Abstract:
Disclosed is a symbol reading device including: an imaging section to capture a symbol and generate an image; a detecting section to detect a size of the symbol; a judging section to judge large or small by comparing the size of the symbol to a pre-set value; a focus movement controlling section to move a focus position of the imaging section to a predetermined position of a farther side when the size of the symbol is smaller than the pre-set value as a result of the judgment, and to move a focus position of the imaging section to a predetermined position of a closer side when the size of the symbol is larger than the pre-set value as a result of the judgment; and an analyzing section to analyze symbol data corresponding to the symbol at a focus position moved by the focus movement controlling section.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2009-047709 filed Mar. 2, 2009, the entire contents of which are incorporated herein by reference. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a symbol reading device, symbol reading method and program recording medium to read a symbol of a barcode or two dimensional code where focus is controlled based on size of a captured symbol. 
         [0004]    2. Description of the Related Art 
         [0005]    Symbols are widely used to identify various pieces of information. A barcode is a symbol representing numeric value information according to specification by one dimensional graphic representation. Lately, a symbol called two dimensional code which holds information in both vertical and horizontal directions is becoming widespread. 
         [0006]    A symbol reading device such as a “handy terminal” (portable terminal for commercial use) images an object including a symbol with an imaging device such as a camera and by analyzing the imaged image with a decoding engine, the symbol reading device reads contents of the symbol. 
         [0007]    When a symbol such as a barcode or two dimensional code is imaged by a symbol reading device including an imaging device such as a digital camera to extract an ID, it is difficult to find a suitable composition or distance to capture the symbol. 
         [0008]    Conventionally, in a digital camera including a seamless focus adjustment function, as a method for selecting the most suitable focus position for capturing an object such as a barcode, the following methods could be used. For example, there is a method of directly measuring a distance to the object with a ranging sensor which uses PSD (Position Sensitive Detector) or by a phase difference method which uses a pair of linear image sensors or measuring a distance by a ranging method using laser irradiation and directly moving the lens to the focus position according to the value. 
         [0009]    Since the above described method consumes only about an instant to determine the best focus, a good response can be provided to the user and there is also a merit of high accuracy. On the other hand, a ranging device (sensor) separate from a camera module is necessary, and thus there is the demerit that the cost increases and the size becomes large. Therefore, such method is often used in a single lens reflex camera where there is relatively allowance for cost and size. 
         [0010]    Also, other than the method described above, there is a contrast method as a method often used in compact digital cameras, etc. 
         [0011]    The contrast method is a method in which images are sequentially captured while moving the focus position from the farthest point to the closest point to find the focus position where the contrast of the captured image is judged to be highest. This method uses the operation of sequentially capturing images while moving the focus position and thus there is a demerit that the method is time consuming. 
         [0012]    For example, Japanese Patent Application Laid-Open Publication No. 2006-25055 discloses a technique where an imaging condition setting section is provided to set the imaging condition corresponding to normal photography and barcode capturing and when the barcode is captured, a suitable imaging condition is set as the imaging condition for barcode capturing with the barcode image fitted in the frame for alignment. 
       BRIEF SUMMARY OF THE INVENTION 
       [0013]    The present invention has been made in consideration of the above situation, and one of the main objects is to provide a symbol reading device, symbol reading method and recording medium where a user can extract an ID of a symbol with high speed by only positioning a symbol within a display screen of a symbol reading device and capturing the symbol. 
         [0014]    In order to achieve any one of the above objects, according to an aspect of the present invention, there is provided a symbol reading device including: 
         [0015]    an imaging section to capture a symbol and generate an image; 
         [0016]    a detecting section to detect a size of the symbol from the captured image generated by the imaging section; 
         [0017]    a judging section to judge large or small by comparing the size of the symbol detected by the detecting section to a pre-set value; 
         [0018]    a focus movement controlling section to move a focus position of the imaging section to a predetermined position of a farther side when the size of the symbol is smaller than the pre-set value as a result of the judgment by the judging section, and to move a focus position of the imaging section to a predetermined position of a closer side when the size of the symbol is larger than the pre-set value as a result of the judgment by the judging section; and 
         [0019]    an analyzing section to analyze symbol data corresponding to the symbol from the captured image captured by the imaging section at a focus position moved by the focus movement controlling section. 
