JP4419700B2 - Image reading device - Google Patents

Description

  The present invention relates to an image reading apparatus including a flat bed scanner (FBS) that reads luminance data of a document placed on a document placing plate, and more specifically, placed on the document placing plate. The present invention relates to an image reading device that detects the size of a document by reading luminance data of the press sheet including the document while the document is pressed against the document placing plate by the press sheet.

  In an image reading apparatus equipped with a so-called flat bed scanner that reads luminance data of a document placed on a transparent document placing plate, for example, in a preliminary scan (pre-scan) before starting the actual reading of the document, By scanning the image about several lines for each main scanning line to detect the document width and detecting the length of the document in the vertical direction by a document detection sensor disposed at a predetermined position, before the reading of the document is started. The document size is detected.

  However, since many image reading apparatuses that detect the document size by the above method are based on the premise that a fixed-size document such as A4 or B4 is loaded, a document other than the fixed-size document is loaded. In some cases, the correct document size cannot be detected. In some cases, the user has to input the document size. Further, even when the original is placed obliquely, the correct original size may not be detected.

  As an apparatus for detecting the document size in consideration of such circumstances, there is an image reading apparatus disclosed in Patent Document 1. As shown in FIG. 11, the image reading apparatus 50 includes a transparent document placing plate 51, and a document cover that presses a document 52 placed on the placing plate 51 from above and closely contacts the document placing plate 51. 53, a light source 54 for irradiating the original 52 with light, a reflection mirror 55 for guiding the reflected light from the original 52 in a predetermined direction, a converging lens 56 for converging the reflected light, a filter 57 for transmitting only the visible light component of the convergent light, A CCD (Charge Coupled Device) 58 for converting the transmitted convergent light into an electrical signal and outputting it is provided.

A plate-like light absorbing member 59 that absorbs light rays is attached to the lower surface of the original cover 53, and a plate-like transparent member 60 that transmits light rays is attached to the lower surface of the light absorbing member 59. When a document reading start command is issued, luminance data on the surface of the document cover 53 including the document 52 is read by the CCD 58 for each main scanning line, and A / D conversion and shading correction are performed on the read luminance data. FIG. 12 is a diagram showing the luminance data density (hereinafter also referred to as “luminance value”) for one line (main scanning line) after shading correction in the luminance data. Is attenuated by the light absorbing member 59, and the black level of the document cover 53 is slightly lower (black) than the black level in the document 52. In order to detect the document size from the luminance data obtained in this way, the image reading apparatus 50 is provided with a comparison processing unit (not shown). In the comparison processing unit, the black level of the document cover 53 is detected. An intermediate value of the black level of the document 52 is set as a reference value Th, and all pixel data having a luminance value equal to or less than the reference signal Th are determined to be outside the document area, and the pixel data of the document and the pixel data outside the document area are determined. An accurate document size is detected by performing the determination process for each main scanning line.

  However, in the image reading device 50 of Patent Document 1, when the image of the light absorbing member 59 including the original 52 with the black edge is read, the luminance value of the edge of the original and the luminance value of the light absorbing member 59 are close to each other. May not be able to distinguish between a document area and a non-document area.

  Further, since the light absorbing member 59 is formed in black, when an original smaller than the standard size is read by specifying the standard size, the image of the original image data is recorded because the standard size is different from the original size. There is a problem in that the edges of the recording paper are recorded in black and the toner is wasted. In order to prevent this, it is necessary to perform processing that is not necessary in normal image processing in which pixel data of a portion recorded in black is converted into white pixel data.

  Further, it is difficult to form the light absorbing member 59 of the document cover 53 with a material that reduces the amount of reflected light compared to the case where the black color in the document 52 is read. Even if possible, the structure of the document cover 53 is complicated. Therefore, it is naturally conceivable that a problem such as an increase in apparatus cost occurs.

  The present invention has been made in view of the above problems, and in an image reading apparatus having a flat bed scanner for reading luminance data of a document placed on a transparent document placing plate, pixel data of a document region It is an object of the present invention to provide an image reading apparatus that can detect pixel data outside a document area and detect an accurate document size even for a document of a non-standard size.

In order to achieve the above object, an image reading apparatus according to claim 1 is an image reading apparatus that performs shading correction on luminance data of a read original on the basis of luminance data of a white reference plate. Reading means for reading luminance data of the press sheet including the original in a state in which the placed original is pressed against the original placing plate by a press sheet having a diffuse reflectance higher than that of the white reference plate; A press sheet including the original after shading correction by shading correction means for shading correction of luminance data of the press sheet including the original on the basis of data, and constant threshold data lower than the luminance value after the shading correction of the press sheet Binarizing means for binarizing the luminance data of the document and the edge of the document based on the binarized data Is characterized by comprising: means out, the.

The image reading apparatus according to claim 2, further comprising means for correcting shading of luminance data of the press sheet including the original with reference to luminance data of the white reference plate in parallel with the processing by the shading correction unit. It is a feature.

The image reading apparatus according to claim 3 is characterized in that the shading correction means performs shading correction on data obtained by performing a thinning process on luminance data of a press sheet including the original .

5. The image reading apparatus according to claim 4, wherein image processing is performed on luminance data composed of pixel data surrounded by an edge of the original detected by the detecting means, out of luminance data of the press sheet including the original. It is characterized by having.

