Patent Publication Number: US-2009231627-A1

Title: Image Processing Apparatus, Image Processing Method, Computer Program for Image Processing

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority under 35 USC 119 of Japanese application no. 2008-066212, filed on Mar. 14, 2008, which is incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to an image processing apparatus and method, and a computer program for image processing. 
     2. Related Art 
     Various types of image processing are known. For example, there are processes for correcting colors and for deforming a subject. Image processing is not limited to image correction and includes processes in which the image is not modified, such as processes for outputting (including printing and display processes) or for classifying images. 
     In order to perform image processing, technology for detecting a person&#39;s face from an image is sometimes used. Related art in this regard is disclosed in JP-A-2004-318204. However, there are often various types of subjects shown in an image that may represent a person&#39;s face. For example, there are a child and an adult. In addition, there are various types of subjects that are similar to a person&#39;s face. For example, there are a doll, a poster representing a person&#39;s face, and the like. Sufficient consideration for detecting a face in consideration of the type of the subject has not been given in the related art. 
     SUMMARY 
     The present invention provides an image processing apparatus, method and computer program that are capable of detecting a face in consideration of the type of subject. The invention may be implemented in the following forms or exemplary embodiments. 
     A first aspect of the invention provides an image processing apparatus including: a size relationship determining unit that determines a size relationship between a size in a target image and an actual size; and a face area detecting unit that detects a face area of the target image that includes at least a partial image of a person&#39;s face. The face area detecting unit detects the face area by using the size relationship. 
     Under such a configuration, the size relationship between the size in the target image and the actual size is determined, and the face area is detected by the size relationship. Accordingly, the face is detected in consideration of the type of subject. 
     In one embodiment of the image processing apparatus, the face area detecting unit detects the face area having a size reflecting a face size in the target image that falls within a range of a size in the target image that can be acquired from a predetermined range of the actual size in accordance with the size relationship. 
     Under such a configuration, the face area having a size reflecting a face size in the target image that falls within a range of a size in the target image that can be acquired from a predetermined range of the actual size in accordance with the size relationship is detected. Accordingly, the face is detected in consideration of the type of subject. 
     In another embodiment of the image processing apparatus, the face area detecting unit includes: a candidate detecting section that detects a candidate area as a candidate for the face area from the target image; a size calculating section that calculates a size reference value that is correlated with the actual size of the face represented by the candidate area in accordance with the size relationship; and a selection section that selects the candidate area that satisfies a selection condition, including a condition in which the size reference value is within a predetermined range, as the face area. 
     Under such a configuration, the candidate area that satisfies a selection condition, including a condition in which the size reference value is within a predetermined range, is selected as the face area. Accordingly, the face is detected in consideration of the type of subject. 
     In another embodiment of the image processing apparatus, the selection condition further includes a condition in which the degree of sharpness of the face represented by the candidate area is higher than a threshold value. 
     Under such a configuration, an area representing a sharp face is detected as a face area. 
     Another embodiment of the image processing apparatus further includes: an image pickup unit that generates image data by performing an image pickup operation; and a process performing unit that performs a determination process in accordance with a match of an image pattern represented by the face area with a predetermined pattern. The image pickup unit sequentially generates the image data by repeating the image pickup operation, and the size relationship determining unit and the face area detecting unit sequentially determine the size relationship and detect the face area by using each image represented by the image data, which is sequentially generated, as the target image. 
     Under such a configuration, the face is detected in consideration of the type of subject for a case where a predetermined process is performed in accordance with the image pattern of the face area. 
     In another embodiment of the image processing apparatus, the determination process includes a process for performing an image pickup operation for an image including the face area that matches the predetermined pattern. 
     Under such a configuration, for picking up an image including a face area that matches a predetermined pattern, the face is detected in consideration of the type of subject. 
     In another embodiment of the image processing apparatus, the target image is generated by an image pickup device, and the size relationship determining unit determines the size relationship by using related information that is related with the target image. The related information includes: image pickup distance information that is related with a distance from the image pickup device to the person at a time when the image pickup operation for the target image is performed; focal length information that is related with a lens focal length of the image pickup device at the time when the image pickup operation is performed; and image pickup element information that is related with a size of a part of a light receiving area of the image pickup element of the image pickup device in which the target image is generated. 
     Under such a configuration, the size relationship is appropriately determined by using the related information. As a result, the face is appropriately detected in consideration of the type of subject. 
     According to a second aspect of the invention, a printer is provided that includes: a size relationship determining unit that determines a size relationship between a size in a target image and an actual size; a face area detecting unit that detects a face area of the target image that includes at least a partial image of a person&#39;s face; an image processing unit that performs a determination process for the target image in accordance with the detected face area; and a print unit that prints the target image processed by the image processing unit. The face area detecting unit detects the face area by using the size relationship. 
     According to a third aspect of the invention, a method of performing image processing is provided. The method includes: determining a size relationship between a size in a target image and an actual size; and detecting a face area of the target image that includes at least a partial image of a person&#39;s face. The face area is detected by using the size relationship. 
     A fourth aspect of the invention provides a computer program for image processing embodied on a computer-readable medium that allows a computer to perform functions including: a function for determining a size relationship between a size in a target image and an actual size; and a function for detecting a face area of the target image that includes at least a partial image of a person&#39;s face. The function for detecting the face area includes a function for detecting the face area by using the size relationship. 
     The invention may be implemented in various forms. For example, the invention may be implemented in forms such as an image processing method, an image processing apparatus, a computer program for implementing the functions of the image processing method or the image processing apparatus, and a recording medium having the computer program recorded thereon. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a block diagram of a printer according to an embodiment of the invention. 
         FIG. 2  is a block diagram showing modules and data that are loaded into a ROM according to an embodiment of the invention. 
         FIG. 3  is a schematic diagram including a model size table according to an embodiment of the invention. 
         FIG. 4  is a flowchart of a printing process according to an embodiment of the invention. 
         FIG. 5  is an explanatory diagram showing the relationship between the number of pixels of an image and the actual size according to an embodiment of the invention. 
         FIG. 6  is a schematic diagram showing a search range SR according to an embodiment of the invention. 
         FIG. 7  is a schematic diagram of a process for searching a face area according to a second embodiment of the invention. 
         FIG. 8  is a schematic diagram of a process for detecting a face area according to a third embodiment of the invention. 
         FIG. 9  is a schematic diagram of a process for detecting a face area according to a fourth embodiment of the invention. 
         FIG. 10  is a block diagram showing modules and data that are stored in a ROM according to a fifth embodiment of the invention. 
         FIG. 11  is a flowchart of a printing process according to the fifth embodiment. 
         FIG. 12  is a schematic diagram showing a detection result of candidates of a face area according to the fifth embodiment. 
         FIG. 13  is a block diagram of a digital still camera according to a sixth embodiment of the invention. 
         FIG. 14  is a block diagram showing modules and data that are stored in a ROM according to the sixth embodiment. 
         FIG. 15  is a schematic diagram representing the determination process for the image data according to the sixth embodiment. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Embodiments of the invention are described herein in the following order.
