JP2009015599A - Method and system for detecting eye position - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically detect eye positions using a simple technique and with high reliability from an original image containing a plurality of face images within one image. <P>SOLUTION: A method for detecting eye positions from the original image containing a plurality of face images comprises: (A) a process for creating an image to be scanned out of the original image, scanning the frame of a face image size therein, and detecting areas in which to detect eye positions; and (B) a process for creating, for each of the areas in which to detect eye positions, a plurality of images of varying brightnesses as images for detection of eye positions, and specifying eye position candidates based on an area where pixels stick together, which area appears in a faded-out face area as each image for detection of eye positions fades in to low brightness from a state in which it fades out at high brightness. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method and a detection system for automatically detecting an eye position from an image including a face image.

  The position of the eye in the face image can be obtained by overlaying a hairstyle model image on the subject's face image to form a hairstyle simulation image, or by overlaying a makeup image such as lips or eyebrows on the subject's face image. In this case, the image is detected for adjusting the size of the image or aligning the image. Detection of the eye position is also performed in face image blindfolding processing, face image frame processing, creation of an image for personal authentication, and the like.

  Conventionally, as a method for detecting an eye position from a face image, a method of detecting a face by extracting a skin color region and further detecting an eye by pattern matching or the like has been used (Non-Patent Document 1, Patent Document 1). ).

2005 5th LSI IP Design Award Winning Paper “Face candidate point detection method that enables fast and reliable face detection” (Nikkei Business Publications) JP 2004-94917 A

  However, the extraction of the skin color area is affected by the lighting environment. Therefore, reliability becomes a problem when an unspecified number of face images taken in various lighting environments are targeted. Further, the pattern matching method has a problem that the amount of calculation becomes enormous.

  On the other hand, an object of the present invention is to enable automatic detection of the position of an eye from an image including a face image with a simple method with high reliability.

  The inventors of the present invention (1) The original image including the face image, the brightness that can distinguish the hair region and the face region, but not the face structure, that is, can roughly determine the hair region and the face region, but the inside of the face Adjust the brightness so that it does not appear at all, or you can see the eyes, nose and mouth, but it is difficult to determine who's face, (2) scan the face size frame on the image, the center part of the frame is When a frame area having high brightness and low brightness around it is detected, the detected area corresponds to each face area included in the original image, so that this area can be extracted as an eye detection target area. 3) When an image with varying brightness is created for each eye detection area, the first pixel that appears in the pupil area is faded in from the faded out image on the high brightness side to the image on the low brightness side. (4) In this case, the pupil region pixels are paired. The eye position candidate can be determined by this, and (5) the eye position candidate from the accumulation result of the appearance frequency over all eye position detection images of the eye position candidates appearing in pairs It was found that can be identified.

That is, the present invention is a method for detecting an eye position from an original image including a face image,
A. Create a scan target image from the original image,
Scanning a face image size frame on the scan target image to detect an area where the peripheral portion has a low brightness as compared with the central portion in the frame as a detection target region of the eye position;
B. For each eye position detection target area, create multiple images with varying brightness as eye position detection images,
As the eye position detection image fades in from a state of fading out at a high brightness to a low brightness, a cluster area of pixels that gradually appears in the eye position detection image is detected,
Select the detected pixel cluster area that appeared as a pair as the eye position candidate,
Identifying eye position candidates based on the frequency of appearance across all eye position detection images of each eye position candidate;
A method for detecting the position of an eye having

The present invention also provides an eye position detection system including an original image acquisition unit including a face image and a calculation unit, wherein the calculation unit creates a scan target image from the original image, the scan target A function that scans a frame of the face image size on the image and detects a frame area whose peripheral area is lighter than the center part in the frame, and sets the detected frame area as a detection target area of the eye position A function that creates multiple images with varying brightness as eye position detection images for each eye position detection target area, as the image fades in from a state that fades out at a high brightness to a low brightness A function for detecting a cluster area of pixels that gradually appear in the eye position detection image, a function for selecting a pair of detected pixel cluster areas that appear as a pair, and a position candidate for each eye Position detection for all eyes Providing a detection system of the position of the eye has a function of identifying the position candidate of the eye based on the frequency of occurrence over the image.