According to the image reading apparatus of the first aspect, even when a document of a non-standard size is placed on the document placing plate or when the document is placed obliquely, the edge of the document is detected. Thus, it is possible to determine the exact document size of the document placed on the document placement plate. In addition, in order to detect the edge of the document, the brightness data of the press sheet including the document after shading correction is binarized with a certain threshold data lower than the brightness value after the shading correction of the press sheet. A constant value can be used for threshold data used for binarization, and binarization processing can be easily performed.

According to the second aspect of the present invention, the image reading apparatus includes means for correcting the shading correction of the brightness data of the press sheet including the document with reference to the brightness data of the white reference plate in parallel with the processing by the shading correction means. Therefore, the processing by the shading correction means for detecting the edge of the document and so-called shading correction can be performed simultaneously. Therefore, there is an advantage that it is not necessary to perform preliminary scanning (pre-scanning) for detecting the edge of the document.

According to the image reading apparatus of the third aspect, compared to the case where the edge of the document is detected using all the luminance data of the press sheet including the document, the processing for detecting the edge of the document can be speeded up. it can. Further, it is possible to reduce power consumption required for processing for detecting the edge of the document.

According to the image reading apparatus of the fourth aspect, the image processing is performed on the luminance data of the unnecessary press sheet among the luminance data of the press sheet including the original read in order to determine the original size. Rather, image processing can be performed only on the luminance data of the original composed of pixel data of the required original area.

  Hereinafter, an image reading apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of an image reading apparatus 1 according to the first embodiment of the present invention. As shown in the figure, the image reading apparatus 1 includes a control unit (MPU: Microprocessing Unit) 2, a document reading unit 3, an image processing circuit 4, a page memory 5, a codec (CODEC: Coder and Decoder) 6, an image memory 7, and a recording unit. 8, an operation unit 9, a display unit 10, a ROM (Read Only Memory) 11, and a RAM (Random Access Memory) 12, and the units 2 to 12 are communicably connected by a bus 13. .

  The control unit 2 controls the operation of each unit of the image reading apparatus 1. The document reading unit 3 reads luminance data of a document, and includes a flat bed scanner (FBS) 15 as shown in FIG. As shown in the figure, the flatbed reading unit 15 includes a transparent document placing plate 16 for placing a document to be read, a light source (not shown) for irradiating light on the placed document, and from the document. A scanning carriage 17 having a reflecting mirror (not shown) for guiding the reflected light in a predetermined direction and reciprocating in the horizontal direction (sub-scanning direction) with respect to the document placing plate 16, and a condensing light that converges the reflected light. A reduction optical system image reading unit including a lens 18 and a line sensor (CCD: Charge Coupled Device) 19 that converts convergent light into an electric signal and outputs the electric signal.

  A document pressing member 21 that can be opened and closed with respect to the document placing plate 16 is provided above the flat bed reading unit 15 with a support unit 20 provided at the back of the upper surface of the main body of the flat bed reading unit 15 as an axis. . On the surface of the document pressing member 21 on the side in contact with the document placement plate 16, the document placed on the document placement plate 16 is pressed from above to be brought into close contact with the document placement plate 16, and as the background of the document. A press sheet 22 is affixed to prevent a shadow from being generated in the peripheral portion of the document.

  After a document is placed on the document placing plate 16 and the document pressing member 21 is closed, when a document reading start command is issued by a predetermined operation of the operation unit 9, the scanning carriage 17 applies to the document placing plate 16. As shown by the arrows in the figure, the document on the document placing plate 16 is scanned while moving horizontally, and the reflected light from the document is guided to the line sensor 19 to form an image and placed on the document placing plate 16. The luminance data of the original document is read for each main scanning line. As will be described later, in order to determine (detect) the exact document size of the document placed on the document placement plate 16 when the document is read, the luminance data of the press sheet 22 including the document is a line sensor. 19 is read and output to a predetermined output destination. In addition, each pixel data constituting the brightness data has its brightness information represented by a numerical value (hereinafter referred to as “brightness value”), and the lower the brightness value, the darker the pixel data becomes (black), and conversely the brightness The higher the value, the brighter (white) the pixel data. Further, each pixel data constituting the luminance data is added with position information, so that it is possible to easily determine which pixel on the document placing plate 16 is read by each pixel data. Yes.

  Although not shown, an automatic document feeder (ADF) is provided above the document pressing member 21. The line sensor 19 scans a document transported by the automatic document transport unit in a state where the scanning carriage 17 is fixed below the translucent plate 23 at a predetermined reading position above the translucent plate 23. It is also possible to read the luminance data of the document conveyed by the automatic document conveyance unit. As a guide for bringing the document passing through the predetermined reading position close to the translucent plate 23, a white tape is attached to a position facing the translucent plate 23 or painted white to form a white color. A white reference plate (shading plate) 24 is provided.

  The press sheet 22 can prevent a shadow from being generated in the peripheral portion of the document as the background of the document, and the lower surface of the press sheet 22 (the surface in contact with the document or the document placing plate 16) is plain and The diffuse reflectance is made of a material higher than that of the white reference plate 24. Therefore, the flatbed reading unit 15 includes the original in a state where the original placed on the original placing plate 16 is pressed against the original placing plate 16 by the press sheet 22 having a diffuse reflectance higher than that of the white reference plate 24. It functions as a reading means for reading the luminance data of the press sheet 22.

