JP2005234298A - Image scanner, focal position adjusting method, and program therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image scanner for performing automatic focal adjustment obtaining high reproducibility and with high precision, and to provide a focal position adjusting method and its program. <P>SOLUTION: Automatic focal adjustment finds a plurality of first sharpness values from the image signal output from an image sensor 111, finds the maximum value from among the plurality of the first sharpness values, extracts the first sharpness value which is a value or larger for multiplying a prescribed rate to the maximum value, finds a second sharpness value from the extracted first sharpness value, and adjusts the focal position on the basis of the second sharpness value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to an image reading apparatus and a focal position adjusting method for reading a transparent original such as a negative film and a positive film and a reflective original such as general paper, and a program used for such a focal position adjustment.

In general, in automatic focus adjustment in an image reading apparatus, the sharpness value at each focus position is obtained while moving the focus position by moving an optical system such as a lens, and the position where the sharpness value is maximized is finally determined. The focus position is set. In this case, the sharpness value is represented by, for example, a sum of differences between adjacent pixels or a square sum of differences between adjacent pixels in the photoelectric conversion element (see, for example, Patent Document 1).
Japanese Patent No. 2944674

  However, in the conventional automatic focus adjustment, the sharpness value is obtained from the difference between all the pixels used for the automatic focus. Therefore, in the portion that is not the edge portion of the image, that is, the portion where the difference between adjacent pixels is small. The signal must also be processed. For this reason, the reproducibility and accuracy are lowered.

  The present invention has been made paying attention to the above-described circumstances, and an object of the present invention is to provide an image reading apparatus and a focus position adjustment method capable of performing automatic focus adjustment with high accuracy and high reproducibility, and An object of the present invention is to provide a program used for such focal position adjustment.

  In order to solve the above problems, in the first aspect of the present invention, there is provided a photoelectric conversion means for photoelectrically converting image light composed of reflected light reflected from a document or transmitted light transmitted through the document and outputting an image signal. An optical system that guides the image light to the photoelectric conversion unit; and a moving unit that moves at least a part of the optical system. The moving unit moves at least a part of the optical system to adjust a focal position. An image reading device to be adjusted, wherein a plurality of first sharpness values are obtained from the image signal output from the photoelectric conversion means, and a maximum value is selected from the plurality of first sharpness values. A first computing means for obtaining a maximum value and a first sharpness value equal to or greater than a value obtained by multiplying the maximum value by a predetermined ratio from the plurality of first sharpness values; From the first sharpness value A second computing means for obtaining a sharpness value, the image reading apparatus is provided, characterized in that a control means for adjusting the focal position based on the second sharpness value.

  In the second aspect of the present invention, photoelectric conversion means for photoelectrically converting image light composed of reflected light reflected from a document or transmitted light transmitted through the document and outputting an image signal; and An image reading apparatus comprising: an optical system that leads to a photoelectric conversion unit; and a moving unit that moves at least a part of the optical system, and the focal position is adjusted by moving at least a part of the optical system by the moving unit. Then, a plurality of first sharpness values are obtained from the image signal output from the photoelectric conversion means while at least a part of the optical system is moved by the movement means, and the plurality of first sharpness values are obtained. A first calculation means for obtaining a maximum value having a maximum value among sharpness values, and a case formed by the first calculation means while moving at least a part of the optical system by the moving means. Image signals are obtained at shorter intervals, a plurality of first sharpness values are obtained from the image signals output from the photoelectric conversion means, and the maximum value is obtained from the plurality of first sharpness values. A second calculation means for extracting a first sharpness value equal to or greater than a value multiplied by a predetermined ratio, and obtaining a second sharpness value from the extracted first sharpness value; There is provided an image reading apparatus comprising: a control unit that controls the moving unit based on a sharpness value to adjust a focal position.

  As can be seen from the above configuration, the present invention does not obtain the sharpness value from the difference between all the pixels used for autofocusing, but obtains a plurality of first sharpness values from the image signal output from the photoelectric conversion means. And obtaining a maximum value having a maximum value from the plurality of first sharpness values, and extracting a first sharpness value equal to or greater than a value obtained by multiplying the maximum value by a predetermined ratio. The second sharpness value is obtained from the extracted first sharpness value, and the focal position is adjusted based on the second sharpness value. That is, a signal at a portion that is not an edge portion of the image, that is, a portion where the difference between adjacent pixels is small is excluded from the focus adjustment processing.

  In this way, if only the first sharpness value greater than or equal to the predetermined value is enabled in the focus adjustment process, only the edge near the peak at the current document level can be detected, and the peak position can be accurately detected. Stable position detection can be performed. That is, it is possible to perform automatic focus adjustment with high accuracy and high reproducibility.

  In the above configuration, the first sharpness value is preferably an absolute value of a difference between adjacent pixels of the photoelectric conversion means. The second sharpness value is preferably a sum of absolute values of differences between adjacent pixels of the photoelectric conversion means. Further, it is desirable that the second sharpness value is a sum of the first sharpness values having a value of 70% or more of the maximum value.

  In the above configuration, it is preferable to perform a smoothing process on the second sharpness value. When smoothing processing is performed in this way, it is possible to determine, as a focal position, one point in consideration of, for example, a plurality of color image signals output from the photoelectric conversion means.

  Further, in the above configuration, the control means further includes third calculating means for obtaining a second-order or higher approximation curve from the second sharpness value, and obtaining a position where the maximum value of the approximate curve is obtained. It is preferable to adjust the focal position based on the position where the maximum value obtained by the third calculating means is obtained. Thus, by taking an approximate curve, it is difficult to pick up variations due to the influence of noise or the like, and an accurate and stable position can be detected. In addition, since only strong edges are calculated, a quadratic curve can be obtained sufficiently.