         [0020]    According to another aspect of the present invention, there is provided a recording medium storing a program readable by a computer of a symbol reading device, to allow the computer to read the program to perform the following process including the steps of: 
         [0021]    detecting a size of a symbol from the captured image generated by a symbol captured by an imaging section; 
         [0022]    judging large or small by comparing the size of the detected symbol to a pre-set value; 
         [0023]    controlling to move a focus position of the imaging section to a predetermined position of a farther side when the size of the symbol is smaller than the pre-set value as a result of the judgment, and to move a focus position of the imaging section to a predetermined position of a closer side when the size of the symbol is larger than the pre-set value as a result of the judgment; and 
         [0024]    analyzing symbol data corresponding to the symbol from the captured image captured by the imaging section at a focus position moved by controlling movement. 
         [0025]    According to another aspect of the present invention, there is provided a symbol reading method performed by a computer of a symbol reading device, to allow the computer to perform the following process including the steps of: 
         [0026]    detecting a size of a symbol from the captured image generated by a symbol captured by an imaging section; 
         [0027]    judging large or small by comparing the size of the detected symbol to a pre-set value; 
         [0028]    controlling to move a focus position of the imaging section to a predetermined position of a farther side when the size of the symbol is smaller than the pre-set value as a result of the judgment, and to move a focus position of the imaging section to a predetermined position of a closer side when the size of the symbol is larger than the pre-set value as a result of the judgment; and 
         [0029]    analyzing symbol data corresponding to the symbol from the captured image captured by the imaging section at a focus position moved by controlling movement. 
         [0030]    According to the above aspects of the present invention, a symbol reading device, symbol reading method and recording medium can be provided, where a user can extract an ID of a symbol with high speed by only positioning a symbol within a display screen of a symbol reading device and capturing the symbol. 
         [0031]    Advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
         [0032]    The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention and wherein; 
           [0033]      FIG. 1  is a block diagram showing a schematic configuration of a symbol reading device  1  of the present embodiment; 
           [0034]      FIG. 2A  to  FIG. 2F  are diagrams showing how focus is adjusted when a two dimensional code is captured; 
           [0035]      FIG. 3  is a diagram showing a relation between distance from an imaging section  10  of the symbol reading device  1  to the two dimensional code which is an object of imaging and a lens position of a focus lens  11   b;    
           [0036]      FIG. 4  is a flowchart showing an example of a two dimensional code reading processing performed in the symbol reading device  1  of the present embodiment; 
           [0037]      FIG. 5  is a flowchart showing an example of a symbol area calculating processing; 
           [0038]      FIG. 6A  to  FIG. 6D  are diagrams showing each scene during symbol area calculating processing; 
           [0039]      FIG. 7  is a flowchart showing another example of a two dimensional reading processing performed in the symbol reading device  1  of the present embodiment; and 
           [0040]      FIG. 8  is a flowchart showing another example of a two dimensional reading processing performed in the symbol reading device  1  of the present embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0041]    An embodiment of the present invention will be described with reference to the drawings. 
         [0042]      FIG. 1  is a block diagram showing a schematic configuration of the symbol reading device  1  of the present embodiment. 
         [0043]    As shown in  FIG. 1 , the symbol reading device  1  includes an imaging section  10 , data processing section  20 , user interface section  30  and acceleration sensor  40 . 
         [0044]    The imaging section  10  includes an imaging lens section  11 , lens driving section  12  and image sensor  13 , and includes a function of capturing an object. 
         [0045]    The imaging lens section  11 , for example, includes a plurality of lenses to gather light in order to capture an object and includes a zoom lens  11   a  to adjust magnification and a focus lens  11   b  to adjust focus, and the like. 
