resolution threshold and the blank page detection resolution are set to 200 dpi. At this time, if the scan resolution is 200 dpi, the resolution conversion unit 24 maintains the resolution without performing resolution conversion. On the other hand, when the scan resolution is 400 dpi, the resolution conversion unit 24 converts the resolution to 200 dpi.

  The threshold value determination unit 28 determines the black pixel number threshold value Nth (S14). The threshold value determination unit 28 outputs a black pixel number threshold value Nth corresponding to the scan resolution (resolution before resolution conversion) of the image data to the blank sheet detection unit 26.

  The threshold value determination unit 28 also sets the black pixel number threshold value for the image data that is the target of blank page detection based on the scan resolution, the black pixel number threshold value Nth for the A4 size, and the image size (width × height). Nth is obtained. For example, the threshold value determination unit 28 calculates a ratio between the image size of the blank sheet detection target and the A4 size, and multiplies the A4 size black pixel number threshold Nth by the ratio, thereby obtaining a black pixel for the image data of the blank sheet detection target. The number threshold Nth is obtained.

As an example, the threshold value determination unit 28 obtains the black pixel number threshold value Nth for the image data to be detected as blank paper according to the following equation. Here, an image to be detected as a blank sheet is assumed to be an image X. The ratio (Ratio) of the size of the image X to the A4 size is defined by the following equation (1), and the black pixel number threshold Nth (x) is defined by the following equation (2).
Ratio = size of image X (width × height) ÷ (width of A4 size × height with the same scanning resolution as image X) Equation (1)
Nth (x) = threshold number of black pixels Nth × Raito for A4 size having the same scan resolution as that of image X (2)

  For example, when the size of the image X is A3 size and the scan resolution is 200 dpi, the threshold value determination unit 28 divides the A3 size (width × height) by the A4 size (width × height) whose scan resolution is 200 dpi. Thus, the ratio (Ratio) is obtained. Then, the threshold value determination unit 28 obtains the black pixel number threshold value Nth (x) for the image X by adding the ratio (Ratio) to the black pixel number threshold value Nth for the A4 size with a scan resolution of 200 dpi. To explain with a specific example, when “500” is preset as the black pixel number threshold Nth for A4 size 200 dpi in the full color mode, the black pixel number threshold Nth for A3 size 200 dpi in the full color mode is an example. , “1000 (= 500 × 2)”.

  Note that the black pixel number threshold value Nth for each scan resolution for each size may be determined in advance for each color mode and stored in a storage unit (not shown). In this case, the threshold value determination unit 28 outputs the black pixel number threshold value Nth stored in the storage unit to the blank paper detection unit 26 without performing the calculation based on the above formulas (1) and (2). .

  For example, when image data with an original size of A3 and scan resolution of 200 dpi is the target of blank page detection processing, the threshold value determination unit 28 sets the 200 dpi black pixel number threshold value Nth (for example, 700) for the A3 size to blank page. It outputs to the detection part 26. On the other hand, when image data with an original size of A3 and scan resolution of 400 dpi is the target of blank page detection processing, the threshold value determination unit 28 sets the 400 dpi black pixel number threshold value Nth (for example, 630) for the A3 size to blank page. It outputs to the detection part 26.

  Next, processing of the blank paper detection unit 26 will be described. The blank paper detection unit 26 binarizes the image data (S15). For example, when the gradation of the image data is defined by a value of 0 to 255 and the binarization threshold is set to 55, the blank sheet detection unit 26 determines that a pixel having a gradation value of 55 or more is a black pixel (gradation). Value 255), and a pixel having a gradation value less than 55 is converted into a white pixel (gradation value 0). Then, the blank sheet detection unit 26 executes a frame erasing process and further removes noise (S16). In the frame erasing process, the blank sheet detection unit 26 removes data within a preset range (for example, 2 mm) from the upper and lower and left and right edges of the image, for example. In the noise removal process, the blank paper detection unit 26 removes, for example, an isolated black pixel that does not have a black pixel around it, and converts the black pixel into a white pixel. Note that the frame removal process and the noise removal process may not be executed.