  In the present invention, an image reading method including the above configuration and a program used for image reading are also provided.

  According to the present invention, it is possible to provide an image reading apparatus and a focus position adjustment method capable of performing automatic focus adjustment with high accuracy and high reproducibility, and a program used for such position adjustment. .

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  1 and 2 schematically show a configuration of an image reading apparatus 1 according to an embodiment of the present invention. As shown in FIG. 1, the image reading apparatus 1 includes an image reading unit 100 and a transmissive light source unit 200, and can read a transmissive original such as a negative film or a positive film and a reflective original such as ordinary paper. It can be done. The image reading apparatus 1 can be connected to a LAN and used as a network scanner, or can be used as an image reading unit of a copying machine (not shown). In this embodiment, the image reading apparatus 1 is shown in FIG. As described above, it is assumed that the computer is connected to the personal computer (host computer) 400 via the interface (I / F) 304.

  The image reading unit 100 includes a housing 101, and a platen 102 for placing a document from which an image is read is disposed on the top surface of the housing 101. A reading carriage 103 is accommodated in the housing 101, and the reading carriage 103 can move along the platen 102. Specifically, the timing belt 113 spanned between the pair of pulleys 114a and 114b is engaged with the frame of the reading carriage 103, and at least one pulley 114a is driven to rotate by driving the reading carriage motor M1. It is like that. Therefore, when the reading carriage motor M1 is driven to rotate the pulleys 114a and 114b, the reading carriage 103 is moved along the platen 102 in the direction of arrow A (the horizontal direction in FIG. Direction).

  Also, inside the reading carriage 103, a line-shaped lamp 105 for irradiating light on a document placed on the platen 102, and an image that is light reflected by the document or transmitted through the document. An optical system including reflection mirrors 106, 107, 108, 109 for reflecting light and an imaging lens 110 for imaging the image light, and image light imaged by the imaging lens 110 are photoelectrically converted. An image sensor (photoelectric conversion means) 111 is accommodated. In this case, the pair of reflecting mirrors 108 and 109 are mounted on a mirror carriage 112, and the mirror carriage 112 is connected to a focus motor M2 (moving means) via a general drive transmission means such as a gear or a cam. Can be moved in the direction indicated by the arrow B (the left-right direction in FIG. 1). Then, by moving the mirror carriage 112 in the direction of arrow B by driving the focus motor M2, the focal position can be moved while maintaining a predetermined optical path length from the lamp 105 to the image sensor 111. Yes. In particular, in the present embodiment, as will be described later, the focal position can be moved 6 mm upward and 2 mm downward at a pitch of 0.2 mm with reference to the upper surface of the platen 102.

  As shown in FIG. 3, the image sensor 111 has three line sensors R (red), G (green), and B (blue) arranged in parallel, and each line sensor R, G , B have a plurality of photoelectric conversion elements (pixels) r, g, b arranged in a line.

  On the other hand, the transmissive light source unit 200 includes a housing 201 as shown in FIG. 1, and a glass 202 is disposed on the bottom surface of the housing 201 so as to face the platen 102. A lamp carriage 204 is accommodated in the housing 201, and two lamps 205a and 205b are accommodated in the lamp carriage 204.

  In addition, the timing belt 203 spanned between the pair of pulleys 206a and 206b is engaged with the frame of the lamp carriage 204. At least one pulley 206a is rotated by driving the lamp carriage motor M3. Accordingly, when the lamp carriage motor M3 is driven to rotate the pulleys 206a and 206b, the lamp carriage 204 can move in the direction of arrow A along the glass 202 via the timing belt 203.

  As shown in detail in FIG. 2, the image reading apparatus 1 includes a CPU (control means, calculation means) 301. The CPU 301 includes a ROM 300, an image processing ASIC 303 that performs various image processing, and Various motors M1, M2, M3 and various lamps 105, 205a, 205b described above are electrically connected. Further, the image sensor 111 is also electrically connected to the CPU 300 via the A / D converter 302.

  The ROM 300 is composed of a flash memory, and stores a control program for controlling the entire image reading apparatus 1 and an autofocus program (the ROM 300 may be provided in the CPU 301). The CPU 301 controls the entire image reading apparatus 1 in accordance with a control program stored in the ROM 300 and performs autofocus control in accordance with an autofocus program stored in the ROM 300. The CPU 301 controls the reading carriage motor M1, the focus motor M2, and the lamp carriage motor M3 via a motor driver (not shown), and controls the lamps 105, 205a, and 205b via an inverter (not shown). .

  The image processing ASIC 303 is connected to a memory 305 storing an image processing program, and an image sensor 111 is electrically connected via an A / D converter 302. Further, the image processing ASIC 303 can be connected to the personal computer 400 via the interface 304.

  Next, a document reading operation by the image reading apparatus 1 having the above configuration will be briefly described.

  First, when the document is a reflection document such as general paper, the user places the document on the platen 102 and selects “reflection document” on the screen of the personal computer 400. Accordingly, the CPU 301 irradiates the original with light from the lamp 105 while moving the reading carriage 103 in the sub-scanning direction (the direction indicated by the arrow A in FIG. 1). Reflected light (image light) reflected by the document enters the image sensor 111 via the reflection mirrors 106, 107, 108, 109 and the imaging lens 110, and is photoelectrically converted by the image sensor 111. Note that the lamps 205a and 205b of the lamp carriage 204 are not lit when reading such a reflective original.