         [0046]    The lens driving section  12  includes a zoom lens driving section  12   a  to move the zoom lens  11   a  in an optical axis direction when capturing the object, focus lens driving section  12   b  to move the focus lens  11   b  in the optical axis direction when capturing the object, and the like. The zoom lens driving section  12   a  and the focus lens driving section  12   b  each include an encoder and rotation amount of each motor can be detected. 
         [0047]    The image sensor  13 , for example, includes a solid imaging element such as CCD (Charge Coupled Device), CMOS (Complementary Metal Oxide Semiconductor), etc., and imports an image formed in the imaging lens section  11  by gathering light and imports the image as digitalized image data. The imported image data is temporarily stored in a memory  21  of the data processing section  20 . 
         [0048]    The data processing section  20  includes a memory  21 , image processing section  22 , image output section  23 , control section  24  and program memory  25 . 
         [0049]    The memory  21  temporarily stores image data (for example, barcode image, etc.) imported by the image sensor  13  each time capturing processing is performed. Also, the memory  21  stores image data, values of various flags, thresholds, etc. necessary for image processing. Further, the memory  21  includes a display memory area for performing storage and read out of display image data to perform image display. 
         [0050]    The image processing section  22  performs predetermined image processing on image data temporarily stored in the memory  21  in order to perform image display. After the image processing is performed on the image data, the image data is stored in the display memory area of the memory  21  as display image data. 
         [0051]    The image output section  23  reads out display image data stored in the display memory area of the memory  21  and generates an RGB signal based on the read out display image data and outputs the generated RGB signal to a liquid crystal display section  31  of the user interface section  30 . Also, the RGB signal is externally output through an external interface  33  of the user interface section  30  so that an image can be displayed by an external device such as a television, PC, projector or the like. 
         [0052]    The control section  24  internally includes a CPU (computer), RAM, etc., and also includes a zoom lens driving control section  24   a , focus lens driving control section  24   b  and blur correction processing section  24   c . The CPU (computer) performs processes of various control operations according to a program for the symbol reading device  1  stored in the program memory  25 . 
         [0053]    The zoom lens driving control section  24   a  calculates and holds in advance the number of pulses (driving amount) necessary to drive the zoom lens  11   a  with the DC motor and controls driving of the zoom lens  11   a  according to the driving amount. 
         [0054]    The focus lens driving control section  24   b  controls the position of the focus lens  11   b  according to an evaluated value of the focus accuracy of the image formed by the imaging lens section  11  such as contrast value or edge amount. Also, the focus lens driving control section  24   b  calculates a focus following position based on the calculated driving amount and drives the focus lens  11   b  to the focus following position. 
         [0055]    The blur correction processing section  24   c  drives a blur correction lens (not shown) of the imaging lens section  11  in a direction orthogonal to the optical axis according to the blur amount of the symbol reading device  1  input from a later described acceleration sensor  40  and controls correction of the blur of the image formed in the image sensor  13 . 
         [0056]    Also, the control section  24  detects the size of the two dimensional code from the captured image generated by the imaging section  10  and compares the size of the detected two dimensional code with a value set in advance to judge which is larger or smaller. As a result of the judgment, if the size of the two dimensional code is smaller than the pre-set value, the focus position of the focus lens  11   b  is moved to a predetermined position of the farther side and when the size of the two dimensional code is larger than the pre-set value, the focus position of the focus lens  11   b  is moved to a predetermined position of the closer side. Then, the symbol data corresponding to the two dimensional code is analyzed with the generated captured image. 
         [0057]    The program memory  25  includes a storage device such as a ROM (Read Only Memory) or Flash Memory and includes a storage medium to store various programs and pieces of data necessary to operate the control section  24 . Specifically, a two dimensional code reading program, which analyzes the two dimensional code to obtain information, and the like are stored in the storage medium. 
         [0058]    The user interface section  30  includes a liquid crystal display section  31 , operation section  32 , external interface section  33  and external memory  34 . 
         [0059]    The liquid crystal display section  31  displays an object image based on an RGB signal output from the image output section  23 . Specifically, the liquid crystal display section  31  displays a live preview image based on a plurality of pieces of image data generated by the imaging section  10  and moving images stored in the external memory  34  while recording and plays moving images stored in the external memory  34 . The liquid crystal display section  31  can include an image memory (not shown) to temporarily store display image data output as necessary from the image output section  23 . 