  According to the method or system of the present invention, in an original image including a face image, a detection target area of an eye position corresponding to each face area is automatically detected, and brightness is detected for each detection target area of the eye position. Since the position of the eyes is identified by forming multiple images with different images, the face of the face included in the original image is independent of the lighting environment, subject skin color, subject pupil color, face orientation in the face image, etc. The position of the eye can be automatically detected in a short time with high reliability.

  According to this method or system, formation of a hairstyle simulation image for fitting various hairstyle images to an arbitrary face image using the eye position as a reference, and a face part after makeup using the eye position as a reference When a simulation image is formed by fitting a plurality of pieces of image information using the eye position as a reference, such as formation of a makeup simulation image for fitting an image to an arbitrary face image, a natural simulation image Can be formed in a short time. In addition, the method or system of the present invention can also be suitably used when performing image processing such as mosaicing and filling with reference to the position of the eye, such as blindfolding processing for personal information protection.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a flowchart showing an embodiment of the eye position detection method of the present invention for detecting the eye position of each face image in an original image including a face image, and FIG. 2 is an implementation of this method. 1 is a block diagram of a detection system 10 for an eye position.

  The system 10 includes an imaging apparatus 1 and a personal computer main body 2, and a display 3, an image scanner 4, a printer 5, and the like are connected to the personal computer main body 2.

  The imaging device 1 is provided as a means for acquiring an original image including a face image, and a commercially available digital camera can be used.

  The personal computer main body 2 is provided as a calculation means, and has an image processing function for converting a color image into a grayscale image and a function for creating an image with a predetermined fade-in ratio.

Here, conversion from a color image to a grayscale image is performed by (1) a method using the average of the maximum and minimum values of R, G, and B for each pixel, and (2) R, G, and B, respectively. (3) After multiplying each value of R, G, and B by a predetermined weighting coefficient (NTSC, etc.), the average value of these values may be used. For example, in the method (3), the following equation Y (output luminance) = 0.298912 × R + 0.568811 × G + 0.114478 × B
Can be used. Such an image processing function can be obtained by, for example, installing commercially available image processing software such as Photoshop made by Adobe System Co. in the personal computer main body 2.

  In addition, for example, when the original image has 256 gradations, an image with a predetermined fade-in ratio can be created as follows.

  First, in an image with 0% fade-in, the pixel values of all the pixels are uniformly set to 255.

  Further, in an image with fade-in x%, pixels having a pixel value of less than 2.55x in the original image have the pixel value of the original image, and pixels having a pixel value of 2.55x or more (provided that x> 0) are uniform. Suppose that it has a pixel value of 255.

  For example, in a 10% fade-in image, pixels with a pixel value of less than 25.5 (= 255 × 0.1) remain the same in the original image, and pixels with a pixel value of 25.5 or more have a uniform pixel value. 255.

  An image with 20% fade-in has a pixel value of less than 51.0 (= 255 × 0.2) in the original image, and a pixel value of 51.0 or higher in the original image remains the same. Set to 255.

  In an image with 100% fade-in, the pixel values of all the pixels remain the pixel values of the original image.

  The PC main body 2 also has a function of changing the contrast according to the change of brightness (for example, a function of decreasing the contrast as the brightness is increased and increasing the contrast as the brightness is decreased), and the image hierarchy. A function that manages by assigning a list number in order from the lowest to the highest, scans a frame of a predetermined size on an image of a predetermined brightness, and detects a frame area in which the peripheral portion has a lower brightness than the central portion in the frame Function, a function to set the detected frame area as a detection target area of the eye position, a function to create a plurality of images whose brightness changes for each detection target area of each eye position, and the brightness level in the image brightness hierarchy A function that detects the cluster area of pixels that gradually appear in the faded-out face area as it fades in from a state that fades out at high brightness to a low brightness. The function of selecting a pair of marginal areas appearing as a pair of eye positions, and the frequency of appearance of each eye position candidate across all levels of the image are counted, and the eye position candidates are narrowed down based on that value. It has functions.

  Furthermore, the personal computer body 2 uses a facial image size adjustment function, a facial image blurring function, the positional relationship between eye position candidates as eye position conditions when specifying a specific eye position from eye position candidates, A function of storing the width of the eye position candidate, the distance between adjacent eye position candidates, a function of selecting an eye position candidate that satisfies the eye position condition, and specifying the position as an eye position .