  On the other hand, when the original is a transparent original such as a film, the user places the transparent original set in a film folder or the like on the platen 102 and selects “transparent original” on the screen of the personal computer 400. Thus, the CPU 301 moves the reading carriage 103 in the sub-scanning direction with the lamp 105 turned off, and in synchronization with this movement, moves the lamp carriage 204 in the sub-scanning direction with the lamps 205a and 205b turned on. Move to. Further, light (image light) from the lamps 205 a and 205 b that has passed through the document enters the image sensor 111 via the reflection mirrors 106, 107, 108, and 109 and the imaging lens 110, and is subjected to photoelectric conversion by the image sensor 111. Is done. Note that the lamp 105 of the reading carriage 103 is not lit when reading such a transparent document.

Further, the image light incident on the image sensor 111 from the reflection original or the transmission original in this way is output as the analog signals s _R , s _G , s _B from the line sensors R, G, B of the image sensor 111. . These analog signals s _R , s _G , and s _B are subjected to gain / offset processing, and then converted to a 16-bit digital signal s ′ for each pixel by the A / D converter 302 to perform image processing. To the ASIC 303 for use. The image processing ASIC 303 performs various image processing such as shading correction, γ correction, and color correction while using the memory 305, and the image signal s ″ subjected to such image processing is transmitted via the interface 304. The image data is output to a personal computer (host computer) 400.

  Next, a method of automatically adjusting the focal position by the image reading apparatus 1 having the above configuration will be described with reference to the flowcharts of FIGS.

  First, the automatic adjustment of the focal position by the image reading apparatus 1 of the present embodiment is started by acquiring a preview image as shown in FIG. 4 (step S1000). In acquiring the preview image, the operator first places the document to be read on the platen 102, selects “reflective document” or “transparent document” on the screen of the personal computer 400, and then selects “preview”. To do. As a result, a preview signal and a “reflective original” reading signal or a “transparent original” reading signal are transmitted from the personal computer 400 to the CPU 301 of the image reading apparatus 1 via the interface (I / F) 304.

  When the CPU 301 receives these signals and recognizes that the original placed on the platen 102 is a reflective original by the “reflective original” reading signal, it drives the reading carriage motor M1 to turn on the lamp 105. By actuating the image sensor 111, the reading carriage 103 is moved along the platen glass 102, and the entire surface of the platen glass 102 is scanned at a low resolution. Then, the CPU 301 transmits the image data obtained by this scanning as preview data to the personal computer 400 via the interface 304.

  When the CPU 301 recognizes that the original placed on the platen 102 is a transparent original by the “transparent original” reading signal, the CPU 301 drives the reading carriage motor M1 and the lamp carry motor M3 to drive the lamps 205a and 205b. The reading carriage 103 and the lamp carriage 204 are moved synchronously along the platen glass 102 by operating the image sensor 111 and the entire surface of the platen glass 102 is scanned at a low resolution. Then, the CPU 301 transmits the image data obtained by this scanning as preview data to the personal computer 400 via the interface 304.

  On the other hand, the personal computer 400 that has received the preview data from the image reading apparatus 1 displays a preview screen 320 on the display 400a based on the received preview data, as shown in FIG. When such a preview screen 320 is displayed, the operator designates a desired capture area (trimming area 325) in the preview screen 320 and designates “autofocus”. As a result, the autofocus signal and the position information of the trimming area 325 are transmitted from the personal computer 400 to the CPU 301 of the image reading apparatus 1 via the interface (I / F) 304.

  When the preview image is acquired as described above, the process of step S1001 is subsequently performed. In step S1001, the CPU 301 calculates the center position O (see FIG. 8) of the trimming area 325 from the position information of the trimming area 325 acquired via the interface 304, and performs main scanning from the calculated trimming center position O. One line (see FIG. 8) consisting of 500 pixels before and after the direction (1000 pixels in total) is set as a focus detection area (line).

  Here, the reason for using the trimming center position O is to take the edge of the image in an optimum state. That is, the operator generally arranges the target to be captured in the center of the trimming region 325, and therefore it is optimal to use the trimming center position O as a reference in order to take an edge of the image. In addition, the reason why the line width of 1000 pixels is set as the focus detection area in the present embodiment is to suppress an increase in processing data amount and a long processing time when the designated trimming area 325 is large. This is because about 1000 pixels is considered to be the minimum area where an edge can be taken. Therefore, the pixel position need not be 1000 pixels as long as the focal position can be acquired with a desired accuracy within a desired time. If the length of the designated trimming area 325 is 1000 pixels or less, the length of the trimming area 325 in the main scanning direction is set as the focus detection area.

  In the apparatus of the present embodiment, the resolution can be changed to 50 to 12800 DPI. In the focus position adjustment described below, the focus position adjustment is performed at 600 DPI. This is because 600 DPI is considered to be the lowest resolution at which the edge of an image can be detected with a general reflective original or transparent original, and this resolution can be changed according to the processing time or the like.

  When the calculation of the center position O of the trimming area 325 and the setting of the focus detection area are performed as described above, the process of step S1002 is performed next time. In step S1002, the carriage 103 (204) is first moved to the trimming center position O calculated in step S1001. Specifically, when the original to be read is a reflective original, the reading carriage motor M1 is driven by the CPU 301 and the reading carriage 103 is moved to the trimming center position O. On the other hand, when the original to be read is a transparent original, the reading carriage motor M1 and the lamp carriage motor M2 are driven, and both the reading carriage 103 and the lamp carriage 204 are moved to the trimming center position O. In step S1002, 1000 pixels of each line sensor R, G, B corresponding to the focus detection area are set as focus detection pixels.