         [0060]    The operation section  32  is a function for a user to perform predetermined operation of the symbol reading device  1  and the operation section  32  outputs an operation signal according to the user operation to the control section  24 . The operation section  32  includes for example a shutter button, selection enter button, play button, capture button, mode switching button and the like. The mode switching button is a button used to switch between a moving image capturing mode for taking moving images and a still image capturing mode for taking still images. 
         [0061]    The external interface  33  is a connection terminal to connect with external devices such as a television, PC, projector or the like, and the external interface  33  performs sending and receiving of data through a predetermined communication cable. 
         [0062]    The external memory  34  includes, for example, a card shaped nonvolatile memory (flash memory), hard disk or the like and the external memory  34  stores a plurality of pieces of image data of object images taken by the imaging section  10  and compressed and encoded by the image processing section  22 . 
         [0063]    The acceleration sensor  40  physically and directly detects movement of the symbol reading device  1  and inputs a measurement value which shows the angular velocity to the control section  24 . 
         [0064]    The ID management section  50  includes an ID extraction section  51  and an ID storage section  52 . The ID extraction section  51  extracts an ID from a barcode image stored in the memory  21  based on an instruction from the control section  24 . The extracted ID is stored in the ID storage section  52 . 
         [0065]    Below, the operation of the digital camera  1  is described with reference to  FIG. 2A  to  FIG. 8 . 
         [0066]      FIG. 2A  to  FIG. 2F  are diagrams showing how focus is adjusted when a two dimensional code is captured. A two dimensional code is a code with a display system including information in a horizontal direction and vertical direction such as a QR code. For example, in three corners of a QR code, there is a design (eye) composed of a black square outer frame, a white square frame inside the black square outer frame and a black square inside the white square frame. Hereinafter, the image of the captured two dimensional code is called the symbol image. When the symbol image is captured, the focus lens  11   b  is to be in the default position (F 0 ). 
         [0067]      FIG. 2A  shows a live preview image when a symbol image is captured from a far point. In the present embodiment, “far” is defined to be a distance of 15 cm from the imaging section  10  of the symbol reading device  1 . When the image is captured from a “far” point, a slightly small symbol image is displayed on the screen of the liquid crystal display section  31  in a state out of focus as shown in  FIG. 2A . In order to resolve the unfocused state, the focus lens  11   b  moved to the farther side (F+) is shown in  FIG. 2B . 
         [0068]      FIG. 2C  shows a live preview image when the symbol image is captured in a focused state. In the present embodiment, a distance (=focus position) where focus is performed smoothly when the focus lens  11   b  is in the default position (F 0 ) is to be 10 cm from the imaging section  10  of the symbol reading device  1 . When capturing is performed in a focused state, a focused symbol image is displayed on the screen of the liquid crystal display section  31  as shown in  FIG. 2D . 
         [0069]      FIG. 2E  shows a live preview image when the symbol image is captured from a close point. In the present embodiment, “close” is defined to be a distance of 5 cm from the imaging section  10  of the symbol reading device  1 . When the image is captured from a “close” point, a slightly large symbol image is displayed on the screen of the liquid crystal display section  31  in a state out of focus as shown in  FIG. 2E . In order to resolve the unfocused state, the focus lens  11   b  moved to the closer side (F−) is shown in  FIG. 2F . 
         [0070]    As described above, in the symbol reading device  1  of the present embodiment, the state of the focus is judged by judging the approximate size of the symbol image and the position of the focus lens  11   b  is moved to the front and back. 
         [0071]      FIG. 3  is a diagram showing a relation between a distance from the imaging section  10  of the symbol reading device  1  to the two dimensional code which is the object and a lens position of the focus lens  11   b.    
         [0072]    For example, when the distance from the imaging section  10  of the symbol reading device  1  to the two dimensional code is close, the symbol image is focused in an area where the symbol image is imaged larger. In other words, the reading can be successfully achieved when the focus lens  11   b  is on the closer side (F−). 