         First Embodiment   Second Embodiment   Third Embodiment   Fourth Embodiment   Fifth Embodiment   Sixth Embodiment   Modified Examples       

     First Embodiment 
       FIG. 1  is a block diagram of a printer  100  according to an embodiment of the invention. Printer  100  includes a control unit  200 , a print engine  300 , a display  310 , an operation panel  320 , and a card interface (I/F)  330 . 
     The control unit  200  is a computer that includes a CPU  210 , a RAM  220 , and a ROM  230 . Control unit  200  controls constituent elements of the printer  100 . 
     The print engine  300  is a printing mechanism that performs a printing operation by using supplied print data. Various printing mechanisms such as a printing mechanism that forms an image by discharging ink droplets onto a printing medium and a printing mechanism that forms an image by transferring and fixing toner on a printing medium may be employed. 
     The display  310  displays various types of information including an operation menu and an image in accordance with an instruction transmitted from the control unit  200 . Various displays such as a liquid crystal display and an organic EL display may be employed. 
     The operation panel  320  is a device that receives a direction from a user. The operation panel  320  may include, for example, operation buttons, a dial, or a touch panel. 
     The card I/F  330  is an interface of a memory card MC. The control unit  200  reads out an image file that is stored in the memory card MC through the card I/F  330 . Then, the control unit  200  performs a printing process by using the read-out image file. 
       FIG. 2  is a block diagram showing modules and data that are loaded into the ROM  230  ( FIG. 1 ). According to this embodiment, a face area detecting module  400 , a size relationship determining module  410 , an image processing module  420 , a print data generating module  430 , and a model size table  440  are stored in the ROM  230 . Modules  400 - 430  are programs that are executed by the CPU  210 . The modules  400 - 430  can transmit or receive data to or from one another through the RAM  220 . The functions of the modules  400 - 430  will be described later in detail. 
       FIG. 3  is a schematic diagram showing an example of a model size table  440 . The model size table  440  stores a correspondence relationship between a model of an image generating device (for example, a digital still camera) and the size of an image pickup element (also referred to as a light receiving device or an image sensor) of the model therein. In this embodiment, it is assumed that the shape of a light receiving area of an image pickup element is a rectangle. In addition, the height SH (the length of a shorter side) and the width SW (the length of a longer side) of the light receiving area (the rectangle) are used as the size of the image pickup element. As described above, the sizes of the image pickup element are determined in advance for the models of the image generating devices. Thus, each model is related to the size of the light receiving area of the image pickup element thereof (the model in this embodiment corresponds to “image pickup element information” of the claims). 
       FIG. 4  is a flowchart of the printing process. The control unit  200  ( FIG. 1 ) starts this printing process in accordance with a user&#39;s direction that is input to the operation panel  320 . In this printing process, the control unit  200  prints an image that is represented by image data included in the image file that is designated by the user&#39;s direction. Hereinafter, the image file that is designated by the user is referred to as a “target image file”, the image data that is stored in the target image file is referred to as “target image data”, and the image that is represented by the target image data is also referred to as a “target image”. 
     In step Step S 110 , the size relationship determining module  410  acquires related information from the target image file. In this embodiment, the image pickup device (for example, a digital still camera) generates an image file in conformity with the Exif (Exchangeable Image File Format) standards. In addition to image data, the image file includes additional information such as the model of the image pickup device and a lens focal length for image pickup in addition to image data. This additional information is related to the target image data. 
     According to this embodiment, the size relationship determining module  410  acquires the following information from the target image file.
         1) subject distance   2) lens focal length   3) digital zoom magnification   4) model name       

     The subject distance represents a distance between the image pickup device and a subject at a time when an image pickup process is performed. The lens focal length represents a lens focal length at the time when the image pickup process is performed. The digital zoom magnification represents the magnification ratio of a digital zoom at the time when the image pickup process is performed. Generally, digital zoom is a process in which a peripheral part of the image data is cropped and pixel interpolation is performed for the remaining image data so as to form the original pixel number. Such information represents settings of operations of the image pickup device at a time when the image pickup process is performed. The model name represents the model of the image pickup device. A typical image pickup device generates image data by performing an image pickup process and generates an image file that includes the image data and the additional information. 
     In Step S 120 , the size relationship determining module  410  determines (sets) the size relationship. The size relationship represents a correspondence relationship between the size of the target image (also referred to as the size in the target image; for example, a length) and the actual size. 
       FIG. 5  is an explanatory diagram showing the relationship between the number of pixels of an image and the actual size.  FIG. 5  is a side view showing the positional relationship of a subject SB, a lens system LS, and an image pickup element IS. The lens system LS includes a plurality of lenses. For simplification, one lens represents the lens system LS in  FIG. 5 . In addition,  FIG. 5  shows the actual size AS (actual length) of the subject, a subject distance SD, a lens focal length FL, the length (the height SH) of the image pickup element IS, a formed image PI that represents the subject SB formed on a light receiving face (imaging face) of the image pickup element IS, the size of the formed image PI (the number SSH of pixels in the height direction), the digital zoom magnification DZR, the size (a total number IH of the pixels in the height direction) of the image, and the size (the number SIH of pixels in the height direction) of the subject on the image. 
     The actual size AS of the subject SB represents a length along the height direction (corresponding to the height direction of the image pickup element IS). The subject distance SD acquired in Step S 110  is almost the same as a distance between the optical center (principal point PP) of the lens system LS and the subject SB. The lens focal length FL represents a distance between the optical center (principal point PP) of the lens system LS and the imaging face of the image pickup element IS. 
     As is well known, a triangle defined by the principal point PP and the subject SB and a triangle defined by the principal point PP and the formed image PI are similar triangles. Accordingly, the following relationship equation of Equation 1 is satisfied. 
       AS:SD=SSH:FL   Equation 1 
     Here, it is assumed that the parameters AS, SD, SSH, and FL are represented in a same unit (for example, “cm”). The principal point of the lens system LS that is viewed from the subject SB side may be different from that of the lens system LS that is viewed from the formed image PI side. However, in the relationship shown in  FIG. 5 , the difference therebetween is sufficiently small, and thus, the difference is not shown. 
     The size SIH of the subject in the image is the same as a value that is acquired from multiplying the size SSH of the formed image PI by the digital zoom magnification DZR (SIH=SSH×DZR). The size SIH is actually represented by the number of pixels. The height SH of the image pickup element IS corresponds to the total number IH of pixels. Accordingly, the size SSH of the formed image PI is represented in units of millimeters by the following Equation 2 by using the number SIH of pixels. 
         SSH =( SIH×SH/IH )/ DZR    Equation 2 
     Here, it is assumed that the height SH of the image pickup element IS is represented in units of millimeters. 
     From Equations 1 and 2, the actual size AS of the subject SB is represented by the following Equation 3. 
         AS =( SD× 100)×(( SIH×SH/IH )/ DZR )/ FL    Equation 3 
     Here, it is assumed that the units of the parameters are set as below. The actual size AS of the subject SB is represented in units of “cm”, the subject distance SD is represented in unit of “m”, the height SH of the image pickup element IS is represented in units of “mm”, and the lens focal length FL is represented in units of “mm”. 