  When the above process is completed, the process proceeds to step S1003. In step S1003, as “pre-processing”, the size of the edge is obtained for each of R, G, and B, and the “post-processing” method is determined according to the obtained result. The “pre-processing” and “post-processing” will be described in detail with reference to the flowcharts of FIGS. 5 to 7. In general, in step S1003, all the edges of R, G, B are strong (adjacent pixels). (When the determination in step S1003 is YES), the process proceeds to step S1004, and the final focus position is obtained from the focus positions of R, G, and B. On the other hand, if the determination in step S1003 is NO, the process proceeds to step S1005, and the final focal position is obtained from the focal position of the luminance signal obtained by mixing R, G, and B.

  Next, the “pre-processing” in step S1003 will be described in detail with reference to the flowchart of FIG.

  In the “preprocessing”, as described above, the size of the edge is determined for each of R, G, and B. Specifically, the focal position is moved at a rough pitch (here, 0.0 mm, 2.0 mm, 4.0 mm), and the absolute value of the difference between adjacent pixels for each of R, G, and B at each focal position (hereinafter, referred to as “below”). By measuring the maximum value of the first sharpness value or first derivative value), the maximum edge near the best focus (final focal position) of the currently set document is obtained. Hereinafter, these processing steps will be described in order.

  First, in step S100, the focal position is set to 0.0 mm. Specifically, when the focus motor M2 is driven by the CPU 301, the mirror carriage 112 is moved, and the focal position is set to 0.0 mm (position on the upper surface of the platen 102).

In this way, when the focal position is set to 0.0 mm, image data is subsequently acquired, and the maximum value of the primary differential value (first sharpness value) is calculated for each of R, G, and B ( Step S101). Specifically, when the original to be read is a reflective original, the lamp 105 is turned on and image data is acquired by the image sensor 111. On the other hand, when the original to be read is a transparent original, the lamps 205a and 205b are turned on and the image sensor 111 acquires image data. Then, from these acquired image data, for each of R, G, and B, the absolute value of the difference between adjacent pixels (primary differential value or first sharpness value) for 1000 pixels previously set in step S1002 D (0, i) = | X (i + 1) −X (i) | (i = 0 to 999) is obtained (see FIG. 9), and R is selected from these absolute values (first sharpness values). , G, B maximum values D (0) _MAXR , D (0) _MAXG , D (0) _MAXB are determined respectively. Thus, if the maximum value is obtained for each of R, G, and B, it can be determined whether or not the document has a color bias.

When the maximum values D (0) _MAXR , D (0) _MAXG , D (0) _MAXB for each of R, G, and B at the focal position of 0.0 mm are determined as described above, even at the focal position of 2.0 mm. Similar processing is performed. That is, first, in step S102, the focal position is set to 2.0 mm. Specifically, the focus motor M2 is driven by the CPU 301 to move the mirror carriage 112, and the focal position is set to 2.0 mm (a position 2 mm upward from the upper surface of the platen 102). Subsequently, in step S103, image data is acquired, and the maximum value of the primary differential value (first sharpness value) is calculated for each of R, G, and B. That is, as in step S101, for each of R, G, and B, the absolute value (primary differential value or first sharpness value) D of the difference between adjacent pixels for 1000 pixels previously set in step S1002 2, i) = | X (i + 1) −X (i) | (i = 0 to 999), and from these absolute values (first sharpness values), the maximum for each of R, G, and B The values D (2) _MAXR , D (2) _MAXG , D (2) _MAXB are determined, respectively.

Further, the same processing is performed at the focal position of 4.0 mm. That is, by driving the focus motor M2 by the CPU 301, the mirror carriage 112 is moved, and the focal position is set to 4.0 mm (a position 4 mm upward from the upper surface of the platen 102) (step S104). Subsequently, for each of R, G, and B, for 1000 pixels, the absolute value of the difference between adjacent pixels (primary differential value or first sharpness value) D (4, i) = | X (i + 1) −X (I) | (i = 0 to 999) is obtained, and the maximum value D (4) _MAXR , D (4) _{MAXG for} each of R, G, and B is obtained from these absolute values (first sharpness values). , D (4) _MAXB is determined (step S105).

When the maximum value of the first sharpness value is determined for each of R, G, and B at each focal position as described above, the maximum value of each of the three focal positions for R, G, and B is now determined. The largest value is selected from the list (step S106). That is, for R, the largest value among the maximum values D (0) _MAXR , D (2) _MAXR , D (4) _MAXR obtained in steps S101, ₁₀₃ , ₁₀₅ is determined as _DMAXR . Similarly, for G, the largest value among the maximum values D (0) _MAXG , D (2) _MAXG , D (4) _MAXG obtained in steps S101, 103, 105 is determined as D _MAXG , and B As for D, the largest value is determined as D _MAXB from the maximum values D (0) _MAXB , D (2) _MAXB , D (4) _MAXB obtained in steps S101, ₁₀₃ , ₁₀₅ .

Thereafter, in step S107, the maximum values D _MAXR , D _MAXG , D _MAXB in each of R, G, B are respectively compared with a predetermined threshold A, and all of the maximum values D _MAXR , D _MAXG , D _MAXB are greater than the threshold A. Judge whether it is large or not. When all of the maximum values D _MAXR , D _MAXG , D _MAXB are larger than the threshold value A (when the determination in step S107 is YES: the edge of the document is strong. Also, even if there is a color deviation, it is high. In the case of bias in level), the process proceeds to the above-described processing in step S1004, and when at least one of the maximum values D _MAXR , D _MAXG , D _MAXB is smaller than the threshold value A (determination in step S107 is performed). In the case of NO: when the edge of the document is strong or when the color deviation is large), the process proceeds to the above-described step S1005. In the present embodiment, the predetermined threshold A is set to 50/256.

  Next, the “post-processing” in step S1004 will be described in detail with reference to the flowchart of FIG.