  FIG. 3 is a block diagram showing a configuration of the document reading unit 3 in the image reading apparatus 1 according to the first embodiment of the present invention. As shown in the figure, the document reading unit 3 includes an AFE (Analog Front End) circuit 26, an A / D conversion circuit 27, a first circuit, in addition to the flat bed reading unit 15 including the line sensor 19 (not shown). A first shading correction circuit 28, a second shading correction circuit 29, a binarization circuit 30, and a discrimination circuit 31 are provided.

  The AFE circuit 26 has each pixel constituting the analog luminance data based on a preset gain setting value with respect to the analog luminance data of the press sheet 22 including the document read by the line sensor 19 of the flatbed reading unit 15. Perform gain adjustment to amplify the luminance value of the data. The A / D conversion circuit 27 performs A / D conversion (Analog to Digital Conversion) on the analog luminance data whose gain has been adjusted in the AFE circuit 26 into digital luminance data.

  The first shading correction circuit 28 performs normal shading correction on the luminance data of the press sheet 22 including the document output from the A / D conversion circuit 27. Here, the normal shading correction is a so-called shading correction that is performed to correct unevenness in the amount of light, the influence of optical components, and variations in pixel sensitivity of the line sensor 19. The first shading correction circuit 28 includes a shading RAM 32, and the luminance of the white reference plate 24 acquired by the line sensor 19 of the flat bed reading unit 15 reading the image of the white reference plate 24 is acquired in the shading RAM 32. Data (hereinafter also referred to as “shading data”) is stored. Specifically, the luminance data of the white reference plate 24 is data for one line in the main scanning direction. The first shading correction circuit 28 performs shading correction (normal shading correction) on the basis of the shading data stored in the shading RAM 32 with respect to the luminance data of the press sheet 22 including the document output from the A / D conversion circuit 27. )I do. As described above, the image reading apparatus 1 has a function of correcting the shading correction of the luminance data of the read document with reference to the luminance data of the white reference plate 24.

  The timing for storing the brightness data of the white reference plate 24 in the shading RAM 32 is not particularly limited as long as it is before the start of reading the brightness data of the press sheet 22 including the original. For example, the power source of the image reading apparatus 1 is turned on. Each time it is turned on, it may be read and stored in the shading RAM 32, or it may be read and stored before the start of reading the luminance data whenever there is an instruction to start reading the luminance data of the press sheet 22 including the original. Further, not only when reading a document but also when a user takes an instruction for taking in the operation unit 9, the luminance data of the white reference plate 24 may be acquired and stored in the shading RAM 32.

  The second shading correction circuit 29 performs document size determination shading correction on the luminance data of the press sheet 22 including the document output from the A / D conversion circuit 27. In the document size determination shading correction, the accurate document size of the placed document is determined with respect to the luminance data of the press sheet 22 including the document placed on the document placing plate 16 read by the line sensor 19. This is a shading correction performed for the purpose.

  As will be described in detail later, the second shading correction circuit 29 is based on data (reference data) obtained by offsetting the luminance data of the white reference plate 24 of the shading RAM 32 included in the first shading correction circuit 28 by a predetermined amount to the white side. It functions as a shading correction unit that performs shading correction on the luminance data of the press sheet 22 including the document output from the A / D conversion circuit 27, and the data after shading correction processed by the second shading correction circuit 29 is binary. Is output to the conversion circuit 30.

The binarization circuit 30 functions as binarization means for binarizing the data after shading correction, and binarizes the data obtained by the shading correction for document size determination by the second shading correction circuit 29 based on a predetermined threshold. (Gradation reduction processing). The discriminating circuit 31 functions as detection means for detecting the edge of the document based on the binarized data, and the line sensor 19 presses the document including the document based on the binarized data by the binarizing circuit 30. A process of discriminating luminance data of the press sheet 22 including the original obtained by reading the image on the surface of the sheet 22 into pixel data in the original area and pixel data outside the original area is performed. The discrimination result of the discrimination circuit 31 is output to the image processing circuit 4.

  The normal shading correction processing by the first shading correction circuit 28 and the shading correction processing for document size determination by the second shading correction circuit 29 are performed in parallel. In parallel with the processing by the shading correction means (second shading correction circuit 29), it functions as means for shading correction of the luminance data of the press sheet 22 including the original with reference to the luminance data of the white reference plate 24.

  The image processing circuit 4 is a means for performing image processing on luminance data composed of pixel data surrounded by the edge of the original detected by the discrimination circuit (detection means) 31 among the luminance data of the press sheet 22 including the original. Function. Specifically, based on the determination result output from the determination circuit 31, the luminance data of the press sheet 22 including the original subjected to the normal shading correction in the first shading correction circuit 28 (hereinafter, normal shading correction is performed). Thereafter, the luminance data is referred to as “image data”), and image processing is performed only on the image data of the document including the pixel data of the document area. Here, the image processing performed by the image processing circuit 4 is image processing for recording an image of image data of a document on a sheet in the recording unit 8, and specifically, γ correction and enlargement / reduction scaling processing. Image processing such as binarization processing. The document image data that has been subjected to the necessary image processing in the image processing circuit 4 in this way is output to the page memory 5. The binarization processing performed in the image processing circuit 4 is not binarization for determining the document size performed in the binarization circuit 30, but for recording the image of the document image data on the paper. This is a binarization process. In the present embodiment, a case where binarization for determining the document size is performed in the binarization circuit 30 will be described. However, the binarization circuit 30 is not provided, and the image processing circuit 4 performs document size. Binarization may also be performed for determining the above.