  Then, the blank sheet detection unit 26 counts the number of black pixels N in the image data for each line (S17), and when the number of black pixels N exceeds the black pixel number threshold Nth (S18, Yes), the original of the image data Is detected as a non-white paper (S19). In this case, the process ends.

  On the other hand, when the black pixel number N is equal to or less than the black pixel number threshold Nth (S18, No) and the black pixel number N is not counted for the entire surface of the image data (S20, No), the blank sheet detection unit 26 performs the next line. The number N of black pixels is counted (S17). When the black pixel number N exceeds the black pixel number threshold Nth (S18, Yes), the blank sheet detection unit 26 detects the document as a non-blank sheet (S19). Thereby, the process ends. On the other hand, when the black pixel number N is equal to or less than the black pixel number threshold Nth (S18, No), the processes of steps S17, S18, and S20 are performed until the blank sheet detection process is performed on the entire image data.

  When the number of black pixels N is counted over the entire surface of the image data (S20, Yes), that is, when the number of black pixels N in all lines is equal to or less than the black pixel number threshold Nth, the blank sheet detecting unit 26 reads the document. Is detected as white paper (S21).

  As described above, the blank page detection unit 26 performs blank page detection for each line of the image data, and ends the blank page detection process when the black pixel count N exceeds the black pixel count threshold Nth.

  To explain with a specific example, when the scan resolution is 200 dpi, the blank sheet detection unit 26 detects a blank sheet based on a black pixel number threshold Nth (for example, 700) for 200 dpi. On the other hand, when the scan resolution is 400 dpi, the blank page detection unit 26 detects a blank page based on a black pixel count threshold Nth (for example, 630) for 400 dpi.

  As described above, the scan resolution is converted to a lower resolution, and the number of pixels to be counted is reduced by detecting blank paper based on the number of black pixels in the image data after the resolution conversion. Thus, the time required for blank sheet detection is shortened. Further, when the resolution is converted, the blank pixel is detected by changing the black pixel number threshold Nth according to the scan resolution, and compared with the case where the black pixel number threshold Nth is not changed according to the scan resolution. In addition to preventing or reducing detection, when blank paper is detected for the same document, variations in detection results due to scan resolution are suppressed.

  Also, by performing blank page detection for each line, compared with the case of blank page detection after counting the number of black pixels on the entire surface of the image data, the time required for blank page detection is greater when the document is non-blank. Shortened. Note that the blank sheet detection unit 26 may perform blank sheet detection by counting the number of black pixels on the entire surface of the image data without performing blank sheet detection for each line.

  Further, the primary detection process is performed by the non-blank detection unit 22 to detect a document that is clearly non-blank, and the original is excluded from the target of the secondary detection process by the blank detection unit 26. The number of image data (number of documents) to be processed by the unit 26 is reduced. As a result, the time required for the secondary detection process is shortened. Since the non-white paper detection unit 22 detects non-white paper based on the data capacity of the image data, the time required for the primary detection processing is shorter than the time required for the secondary detection processing. Therefore, the total processing time of the processing time of the non-blank paper detection unit 22 and the processing time of the blank paper detection unit 26 is shorter than the time required for the blank paper detection unit 26 to process all image data (all originals). . On the other hand, since the blank sheet detection unit 26 detects a blank sheet based on the number of black pixels of the image data, the blank sheet is detected more accurately than the non-blank sheet detection unit 22 detects a blank sheet based on the data capacity. Further, since only the document that is clearly non-white paper is detected by the non-white paper detection unit 22, the document that belongs to the white / non-white paper boundary is not detected to be white or non-white paper. Therefore, a non-white paper detection error by the non-white paper detection unit 22 is prevented or reduced. As described above, by executing the primary detection process and the secondary detection process, erroneous detection of blank paper is prevented or reduced as compared with the case where only the primary detection process is performed, and the secondary detection process. Compared with the case where only the blanking is performed, the time required for blank sheet detection is shortened.