  In this “post-processing”, as described above, the final focus position is obtained from the focus positions of R, G, and B. Specifically, the focal position is moved from −2.0 mm to 6.0 mm with a fine pitch (0.2 mm), and the sum of absolute values of differences between adjacent pixels for each of R, G, and B at each focal position (hereinafter referred to as “below”). , A second sharpness value), and a final focal position P is obtained from these second sharpness values. Hereinafter, these processing steps will be described in order.

  First, in step S200, the focal position is set to -2.0 mm. Specifically, when the focus motor M2 is driven by the CPU 301, the mirror carriage 112 is moved, and the focal position is set to −2.0 mm (a position 2.0 mm downward from the upper surface of the platen 102).

In this way, when the focal position is set to −2.0 mm, image data is subsequently acquired, and the sum of the primary differential values (first sharpness values) for each of R, G, and B, that is, the second value is obtained. A sharpness value is calculated (step S201). In this case, only primary differential values of 70% or more of the maximum values D _MAXR , D _MAXG , D _MAXB for each color component obtained in step S106 are extracted and added. Specifically, when the original to be read is a reflective original, the lamp 105 is turned on and image data is acquired by the image sensor 111. On the other hand, when the original to be read is a transparent original, the lamps 205a and 205b are turned on and the image sensor 111 acquires image data. Then, from these acquired image data, for each of R, G, and B, the absolute value of the difference between adjacent pixels (primary differential value or first sharpness value) for 1000 pixels previously set in step S1002 D (−2.0, i) = | X (i + 1) −X (i) | (i = 0 to 999) is obtained, and the primary differential D (−2.0, i) The sum of (i = 0 to 999) (M = Σ | x (i + 1) −x (i) | (second sharpness value) is obtained, but in this case, as described above, in step S106 _Only the primary differentials D (−2.0, i) of 70% or more of the maximum values D _MAXR , D _MAXG , D _MAXB for each color component obtained are extracted and added, and M (− 2.0) _R , M (−2.0) _G and M (−2.0) _B are obtained, respectively.

  In this way, by enabling only the primary differential value of 70% or more of the maximum value, only the edge near the peak at the current document level can be detected, and the peak position is accurately and stably detected. The position can be detected. The numerical value of 70% can be variously changed according to the processing conditions and the like, and is desirably set as appropriate based on the processing conditions and the like.

As described above, the second sharpness values M (−2.0) _R , M (−2.0) _G , and M (−2) for each of R, G, and B at the focal position of −2.0 mm. 0.0) After obtaining _B , the focus motor M2 is driven to move the mirror carriage 112, and the focal position is moved from −2.0 mm to +6.0 mm at a pitch of 0.2 mm. Similarly, the second sharpness value is obtained for each of R, G, and B (steps S202, 203, and 204). When such data is extracted, a curve indicating the second sharpness value for each focal position is obtained for each of R, G, and B, as shown in FIG.

  When such a curve is obtained, this time, in step S205, for each of R, G, and B, an approximate quadratic curve is obtained from the second sharpness value at each focal position obtained in steps S200 to S204. (Approximate quadratic curves of the R, G, and B curves in FIG. 10A are obtained (see FIG. 10B)... Smoothing process). Thus, by taking an approximate curve, it is difficult to pick up variations due to the influence of noise or the like, and an accurate and stable position can be detected. In addition, since calculation is performed using only strong edges (only the first derivative value of 70% or more of the maximum value), a sufficient focal position can be obtained with a quadratic curve, and higher orders than the second order such as the third order and the fourth order. Thus, it is not necessary to obtain an approximate curve, and the time can be shortened.

When the approximate quadratic curve is obtained, it is subsequently determined whether or not the maximum value of the approximate quadratic curve is obtained (step S206). When the maximum value is obtained, the focal positions P _R , P _G , and P _B (see FIG. 10B) corresponding to the maximum value are obtained (step S207), and when the maximum value is not obtained, the maximum value is obtained. determining a focal position corresponding to the value P _R, P _G, as P _B (step S208). Note that the case where the maximum value cannot be obtained is a case where the coefficient relating to the square term of the approximate curve is positive (when only a minimum value is obtained) or a case where there is no maximum value between -2 mm and +6 mm. .

As described above, when the focal positions P _R , P _G , and P _B are obtained for all of R, G, and B (step S209), the focal positions P _R , P _{G of} R, G, and B are then used. , P _B are obtained (simple average), and this average position is set as the final focal position P (see FIG. 10B) (step S210). By averaging in this way, it is possible to determine a single point P in consideration of all colors, but not only a simple average here but also a more accurate position is determined by weighting according to the characteristics of the optical system. be able to.

  When the final focal position P is obtained in this way, the focus motor M2 is driven to move the mirror carriage 112, and the focal position is moved to the focal position P obtained in step S210 (step S211). Then, by driving the reading carriage motor M1, the reading carriage 103 is moved in the sub-scanning direction from the reading start position of the trimming area 325 (the left end line of the trimming area 325) shown in FIG. To do.

  In the above processing, the first sharpness value and the second sharpness value are obtained by changing the focal position at a fine pitch, but the first sharpness value obtained in advance in the “preprocessing” is used to obtain the first sharpness value. 2 may be obtained, or the first sharpness value and the second sharpness value may be obtained by changing the focal position at a pitch coarser or finer than the 0.2 mm pitch.

  Next, the “post-processing” in step S1005 will be described in detail with reference to the flowchart of FIG.