  As shown in FIG. 1, the eye position detection method using this system 10 is roughly composed of the following two steps A and B.

A. Detecting a detection target region of an eye position from an original image including a face image;
B. A step of finally identifying the position of the eye from the detection target region of the position of the eye,
(1) A step of detecting eye position candidates in a detection target region of each eye position
(2) A step of finally specifying the eye position from the eye position candidates detected in the detection target area of each eye position

  In the process A, first, an original image having a face image as a detection target of the eye position is acquired in the personal computer main body 2. For example, the original image may be obtained by taking a photograph including a face image with the imaging device 1 and loading the photograph into the personal computer main body 2, or reading a photograph including the face image using the image scanner 4, such as the Internet. Such an image may be acquired using the communication line.

  As the original image, the number of face images included in one original image may be singular or plural. However, the present invention is particularly effective when there are a plurality of facial images, and a plurality of facial images are preferable. . As the original image, the ratio of the maximum size to the minimum size of each face image included in the original image is 1 to 3 times, preferably about 1.5 to 2.5 times the length of the face. Some are preferable from the viewpoint of eye position detection accuracy.

  Next, if necessary, the size of the original image is adjusted to a size suitable for the eye position detection process. More specifically, it is preferable to change the screen size to about 480 × 360 to 320 × 240 pixels from the viewpoint of detection speed and detection accuracy.

  Further, if the face image is sharp, many fine edges appear in subsequent image processing, resulting in noise for detection of eye position candidates. Therefore, the original image is blurred as necessary. In this case, it is preferable that the degree of blurring is weak to medium. For example, for each pixel, the weighting blur filter of 1 to 5 is used for the pixel of interest and the surrounding 25 pixels. Performs blurring to output the average value. This blurring process may be performed a plurality of times as necessary.

  Furthermore, in the eye position detection method of the present invention, since it is not necessary to be a color image, when the acquired original image is a color image, it is converted into a grayscale image in order to reduce subsequent processing amount. It is preferable.

  Next, as shown in FIG. 3, in the acquired original image 20, a frame 30 having a suitable face image size is set in advance. Usually, the size of the frame 30 is set to be a rectangular frame 30 with one side being about 2 to 3 times the eye distance L1 of the individual face images included in the original image 20 having the largest distance between the eyes. preferable. Although it is not necessary to strictly define the size of the frame 30, the operator of the system appropriately sets a frame size suitable for the original image 20 from the viewpoint of capturing the detection target without omission and accurately performing the detection. It is preferable. This setting may be made any time after the original image 20 is acquired and before the face image size frame 30 is scanned on the scanning target image 21 described below.

  Then, a scanning target image 21 is created from the original image 20. As shown in FIG. 4A, by changing the brightness of the original image 20 as the scanning target image 21, the hair area and the face area can be discriminated, but the face feature cannot be discriminated, that is, the hair area and the face area are approximately It is preferable to create an image in which the inside of the face does not appear at all, or the face, eyes, nose, and mouth are known but it is difficult to determine who the face is.

  The method of creating the scanning target image 21 depends on the photographing conditions of the original image 20, but basically it is preferable to create an image with a fade-in of 25 to 35% as the fade-in ratio described above from the original image. Note that the scanning target image 21 may be formed as a negative image with inverted gradation as shown in FIG. 4B.

  The method of creating the scan target image 21 is not limited to the above-described method of creating an image having a predetermined fade-in ratio, and various binarization processing methods can be applied. For example, various binarization processes (generally referred to as variable threshold processes) for determining a threshold value based on the characteristics of the original image, such as a binarization process using the central brightness value of the brightness histogram of the original image 20 as a threshold value. Thus, the scan target image 21 can be created.

  In addition, when the original image 20 is extremely bright or dark, the scan target image 21 is preferably created after the brightness correction is performed on the original image 20 in advance as follows. That is, for the original image 20 that is too bright as shown in FIG. 5A or the original image 20 that is too dark as shown in FIG. 5B, a brightness histogram of the original image 20 is created. After the count value of the pixel value which is a count number of 5% to 15%, preferably 3% to 8% or less is set to zero, the maximum pixel value Xmax and the minimum pixel among the pixel values whose count number is not zero The value Xmin is obtained. Next, as shown in FIG. 5B, the brightness correction of the original image is performed by substituting the pixel value Xi of the original image into the following equation to obtain the pixel value after the brightness correction.