  The page memory 5 is a memory that stores image data of a document that has been subjected to image processing in the image processing circuit 4. The codec 6 encodes / decodes image data. Here, the image data of the document in the page memory 5 on which the image processing circuit 4 has performed the required image processing is converted into MH (Modified Huffman), MR (Modified Read), MMR (Modified Modified Read), JBIG (Joint Bi-level). The image data is encoded by an Image Group) method and the encoded image data is decoded.

  The image memory 7 stores image data encoded by the codec 6, image data directly output from the image processing circuit 4, and the like. The recording unit 8 records an image of the image data read from the image memory 7 on a sheet. As a recording method in the recording unit 8, various recording methods such as an electrophotographic method and an ink jet recording method can be used.

  As illustrated in FIG. 2, the operation unit 9 includes a start key 33 for instructing the document reading unit 3 (not shown) to start reading a document, a numeric keypad 34 for inputting the number of copies, and the document reading magnification. Various operation keys linked to the display unit 10 are provided, such as a magnification setting key 35 for setting the image density and a density setting key 36 for setting the reading density of the document. The display unit 10 includes a liquid crystal display (LCD) 37 that displays various setting screens and operation states of the image reading device 1 with characters and graphics, an LED lamp 38 that is turned on or off, and the like. I have.

  The ROM 11 stores various programs for controlling the operation of each unit of the image reading apparatus 1 by the control unit 2. The processing operation of each unit of the image reading apparatus 1 is performed according to instructions issued by the control unit 2 based on various programs stored in the ROM 11. The RAM 12 stores various data such as setting information and operation information used for the processing operation of the image reading apparatus 1 in a readable and writable state.

  Hereinafter, processing performed in the image reading apparatus 1 configured as described above from when the luminance data of the press sheet 22 including the original is read by the flatbed reading unit 15 until it is stored in the page memory 5 will be described. This will be described with reference to FIGS. First, when the user places a document on the document placing plate 16 of the flat bed reading unit 15 and closes the document pressing member 21, the flat key reading unit 15 is pressed when the start key 33 of the operation unit 9 is pressed. When the scanning carriage 17 scans the press sheet 22 including the original in the horizontal direction (sub-scanning direction) along the original placement plate 16, the line sensor 19 performs main scanning on the luminance data of the press sheet 22 including the original. Read line by line.

  In this way, the luminance data of the press sheet 22 including the original read by the line sensor 19 of the flat bed reading unit 15 is sequentially output to the AFE circuit 26 as shown in FIG. Gain adjustment is performed based on a preset gain setting value. Subsequently, the luminance data of the press sheet 22 including the original whose gain has been adjusted in the AFE circuit 26 is output to the A / D conversion circuit 27, and the analog luminance data is changed to digital luminance data in the A / D conversion circuit 27. A / D conversion is performed.

  Next, the luminance data of the press sheet 22 including the document A / D converted by the A / D conversion circuit 27 is simultaneously output to the first shading correction circuit 28 and the second shading correction circuit 29. The first shading correction circuit 28 performs normal shading on the luminance data of the press sheet 22 including the document output from the A / D conversion circuit 27 based on the luminance data of the white reference plate 24 stored in the shading RAM 32 in advance. to correct. In this manner, the image data of the press sheet 22 including the original that has been subjected to the normal shading correction in the first shading correction circuit 28 is output to the image processing circuit 4.

  On the other hand, the luminance data of the press sheet 22 including the original is also output from the A / D conversion circuit 27 to the second shading correction circuit 29, but all the luminance data of the press sheet 22 including the original is output. Instead, the brightness data of the press sheet 22 including the original subjected to the thinning process is output to the second shading correction circuit 29. For example, when the luminance data of the press sheet 22 including the original read at a resolution of 600 dpi in the main scanning direction of the original is output from the A / D conversion circuit 27 to the first shading correction circuit 28, this is thinned out. Luminance data of the press sheet 22 including the processed 125 dpi document is output from the A / D conversion circuit 27 to the second shading correction circuit 29. This is because high-definition data of 600 dpi is not necessary to determine the document size, and data of about 125 dpi is sufficient. However, when high-definition data is used, it is possible to determine a more accurate original size than when low-definition data is used. In consideration of this, the ratio of the pixel data to be thinned out with respect to the luminance data of the press sheet 22 including the original may be determined. Therefore, the second shading correction circuit 29 functioning as a shading correction means performs shading correction on the data obtained by thinning the luminance data of the press sheet 22 including the original.

  FIG. 4A shows the luminance data (Image) of the press sheet 22 including the original read by the line sensor 19 of the flatbed reading unit 15 and the luminance data (P) of the white reference plate 24 read from the shading RAM 32. It is the figure illustrated about the line (main scanning line). In the second shading correction circuit 29, the luminance data of the white reference plate 24 read from the shading RAM 32 is offset by a predetermined amount to the white side so that the state shown in FIG. The reference data (W) is input. Then, the second shading correction circuit 29 performs shading correction on the luminance data of the press sheet 22 including the document with reference to the input reference data. The second shading correction circuit 29 performs shading correction for document size determination pixel by pixel on the luminance data of the press sheet 22 including the document, so that the reference data is input to the second shading correction circuit 29 pixel by pixel. Is done.