     The size relationship determining module  410  sets the size relationship in accordance with Equation 3. As described above, according to this embodiment, the size relationship represents a ratio of lengths. 
     Next, in Step S 130 , the face area detecting module  400  ( FIG. 2 ) sets a search range in accordance with the size relationship.  FIG. 6  is a schematic diagram showing the search range SR according to this embodiment. In  FIG. 6 , a plurality of image patterns IPTN is shown. Each image pattern IPTN shows a rectangular shape that includes an image of two eyes, a nose, and a mouth of a person. The image patterns IPTN are similar, and the image patterns IPTN have different sizes (for example, heights). According to this embodiment, the face area detecting module  400  ( FIG. 2 ) detects an area of the target image IMG that matches the image pattern IPTN as a face area. Here, when a large image pattern IPTN is used, a face included in the target image that has a large size can be detected. On the other hand, when a small image pattern IPTN is used, a face included in the target image that has a small size can be detected. 
     The face area detecting module  400  ( FIG. 2 ) determines the size range (the search range SR) of the image pattern IPTN in accordance with the size relationship. According to this embodiment, the aspect ratio of the image pattern IPTN is constant regardless of the size thereof. Accordingly, the search range SR may be regarded to represent the height range or the width range of the image pattern IPTN. 
     The search range SR is determined such that the range of the actual size corresponding to the search range SR is a predetermined range appropriate to the face of a person. As the appropriate range of the actual size, for example, a range of 5 cm to 50 cm may be employed. The face area detecting module  400  determines the range of the size SIH (the number of pixels) in the target image by applying this range of the actual size as the actual size AS ( FIG. 5 ) included in Equation 3. The determined range becomes the search range SR. The face area detecting module  400  can detect a face of which the actual size (the size corresponding to the height of the face area) is within the range of 5 cm to 50 cm by using the image pattern IPTN that is within the search range SR. As a result, detection of an excessively small face (for example, the face of a doll) or an excessively large face (for example, a face shown in a poster) can be suppressed. The predetermined range that is appropriate to a face of a person may be a range other than the range of 5 cm to 50 cm, and is preferably determined experimentally in advance. 
     In Step S 140 , the face area detecting module  400  detects a face area by using the image pattern IPTN that is in correspondence with the image pattern size within the search range SR. In the embodiment of  FIG. 6 , three image patterns IPTN 1 , IPTN 2 , and IPTN 3  having different sizes are used. The face area represents an area of the target image in which an image of at least a part of a face is included. 
     In  FIG. 6 , the result of detection of a face area from the target image IMG is shown. In this embodiment, the shape of the target image is a rectangle. The image height IH and the image width IW represent the height (the length of a shorter side) of the target image and the width (the length of a longer side) of the target image (in units of the numbers of pixels). The face area detecting module  400  detects face areas located in various positions within the target image IMG by moving the image pattern IPTN within the target image IMG. When one target image represents a plurality of faces, the face area detecting module  400  detects a plurality of face areas. 
     In the target image IMG shown in  FIG. 6 , a person Pi and a poster PS are shown. The poster PS represents a person P 2 . The actual size of the face of the person P 2  shown in the poster PS is sufficiently larger than the size of the face of the actual person. As a result, the face area detecting module  400  detects the face area FA that represents the face of the person P 1 . However, the area that represents the face of the person P 2  within the poster PS is not detected as a face area. 
     In addition, the face area detecting module  400  uses a plurality of image patterns that are prepared in advance as the plurality of image patterns IPTN. The face area detecting module  400  may be configured to generate a plurality of image patterns having different sizes by appropriately scaling one image pattern IPTN. In any case, the interval of the image patterns IPTN is preferably experimentally determined in advance so as to appropriately detect faces of persons that have various sizes. 
     In Step S 300 , the image processing module  420  determines whether a face area has been detected. When a face area has been detected, the image processing module  420  performs the image processing of Steps S 310 , S 312 , and S 330  for the face of a person. Various processes can be employed as the processing for the person&#39;s face. For example, a process for correcting the color of the face (particularly, the skin) may be employed. As the color correcting process, for example, a process for enhancing the brightness of the skin color or for approximating the skin color to a predetermined color may be employed. Instead of the color correcting process, a deformation process for decreasing the width of a face may be employed. In any case, in Step S 310 , the face processing module  420  acquires information on the detected face (for example, the average color and average luminance of pixels representing the skin of the face and the width (the number of pixels) of the face). In Step S 312 , the image processing module  420  calculates parameters of the image processing by using the acquired information (for example, the adjustment amounts of color and brightness and the deformation amount of the width of the face). In Step S 330 , the image processing module  420  performs image processing in accordance with the parameters of the image processing. 
     On the other hand, when a face area has not been detected, the image processing module  420  performs standard image processing in Steps S 320  and S 330 . Various processes may be employed as the standard image processing. For example, a process for adjusting the white balance of the target image may be performed, or a process for approximating the average brightness within the target image to predetermined brightness may be performed. In any case, in Step S 320 , the image processing module  420  calculates the parameters of the image processing by using the target image (for example, the adjustment amount of white balance and a tone curve for adjusting brightness). In Step S 330 , the image processing module  420  performs the image processing in accordance with the parameters of the image processing. 
     In Step S 340 , the print data generating module  430  generates print data by using image data that has been processed by the image processing module  420 . Any format that is appropriate to the print engine  300  may be employed as the format of the print data. For example, according to this embodiment, the print data generating module  430  generates the print data that represents record states of each ink dot by performing a resolution converting process, a color converting process, and a halftone process. Then, the print data generating module  430  supplies the generated print data to the print engine  300 . The print engine  300  performs a printing process based on the received print data. Then, the process shown in  FIG. 4  is completed, The print data generating module  430  and the print engine  300  cooperatively correspond to a “print unit” of the claims. 
     As described above, according to this embodiment, the search range SR of the size of the image pattern IPTN is determined based on the predetermined range of the actual size in accordance with the size relationship. Accordingly, the actual size that can be acquired from the size within the search range SR in accordance with the size relationship is within the predetermined range. Here, the size (for example, the height) of the image pattern IPTN represents the size of a rectangle that includes two eyes and a mouth. In other words, the size of the image pattern IPTN represents the size in the target image which reflects the size of a face. Accordingly, detection of an area representing an excessively large face, such as an area that represents a face shown in a poster, or an area representing an excessively small face, such as an area that represents the face of a doll, is suppressed. In other words, according to this embodiment, the face area is detected by distinguishing a subject representing a face of an actual size that is appropriate as a person from a subject representing a face of an actual size that is excessively small or excessively large. As described above, the face is detected in consideration of the type of a subject. In particular, according to this embodiment, the face area detecting module  400  does not detect any face area in accordance with an image pattern IPTN having a size beyond the search range SR. Accordingly, the face area detecting module  400  can perform detection of the face area at a high speed. The face area detecting module  400  may be configured to determine the search range SR based on various values relating to the size of the image pattern IPTN, instead of the size of the image pattern IPTN. 