  In this embodiment, since blank page detection is performed by software processing, it is not necessary to use a dedicated circuit.

  In the above embodiment, the case where the primary detection process is performed by the non-blank sheet detection unit 22 and then the secondary detection detection process is performed by the blank sheet detection unit 26 has been described. However, the primary detection process by the non-blank sheet detection unit 22 is performed. Instead, the blank page detection unit 26 may perform blank page detection. In this case, the blank page detection unit 26 performs blank page detection for image data whose data volume is equal to or less than the data volume threshold, and performs blank page detection for image data whose data volume is larger than the data volume threshold. It will be. Therefore, compared with the case where the primary detection process and the secondary detection process are combined, the time required for blank sheet detection becomes longer. However, even in such a case, since the blank page detection unit 26 performs blank page detection by changing the black pixel number threshold Nth according to the scan resolution, the black pixel number threshold Nth is not changed according to the scan resolution. Compared to the above, not only the detection error of the blank page is prevented or reduced, but also the detection result variation due to the scanning resolution is suppressed when the blank page is detected for the same document.

  Note that the image processing apparatus 20 is realized by cooperation of hardware resources and software, for example. Specifically, the image processing apparatus 20 includes a processor such as a CPU (not shown). When the processor reads and executes a program stored in a storage device (not shown), the functions of the non-blank sheet detection unit 22, the resolution conversion unit 24, the blank sheet detection unit 26, the threshold value determination unit 28, and the output unit 30 are performed. Realized. The program is stored in the storage device via a storage medium such as a CD or DVD, or via communication means such as a network.

  DESCRIPTION OF SYMBOLS 10 Image forming apparatus, 12 Image reading part, 20 Image processing apparatus, 22 Non-blank sheet detection part, 24 Resolution conversion part, 26 Blank sheet detection part, 28 Threshold determination part, 30 Output part

Invention receives the image information generated by reading more reading resolution document, the resolution of the image information, and conversion means you lower rather conversion than the reading resolution, the converting means according to claim 1 comparison based on the result, the number of pixels the pixel is preset density value or higher in the image information after the resolution conversion between the density value and the preset concentration values of the pixels constituting the converted image information by detects said the detected number of pixels, based on the image prime threshold magnitude relation has a white paper detection means for detecting a blank, wherein the blank detecting means, the higher than first reading resolution In the image processing apparatus, when the original is read at two reading resolutions, a blank sheet is detected using a pixel number threshold smaller than the pixel number threshold at the first reading resolution .

The invention according to claim 2 receives image information generated by reading a document at a reading resolution, and converts the resolution of the image information to be lower than the reading resolution, and the conversion means converts the image information resolution. Based on the comparison result between the density value of each pixel constituting the image information and a preset density value, the number of pixels that are equal to or less than the preset density value in the image information after resolution conversion is detected, Blank sheet detecting means for detecting a blank sheet on the basis of the magnitude relationship between the detected number of pixels and a pixel number threshold, wherein the blank sheet detecting means has a second reading resolution higher than the first reading resolution. In the image processing apparatus, when the original is read, a blank sheet is detected by using a pixel number threshold larger than a pixel number threshold at the first reading resolution .

The invention according to claim 3, before Symbol conversion means, if the reading resolution is equal to or smaller than a preset resolution threshold, keeping the resolution of the image information without converting the resolution as blank detection resolution, When the reading resolution exceeds the resolution threshold, the resolution of the image information is converted to the blank paper detection resolution, and the pixel number threshold when the resolution is converted is smaller than the pixel number threshold when the resolution is not converted, The image processing apparatus according to claim 1 or 2, wherein the image processing apparatus is configured as described above.

The invention according to claim 4, wherein the blank detecting means, wherein performs the comparison and the number of pixels detected with the preset density value in units of lines, number of pixels per line and each line of pixels threshold detecting a blank on the basis of the magnitude relation, it is an image processing apparatus according to any one of claims 1 to 3, characterized in.