  Although not shown, the document reading unit 3 is configured by a dedicated circuit such as an ASIC (Application Specific Integrated Circuit) and includes a document output from the A / D conversion circuit 27 by an arithmetic processing circuit included in the ASIC. Data obtained by thinning the luminance data of the press sheet 22 is output to the second shading correction circuit 29, or the luminance data of the white reference plate 24 stored in the shading RAM 32 is offset by a predetermined amount to the white side. It is possible to output the processed data to the second shading correction circuit 29. Further, the second shading correction circuit 29 corrects the luminance data of the press sheet 22 including the original subjected to the thinning process, and corrects the luminance data of the white reference plate 24 offset by a predetermined amount to the white side in order to correct the shading correction for the original size. It is not necessary to input all to the second shading correction circuit 29. Therefore, the second shading correction circuit 29 is subjected to the thinning process on the luminance data of the white reference plate 24 offset by a predetermined amount on the white side in the same manner as the luminance data of the press sheet 22 including the original. Is entered.

  FIG. 4C shows the data after the shading correction by the second shading correction circuit 29. The binarization circuit 30 performs a process of binarizing the data after the shading correction based on a predetermined threshold (Threshold). FIG. 4D is a diagram illustrating data binarized by the binarization circuit 30. Here, the data indicating the value “1” is the pixel data (the press data obtained by reading the image of the press sheet 22 from the original pixel data having the luminance value before the process for determining the document size is performed. Sheet area pixel data), and data indicating a value of “0” sandwiched by a data group indicating a value of “1” is before the process for determining the document size is performed. This indicates that the original pixel data having a luminance value is pixel data (original area pixel data) obtained by reading an image of the original. The discriminating circuit 31 detects the edge of the document based on the binarized data. More specifically, based on the binarized data, the luminance data of the press sheet 22 including the original is discriminated into pixel data in the original area and pixel data outside the original area (press sheet 22). In this way, when the discrimination circuit 31 performs the process of discriminating the luminance data of the press sheet 22 including the original into the pixel data of the original area and the pixel data of the press sheet area, the result of the determination is the image processing circuit 4. Is output.

  When the image data of the press sheet 22 including the original that has been subjected to the normal shading correction by the first shading correction circuit 28 and the determination result from the determination circuit 31 are input, the image processing circuit 4 is based on the input determination result. Thus, image processing is performed only on necessary data among the image data of the press sheet 22 including the input original. That is, image processing such as enlargement / reduction scaling processing is performed only on pixel data in the document area of the image data of the press sheet 22 including the document. Image data of a document composed of pixel data that has been subjected to necessary image processing in the image processing circuit 4 in this manner is stored in the page memory 5. Although not shown, the original image data stored in the page memory 5 is encoded by the codec 6 using a predetermined encoding method and then temporarily stored in the image memory 7 for processing operation of the recording unit 8. These are sequentially read out and decoded by the codec 6, and the image is recorded on the paper in the recording unit 8.

  As described above, according to the image reading apparatus 1, the pixel data constituting the luminance data of the press sheet 22 including the document is processed by the processing of the second shading correction circuit 29, the binarization circuit 30, and the determination circuit 31. Therefore, it is possible to discriminate between pixel data in the document area and pixel data outside the document area, and thereby an accurate document size can be detected. Further, the processing performed in each of these units 29 to 31 is not performed on all the luminance data of the press sheet 22 including the original, but is performed on the data subjected to the thinning processing, and therefore all the data The processing can be performed at a higher speed than the processing for detecting the edge of the document using the above, and the above-described units 29 to 31 for detecting the edge of the document execute the processing. There is an advantage that the electric power (power consumption) required for the operation can be reduced. Further, since the normal shading correction by the first shading correction circuit 28 and the shading correction for document size determination by the second shading correction circuit 29 are performed in parallel, before the actual reading of the document to determine the document size. There is an advantage that it is not necessary to perform a pre-scan.

  Next, an image reading apparatus 1A according to a second embodiment of the present invention will be described. In the second embodiment, a case will be described in which the brightness data of a press sheet including a document is subjected to shading correction (shading correction for document size determination) based on the brightness data of the press sheet 22. The overall configuration of the image reading apparatus 1A and the partial configuration of the document reading unit 3A are the same as those of the image reading apparatus 1 according to the first embodiment shown in FIGS. Components having the same numbers are assigned the same reference numerals, and descriptions thereof are omitted. Mainly different points (configuration of the document reading unit) will be described below.

  FIG. 5 is a block diagram showing a configuration of the document reading unit 3A in the image reading apparatus 1A according to the second embodiment of the present invention. As illustrated, the document reading unit 3A is different from the document reading unit 3 of the image reading apparatus 1 illustrated in FIG. 3 in that a shading RAM 40 is provided in the second shading correction circuit 29. The shading RAM 40 stores brightness data of the press sheet 22 used as a reference when the second shading correction circuit 29 performs shading correction for document size determination. The brightness data of the press sheet 22 is obtained when the line sensor 19 of the flat bed reading unit 15 is in a state where no original is placed on the original placement plate 16 or in an area where no original is placed. One line of data in the main scanning direction obtained by reading an image. That is, the brightness data of the press sheet 22 that does not include a document.