  In this “post-processing”, as described above, the focal position of the luminance signal obtained by mixing R, G, and B is obtained, and the final focal position is obtained. Specifically, first, when the focus motor M2 is driven by the CPU 301, the mirror carriage 112 is moved, and the focal position is set to −2.0 mm (a position 2.0 mm downward from the upper surface of the platen 102). (Step S300). In this way, when the focal position is set to −2.0 mm, the image data is acquired to obtain a luminance signal, and the sum of the first derivative values of the luminance signal is calculated (step S301). Specifically, the sum (second sharpness value) of the first derivative of the luminance signal (gray signal) is obtained from data for one line of 1000 pixels. That is, when the original to be read is a reflective original, the lamp 105 is turned on to acquire image data by the image sensor 111. When the original to be read is a transparent original, the lamps 205a and 205b are turned on. Then, image data is acquired by the image sensor 111. Then, each color signal output from each pixel of the R, G, B line sensor (density signal output from each pixel of the R, G, B line sensor) is mixed to obtain a luminance signal K (−2.0). , I) = (77R (i) + 150G (i) + 29B (i)) / 256 (i = 1 to 1000) and sum of absolute values of differences between adjacent pixels of the luminance signal (second sharpness) Value), that is, C (−2.0) = Σ | K (i + 1) −K (i) | (i = 0 to 999) is obtained (see FIG. 11). In this way, the luminance signal is obtained from each color signal, and the focal position is obtained using this luminance signal, so that the position of the color in the color image or the original with a weak edge can be detected more accurately and stably. Will be able to.

  Note that the luminance signal can be obtained by (77 * R + 150 * + 29 * B) / 256 as described above. In this case, the coefficients applied to the R, G, and B color signals are generally predetermined coefficients for obtaining the luminance signal from the digital color information, but other commonly used coefficients may be used. Absent. In addition, when the balance is unique to the optical system, a more beautiful grayscale can be created by detecting the desired position by changing the ratio of the coefficients in accordance with the balance. . In the present embodiment, since each color signal is handled as 8 bits, the above coefficient is used, but it goes without saying that the coefficient is changed according to the number of bits.

  As described above, when the second sharpness value of the luminance signal at the focal position −2.0 mm is obtained, the focus motor M2 is driven to move the mirror carriage 112, and the focal position is changed from −2.0 mm to +6. The second sharpness value C (P) of the luminance signal (P = each focal position, from −2.0 mm to 6.0 mm) in the same manner as in step S <b> 301 while moving at a pitch of 0.2 mm to 0 mm. 0.2 mm pitch) is obtained (steps S302, 303, 304). In this way, when the second sharpness value of the luminance signal is plotted for each focal point, a curve as shown on the upper side of FIG. 12A (the second luminance color signal for each focal point position). Curve showing the sharpness value).

  If such a curve is obtained, then in step S305, the second sharpness value of each focal position obtained in steps S300 to 304 is subjected to a smoothing process. In this case, for example, an average value of five points, for example, an average value of a total of five pixels including the target pixel and two pixels before and after the target pixel is obtained (for example, when the target pixel is C (2.4), the average value is ( C (2.0) + C (2.2) + C (2.4) + C (2.6) + C (2.8)) / 5) The process is applied. In addition, the curve after the smoothing process is shown below (a) of FIG.

  Subsequently, a maximum value is obtained from the second sharpness value of each focal position after the smoothing process, and a quadratic approximate curve is obtained using a value of ± 2 mm (10 locations at a 0.2 mm pitch) of the maximum value. (See (b) of FIG. 12) is obtained (step S306).

  When the approximate quadratic curve is obtained, it is subsequently determined whether or not the maximum value of the approximate quadratic curve is obtained (step S307). When the maximum value is obtained, the maximum value is calculated (step S308), and when the maximum value is not obtained, the maximum value is obtained (step S309). The case where the maximum value cannot be obtained is a case where the coefficient relating to the square term is positive or a case where there is no maximum value between -2 mm and +6 mm. Then, the focal position corresponding to the maximum value obtained in step S308 or the focal position corresponding to the maximum value obtained in step S309 is obtained as the final focal position P (step S310).

  When the final focal position P is thus obtained, the focus motor M2 is driven to move the mirror carriage 112, and the focal position is moved to the focal position P obtained in step S310 (step S311). Then, by driving the reading carriage motor M1, the reading carriage 103 is moved in the sub-scanning direction from the reading start position (the left end line of the trimming area 325) of the trimming area 325 shown in FIG. To do.

  Note that the CPU 301 performs all the operations and controls described above with reference to the flowchart. In this case, the CPU 301 may be operated using a recording medium in which a program for causing the CPU (computer) 301 to execute the calculation and control is used, or the program may be incorporated in the CPU 301 itself. .

  Alternatively, the focal position may be obtained by installing a focal position adjustment program in a personal computer as part of a control program (driver software) for controlling the image reading apparatus.

  As described above, in the present embodiment, a plurality of first sharpness values are obtained from the image signal output from the image sensor 111 instead of obtaining the sharpness value from the difference between all the pixels used for autofocus. And obtaining a maximum value having a maximum value from among the plurality of first sharpness values, and extracting a first sharpness value equal to or greater than a value obtained by multiplying the maximum value by a predetermined ratio. The second sharpness value is obtained from the extracted first sharpness value, and the focal position is adjusted based on the second sharpness value. That is, a signal at a portion that is not an edge portion of the image, that is, a portion where the difference between adjacent pixels is small is excluded from the focus adjustment processing. In this way, if only the first sharpness value greater than or equal to the predetermined value is enabled in the focus adjustment process, only the edge near the peak at the current document level can be detected, and the peak position can be accurately detected. Stable position detection can be performed. That is, it is possible to perform automatic focus adjustment with high accuracy and high reproducibility.