The invention according to claim 5, the computer receives the image information generated by reading more reading resolution document, the resolution of the image information, comprising the steps of low rather conversion than the reading resolution, is the conversion was based on a comparison result of a preset density value and density value of each pixel constituting the image information, and detects the number of pixels the at preset density value or higher in the image information after the resolution conversion , based on the the number of pixels that have been detected, the image prime threshold magnitude relation, the steps of detecting the blank, is executed, in the step of detecting the blank, the second reading is higher than the first reading resolution resolution When the original is read, the program detects a blank sheet using a pixel number threshold smaller than the pixel number threshold at the first reading resolution .
According to a sixth aspect of the present invention, a computer receives image information generated by reading a document at a reading resolution, and converts the resolution of the image information to be lower than the reading resolution; Based on the comparison result between the density value of each pixel constituting the image information and a preset density value, the number of pixels that are equal to or less than the preset density value in the image information after resolution conversion is detected. A step of detecting a blank sheet based on a magnitude relationship between the detected number of pixels and a pixel number threshold, and the step of detecting the blank sheet includes a second reading resolution higher than the first reading resolution. When the original is read, the program detects a blank sheet using a pixel number threshold larger than the pixel number threshold at the first reading resolution.

According to the first, second, fifth , and sixth inventions, compared to the case where the pixel number threshold is not changed according to the reading resolution, false detection of blank paper is prevented or reduced, and the resolution is not converted. In comparison, the time required for blank sheet detection is shortened.

Further, preset concentration values or the number of pixels, or a preset density value less than the number of pixels is, even if vary depending on the reading resolution, blank erroneous detection is prevented or reduced The

According to the third aspect of the invention, erroneous detection of blank paper is prevented or reduced compared to the case where the pixel number threshold is not changed between when the resolution is converted and when the resolution is not converted.

According to the fourth aspect of the present invention, compared with the case where the number of pixels is not detected for each line, the time required for blank sheet detection is shortened.

Claims (7)

Resolution conversion means for receiving image data generated by scanning a document according to a scan resolution and converting the resolution of the image data to a resolution lower than the scan resolution;
Blank page detection that detects blank pages based on the magnitude relationship between the number of pixels detected from the image data after resolution conversion based on a comparison result with a preset density value and the pixel number threshold corresponding to the scan resolution Means,
Have
The blank sheet detecting means detects a blank sheet by changing the pixel number threshold according to the scan resolution.
An image processing apparatus. The blank sheet detecting means detects the blank sheet by changing the pixel number threshold according to the resolution conversion rate.
The image processing apparatus according to claim 1. The blank sheet detecting means detects the blank sheet by decreasing the pixel number threshold as the resolution before conversion is higher.
The image processing apparatus according to claim 2. The resolution conversion unit maintains the resolution of the image data as a blank page detection resolution without converting the resolution when the scan resolution is equal to or lower than a preset resolution threshold, and the scan resolution exceeds the resolution threshold. In this case, the resolution of the image data is converted to the blank paper detection resolution,
The pixel number threshold when the resolution is converted is smaller than the pixel number threshold when the resolution is not converted,
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. A non-blank sheet detecting means for detecting a non-blank sheet based on the information amount of the image data before resolution conversion;
If the non-blank sheet detecting means does not detect that the document is non-blank, the resolution converting means performs resolution conversion, and the blank sheet detecting means executes blank sheet detection.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. The blank sheet detection means detects the number of pixels having a density equal to or higher than a preset density for each line, and detects blank sheets based on the magnitude relationship between the number of pixels for each line and the pixel number threshold.
The image processing apparatus according to claim 1, wherein the image processing apparatus is an image processing apparatus. On the computer,
Receiving image data generated by scanning a document according to a scan resolution, and converting the resolution of the image data to a resolution lower than the scan resolution;
Changing the pixel number threshold according to the scan resolution;
A step of detecting a blank sheet based on a magnitude relationship between the number of pixels detected from the image data after resolution conversion based on a comparison result with a preset density value and the pixel number threshold corresponding to the scan resolution. When,
A program characterized by having executed.

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