JP2007080087A - Facial parts extraction method and face authentication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a facial parts extraction method capable of extracting the facial parts image comprising a stable binary image, without affected by image brightness or contrast, illumination direction, etc. <P>SOLUTION: The facial parts extraction section 4 processes a grayscale image into a differential intensity image by differential processing, performs processing for sorting pixels in the descending order of differential intensity within a predefined area of the differential intensity image including the facial parts to extract, then sets threshold for a region selected by a specified number of pixels, associated with the facial parts as a region with intense concentration change and the rest region as a region with non-intense concentration change, and outputs the differential intensity image as the binarized image by use of the thresholds. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a face component extraction method and face authentication apparatus necessary for face authentication.

  As a device for searching for parts such as eyes and mouth of a face used for face authentication, there is provided a face part search method for detecting the density of an image part of a face area and detecting the face part based on the density ( Patent Document 1).

There is also provided an apparatus for determining a region of an eye or mouth using pixel value information such as shading change or a histogram and cutting out a face part region (Patent Document 2).
JP 2003-281539 A (left column on page (1)) Japanese Patent Laid-Open No. 8-221591 (paragraph numbers 0015 and 0023)

  By the way, in the method of detecting and extracting a facial part using shading as disclosed in Patent Documents 1 and 2, it is affected by the brightness and contrast of the image, the illumination irradiation direction, and the like. When extracting a component image, there is a problem that the binarized image changes due to the above-described influence.

  The present invention has been made in view of the above-described points, and the object of the present invention is to make a facial component composed of a stable binary image without being affected by the brightness, contrast, illumination illumination direction, and the like of the image. It is an object of the present invention to provide a face component extraction method and a face authentication device that can extract an image.

  In order to achieve the above-mentioned object, in the invention of the facial part extraction method according to claim 1, after searching for a facial part from a grayscale image in which a person is imaged, a pixel having a sharp density change in the grayscale image of the facial part and its vicinity A face component extraction method for extracting a binarized image as a face component image by selecting a pixel having a large density change and a pixel in the vicinity thereof as a pixel including information indicating a face component, and after searching for a facial part Then, the grayscale image of the facial part is differentiated to obtain a differential intensity image, and the pixels are rearranged in the differential intensity order within the predetermined area including the facial part to be extracted in the differential intensity image, and based on the differential intensity order after the rearrangement. In this case, the selected number of pixels corresponding to the face part is selected, and a differential intensity binarized image obtained by binarizing the selected part and other parts is extracted as a face part image.

  According to the invention of the face part extraction method of claim 1, the face part image binarized with the threshold value can be extracted using the number of pixels of the face part included in the predetermined area to be rearranged for the differential intensity. Therefore, stable face component extraction can be performed without being affected by image brightness, contrast, illumination irradiation direction, and the like.

  According to a second aspect of the present invention, the rearrangement of the differential intensities is performed in descending order of the differential intensities, and the number of designated pixels associated with the face part from the higher one of the differential intensities. This method is characterized in that the selected portion is binarized, and the selected portion is binarized as a flat portion where the concentration change is intense and the other portions are not drastically changed in concentration.

  According to the invention of the method for extracting a facial part of claim 2, facial parts are extracted by paying attention to a part having a large differential intensity and a sharp density change, and the brightness, contrast, illumination illumination of the image as in the case of claim 1. Stable facial parts can be extracted without being affected by the direction.

  According to a third aspect of the present invention for extracting a facial part, in the first aspect of the invention, the rearrangement of differential intensities is performed in the order of decreasing differential intensities, and the designated number of pixels associated with the facial part from the one with the lower differential intensities. The selected portion is selected as a flat portion where the concentration does not change drastically, and the other portion is binarized as a portion where the concentration changes drastically.

  According to the invention of the facial part extraction method of claim 3, facial parts are extracted in a manner that pays attention to a flat part having a low differential intensity and a low density change, and the brightness and contrast of the image as in claim 1, Stable facial component extraction can be performed without being affected by the illumination direction.

  According to a fourth aspect of the present invention, the number of pixels constituting the facial part according to any one of the first to third aspects is obtained in advance from a reference face image, and extracted based on the reference number of pixels. The specified number of pixels is determined according to the size of the target face.