Needless to say, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the scope of the invention. For example, in the above-described embodiment, the focal position is changed by moving the reflecting mirrors 108 and 109 in the sub-scanning direction, but the imaging lens 110 and the image sensor 111 are moved instead of or together with the reflecting mirror. The focal position may be changed by doing so. In the above-described embodiment, in the “post-processing” in step S1004, the first sharpness value that is 70% or more of the maximum value of the first sharpness value is extracted and added. Although the sharpness value is obtained, the ratio of the first sharpness value to be extracted to the maximum value is not limited to 70%. In the above-described embodiment, the absolute value | X (i + 1) −X (i) | of the difference between adjacent pixels is used as the first sharpness value. However, the first sharpness value is For example, any value can be used as long as the difference between output values between adjacent pixels is known, such as the square of the absolute value of the difference between adjacent pixels (| X (i + 1) −X (i) | ² ). Similarly, in the above-described embodiment, the sum Σ | x (i + 1) −x (i) | of the absolute values of differences between adjacent pixels is used as the second sharpness value. The sharpness value may be, for example, the sum of squares of the absolute values of differences between adjacent pixels (Σ | X (i + 1) −X (i) | ² ). In the above-described embodiment, a linear sensor is used as the photoelectric conversion unit. However, a planar sensor may be used. In the above-described embodiment, focus adjustment is performed using signals of all R, G, and B color components. For example, focus adjustment is performed using one color component signal or two color component signals. May be. In the above-described embodiment, “preprocessing” is performed in which the focal position is roughly moved to obtain D _max at each focal position. However, this “preprocessing” may not be performed. In the above-described embodiment, in the “post-processing” in step S1005, the mixing ratio of each color signal R, G, B is set to 77: 150: 29 (about 3: 6: 1). The mixing ratio and the color to be mixed are arbitrary.

  The present invention can be applied to all image reading apparatuses and methods and programs that read an image by adjusting a focal position.

1 is a schematic diagram illustrating a configuration example of an optical system mainly of an image reading apparatus to which the present invention is applicable. FIG. 2 is a block diagram schematically showing a configuration example mainly of a control system of the image reading apparatus of FIG. 1. It is a schematic diagram of the image sensor integrated in the optical system of the image reading apparatus of FIG. It is a flowchart which shows the first step of the focus position adjustment process based on one Embodiment of this invention. It is a flowchart which shows the "preprocessing" contained in the focus position adjustment process which concerns on one Embodiment of this invention. It is a flowchart which shows the "post-processing" which calculates | requires the final focus position from each R, G, B focus position. It is a flowchart which shows the "post-processing" which calculates | requires the focus position of the luminance color signal which mixed R, G, and B, and acquires the last focus position. FIG. 5 is a preview screen displayed on the display of a personal computer in step S1000 of FIG. FIG. 7 is an explanatory diagram for describing a method of obtaining a first sharpness value in “post-processing” in FIG. 6. (A) is a curve showing the second sharpness value for each focus position for each of R, G, and B in the “post-processing” of FIG. 6, and (b) is a curve of the R, G, and B curves of (a). It is an approximate quadratic curve. FIG. 8 is an explanatory diagram for explaining a method of obtaining a luminance signal and a second sharpness value in “post-processing” in FIG. 7. (A) is a curve (upper side) showing the second sharpness value of the luminance signal for each focal position in the “post-processing” of FIG. 7, a curve (lower side) obtained by smoothing this curve, and (b) (A) It is an approximate quadratic curve created using the values at 10 locations before and after the maximum value in the lower curve.

Explanation of symbols

1 Image reader 111 Image sensor (photoelectric conversion means)
105, 106, 107, 108, 109 Reflection mirror (optical system)
301 CPU (control means, calculation means)
M2 Focus motor (moving means)

Claims (15)