However, if Xi <Xmin, Xi = Xmin,
If Xi> Xmax, Xi = Xmax.

  The brightness correction method is not limited to the above-described method, and various methods can be applied. For example, an arbitrary image is used as a reference image in advance, the average brightness is measured, and an appropriate brightness change amount for creating a scan target image is determined, and the ratio of the average brightness of the original image to the average brightness of the reference image is calculated. Then, the brightness of the original image is corrected by changing the brightness of the original image by an amount obtained by multiplying the appropriate brightness change amount in the reference image by the average brightness ratio.

  Here, the appropriate brightness change amount in the reference image is determined as follows. First, an image in which the average brightness of the reference image is changed by one gradation in both the light and dark directions is detected, and the detection target area of the eye position shown below is detected for each image, and the detection result is actually It is judged visually whether it matches with the area where the face image exists, and the success rate of the detection is calculated. Then, the average brightness of the image with the highest success rate is obtained, and the difference between this and the average brightness of the reference image is set as the appropriate brightness change amount.

  As the reference image, face images of 5 to 20 persons are shown, and the ratio of the maximum size and the minimum size of each face image is preferably within 1 to 3 times the face length. The eye position detection target area may be set by the following method.

  Next, as shown in FIG. 6, a face image size frame 30 is scanned on the scan target image 21, and a frame region (shown in FIG. 6) in which the peripheral portion has a lower brightness than the central portion in the frame. As described above, in the negative image, the areas 30a to 30e in which the peripheral part has higher brightness than the center part are detected, and the detected frame areas 30a to 30e are set as the eye position detection target areas. More specifically, when the length of one side of the face image size frame 30 on the scanning target image 21 is X pixels, 1 to 0.35 X pixels, preferably 0.2 X to 0.3 X pixels, more preferably 0.23. The frame area is detected on the basis of the following criteria (1) to (3) by moving X to 0.27 X pixels vertically and horizontally. The scanning of the frame 30 and the detection of the following frame region may be performed simultaneously, or the frame region may be detected after the scanning is completed.

When the face image size frame 30 is divided into 3 × 3 9 areas,
(1) The existence ratio of regions having pixel values of 254 or less (regions that are not white) has a higher average value in the surrounding eight regions than the central region
(2) The existence ratio of the region having a pixel value of 254 or less is higher in the upper central region than in the central region.
(3) The existence ratio of the region having a pixel value of 254 or less is higher in the central left region or the central right region than in the central region.

  Of these criteria, (1) is for people with different skin and hair colors, with or without head hair, and in grayscale images, the face area is the head, hat, clothing, and other This is based on the fact that it is brighter than the surroundings of the face area, and is a reference necessary for detecting the face area.

  (2) is a front face image, when there is a dark region of head hair above the bright area of the face on the image, (3) is on the image, right side of the face, like a sideways face image Alternatively, this corresponds to the case where a dark region of hair exists on the left side, and these are used when the detection target region of the eye is set to be excessively wide only under the condition (1). Therefore, it is preferable to detect a frame area that satisfies only the condition (1) when priority is given to preventing detection omissions, and a frame that satisfies (1) and (2) at the same time if the purpose is to reduce the computation time. It is preferable to detect a region or a frame region that satisfies (1) and (3) simultaneously.

  After the eye position detection target areas 30a to 30e are set in this way, in step B, eye position candidates are detected for each detection target area of each eye position of the original image. In order to detect the eye position candidates, first, a plurality of eye position detection images with varying brightness are formed as eye position detection images for each eye position detection target region. More specifically, for example, as shown in FIG. 7, a fade-in image in which the brightness is gradually decreased from 0% fade-in according to the above-described image forming method having a predetermined fade-in ratio is reduced from 10% to 80% by 1%. Create about 70 levels in increments.

  In creating the fade-in image hierarchy, in order to increase the processing speed while maintaining the detection accuracy, the size of one side of each of the detection target areas 30a to 30e is larger than 80 to 120 pixels in advance. It is preferable to adjust the image size of each of the detection target areas 30a to 30e so that the size of the pixel becomes 80 to 120 pixels, and it is preferable to perform a blurring process as necessary in order to reduce noise.