     Second Embodiment 
       FIG. 7  is a schematic diagram of a process for searching a face area according to a second embodiment of the invention. A difference between the first embodiment shown in  FIG. 6  and the second embodiment is that a detection window DW is used instead of the image pattern IPTN in the second embodiment. The sequence of the printing process is the same as that shown in  FIG. 4 . However, the contents of two steps of Steps S 130  and S 140  are different from those of the first embodiment. Other steps are the same as those of the first embodiment. In addition, the configuration of a printer is the same as that of the printer  100 , which is shown in  FIGS. 1 and 2 , according to the first embodiment. 
     According to the second embodiment, a face area detecting module  400  detects a face area by using a learning-completed neural network, instead of pattern matching. Here, the face area detecting module  400  determines a detection target area IDW within a target image IMG by using the detection window DW (the target area IDW is an area inside the detection window DW). The face area detecting module  400  determines whether the target area IDW is a face area by using pixel values of the target area IDW. This determination is performed in accordance with the neural network. According to this embodiment, the neural network is built such that a target area XDW is determined to be a face area for a case where the target area IDW includes images of two eyes, a nose, and a mouth. The face area detecting module  400  detects face areas located in various positions within the target image IMG by moving the detection window DW within the target image IMG. In this embodiment, the shape of the detection window DW is a rectangle. 
     In  FIG. 7 , a plurality of the detection windows DW having different sizes is shown. The detection windows DW are similar, and the sizes (for example, the heights) of the detection windows DW are different from one another. According to this embodiment, the face area detecting module  400  detects a face area based on relative positions within the detection window DW. In other words, when a small detection window DW is used, a small face is detected. On the other hand, when a large detection window DW is used, a large face is detected. As described above, the size of the detection window DW is related with the size of a detected face (that is, a face area) in the target image. As the size of the detection window DW becomes larger, the face area detecting module  400  detects a face area representing a larger face. 
     In Step S 130  of  FIG. 4 , the face area detecting module  400  ( FIG. 2 ) determines the range (the search range SRW) of the size of the detection window DW in accordance with the size relationship. According to this embodiment, the aspect ratio of the detection window DW is constant regardless of the size thereof. Accordingly, the search range SRW can be regarded to represent the range of the height or the width of the detection window DW. In addition, determination on the search range SRW is performed in the same manner as in determination on the search range SR according to the first embodiment of  FIG. 6 . In other words, the search range SRW is determined such that the range of the actual size corresponding to the search range SRW is a predetermined range appropriate to a person&#39;s face. 
     In Step S 140 , the face area detecting module  400  detects a face area by using the detection window DW that is in correspondence with the detection window size within the search range SRW. In the embodiment of  FIG. 7 , three detection windows DW 1 , DW 2 , and DW 3  having different sizes are used. In  FIG. 7 , a target image IMG that is the same as that of  FIG. 6  is shown. The face area detecting module  400  detects a face area FA that represents a face of a person P 1 . However, an area that represents the face of a person P 2  within the poster PS is not detected as a face area. The reason is that the actual size of the face of the person P 2  is sufficiently larger than the size of a real person&#39;s face. 
     As described above, according to the second embodiment, the search range SRW of the size of the detection window DW is determined based on the predetermined range of the actual size in accordance with the size relationship. Accordingly, the actual size that can be acquired from the size within the search range SRW in accordance with the size relationship is within the predetermined range. Here, the size (for example, the height) of the detection window DW represents the size of a rectangle that includes two eyes, a nose, and a mouth. In other words, the size of the detection window DW represents the size in the target image which reflects the size of a face. Accordingly, detection of an area representing an excessively large face or an excessively small face as a face area is suppressed. As a result, a face is detected in consideration of the type of a subject. In particular, according to this embodiment, the face area detecting module  400  does not detect any face area in accordance with a detection window DW having a size beyond the search range SRW. Accordingly, the face area detecting module  400  can perform detection of the face area at a high speed. The face area detecting module  400  may be configured to determine the search range SRW based on various values relating to the size of the detection window DW, instead of the size of the detection window DW. 
     Third Embodiment 
       FIG. 8  is a schematic diagram of a process for detecting a face area according to a third embodiment of the invention. A difference between the first embodiment of  FIG. 6  and the third embodiment is that, in the third embodiment, a target image IMG is scaled instead of scaling the image pattern IPTN. The sequence of the printing process is the same as that shown in  FIG. 4 . However, the contents of the two steps S 130  and S 140  are different from those of the first embodiment. Other steps are the same as those of the first embodiment. In addition, the configuration of a printer is the same as that of the printer  100 , which is shown in  FIGS. 1 and 2 , according to the first embodiment. 
     According to the third embodiment, a face area detecting module  400  ( FIG. 2 ) detects a face area by using an image pattern IPTN_S of a predetermined size. In this embodiment, the shape of the image pattern IPTN_S is a rectangle, and the size (for example, the numbers of pixels in the vertical and horizontal directions) of the image pattern IPTN_S is fixed. 
     The face area detecting module  400  generates a scaled image SIMG by scaling (enlarging or reducing) the target image IMG. In this embodiment, this scaling process is performed without changing the aspect ratio. Then, the face area detecting module  400  detects an area of the scaled image SIMG that matches the image pattern IPTN_S. Various known methods may be employed as a scaling method. For example, the target image IMG may be reduced by thinning out pixels. In addition, pixel values of an image after being reduced may be determined based on an interpolation process (for example, linear interpolation). Similarly, pixel values of an image after being enlarged may be determined based on an interpolation process. 
     Here, the ratio of the size of the scaled image SIMG to the size of the target image IMG is referred to as a scaling ratio (as the size, for example, the number of pixels in the height direction or the number of pixels in the width direction may be employed). When the scaling ratio is large, the ratio of the size of the image pattern IPTN_S to the size of the scaled image SIMG is small. Accordingly, in such a case, a face having a small size in the target image IMG can be detected. To the contrary, when the scaling ratio is small, the ratio of the size of the image pattern IPTN_S to the size of the scaled image SIMG is large. Accordingly, in such a case, a face having a large size in the target image IMG can be detected. The scaling ratio may be smaller than one or larger than one. 
     As described above, the scaling ratio has a correlation with the size of the face area that is detected from the target image IMG (there is a negative correlation). The size of the detected face area in the target image IMG is the same as a size acquired from dividing the size of the image pattern IPTN_S by the scaling ratio. On the other hand, as described above, an appropriate range of the size of the face area in the target image IMG is determined based on a predetermined range (for example, 5 cm to 50 cm) of the actual size and the size relationship (Equation 3:  FIG. 5 ). 