Photoelectric conversion means for photoelectrically converting image light composed of reflected light reflected from the document or transmitted light transmitted through the document and outputting an image signal; an optical system for guiding the image light to the photoelectric conversion means; and the optical system An image reading apparatus that adjusts a focal position by moving at least a part of the optical system by the moving unit.
A first calculation for obtaining a plurality of first sharpness values from the image signal output from the photoelectric conversion means and for obtaining a maximum value having a maximum value from the plurality of first sharpness values. Means,
A first sharpness value equal to or larger than a value obtained by multiplying the maximum value by a predetermined ratio is extracted from the plurality of first sharpness values, and a second sharpness value is extracted from the extracted first sharpness value. A second computing means for obtaining a degree value;
Control means for adjusting the focus position by controlling the moving means based on the second sharpness value;
An image reading apparatus comprising: Photoelectric conversion means for photoelectrically converting image light composed of reflected light reflected from the document or transmitted light transmitted through the document and outputting an image signal; an optical system for guiding the image light to the photoelectric conversion means; and the optical system An image reading apparatus that adjusts a focal position by moving at least a part of the optical system by the moving unit.
While moving at least a part of the optical system by the moving unit, a plurality of first sharpness values are obtained from the image signal output from the photoelectric conversion unit, and the plurality of first sharpness values are obtained. First computing means for obtaining a maximum value having a maximum value from
The image signal output from the photoelectric conversion unit is obtained by acquiring image signals at a shorter interval than the case of the first calculation unit while moving at least a part of the optical system by the moving unit. A plurality of first sharpness values are obtained from the first sharpness values, and a first sharpness value equal to or greater than a value obtained by multiplying the maximum value by a predetermined ratio is extracted from the plurality of first sharpness values. Second computing means for obtaining a second sharpness value from the first sharpness value obtained;
Control means for adjusting the focal position by controlling the moving means based on the second sharpness value;
An image reading apparatus comprising:   The image reading apparatus according to claim 1, wherein the first sharpness value is an absolute value of a difference between adjacent pixels of the photoelectric conversion unit.   The image reading apparatus according to claim 1, wherein the second sharpness value is a sum of absolute values of differences between adjacent pixels of the photoelectric conversion unit.   The image reading apparatus according to claim 1, wherein the second sharpness value is a sum of the first sharpness values having a value of 70% or more of the maximum value.   The image reading apparatus according to claim 1, wherein a smoothing process is performed on the second sharpness value.   The optical system includes a reflection mirror that reflects reflected light or transmitted light from a document, and an imaging lens that forms an image on the photoelectric conversion unit with light passing through the reflection mirror, and the moving unit includes the reflection mirror. The image reading apparatus according to claim 1, wherein the image reading apparatus is moved. A third calculating means for obtaining an approximate curve of quadratic or higher from the second sharpness value and obtaining a position where the maximum value of the approximate curve is obtained;
The image reading apparatus according to claim 1, wherein the control unit adjusts a focal position based on a position where the maximum value obtained by the third calculation unit is obtained.   The image reading apparatus according to claim 1, wherein the photoelectric conversion unit includes a plurality of line sensors arranged in parallel to photoelectrically convert light of different colors. The first calculation means obtains the first sharpness value and the maximum value of the first sharpness value for each line sensor from a plurality of color image signals output from the line sensors,
The said 2nd calculating means calculates | requires the said 1st and 2nd sharpness value for every line sensor from the image signal of the several colors output from the said each line sensor, It is characterized by the above-mentioned. Image reading apparatus. The second calculating means further includes a third calculating means for obtaining a quadratic approximate curve for each line sensor from the second sharpness value obtained by the second calculating means and obtaining a maximum value of each approximate curve. ,
The image reading apparatus according to claim 10, wherein the control unit adjusts a focal position based on an average position of each position where a maximum value of each approximate curve obtained by the third calculation unit is obtained. apparatus. Photoelectric conversion means for photoelectrically converting image light composed of reflected light reflected from the document or transmitted light transmitted through the document and outputting an image signal; an optical system for guiding the image light to the photoelectric conversion means; and the optical system A focus position adjusting method for an image reading apparatus, wherein the focus position is adjusted by moving at least a part of the optical system by the moving means.
Obtaining a plurality of first sharpness values from the image signal output from the photoelectric conversion means, and obtaining a maximum value having a maximum value from the plurality of first sharpness values,
A first sharpness value equal to or larger than a value obtained by multiplying the maximum value by a predetermined ratio is extracted from the plurality of first sharpness values, and a second sharpness value is extracted from the extracted first sharpness value. Find the degree value,
Adjusting the focal position based on the second sharpness value;
A method for adjusting the focal position. Photoelectric conversion means for photoelectrically converting image light composed of reflected light reflected from the document or transmitted light transmitted through the document and outputting an image signal; an optical system for guiding the image light to the photoelectric conversion means; and the optical system A focus position adjusting method for an image reading apparatus, wherein the focus position is adjusted by moving at least a part of the optical system by the moving means.
While moving at least a part of the optical system by the moving unit, a plurality of first sharpness values are obtained from the image signal output from the photoelectric conversion unit, and the plurality of first sharpness values are obtained. A first calculation step for obtaining a maximum value having a maximum value from
While moving at least a part of the optical system by the moving means more finely than in the case of the first calculation step, a plurality of first sharp edges are generated from the image signal output from the photoelectric conversion means. A degree value is obtained, and a first sharpness value equal to or greater than a value obtained by multiplying the maximum value by a predetermined ratio is extracted from the plurality of first sharpness values, and the extracted first sharpness value is obtained. A second calculation step for obtaining a second sharpness value from the value;
An adjusting step for adjusting the focal position by controlling the moving means based on the second sharpness value;
A focal position adjustment method comprising: Photoelectric conversion means for photoelectrically converting image light composed of reflected light reflected from the document or transmitted light transmitted through the document and outputting an image signal; an optical system for guiding the image light to the photoelectric conversion means; and the optical system A program used for adjusting the focal position of an image reading apparatus that adjusts a focal position by moving at least a part of the optical system by the moving means.
Obtaining a plurality of first sharpness values from the image signal output from the photoelectric conversion means, and obtaining a maximum value having a maximum value from the plurality of first sharpness values;
A first sharpness value equal to or larger than a value obtained by multiplying the maximum value by a predetermined ratio is extracted from the plurality of first sharpness values, and a second sharpness value is extracted from the extracted first sharpness value. Obtaining a degree value;
Determining a focal position based on the second sharpness value;
A program that causes a computer to execute. Photoelectric conversion means for photoelectrically converting image light composed of reflected light reflected from the document or transmitted light transmitted through the document and outputting an image signal; an optical system for guiding the image light to the photoelectric conversion means; and the optical system A program used for adjusting the focal position of an image reading apparatus that adjusts a focal position by moving at least a part of the optical system by the moving means.
While moving at least a part of the optical system by the moving unit, a plurality of first sharpness values are obtained from the image signal output from the photoelectric conversion unit, and the plurality of first sharpness values are obtained. A first calculation step for obtaining a maximum value having a maximum value from
While moving at least a part of the optical system by the moving means more finely than in the case of the first calculation step, a plurality of first sharp edges are generated from the image signal output from the photoelectric conversion means. A degree value is obtained, and a first sharpness value equal to or greater than a value obtained by multiplying the maximum value by a predetermined ratio is extracted from the plurality of first sharpness values, and the extracted first sharpness value is obtained. A second calculation step for obtaining a second sharpness value from the value;
Determining a focal position based on the second sharpness value;
A program that causes a computer to execute.

Images