  Here, the second shading correction circuit 29 is input based on the luminance data of the press sheet 22 stored in the shading RAM 40, not the luminance data of the white reference plate 24 stored in the shading RAM 32. It functions as a shading correction means for correcting the shading of the luminance data of the press sheet 22 including the original. As described above, not all the luminance data of the press sheet 22 including the original is input to the second shading correction circuit 29, but the press sheet 22 including the original with a part of the pixel data thinned out. Since the luminance data is input, the shading RAM 40 stores the luminance data of the press sheet 22 that has been subjected to the same thinning process as the thinning process performed on the luminance data of the press sheet 22 including the document. ing.

  6A shows one line of luminance data (Image) of the press sheet 22 including the original read by the line sensor 19 of the flatbed reading unit 15 and luminance data (S) of the press sheet 22 read from the shading RAM 40. FIG. It is the figure illustrated about (main scanning line). Similar to the second shading correction circuit 29 of the image reading apparatus 1 according to the first embodiment described above, when the luminance data of the press sheet 22 including the thinned document is input, the second shading correction circuit 29 reads out the luminance data of the illustrated press sheet 22 from the shading RAM 40, and performs shading correction on the luminance data of the press sheet 22 including the original (for original size determination) with reference to the read luminance data of the press sheet 22. FIG. 5B shows the data after shading correction. The binarization circuit 30 binarizes the data after the shading correction based on a predetermined threshold (Threshold). FIG. 4C shows data binarized by the binarization circuit 30. FIG. Here, the data indicating the value of “1” indicates the pixel data of the press sheet area as in FIG. 4D, and is sandwiched between the data groups indicating the value of “1”. Data indicating a value of “0” indicates pixel data of the document area. The discriminating circuit 31 detects the edge of the document based on the binarized data. Specifically, a process is performed for determining the luminance data of the press sheet 22 including the original into pixel data in the original area and pixel data outside the original area.

  As described above, according to the image reading apparatus 1B according to the second embodiment, the shading correction for document size determination can be performed using the brightness data of the press sheet 22 instead of the brightness data of the white reference plate 24. it can. Here, the binarization circuit 30 binarizes the data after shading correction performed by the second shading correction circuit 29 for shading correction for document size determination, and the discrimination circuit 31 is based on the binarized data. However, it is also possible to detect the edge of the document without performing shading correction for determining the document size.

  Hereinafter, an image reading apparatus 1B according to a third embodiment of the present invention that detects the edge of a document without performing shading correction for document size determination on luminance data of the press sheet 22 including the read document will be described. To do. The entire configuration of the image reading apparatus 1B and the partial configuration of the document reading unit 3B are the same as those of the image reading apparatus 1 according to the first embodiment shown in FIG. The same reference numerals are assigned to the components, and the description thereof is omitted. Mainly different points (configuration of the document reading unit) will be described below.

  FIG. 7 is a block diagram showing the configuration of the document reading unit 3B in the image reading apparatus 1B according to the third embodiment of the present invention. As shown in the figure, the document reading unit 3B is not provided with a second shading correction circuit 29 as a circuit for performing shading correction on the document reading unit 3 of the image reading apparatus 1 shown in FIG. The difference is that only the shading correction circuit 41 (first shading correction circuit 28) is provided. Similar to the first shading correction circuit 28, the shading correction circuit 41 includes a shading RAM 42 (shading RAM 32), in which luminance data of the white reference plate 24 is stored.

  In addition, the binarization circuit 30 functions as binarization means for binarizing the luminance data of the press sheet 22 including the original by using threshold data obtained by offsetting the luminance data of the white reference plate 24 to the white side. The discriminating circuit 31 functions as detection means for detecting the edge of the document based on the binarized data binarized by the binarizing circuit 30.

  Note that the luminance data of the press sheet 22 including the document output from the A / D conversion circuit 27 is output to the shading correction circuit 41 and the binarization circuit 30 at the same time. In parallel with the processing by the binarization means (binarization circuit 30), it functions as a means for shading correction of the luminance data of the press sheet 22 including the original with reference to the luminance data of the white reference plate 24. Similarly to the second shading correction circuit 29 in the first embodiment, the binarization circuit 30 is input with the luminance data of the press sheet 22 including the original subjected to the thinning process. . Therefore, the binarization circuit 30 binarizes the data obtained by thinning the luminance data of the press sheet 22 including the original.

  Also in the document reading unit 3B, the luminance data of the press sheet 22 including the document A / D converted by the A / D conversion circuit 27 is simultaneously output to the shading correction circuit 41 and the binarization circuit 30. Similar to the first shading correction circuit 28, the shading correction circuit 41 performs normal shading correction on the luminance data of the press sheet 22 including the input original, and the image data after the shading correction is converted into the image processing circuit 4. To output.