  According to the invention of the face part extraction method of claim 4, since the binarization threshold can be set according to the size of the face to be extracted, the face part extraction can be performed accurately.

  In the invention of the face component extraction method of claim 5, in the invention of any one of claims 1 to 4, the number of pixels required for face authentication is effective for face authentication and for a part having a large individual difference. It is characterized in that it is separately obtained in advance.

  According to the invention of the face part extraction method of claim 5, when face authentication is performed based on the extracted face part image, there are large individual differences such as wrinkles on the nose, chin lines, eyeglass frames, etc. Authentication with face parts that are difficult to perform is also possible.

  According to a sixth aspect of the present invention, the region extracted as a differential intensity binarized image is subjected to an expansion process.

  According to the sixth aspect of the present invention, it is possible to use information unique to a face part possessed by peripheral pixels having a high differential intensity.

  According to a seventh aspect of the present invention, the predetermined region is a region grouped for each region that is similarly affected by the illumination direction. And

  According to the invention of the facial part extraction method of claim 7, the order of the differential intensity can be rearranged without the influence of the brightness distribution, and the facial part image which is not affected by the difference of the brightness distribution can be extracted.

  According to an invention of a facial part extraction method of an eighth aspect, in the invention of any one of the first to seventh aspects, after the rearrangement, the differential intensity near the lowest position at the specified number of pixels satisfies a predetermined differential intensity value. If not, the imaging parameter of the imaging camera is controlled so as to exceed a predetermined differential intensity value.

  According to the invention of the face part extraction method of claim 8, it is possible to secure the differential strength for performing proper face part extraction.

  According to a ninth aspect of the present invention, there is provided a face component extracting method according to the first to eighth aspects, wherein when the density value distribution of the grayscale image does not satisfy a predetermined range, the density value distribution is a predetermined range distribution. The imaging parameter of the imaging camera is controlled to satisfy the area.

  According to the invention of the facial part extraction method of claim 9, it is possible to ensure the differential strength for performing proper facial part extraction.

  According to another aspect of the present invention, the facial part extracting means for extracting a facial part as a binarized image by the facial part extracting method according to any one of claims 1 to 9, and the binarized image from the facial part extracting means. It is characterized in that the face authentication determination process is performed by density matching or density gradient direction matching using the pixel value of the location that is captured and associated with the face part.

  According to the invention of the face authentication apparatus of claim 10, since face authentication is performed using face parts that are stably extracted without being affected by the brightness, contrast, illumination illumination direction, etc. of the face, the face is highly accurate. Authentication can be performed.

  The present invention can extract a facial part image binarized with a threshold value using the number of pixels of a facial part included in a predetermined area to be rearranged for differential intensities. There is an effect that it is possible to provide a face part extraction method capable of performing stable face part extraction without being affected by a direction or the like, and to provide a face authentication apparatus capable of performing face authentication with high accuracy.

  Embodiments of the present invention will be described below.

(Embodiment 1)
FIG. 1 shows the overall configuration of a face authentication apparatus X employed as a face component extraction method of the present embodiment. The face authentication apparatus X includes an imaging camera 1, an image data input unit 2, and a face position search unit 3. And a face part extraction unit 4 adopting the present embodiment, a face authentication part 5 that performs face authentication using the extracted face part image, and the like.

  The face authentication apparatus X performs authentication processing according to the flowchart shown in FIG.

That is, captured image data composed of, for example, a gray image of the upper body of the person to be authenticated photographed by the imaging camera 1 is input to the image data input unit 2 (step S1). The image data input unit 2 performs processing for storing captured image data in the image data buffer 2a.
Next, the face position search unit 3 searches for and extracts a face position from the captured image on the image data buffer 2a (step S3).

  The face position search method in the face position search unit 3 is not particularly limited, and any known method may be adopted as appropriate. For example, a density gradient direction from a captured image and a face detection template image prepared in advance. Extract an image, and extract information on the distance between the reference point on the extracted density gradient direction image and the reference coordinate point, and the angle at which the line connecting the reference point and the coordinate point intersects the horizontal axis passing through the coordinate point The shape feature is separated for each value of the density gradient direction of the face detection template image from the extracted distance and angle information, and the value of the density gradient direction at the coordinate point used as the reference for the density gradient direction image of the captured image and There is a method of performing a voting process on a reference point candidate point in a density gradient direction image of a captured image based on the shape feature and detecting a face position based on a voting result.