         [0073]    Also, when the distance from the imaging section  10  of the symbol reading device  1  to the two dimensional code is near the focus position, the symbol image can be focused without moving the focus lens  11   b  from the default position (F 0 ). In the present embodiment, by performing image analysis processing, the image being slightly unfocused is allowable. Therefore, decoding can be successfully achieved in a relatively wide range. 
         [0074]    Also, when the distance from the imaging section  10  of the symbol reading device  1  to the two dimensional code is far, the symbol image is focused in an area where the symbol image is imaged smaller. In other words, the reading can be successfully achieved when the focus lens  11   b  is on the farther side (F+). 
       First Embodiment 
       [0075]      FIG. 4  is a flowchart showing an example of two dimensional code reading processing performed in the symbol reading device  1  of the present embodiment. This two dimensional code reading processing is realized by the control section  24  performing the two dimensional code reading program stored in the program memory  25 . 
         [0076]    As shown in  FIG. 4 , in step S 101 , the position of the focus lens  11   b  is moved to the default position (F 0 ). 
         [0077]    In step S 102 , the symbol image being imaged by the imaging section  10  is displayed through on the liquid crystal display section  31 . 
         [0078]    In step S 103 , it is judged whether or not the capture button of the operation section  32  has been pressed or not by the user. When the capture button is pressed, the processing advances to the next step S 104  and when the capture button is not pressed, the processing advances to step S 102 . 
         [0079]    In step S 104 , the symbol area calculating processing is performed. The symbol area calculating processing is specifically described with reference to  FIG. 5  and  FIG. 6A  to  FIG. 6D . 
         [0080]      FIG. 5  is a flowchart showing an example of the symbol area calculating processing. Also,  FIG. 6A  to  FIG. 6D  are diagrams showing each scene during symbol area calculation processing. 
         [0081]    As shown in  FIG. 5 , in step S 201 , the original image (see  FIG. 6A ) displayed through in step S 102  shown in  FIG. 4  is binarized (see  FIG. 6B ). 
         [0082]    In step S 202 , the original image binarized in step S 201  is divided into blocks (see  FIG. 6C ). For example, a QVGA (320×240) image is divided into 40×30 blocks in a unit of 8 pixels. A suitable unit of pixels is set in advance by evaluation experiment. 
         [0083]    In step S 203 , each block divided in step S 202  is divided into a black block and a white block. The set value to determine a black block is calculated in advance by evaluation experiment. The set value can be changed later to adapt to the actual environment. 
         [0084]    In step S 204 , the mass of the black block near the center of the original image is searched (see  FIG. 6D ). Specifically, the mass block is extracted by performing labeling processing on the original image. 
         [0085]    In step S 205 , the total number of blocks occupying the mass of the black block is counted. 
         [0086]    Next, in step S 105  shown in  FIG. 4 , it is judged whether or not the size is smaller than the set value  1 . The set value  1  is the value b shown in  FIG. 3 , in other words, the boundary point between the range which can be captured by the default position (F 0 ) and the range which can be captured by the farther side (F+). When the size is smaller than the set value  1 , the processing advances to the next step S 106 , and when the size is the set value  1  or larger, the processing advances to step S 107 . 
         [0087]    In step S 106 , the focus lens  11   b  is moved to the farther side (F+). 
         [0088]    In step S 107 , it is judged whether or not the size is larger than the set value  2 . The set value  2  is the value a shown in  FIG. 3 , in other words, the boundary point between the range which can be captured by the default position (F 0 ) and the range which can be captured by the closer side (F−). When the size is larger than the set value  2 , the processing advances to the next step S 108  and when the size is the set value  2  or smaller, the processing advances to step S 109 . 
         [0089]    In step S 108 , the focus lens  11   b  is moved to the closer side (F−). 
         [0090]    In step S 109 , a high resolution VGA captures a still image in the imaging section  10 . 
         [0091]    In step S 110 , the still image captured in step S 109  is analyzed and decoding processing is performed. 