     In Step S 130  of  FIG. 4 , the face area detecting module  400  determines an appropriate range (the search range SRR) of the scaling ratio based on the size (for example, the number of pixels in the vertical direction) of the image pattern IPTN_S, the predetermined range (for example, 5 cm to 50 cm) of the actual size, and the size relationship. Here, the search range SRR is determined such that the actual size of the detected face area corresponding to the size in the target image IMG is within a predetermined range. In other words, the search range SRR is determined such that the size of the detected face area in the target image IMG is within the range of the size in the target image IMG that is acquired from the predetermined range of the actual size based on the size relationship. For example, a maximum value of the scaling ratio is set as a value acquired from dividing the size (for example, the height) of the image pattern IPTN_S by the size in the target image that can be acquired from a minimum value (for example, 5 cm) of the predetermined range based on the size relationship. In addition, the minimum value of the scaling ratio is set as a value that can be acquired from dividing the size of the image pattern IPTN_S by the size in the target image that can be acquired from the maximum value (for example, 50 cm) of the predetermined range based on the size relationship. 
     In Step S 140 , the face area detecting module  400  detects a face area by using the scaled image SIMG that is in correspondence with the scaling ratio within the search range SRR. In  FIG. 8 , three scaled images SIMG 1 , SIMG 2 , and SIMG 3  having different scaling ratios are used. The interval of the used scaling ratios is preferably experimentally determined in advance so as to appropriately detect faces of persons that have various sizes. 
     In a lower part of  FIG. 8 , a second scaled image SIMG 2  is shown. This second scaled image SIMG 2  is an image that is generated from the same target image IMG as that of  FIG. 6 . The face area detecting module  400  detects a face area FA_S representing the face of the person P 1  from this second scaled image SIMG 2 . However, an area that represents the face of a person P 2  within the poster PS is not detected as a face area. The reason is that the actual size of the face of the person P 2  is sufficiently larger than the actual size of a person&#39;s face. 
     As described above, according to this embodiment, the search range SRR of the scaling ratio is determined based on the predetermined range of the actual size and the size of the image pattern IPTN_S in accordance with the size relationship. Here, the search range SRR is determined such that the actual size of the detected face area is within a predetermined range. Accordingly, detection of an area representing an excessively large face (for example, an area that represents a face shown in a poster) or an area representing an excessively small face (for example, an area that represents the face of a doll) as a face area is suppressed. As a result, a face is detected in consideration of the type of a subject. In particular, according to this embodiment, the face area detecting module  400  does not detect any face area in accordance with a scaling ratio beyond the search range SRR. Accordingly, the face area detecting module  400  performs detection of the face area at a high speed. 
     Fourth Embodiment 
       FIG. 9  is a schematic diagram of a process for detecting a face area according to a fourth embodiment of the invention. A difference between the third embodiment of  FIG. 8  and the fourth embodiment of  FIG. 9  is that, in the fourth embodiment, a detection window DW_S of a predetermined size is used instead of the image pattern IPTN_S. In the fourth embodiment, the shape of the detection window DW_S is a rectangle, and the size (for example, the numbers of pixels in the vertical and horizontal directions) of the detection window DW_S is fixed. The sequence of the printing process is the same as that shown in  FIG. 4 . However, the contents of two steps of Steps S 130  and S 140  are different from those of the first embodiment. Other steps are the same as those of the first embodiment. In addition, the configuration of a printer is the same as that of the printer  100 , which is shown in  FIGS. 1 and 2 , according to the first embodiment. 
     According to the fourth embodiment, a face area detecting module  400  detects a face area by using a learning-completed neural network, in the same manner as in the embodiment of  FIG. 7 . In addition, the face area detecting module  400 , in the same manner as in the embodiment shown in  FIG. 8 , substantially adjusts the size of the detection window in the target image IMG by adjusting the scaling ratio. Accordingly, detection of an area representing an excessively large face or an excessively small face as a face area is suppressed, and a face is detected in consideration of the type of a subject. In particular, according to this embodiment, the face area detecting module  400  does not detect any face area in accordance with a scaling ratio beyond the search range SRR. Accordingly, the face area detecting module  400  performs detection of the face area at a high speed. 
     Fifth Embodiment 
       FIG. 10  is a block diagram showing modules and data that are stored in a ROM  230  according to a fifth embodiment of the invention. A difference between the embodiment of  FIG. 2  and the fifth embodiment is that a face area detecting module  400 A, instead of the face area detecting module  400 , is stored. The face area detecting module  400 A includes a candidate detecting module  402 , a size calculating module  404 , and a selection module  406 . The configuration of a printer is the same as that of the printer  100 , which is shown in  FIG. 1 , according to the first embodiment. 
       FIG. 11  is a flowchart of a printing process according to the fifth embodiment. In Step S 200 , the candidate detecting module  402  ( FIG. 10 ) detects candidates of a face area from a target image by analyzing data of the target image. The face area represents an area of the target image that includes at least a part of a face. The candidate detecting module  402  detects candidates of a face area regardless of the sizes in the target image. 
       FIG. 12  is a schematic diagram showing the detection result of candidates of a face area. In a target image IMGa shown in  FIG. 12 , a person P 1   a , a poster PSa, and a person P 3   a  that is located far are shown. The poster PSa represents a person P 2   a . Here, it is assumed that the actual size of the face of the person P 2   a  shown in the poster PSa is sufficiently larger than the size of a real person&#39;s face. In addition, the person P 3   a  is shown blurrily. The reason is that the person P 1   a  is in focus but the person P 3   a  is out of focus. 
     Three face area candidates CA 1 , CA 2 , and CA 3  are detected from the target image IMGa. As shown in  FIG. 12 , according to this embodiment, a rectangle area that includes images of two eyes, a nose, and a mouth is detected as a candidate for a face area. When a face is shown to be small, a small face area is detected. On the other hand, when the face is shown to be large, a large face area is detected. As described above, the size of the face area (candidate) is related to the size of the face in the target image. In addition, the aspect ratio of the face area may be changed in accordance with the face included the target image. Alternatively, the aspect ratio may be fixed. As the detected face area, any arbitrary area that includes an image of at least a part of a face may be used. For example, the face area may include an entire face. 
     According to this embodiment, as in the above-described embodiments, the shape of the target image IMGa is a rectangle. The image height IHa and the image width IWa represent the height (the length of a shorter side) of the target image IMGa and the width (the length of a longer side) of the target image (in units of the numbers of pixels). The height SIH 1  of the face area and the width SIW 1  of the face area represent the height and the width of the first face area candidate CA 1  (in units of the numbers of pixels). Similarly, the height SIH 2  of the face area and the width SIW 2  of the face area represent the height and the width of the second face area candidate CA 2 . In addition, the height SIH 3  of the face area and the width SIW 3  of the face area represent the height and the width of the third face area candidate CA 3 . 
     Various known methods can be used as a detection method for a face area (candidate) by using the candidate detecting module  402 . According to this embodiment, a face area is detected by performing a pattern matching process by using template images of an eye and template images of a mouth which are organs of a face. Various methods in which pattern matching using templates is performed (for example, see JP-A-2004-318204) can be used as the detection method for a face area. 
     In Step S 210  of  FIG. 11 , as in Step S 110  of  FIG. 4 , the size relationship determining module  410  ( FIG. 10 ) acquires related information from a target image file. Then, the size relationship determining module  410  determines (sets) the size relationship in accordance with Equation 3 described with reference to  FIG. 5 . 