  Now, the gray image of the face position searched by the face position search unit 3, that is, the face image (see, for example, FIG. 3A) is sent to the face component extraction unit 4, and the face component extraction unit 4 performs the face such as eyes and mouth. A binarized image of the part is extracted (step S4).

  Here, the face part extraction unit 4 selects and binarizes the pixels having a large density change and the neighboring pixels as the face image including information indicating the face part in the pixel having a large density change and the neighboring pixels in the face image. The image is extracted as a face part image, and a processing operation is performed according to the flowchart of FIG. That is, first, a gray image of a facial part is input (step S30), and the gray image is differentiated in step S31 to obtain a differential intensity image. Within the differential intensity image, within a predetermined region including a facial part to be extracted. A process of rearranging the pixels in descending order of differential intensity is performed (step S32).

Here, the predetermined area is a grouping of areas having the same brightness distribution difference in the illumination direction irradiated to the person who is the subject at the time of shooting. For example, in the case of a face, the following three types are assumed in the positional relationship between the face and illumination.
(1) When the illumination is arranged in the lateral direction of the face, either the left or right side of the face is bright and the opposite is dark.
(2) When illumination is arranged above or below the face, either the top or bottom of the face is bright and the opposite is dark.
(3) When the illumination is arranged obliquely above or below the face, for example, the face is divided into four parts and the side near the illumination is bright, and the opposite is dark.

  If the face is divided into four parts, it can be easily imagined that the illumination can be obtained in the same manner when the illumination is arranged in the horizontal direction or when it is arranged above or below.

  If the relationship between the illumination and the face position is known in advance, the region may be divided accordingly. If the relationship is not known, for example, four divisions are adopted as a division that can correspond to any of them.

  Furthermore, if it is assumed that there is little difference in brightness in the vertical and horizontal directions, the entire face may be treated as one area.

  It can be easily imagined that the same effect can be obtained even when there is little difference in brightness between the top, bottom, left and right in the case of dividing into four or two.

  FIG. 3 (a) shows that there is no significant difference in the brightness portions of the face in the vertical and horizontal directions, and that there is little separation, and the entire face is regarded as one area, and the differential intensity over the entire area. 3 (b) shows a case where the face is divided into left and right parts, and FIG. 3 (c) shows a case where the face is divided into four parts up, down, left and right.

  Here, for example, a bubble sort is adopted as an algorithm for rearranging in the order of differential intensity. This bubble sort is performed by comparing the value A of the last element of the array arranged at random with the value B of the element immediately above, and if A> B, the element of value A and the element of value B Reverse the order of the order. Next, a comparison is made between the last one element (the element of the previous value A) and the value C of the element two above from the last. For example, if A> C, the element of the value A and the value C Reverse the order of the elements. When such comparison and rearrangement are sequentially performed and the comparison with the value of the first element of the array is completed, the element having the largest value is included as the first element of the array. Then start again by comparing the value of the last element of the array with the value of the element above it, and when the first to the second of the array are performed, the value with the largest first element and the second element Will be the second largest value. By repeating the sequential comparison and rearrangement in this way, it is possible to rearrange all the elements of the array.

  When the rearrangement process is completed as described above, it is determined in step S34 whether or not the differential intensity condition is appropriate. If it is determined that the differential intensity condition is appropriate, the facial parts to be extracted from the top of the magnitude of the differential intensity are determined. A threshold value is set with a part selected corresponding to the designated number of associated pixels as a part where the density change is severe, and the other part as a flat part where the density change is not severe, and the differential intensity image is binarized with this threshold value. (Step S35). The number of pixels specified here is specified by assigning the number of pixels associated with the face part divided into the grouped areas. Note that the number of pixels designated corresponding to the face part is the number of pixels constituting the eyes, mouth, eyebrows, and nostrils. In addition, it is difficult to specify the position because the position of the wrinkles of the nose, wrinkles of the mouth, lines of the chin, eyeglasses, etc. Alternatively, the number of pixels necessary for selecting effective pixels may be separately measured and used for face authentication.