         [0092]    In step S 111 , it is judged whether or not the decoding of the still image succeeded or not. When the decoding succeeds, the two dimensional code reading processing ends and when the decoding does not succeed, the processing advances to the next step S 112 . 
         [0093]    In step S 112 , it is judged whether or not the number of retries of the decoding processing is exceeded or not. The number of retries can be set freely by the user. When the number of retries is exceeded, the processing advances to the next step S 113  and when the processing is not exceeded, the processing advances to step S 109 . 
         [0094]    In step S 113 , a message showing the decoding has failed is displayed on the liquid crystal display section  31 . When this message is displayed, the two dimensional code reading processing ends. 
         [0095]    As described above, in the first embodiment, an approximate size (the area occupying the captured image) of the two dimensional code is judged from the captured image and when the size is smaller than the smaller value of the values set in advance, the position of the focus lens  11   b  is moved to the predetermined position of the farther side and when the size is larger than the larger value of the values set in advance, the position of the focus lens  11   b  is moved to the predetermined position of the closer side. Also, when neither case applies, the capturing operation is performed again with the position of the focus lens  11   b  as is, and the image is analyzed and the decoding processing is performed. 
         [0096]    In other words, instead of judging each image one by one while moving the focus adjustment mechanism one step at a time (repeating a cycle of “image capture→image determination→focus movement” a plurality of times) in order to move to a more desirable focus position, the focus position is moved in one step to a predetermined position set in advance and excess capturing time and image determination time will not be necessary. Also, power consumption necessary for such excess operation will not be necessary. Therefore, both a good response and reduction of power consumption can be achieved. 
         [0097]    Such technique is especially effective in a camera module such as a liquid lens where the focus movement is much faster than the capturing time of each frame. 
       Second Embodiment 
       [0098]      FIG. 7  and  FIG. 8  are flowcharts showing another example of two dimensional code reading processing (two dimensional code reading processing  2 ) performed in the symbol reading device  1  of the present embodiment. 
         [0099]    As shown in  FIG. 7 , in step S 301 , the position of the focus lens  11   b  is moved to the default position (F 0 ). 
         [0100]    In step S 302 , the symbol image imaged by the imaging section  10  is displayed through on the liquid crystal display section  31 . 
         [0101]    In step S 303 , it is judged whether or not the user pressed the capture button of the operation section  32 . When the capture button is pressed, the processing advances to the next step S 304  and when the capture button is not pressed, the processing advances to step S 302 . 
         [0102]    In step S 304 , a high resolution VGA captures a still image in the imaging section  10 . 
         [0103]    In step S 305 , the still image captured in step S 304  is analyzed and the decoding processing is performed. 
         [0104]    In step S 306 , it is judged whether or not the decoding of the still image succeeded or not. When the decoding succeeds, the two dimensional code reading processing ends and when the decoding does not succeed, the processing advances to the next step S 307 . 
         [0105]    In step S 307 , it is judged whether or not the number of retries of the decoding processing is exceeded or not. The number of retries can be set freely by the user. When the number of retries is exceeded, the processing advances to the next step S 308  and when the number of retries is not exceeded, the processing advances to step S 309 . 
         [0106]    In step S 308 , a message showing that the decoding failed is displayed on the liquid crystal display section  31 . When the message is displayed, the two dimensional code reading processing ends. 
         [0107]    In step S 309 , it is judged whether or not the symbol size can be estimated. The symbol size is the size of the symbol image. The estimate of the symbol size is performed based on the portion (eye portion of the two dimensional code) showing the coordinate position included in the captured image. The eye is a design positioned in three corners of a QR code, and each eye is composed of a black square outer frame, a white square frame inside the black square outer frame and a black square inside the white square frame. The eye is defined so that the ratio of the width of the black portions and white portions along a line crossing the center of the eye is to be “1:1:3:1:1”. When the size of the symbol size can be estimated by the relation of the position of the three eyes, the processing advances to step S 315  shown in  FIG. 8  and when the symbol size cannot be estimated, the processing advances to the next step S 310 . 