     In Step S 220 , the size calculating module  404  ( FIG. 10 ) calculates an actual size corresponding to the face area candidate in accordance with the size relationship. In this embodiment, the size calculating module  404  calculates the actual size corresponding to the height of the face area candidate. As described above, the size of the face area candidate is related to the size of the face in the target image. Accordingly, the calculated actual size has a positive correlation with the actual size (for example, a length from the top of a head to a front end of a chin) of a face of a subject. In other words, as the calculated actual size is increased, the actual size of the face of the subject increases. The actual size corresponds to a “size reference value” of the claims. 
     In Step S 230 , the selection module  406  ( FIG. 10 ) determines whether the face area candidate satisfies the following Condition C1. 
     Condition C1: the actual size is smaller than 50 cm, and the actual size is larger than 5 cm. 
     A case where the face area candidate satisfies this condition C1 indicates that there is a high possibility that the face represented by the face area candidate is a real person&#39;s face. The range that is appropriate to the face of a person may be other than the range of 5 cm to 50 cm and is preferably determined experimentally in advance. 
     When the face area candidate satisfies this condition C1, the selection module  406  analyzes the face area candidate and calculates the edge strength within the face in Step S 240 . According to this embodiment, the selection module  406  calculates the edge strength of each pixel that represents the face. Various values may be used as the edge strength. For example, an absolute value of the result that is obtained from applying a Laplacian filter to the luminance values of each pixel may be used as the edge strength. Various methods may be used as a method of determining the pixels representing a face. For example, skin-colored pixels within the face area candidate may be selected as pixels that represent a face. Here, the skin-colored pixel indicates a pixel that represents a color in a predetermined skin-color range. In addition to the skin-colored pixels within the face area candidate, skin-colored pixels in the peripheral part of the face area candidate may be selected. 
     In Step S 250 , the size calculating module  404  determines whether the face area candidate satisfies the following condition C2. 
     Condition C2: A maximum value of the edge strength is larger than a predetermined threshold value. 
     As the sharpness of a face becomes stronger, the maximal value of the edge strength increases. Accordingly, the maximal value of the edge strength indicates the degree of sharpness of a face. As described above, this condition C2 represents a case where the degree of sharpness of a face is higher than the threshold value. In addition, when the face area candidate satisfies this condition C2, there is a high possibility that the face represented by the face area candidate is in focus at a time of photographing the target image. On the other hand, when this condition C2 is not satisfied, there are many cases that the face represented by the face area candidate is out of focus. In such a case, there is a high possibility that the subject distance SD and the lens focal length FL which are shown in  FIG. 5  are not appropriate to each other. 
     When the face area candidate satisfies condition C2, the selection module  406  ( FIG. 10 ) selects the face area candidate as a face area (Step S 260 ). When either one of conditions C1 and C2 is not satisfied, the selection module  406  excludes the face area candidate from the face area. 
     The face area detecting module  400 A ( FIG. 10 ) repeats the processes of Steps S 220 -S 260  of  FIG. 11  for each detected face area candidate. When the processes for all the face area candidates are completed (Step S 270 : Yes), the process proceeds to Step S 300 . The process of Step S 300  and processes thereafter are the same as the processes of Step S 300  and thereafter which are shown in  FIG. 4 . 
     The result of detection of the face area in the above-described processes is shown in  FIG. 12 . The actual size of the second face area candidate CA 2  is larger than 50 cm, and thus the second face area candidate CA 2  is excluded from the face area (Step S 230 ). In addition, the face of the third image area candidate CA 3  is blurred, the third face area candidate CA 3  is excluded from the face area (Step S 250 ). Then, the first face area candidate CA 1  is selected as the face area. 
     As described above, according to this embodiment, when the size of a face area candidate in the target image is within the range of the size in the target image which can be acquired from a predetermined range of the actual size in accordance with the size relationship, the face area candidate is selected as the face area. In other words, when the actual size corresponding to the size of a face area candidate in the target image is within the predetermined range, the face area candidate is selected as the face area. As a result, detection of an area representing an excessively large face (for example, an area that represents a face shown in a poster) or an excessively small face (for example, an area that represents the face of a doll) as a face area is suppressed, and a face is detected in consideration of the type of subject. 
     In addition, when the degree of sharpness of a face is higher than the threshold value, the face area candidate is selected as a face area. Accordingly, an area representing a sharp face can be detected as a face area. In this way, a sharp face that can easily attract the attention of an observer of the target image can be detected as a face area. In addition, selection of an out-of-focus face as a face area is suppressed. Moreover, selection of a face area based on the actual size that is calculated based on the inappropriate subject distance SD and the lens focal length FL is suppressed. 
     Sixth Embodiment 
       FIG. 13  is a block diagram of a digital still camera  500  according to a sixth embodiment of the invention. Digital still camera  500  includes a control unit  200 , an image pickup unit  600 , a display  610 , an operation unit  620 , and a card I/F  630 . 
     The image pickup unit  600  generates image data by performing an image pickup operation. The image pickup unit  600  includes a lens system, an image pickup element, and an image data generating part (not shown). The image pickup unit  600  sequentially generates the image data by repeating the image pickup operation. 
     The display  610 , the operation unit  620 , and the card I/F  630  are the same as the display  310 , the operation panel  320 , and the card I/F  330  that are shown in  FIG. 1 . 
     The hardware configuration of the control unit  200  is the same as that of the embodiment of  FIG. 1 .  FIG. 14  is a block diagram showing modules and data that are stored in a ROM  230  ( FIG. 13 ). A difference between the embodiment of  FIG. 2  and the sixth embodiment is that, in the sixth embodiment, an image pickup processing module  432  is disposed instead of the print data generating module  430 . 
     The image pickup processing module  432  ( FIG. 14 ) of the control unit  200  ( FIG. 13 ) controls the image pickup unit  600  to start repetition of an image pickup operation in response to a user&#39;s direction. This repetition of the image pickup operation is performed for determining whether an image pattern represented by a face of the subject matches a predetermined image pattern. The control unit  200  sequentially detects a face area for each image data that is sequentially generated by the image pickup unit  600 . According to this embodiment, the face area detecting module  400  and the size relationship determining module  410  detect a face area in the same sequence as in Steps S 110 -S 140  of  FIG. 4 . Any of the processes of  FIGS. 6-9  may be employed as the detailed process. The size relationship determining module  410  acquires a subject distance, a lens focal length, and digital zoom magnification from the image pickup unit  600 . The size relationship determining module  410  uses predetermined values as the size (for example, a height SH) of an image pickup element and the size (for example, an image height IH) of the image data. As described above, according to this embodiment, the size relationship determining module  410  can determine the size relationship without using the image data. 