  FIG. 8A shows the luminance data (Image) of the press sheet 22 including the original read by the line sensor 19 of the flatbed reading unit 15 and the luminance data (P) of the white reference plate 24 read from the shading RAM 42 as 1. It is the figure illustrated about the line (main scanning line). The document reading unit 3B offsets the luminance data of the white reference plate 24 to the white side and performs binarization processing so that the state shown in FIG. (T) is generated, thinned out, and input to the binarization circuit 30. Then, the binarization circuit 30 binarizes the luminance data of the press sheet 22 including the document based on the input threshold data. FIG. 8C is a diagram illustrating data binarized by the binarization circuit 30. Here, the data indicating the value of “1” indicates the pixel data of the press sheet area as in FIG. 4D, and is sandwiched between the data groups indicating the value of “1”. Data indicating a value of “0” indicates pixel data of the document area. The discriminating circuit 31 detects the edge of the document based on the binarized data. Specifically, a process is performed for determining the luminance data of the press sheet 22 including the original into pixel data in the original area and pixel data outside the original area.

  As described above, according to the image reading apparatus 1B according to the third embodiment, the document size can be determined without performing the document size determination shading correction. Here, the binarization circuit 30 binarizes and binarizes the luminance data of the press sheet 22 including the original with threshold data obtained by offsetting the luminance data of the white reference plate 24 stored in the shading RAM 42 to the white side. The case where the discrimination circuit 31 detects the edge of the document based on the later data has been described, but the brightness data of the press sheet 22 including the document is binarized by threshold data obtained by offsetting the brightness data of the press sheet 22 to the black side. You may make it do.

  Hereinafter, the luminance data of the press sheet 22 including the original is binarized by threshold data obtained by offsetting the luminance data of the press sheet 22 to the black side, and the edge of the original is detected based on the binarized data. An image reading apparatus 1C according to the fourth embodiment will be described. The entire configuration of the image reading apparatus 1C and the partial configuration of the document reading unit 3C are the same as those of the image reading apparatus 1 according to the first embodiment shown in FIGS. Components having the same numbers are assigned the same reference numerals, and descriptions thereof are omitted. Mainly different points (configuration of the document reading unit) will be described below.

  FIG. 9 is a block diagram showing the configuration of the document reading unit 3C in the image reading apparatus 1C according to the fourth embodiment of the present invention. As shown in the figure, the document reading unit 3C is not provided with a second shading correction circuit 29 as a circuit for performing shading correction on the document reading unit 3 of the image reading apparatus 1 shown in FIG. The difference is that only the shading correction circuit 41 (first shading correction circuit 28) is provided. As with the first shading correction circuit 28, the shading correction circuit 41 includes a shading RAM 42 (shading RAM 32).

  In addition, the binarization circuit 30 functions as a binarization unit that binarizes the luminance data of the press sheet 22 including the original by using threshold data obtained by offsetting the luminance data of the press sheet 22 to the black side. The circuit 31 functions as a detection unit that detects the edge of the document based on the binarized data obtained by the binarization circuit 30. Here, the binarization circuit 30 includes a register 43, and threshold data generated based on the luminance data of the press sheet 22 is stored in the register 43. Here, the threshold data is specifically obtained by reading the image of the press sheet 22 when the flatbed reading unit 15 does not place a document on the document placing plate 16 or in an area excluding the document. One line of data is offset to the black side in the main scanning direction. Since the binarization circuit 30 receives the luminance data of the press sheet 22 including the original subjected to the thinning-out process, as in the binarization circuit 30 described in the third embodiment of the present invention. After the above-described offset, the data subjected to the thinning process in the same manner as this is stored in the register 43 as threshold data.

  Also in the document reading unit 3C, the luminance data of the press sheet 22 including the document A / D converted by the A / D conversion circuit 27 is simultaneously output to the shading correction circuit 41 and the binarization circuit 30. Similar to the first shading correction circuit 28, the shading correction circuit 41 performs normal shading correction on the luminance data of the press sheet 22 including the input original, and the image data after the shading correction is converted into the image processing circuit 4. To output.

  FIG. 10A shows luminance data (Image) of the press sheet 22 including the original read by the line sensor 19 of the flat bed reading unit 15 and luminance data (S) of the press sheet 22 before being offset to the black side. It is the figure illustrated about one line. The document reading unit 3C generates threshold data for performing binarization processing by offsetting the luminance data of the press sheet 22 to the black side so that the state shown in FIG. The thinning process is performed and stored in the register 43 in advance. The binarization circuit 30 binarizes the luminance data of the press sheet 22 including the original based on the threshold data stored in the register 43. FIG. 4C shows data binarized by the binarization circuit 30. FIG. Here, the data indicating the value of “1” indicates the pixel data of the press sheet area as in FIG. 4D, and is sandwiched between the data groups indicating the value of “1”. Data indicating a value of “0” indicates pixel data of the document area. The discriminating circuit 31 detects the edge of the document based on the binarized data. More specifically, a process for determining the luminance data of the press sheet 22 including the document into pixel data in the document area and pixel data outside the document area is performed.

  According to the image reading apparatuses 1 to 1C described above, the document size is determined by discriminating the pixel data in the document area and the pixel data outside the document area, so that the document is inclined on the document placement plate 16. Even if the document is placed or the placed document is not a standard size document, the exact document size can be determined. Further, since the surface of the press sheet 22 that presses the document is made of a material having a diffuse reflectance higher than that of the white reference plate 24, a document having a solid black edge as in a conventional image reading apparatus is used. When read, there is no problem that the pixel data of the document and the pixel data of the press sheet 22 may not be distinguished. In addition, as described above, the luminance data of the press sheet 22 including the original is subjected to shading correction, and then binarized to determine the original size, and binarized without performing shading correction to determine the original size. However, in the former case, a constant (predetermined) value can be used as the threshold value used in the binarization process. It has the advantage of being easy to do.