         [0108]    In step S 310 , the symbol area calculating processing is performed. The symbol area calculating processing is described specifically above with reference to  FIG. 5  and  FIG. 6A  to  FIG. 6D , and thus the description is omitted here. 
         [0109]    In step S 311 , it is judged whether or not the size is smaller than the set value  1 . The set value  1  is the value b shown in  FIG. 3 , in other words, the boundary point between the range which can be captured by the default position (F 0 ) and the range which can be captured by the farther side (F+). When the size is smaller than the set value  1 , the processing advances to the next step S 312 , and when the size is the set value  1  or larger, the processing advances to step S 313 . 
         [0110]    In step S 312 , the focus lens  11   b  is moved to the farther side (F+). 
         [0111]    In step S 313 , it is judged whether or not the size is larger than the set value  2 . The set value  2  is the value a shown in  FIG. 3 , in other words, the boundary point between the range which can be captured by the default position (F 0 ) and the range which can be captured by the closer side (F−). When the size is larger than the set value  2 , the processing advances to the next step S 314  and when the size is the set value  2  or smaller, the processing advances to step S 304 . 
         [0112]    In step S 314 , the focus lens  11   b  is moved to the closer side (F−). 
         [0113]    Next, in step S 315  shown in  FIG. 8 , it is judged whether or not the estimated size (calculated by the distance between the portions showing the coordinate position) is smaller than a set value  3 . The set value  3  is the value b shown in  FIG. 3 , in other words, the boundary point between the range which can be captured by the default position (F 0 ) and the range which can be captured by the farther side (F+). When the estimated size is smaller than the set value  3 , the processing advances to the next step S 316  and when the estimated size is the set value  3  or larger, the processing advances to step S 317 . 
         [0114]    In step S 316 , the focus lens  11   b  is moved to the farther side (F+). 
         [0115]    In step S 317 , it is judged whether or not the estimated size is larger than the set value  4 . The set value  4  is the value a shown in  FIG. 3 , in other words, the boundary point between the range which can be captured by the default position (F 0 ) and the range which can be captured by the closer side (F−). When the estimated size is larger than the set value  4 , the processing advances to the next step S 318  and when the estimated size is the set value  4  or smaller, the processing advances to step S 304 . 
         [0116]    In step S 318 , the focus lens  11   b  is moved to the closer side (F−). 
         [0117]    As described above, in the second embodiment, it is judged whether or not the symbol size can be estimated based on the eye portion (portion showing the coordinate position) of the two dimensional code, and when the symbol size can be estimated, the position of the focus lens  11   b  is adjusted based on the symbol size and the image is analyzed to perform decoding processing. 
         [0118]    With this, even if the decoding of the two dimensional code fails, if the estimate of the symbol size was possible, the image can be analyzed and the decoding processing can be performed without capturing the two dimensional code again. Consequently, unnecessary capturing movement can be omitted. 
         [0119]    The present embodiment is specifically described above, however, the present embodiment is not limited to the above embodiment and modifications can be made without leaving the scope of the embodiment. 
         [0120]    For example, the above described embodiment describes processing when a two dimensional code is captured as a symbol, however similar processing can be performed when a one dimensional barcode is captured. 
         [0121]    Also, in the above described embodiment, “far” is defined as a distance of 15 cm from the imaging section  10 , “focus position” is defined as a distance of 10 cm from the imaging section  10  and “close” is defined as a distance of 5 cm from the imaging section  10 , however, the distance is not limited to this, and any setting is possible according to the specifications of the imaging section  10 . 
         [0122]    Also, in the above described embodiment, two different values are used as a set value when judging the approximate size of the symbol, however, one set value can be used. When one set value is used, the focus position of the focus lens  11   b  is moved to a predetermined position of the farther side when the size of the symbol is smaller than the set value and the focus position of the focus lens  11   b  is moved to a predetermined position of the closer side when the size of the symbol is larger than the set value. 
         [0123]    The detailed configuration and the detailed operation of each device composing the symbol reading device  1  can be suitably modified without leaving the scope of the invention. 
         [0124]    Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.