  FIG. 4 shows a binarized image of the differential intensity image corresponding to the grouping of FIG.

  For example, the gray image of the face position when imaged without illumination is shown in FIG. 4 (a-1), and the image rearranged in the order of the differential intensity and binarized under the above conditions is shown in FIG. 4 (a-2). . Further, the gray image of the face position when the illumination irradiation direction is irradiated from the left side with respect to the face of the person is as shown in FIG. 4B-1, and is rearranged in the order of the differential intensity and binarized under the above conditions. 4 (b-2), and the gray image of the face position when the illumination irradiation direction is irradiated from the front to the face of the person is shown in FIG. 4 (c-1). An image binarized under the above conditions is shown in FIG. Furthermore, the gray image of the face position when the illumination irradiation direction is irradiated from the right side with respect to the face of the person is as shown in FIG. 4 (d-1), and is rearranged in the order of the differential intensity and binarized under the above conditions. The image is as shown in FIG.

  The specified number of pixels for setting the threshold value described above is obtained by checking in advance the number of pixels constituting the face part to be extracted using a reference face image and registering it in the storage unit 4a. By setting the binarization threshold after rearrangement in the order of differential intensity, it is necessary to be stable without being affected by the brightness of the image, contrast, and illumination illumination direction (illumination illumination conditions) as shown in FIG. Facial parts can be extracted.

  By the way, when the differential intensity image is binarized with a fixed threshold value, the gray image of the face position when imaged without illumination shown in FIG. 5 (a-1) becomes FIG. 5 (a-2). In the case of the gray image of the face position when the illumination irradiation direction shown in FIG. 5B-1 is irradiated from the left side toward the face of the person, it becomes FIG. 5B-2, and FIG. In the case of the gray image of the face position when the illumination irradiation direction shown in 1) is applied from the front to the face of the person, it is as shown in FIG. Further, in the case of the gray image of the face position when the illumination irradiation direction shown in FIG. 5D-1 is irradiated from the right side with respect to the human face, it becomes FIG. 5D-2.

  In the case of FIG. 5, it can be seen that the differential intensity binarized image changes due to the influence of the illumination irradiation direction. When such a fixed threshold value is used, it is also affected by the brightness and contrast of the image.For example, in a gray image with a high contrast, the differential intensity value increases, but in a gray image with a low contrast, the differential intensity value also increases. Since it becomes smaller, the obtained differential intensity binarized image changes. That is, the face part image used for face authentication is not stable, and the accuracy of face authentication is lowered.

  By the way, when it is determined in step S34 described above that the differential intensity is not appropriate, in the present embodiment, a signal for converting and controlling the imaging parameters (for example, contrast and offset value) of the imaging camera 1 is sent from the facial component extraction unit 4 to the imaging camera. 1 is controlled (step S36), and the processing from step S1 in FIG. 2 is performed again.

  In other words, the lowest contrast value may not satisfy the specified differential intensity value in the state of low contrast in the intermediate gray level due to backlighting, saturation with sticking to the upper limit value or lower limit value due to being too bright or too dark. Get up. For example, the brightness distribution histogram in the face image with appropriate contrast shown in FIG. 6A is as shown in FIG. 6B, and the differential intensity distribution histogram is as shown in FIG. 6C. As shown in FIG. 7B, the luminance distribution histogram of the face image with insufficient contrast is as shown in FIG. 7B, and the differential intensity distribution histogram is as shown in FIG. 7C. The state where the differential intensity value is small is a flat state where there is no change in brightness, and the direction value may vary due to slight noise. In such a case, as described above, the imaging parameter is sent from the face part extraction unit 4 to the imaging camera 1 and controlled to obtain an appropriate differential intensity.

  The determination to control the imaging camera 1 includes determination based on the average value of the differential intensity distribution, or the analogy result of the lowest value from the differential intensity distribution in the middle of the sorting of the differential intensity, and further before the differential processing. For example, it may be determined that the imaging camera 1 is to be controlled when the distribution value of the grayscale pixels is not satisfying the distribution range of a predetermined range.