     The image pickup processing module  432  ( FIG. 14 ) sequentially determines whether an image pattern represented by a face area matches a predetermined image pattern.  FIG. 15  is a schematic diagram representing the determination process for the image data. Parts of a plurality of images that are sequentially generated by the image pickup unit  600  (IMG 101 , IMG 102 , and IMG 103 ) are shown in  FIG. 15 . From these images, face areas FA are detected. The image pickup processing module  432  sequentially determines whether the image patterns represented by the face areas FA match a predetermined image pattern (referred to as a “reference pattern SP”). In  FIG. 15 , the patterns are not matched in the first two images IMG 101  and IMG 102 . However, in the third image IMG 103 , the patterns are matched. A known pattern matching method can be used as a method of determining whether two image patterns are matched. For example, the determining process may be performed by appropriately scaling the size of the reference pattern SP. 
     As the pattern of the face area FA matches the reference pattern SP, the image pickup processing module  432  outputs an image pickup direction to the image pickup unit  600 . The image pickup unit  600  generates image data by performing an image pickup operation in accordance with the direction. By performing this image pickup operation, image data representing an image including a face area that matches the reference pattern SP is generated. According to this embodiment, the reference pattern SP represents a smiling face. Accordingly, as the face of the subject represented by the face area is changed to a smiling face, an image representing the smiling face is automatically picked up. As described above, the image pickup processing module  432  picks up the image including the face area that matches the reference pattern SP. The reference pattern SP is not limited to a pattern representing the smiling face, and any arbitrary pattern may be used as the reference pattern SP. Hereinafter, the image pickup operation performed in accordance with a direction of the image pickup processing module  432  is referred to as “pattern image pickup”. In addition, the image data that is generated by the pattern image pickup is referred to as “pattern image pickup data”. 
     The image pickup unit  600  ( FIG. 13 ) supplies the pattern image pickup data to the control unit  200 . The image pickup processing module  432  ( FIG. 14 ) stores an image file, in which the pattern image pickup data is stored, in a memory card MC. In this embodiment, the memory card MC is a non-volatile memory. Accordingly, a user can use the pattern image pickup data in an easy manner. In addition, the memory card MC is a memory that can be detachably attached. Accordingly, a user can carry the pattern image pickup data in a simple manner. 
     Regarding settings of the operations of the image pickup unit  600 , the setting for the pattern image pickup may be different from that for the sequential image pickup operation. For example, the image pickup unit  600  may be configured to generate image data having a small number of pixels for the sequential image pickup operation and image data having a large number of pixels for the pattern image pickup. Generally, a setting in which a processing load is low is preferably used for the sequential image pickup operation. In such a case, the speed of repetition of the image pickup operation can be increased. On the other hand, a setting for generating image data of a high definition is preferably used in the pattern image pickup. 
     The method of detecting a face area is not limited to the method of  FIG. 4 . For example, the method of Steps S 200 -S 270  of  FIG. 11  may be used. 
     The image pickup processing module  432  ( FIG. 14 ) according to this embodiment corresponds to a “process performing unit” of the claims. A process that is performed for a case where the image pattern of the face area matches the reference pattern SP is not limited to an image pickup process or generation of an image file, and other processes may be used. For example, a process for adjusting the skin color within the face area may be performed. In addition, a printer may be connected to the digital still camera  500  through a communication path. In such a case, the target image may be printed by using the printer. 
     In addition, the control unit  200  ( FIG. 13 ) may perform a process that is the same as the process according to the embodiments shown in  FIGS. 4 and 11  for the image data generated by the image pickup operation, regardless of match of the image pattern of the face area to the reference pattern SP. For example, the control unit  200  directs the image pickup unit  600  to perform an image pickup operation in accordance with a user&#39;s direction. The image pick unit  600  generates the image data by performing an image pickup operation and supplies the generated image data to the control unit  200 . The control unit  200  performs image processing by using the received image data and stores the image file in which the image data, for which the image processing is completed, is stored in the memory (for example, the memory card MC). 
     The process of  FIGS. 4 and 11  may be used as the image processing by using the control unit  200 . However, according to this embodiment, the image processing module  420  ( FIG. 14 ) stores the image file in the memory card MC, instead of performing the printing operation in Step S 340 . 
     MODIFIED EXAMPLES 
     Constituent elements of the above-described embodiments that are not claimed as independent claims are additional elements and may be omitted appropriately. The invention is not limited to the above-described embodiments or examples and may be performed in various forms without departing from the scope of the invention. For example, the following changes in forms can be made. 
     Modified Example 1 
     In the above-described embodiments, as the method of detecting a face area (or a candidate area thereof) by using an image pattern, various methods in which a predetermined image pattern representing at least a part of a face is used may be used. For example, one face area may be detected by using a plurality of image patterns that represent different parts within a face (for example, both an image pattern representing eyes and a nose and an image pattern representing a nose and a mouth may be used). In addition, the shape of the image pattern is not limited to a rectangle, and other shapes may be used. 
     In addition, in the above-described embodiments, the shape of the detection window is not limited to a rectangle, and other shapes may be used. 
     In addition, in the above-described embodiments, the method of detecting a face area (or a candidate area thereof) that includes at least a partial image of a face is not limited to a method using pattern matching or neural networks, and other methods can be used. For example, boosting (for example, AdaBoost) or a support vector machine can be used. In addition, a face area may be detected by combining the above-described methods. For example, the methods of  FIGS. 6 and 7  may be combined. In such a case, a common face area that is detected by using both the methods is preferably used as a finally detected face area. Similarly, the methods of  FIGS. 8 and 9  may be combined. In addition, an arbitrary combination of the methods of  FIGS. 6-9  may be used. In any case, a final detection result may be determined by appropriately combining detection results according to a plurality of methods by using logical sum or logical product. 
     In addition, in the above-described embodiments, a range of a relatively small size may be used as the predetermined range of the actual size. In such a case, the face of a child can be detected. In addition, a range of a relatively large size may be used as this range. In such a case, the face of an adult can be detected. The range of the actual size is not limited to a range that is appropriate to a real person&#39;s face, and a range appropriate to another subject (for example, a doll or a poster) that is similar to a person&#39;s face may be used. 
     In addition, in the above-described embodiments, the method of detecting a face area is not limited to a method of detecting a face area by using a predetermined range of the actual size. Thus, as the method of detecting a face area, various methods such as a method in which a face area is detected by using the size relationship may be used. For example, the range of the actual size may be determined by a user. 
     Modified Example 2 
     In the above-described embodiments, various values related with the actual size of a face may be used as the size reference value. For example, the size reference value may be in correspondence with various sizes that reflect the size of a face. In other words, the size reference value may be in correspondence with various sizes that are related with a face. For example, as in the above-described embodiments, the size reference value may be in correspondence with the size of a face area in the target image. Here, the length of the image pickup element IS in the width direction (corresponding to a longer side of the light receiving area) may be used. In addition, the size reference value may be in correspondence with a distance between two positions acquired with reference to positions of organs within a face. For example, the size reference value may be in correspondence with a distance between a center position of two eyes and a mouth. In any case, the size calculating module  404  ( FIG. 10 ) can calculate the size reference value based on various sizes (the sizes in the target image) that reflect the size of a face. As an example, it is assumed that the size reference value corresponds to the distance between the center position of the two eyes and the mouth. In such a case, the size calculating module  404  preferably calculates the size reference value based on the distance (the number of pixels) between the center position of two eyes and the mouth in the target image. Here, the size calculating module  404  preferably uses the eyes and the mouth that are detected by the candidate detecting module  402 . The size reference value is not limited to a distance (length) and may be in correspondence with various sizes such as an area. 