  Note that the luminance data of the white reference plate 24 and the luminance data of the press sheet 22 read by the line sensor 19 of the flat bed reading unit 15 include noise, and the luminance data in a state including this noise is used. If the threshold data is generated, there is a possibility that the pixel data in the original area and the pixel data outside the original area cannot be accurately determined. Therefore, in the image reading apparatuses 1 to 1C according to the present embodiment, the luminance data corrected by taking an average value obtained by a plurality of readings and averaging with surrounding pixel data is stored in the shading RAM 32 (42). It has come to be used. Therefore, the binarization circuit 30 can perform binarization processing for accurately discriminating between pixel data in the document area and pixel data outside the document area.

  Further, in the present embodiment, the case where the processing for performing the normal shading correction on the luminance data of the press sheet 22 including the read document and the processing for detecting the edge of the document are performed in parallel has been described. The process of detecting the edge of the document and determining the document size may be performed in the preliminary scan (pre-scan), and the original document may be read based on the determination result in the preliminary scan. Specifically, the luminance data of the press sheet 22 including the original obtained by performing the preliminary scanning of the original is subjected to a process of discriminating the pixel data of the original and the pixel data of the press sheet 22, and is determined to be the pixel data of the original. The area constituted by the pixel data is determined as the original area, and the main reading is performed only on the original area.

  The configuration of the image reading apparatuses 1 to 1C shown in the present embodiment is only one aspect of the image reading apparatus according to the present invention, and it is needless to say that the design can be changed as appropriate without departing from the gist of the present invention. For example, the present invention can be realized as a copying apparatus, a facsimile apparatus, a scanner apparatus, and a complex machine thereof.

  The present invention is applicable, for example, to various apparatuses including a flatbed scanner that reads luminance data of a document placed on a document placement plate.

1 is a block diagram illustrating a configuration example of an image reading apparatus according to a first embodiment of the present invention. FIG. 4 is a schematic perspective view for explaining a flat sheet reading unit and a press sheet attached to a document pressing member provided to be openable and closable with respect to a document placing plate included in the reading unit. FIG. 2 is a block diagram illustrating a configuration of a document reading unit in the image reading apparatus according to the first embodiment of the present invention. FIG. 5 is a diagram for explaining document size determination shading correction and binarization processing for determining the document size performed in the image reading apparatus according to the first embodiment of the present invention. FIG. 6 is a block diagram illustrating a configuration of a document reading unit in an image reading apparatus according to a second embodiment of the present invention. FIG. 10 is a diagram for describing document size determination shading correction and binarization processing for determining a document size performed in an image reading apparatus according to a second embodiment of the present invention. FIG. 10 is a block diagram illustrating a configuration of a document reading unit in an image reading apparatus according to a third embodiment of the present invention. FIG. 10 is a diagram for explaining binarization processing and the like for determining a document size performed in an image reading apparatus according to a third embodiment of the present invention. FIG. 10 is a block diagram illustrating a configuration of a document reading unit in an image reading apparatus according to a fourth embodiment of the present invention. FIG. 10 is a diagram for explaining binarization processing and the like for determining a document size performed in an image reading apparatus according to a fourth embodiment of the present invention. FIG. 10 is a schematic cross-sectional view illustrating a configuration of a document reading unit of a conventional image reading apparatus. FIG. 10 is a diagram for explaining document size determination processing performed in a conventional image reading apparatus.

Explanation of symbols

1, 1A, 1B, 1C Image reading device 2 Control unit (MPU)
3, 3A, 3B, 3C Document reading unit 4 Image processing circuit 15 Flatbed reading unit 16 Document placing plate 19 Line sensor 22 Press sheet 24 White reference plate 28 First shading correction circuit 29 Second shading correction circuit 30 Binary Circuit 31 Discriminating circuit 32, 40, 42 Shading RAM
41 Shading correction circuit 43 Register

Claims (4)

In an image reading apparatus that performs shading correction on luminance data of a read document with reference to luminance data of a white reference plate,
Reading means for reading luminance data of the press sheet including the original while the original placed on the original placement plate is pressed against the original placement plate by a press sheet having a diffuse reflectance higher than that of the white reference plate The shading correction means for shading correction of the brightness data of the press sheet including the original document with reference to the brightness data of the press sheet, and constant threshold data lower than the brightness value after the shading correction of the press sheet, after the shading correction An image reading apparatus comprising: binarizing means for binarizing luminance data of a press sheet including the original; and detecting means for detecting an edge of the original based on the binarized data. . The image reading apparatus according to claim 1, further comprising means for correcting shading of luminance data of a press sheet including the original with reference to luminance data of the white reference plate in parallel with processing by the shading correction unit. apparatus. The image reading apparatus according to claim 2, wherein the shading correction unit performs shading correction on data obtained by performing a thinning process on luminance data of a press sheet including the original . 2. The image processing apparatus according to claim 1, further comprising: a unit that performs image processing on luminance data including pixel data surrounded by an edge of the original detected by the detecting unit out of luminance data of the press sheet including the original. 4. The image reading device according to any one of items 1 to 3 .

Images