  In forming a fade-in image, it is preferable to lower the contrast as the lightness is increased and raise the contrast as the lightness is lowered because the eye part appears more clearly in the fade-in image.

  In addition, as the eye position detection image, for example, by gradually changing the γ value, a plurality of images having lightness changes as shown in FIG. 7 may be formed. It is possible to use.

  As can be seen from FIG. 7, when the brightness of a detection target region is increased and the brightness is reduced from an image that has been completely faded out to form a fade-in image hierarchy, normally, first, a cluster of pixels is formed in the pupil. Then, a block of pixels is detected in the nose and mouth. The cluster of pixels in the pupil region appears as a pair of left and right. Therefore, a cluster of a pair of left and right pixels is selected as an eye position candidate. Depending on the hierarchy, pixel cluster areas appear in pairs in areas such as the mouth, eyebrows, and forehead in addition to the pupils. At this stage, these pixel cluster areas are also selected as eye position candidates.

  In the detection of the cluster area of pixels, an image whose brightness has changed may be formed as a negative image as shown in FIG.

  FIG. 9 shows a block of pixel clusters appearing in the face area in a fade-in image (negative image) in a hierarchy with a detection target area 30e for the eye position, and a pair of these areas. Are connected by a straight line.

It is preferable to set the following (1) and (2) in advance as conditions for selecting a candidate for the eye position among the clustered regions of the paired pixels.
(1) The lateral distance of the cluster area of a pair of left and right pixels is within a certain range.
(2) The vertical distance between the left and right pixel cluster areas is within a certain range.

  Next, as shown in FIG. 10, a pair of eye position candidates appearing for each fade-in image is accumulated over all layers of the eye position detection image, and the appearance frequency is counted. Create a ranking list in descending order. In this count, the eye position candidate that appears first when the brightness is gradually reduced from the faded-out face image and continues to appear until the final stage is normally the maximum count (ranking first). Therefore, those with a count value of 2 or less are excluded from eye position candidates, and in principle, the position of the eye position candidate with the maximum count is narrowed down as an eye position candidate.

However, if the following conditions (a) to (c) are all satisfied, or if the condition (d) is satisfied, the position of the eye position candidate with the second largest count is set as the eye position. As specified.
(a) When the second position candidate for the ranking is higher than the first position candidate for the ranking
(b) When the distance between the center of the eye position candidate of the 2nd ranked eye is longer than the distance between the centers of the position candidate of the 1st ranked eye
(c) When the left and right pupil regions of the second ranking eye position candidate are both outside the positions corresponding to the left and right pupils of the first ranking eye candidate
(d) The vertical distance between the first position candidate of the ranking and the second position candidate of the ranking is about the distance between the eyes and the eyebrows, and the first position candidate of the ranking is ranked first. When the position is above the second position candidate

  Of these, (a) to (c) are intended to prevent erroneous determination of the position of the mouth as the position of the eye, while the first ranking in the ranking may rarely be the mouth area. d) is for preventing erroneous determination that the eyebrows around the eyes are the positions of the eyes.

  As described above, as shown in FIG. 11, it is possible to accurately detect eye position candidates (more precisely, the position of the pupil) in the detection target area of each eye position.

  The above eye position candidate specifying method is performed for each of the detection target regions 30a to 30e of the eye positions set in step A. In addition, if an eye position candidate cannot be specified in a detection target area of any eye position, the area is treated as having no eyes thereafter.

  Thus, the eye positions specified in the detection target areas of the individual eye positions are finally overlapped with the corresponding positions of the original image as shown in FIG. 12, and are set as the eye positions of the individual face images in the original image. It becomes possible.

  The method for detecting the eye position according to the present invention is accurate regardless of changes in the skin color, pupil color, face orientation, and lighting environment of each subject to be detected as the eye position in a plurality of face images. The eye position can be detected at a high processing speed by a simple calculation method. Therefore, it is possible to detect the position of the eyes from a plurality of face images regardless of whites or blacks.

  The eye position thus detected creates an image for personal authentication when a hairstyle simulation image is formed, a makeup simulation image is formed, a face image is blindfolded, a face image is framed. It can be used in various scenes where detection of the eye position is required.