     As described above, various sizes that are related with the size of a face may be used as the size in the target image that reflects the size of a face. 
     Modified Example 3 
     In the above-described embodiments, any arbitrary relationship that represents a relationship between the size in the target image and the actual size may be used as the size relationship. For example, the size is not limited to a distance (length), and an area may be used as the size. 
     In addition, in the above-described embodiments, the information used for determining the size relationship preferably includes the following information. 
     1) image pickup distance information that is related with a distance from the image pickup device to a person at a time when the target image is picked up 
     2) focal length information that is related with a lens focal length of the image pickup device at a time when the image pickup operation is performed 
     3) image pickup element information that is related with the size of a part of the light receiving area of the image pickup element of the image pickup device in which the target image is generated 
     In the embodiment of  FIG. 5 , the digital zoom magnification DZR is used in addition to the above-described information. However, when image data that is generated by an image pickup device that does not have a digital zoom function is used, the size relationship determining module  410  ( FIGS. 2 and 10 ) preferably determines the size relationship without using the digital zoom magnification DZR. 
     A combination of a maker name and a model name may be used as the image pickup element information. There is a type of image pickup device that generates image data by cropping pixels located in the peripheral part of an image pickup element (entire light receiving area) in accordance with a user&#39;s direction. When such image data is used, the size relationship determining module  410  preferably uses the size of the light receiving area occupied by the remaining pixels after the crop process (that is, the size of a part of the light receiving area in which the target image is formed), instead of the size of the image pickup element (more particularly, the entire light receiving area). The size relationship determining module  410  can calculate the size of the part based on a ratio of the size of image data with crop to the size (for example, the height or the width) of image data without any crop and the size of the entire light receiving area (it is preferable that this information is determined by the image pickup element information). In addition, when the target image (target image data) is generated without any crop, the entire light receiving area of the image pickup element corresponds to the part in which the target image is generated. In any case, the image pickup element information preferably defines the length of at least one side between the longer side and the shorter side of the light receiving area. When the length of one side is determined, the length of the other side can be determined based on the aspect ratio of the target image. 
     In addition, there is a type of the image pickup device in which the range of the subject distance, instead of the subject distance SD, is recorded in the image file. When such an image file is used, the size relationship determining module  410  preferably uses the range of the subject distance instead of the subject distance SD. The range of the subject distance, for example, represents three levels of a “macro”, a “close view”, and a “distant view” as the subject distance. In such a case, representative distances of three levels are preferably attached in advance and the size relationship determining module  410  determines the size relationship by using the representative distances. 
     Various methods in which related information related with the target image is used may generally be used as a method of determining the size relationship. Here, any arbitrary information that can be used for determining the correspondence relationship between the size (for example, the length in units of the number of pixels) in the target image and the actual size may be used as the related information. For example, the image pickup device may output the ratio of the actual length (for example, in units of centimeters) to the length (the number of pixels) in the image. When such a ratio can be used, the size relationship determining module  410  preferably determines the size relationship by using the ratio. 
     Modified Example 4 
     In the face detecting process shown in  FIG. 11 , the degree of sharpness of a face that is used in Steps S 240  and S 250  is not limited to the maximum value of the edge strength within the face. Thus, various values representing sharpness of a face can be used. For example, an integrated value that can be acquired by integrating the edge strengths of a plurality of pixels that represents a face can be used. Various values that are represented by a function of the edge strengths of each pixel, such as, for example, an average value, a maximum value, a mode value, or a median may be used as the integrated value. In addition, at least a part of a plurality of pixels that represents a face is preferably used for determining the degree of the sharpness. 
     In addition, in the face detecting process of  FIG. 11 , Steps S 240  and S 250  may be omitted. 
     Modified Example 5 
     In the above-described embodiments, any arbitrary use can be applied as the use of the result of detection of the face area. For example, the image processing module  420  ( FIGS. 2 and 10 ) may perform a deformation process for thinning the width of the detected face. In addition, the image processing module  420  may select the image, of which a face area is detected, from among a plurality of images. The selected image may be used arbitrarily. For example, the selected image may be used for a printing process or copied to a predetermined folder. 
     Modified Example 6 
     In the above-described embodiments, the image processing apparatus that detects a face area is not limited to the printer  100  ( FIG. 1 ) or the digital still camera  500  ( FIG. 13 ). Thus, any arbitrary image processing apparatus may be used as the image processing apparatus. For example, a general-purpose computer may be configured to detect a face area from the target image. 
     In addition, the configuration of the image processing apparatus is not limited to the configurations shown in  FIGS. 1 and 13 , and other configurations may be used. Generally, any arbitrary configuration in which the face area detecting module  400  (or the face area detecting module  400 A) and the size relationship determining module  410  are included may be used. For example, the image processing apparatus may acquire the target image data from an image generating device (for example, an image pickup device such as a digital still camera) through a communication cable or a network. In addition, the image processing apparatus may have a rewritable non-volatile memory in which the model size table  440  ( FIG. 2 ) is stored. In addition, the size relationship determining module  410  may update the model size table  440 . An update according to a user&#39;s direction and an update of a new model size table  440  that is downloaded through a network may be employed, for example. 
     Modified Example 7 
     In the above-described embodiments, the image data to be processed is not limited to image data that is generated by a digital still camera (still screen image data), and image data that is generated by various image generating devices can be used. For example, image data that is generated by a digital video camera (moving picture data) may be used. In such a case, the modules  400  and  410  of  FIG. 2  preferably perform determination on the size relationship and detection of a face area by using at least a part of a plurality of frame images that is included in a moving picture as a target image. In addition, the image processing module  420  may be configured to select a moving picture that includes a frame image, in which a face area is detected, from among a plurality of moving pictures. In such a case, a user can use a moving picture in which a person&#39;s face is shown in a simple manner by using the selected moving picture. In addition, selection of a moving picture that includes a target image (frame image) is also the process (a process on the target image) for the target image. 
     Modified Example 8 
     In the above-described embodiments, a part of the configuration implemented by hardware may be changed to be implemented by software, or a part or the whole of the configuration that is implemented by software may be changed to be implemented by hardware. For example, the function of the face area detecting module  400  shown in  FIG. 1  may be implemented by using a hardware circuit having a logic circuit. 
     In addition, when a part or the whole of the function of an embodiment of the invention is implemented by software, the software (computer program) may be provided in a form in which the software is stored in a computer-readable recording medium. The “computer-readable recording medium” according to an embodiment of the invention is not limited to a portable recording medium such as a flexible disk or a CD-ROM and includes an internal storage device of a computer such as various types of RAMs and ROMs and an external storage device, which is fixed to a computer, such as a hard disk.