  The present invention forms a hairstyle simulation image that fits various hairstyle images to an arbitrary face image using an eye position as a reference, and a partial image of a face after makeup using an eye position as an arbitrary face This is useful in various scenes where eye position detection is required in image processing of a plurality of face images, such as formation of a makeup simulation image to be fitted to an image, face image blindfolding processing, and face image frame processing.

It is a flowchart of the detection method of an eye position. It is a block diagram of an eye position detection system. It is explanatory drawing of the setting method of the frame of a face image size. It is a scanning target image (positive image). It is a scanning target image (negative image). It is a brightness histogram. It is a brightness histogram. It is the scanning object image which detected the detection object area | region. It is an eye position detection image in which the brightness is changed in each detection target region. It is a negative image of the eye position detection image in which the brightness is changed in each detection target region. It is explanatory drawing of the cluster area | region of the pixel in the fade-in image of a certain detection object area | region. It is explanatory drawing of the state which accumulated the eye position candidate over all the hierarchy of the eye position detection image. It is an eye position detection image displaying the detected eye position in each detection target region. It is a figure which shows the state which accumulated the detection target area | region of the position of an eye on the original image in the original image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging device 2 Personal computer body 3 Display 4 Image scanner 5 Printer 10 Eye position detection system 20 Original image 21 Scan target image 30 Face image size frames 30a to 30e Eye position detection target region L1 Distance between eyes

Claims (6)

A method for detecting an eye position from an original image including a face image,
A. Create a scan target image from the original image,
Scanning a face image size frame on the scan target image and detecting an area in which the peripheral portion has low brightness as compared to the central portion in the frame as a detection target region of the eye position;
B. For each eye position detection target region, create a plurality of eye position detection images whose brightness has changed as eye position detection images,
As the eye position detection image fades out from a high lightness fade-out state to a low lightness, a cluster area of pixels that gradually appears in the eye position detection image is detected.
Select the clustered areas of the detected pixels that appear as a pair as eye position candidates,
Identifying eye position candidates based on the frequency of appearance across all eye position detection images of each eye position candidate;
A method for detecting the position of an eye.   The method of detecting an eye position according to claim 1, wherein in step A, the scan target image is created by performing brightness correction on the original image.   The eye according to claim 1 or 2, wherein in step A, a rectangular frame having one side that is 2 to 3 times the maximum value of the interval between the eyes of each face image included in the original image is set as the frame of the face image size. Position detection method. In step A, when the original image has 256 gradations, an image with 0% fade-in has all pixels having a pixel value of 255 and an image with fade-in x% (where x> 0) A pixel having a pixel value of less than 2.55x has a pixel value of the original image, and a pixel having a pixel value of 2.55x or more has a uniform pixel value of 255. Form an image with a fade-in of 25-35%,
The face image size frame is divided into 3 × 3 9 areas, and the face image size frame satisfies the following (1), (2), and (3). The method for detecting an eye position according to any one of claims 1 to 3, wherein the eye position is detected as a detection target region.
(1) The existence ratio of areas with pixel values of 254 or less is higher in the surrounding 8 areas than in the central area.
(2) The existence ratio of the region having a pixel value of 254 or less is higher in the upper central region than in the central region.
(3) The existence ratio of the region having a pixel value of 254 or less is higher in the central left region or the central right region than in the central region.   The eye position detection method according to claim 1, wherein after the grayscale image is created from the original image, the scanning target image is created from the grayscale image. An eye position detection system including an original image acquisition unit including a face image and a calculation unit, wherein the calculation unit includes:
A function for creating an image to be scanned from an original image, a function for scanning a frame of a face image size on the image to be scanned, and detecting a frame region whose peripheral portion is lighter than the central portion in the frame A function for setting the detected frame area as a detection target area for the eye position, a function for creating a plurality of images whose brightness is changed as an eye position detection image for each detection target area for each eye position, A function that detects a cluster area of pixels that gradually appears in the eye position detection image as it fades in from a state faded out to a low brightness, and the detected cluster area of pixels appears as a pair. An eye position detection system having a function of selecting eye position candidates and a function of specifying eye position candidates based on the appearance frequencies of all eye position candidates over all eye position detection images.