  As described above, in the face part extraction of the present embodiment, the number of designated pixels associated with the face part in the reference face actually obtained in advance after rearranging the differential intensity values in the predetermined area including the face part. Select from the top of the differential intensity value by the amount, and binarize the selected part as a flat part where the density change is intense and the other part is not so intense in density change, and extract the facial part image. Therefore, it is possible to obtain a stable binary image including face parts necessary for face recognition without being affected by the brightness, contrast, illumination direction, etc. of the image. Also gets higher.

  In the above case, the number of pixels of the facial part used as the threshold for binarization is obtained by measuring the number of pixels of the standard facial part in advance, but the size of the facial part to be extracted changes. For example, the number of pixels designated in proportion may be changed. For example, measure the size of the face to be authenticated by area, etc., compare the number of reference pixels with the measured face size, change the number of reference pixels according to the comparison result, and specify the number of pixels , It is possible to extract a facial part image that matches the size of the facial part of the person to be authenticated.

  Further, in the above-described case, the predetermined area is rearranged in intensity differentiation in the left, right, up, down, left, or right of the face image, but as shown in FIG. Defines the nose area, registers the number of pixels in that area, that is, the number of pixels of the face part and the position of each area in the storage unit 4a, and sets the area of each face part in the registered reference face image. Alternatively, it may be a predetermined area in which rearrangement is performed in the order of differential intensity values.

  FIG. 9 shows a case where the order of the differential intensities is rearranged in each area of the eyes and mouth, and in the case of the gray image of the face position when imaged without illumination shown in FIG. 9 (a-2), and in the case of the gray image of the face position when the illumination irradiation direction shown in FIG. 9 (b-1) is irradiated from the left side with respect to the human face, FIG. 2), and in the case of the gray image of the face position when the illumination irradiation direction shown in FIG. 9C-1 is irradiated from the front to the human face, FIG. 10C-2 is obtained. Further, in the case of the gray image of the face position when the illumination irradiation direction shown in FIG. 9D-1 is irradiated from the right side with respect to the face of the person, it becomes FIG. 9D-2.

  In the above-described rearrangement in the order of the differential strength, the rearrangement is performed in descending order of the differential strength value. In other words, it is effective when the number of pixels with larger differential strength is selected, such as when the number of pixels of the face part included in the predetermined area where the differential strength is rearranged is 50% or more of the total number of pixels. Thus, it is possible to shorten the time for the rearrangement process in which the differential strengths are arranged in order from the one with the lower differential strengths than in the order of the higher differential strengths. When the above-described bubble sort rearrangement method is used, the position of the array may be reversed when the values are small when comparing the element values. In this case, the portion selected from the smaller of the designated number of pixels associated with the face part actually measured in advance is set as a flat portion where the density change is not intense, and the other portion is set as a portion where the density change is intense. To do.

  Further, in the above method, extraction can be performed where the differential intensity is large, but there is a high possibility that the density change still exists in one pixel outside the area. In other words, where the differential intensity is small, the direction value also varies widely and lacks reliability, so it is sorted out in the order of differential intensity and excluded as a flat place, but the differential intensity pixel has information specific to the object. It is thought that there is. Therefore, after the above binarized image is extracted, expansion processing may be performed, and the expanded processing region may be extracted as a region having a high density, that is, a face part region.

  FIG. 10 shows a case where the order of differential intensities is rearranged in each area of the eye and mouth and an expansion process is performed. The contrast of the face position when the image is taken without illumination shown in FIG. In the case of an image, it becomes FIG. 10 (a-2), and in the case of a gray image of the face position when the illumination irradiation direction shown in FIG. 10 (b-1) is irradiated from the left side toward the face of a person. 9 (b-2), and in the case of the gray image of the face position when the illumination irradiation direction shown in FIG. 10 (c-1) is irradiated from the front to the face of the person, FIG. ) Further, in the case of the gray image of the face position when the illumination irradiation direction shown in FIG. 10D-1 is irradiated from the right side with respect to the face of the person, it becomes FIG. 10D-2.

  Here, when a binary image of differential intensity is created by the face part extraction unit 4 as described above, the face authentication unit 5 takes in the binarized image and sets the pixel value of the location associated with the face part. Then, face authentication determination processing is performed by density matching or the above-described density gradient direction matching (step S4), and processing for outputting the authentication result to the outside is performed (step S5).

  Although an appropriate method may be used as the face authentication method in the face authentication unit 5, an example of the face authentication method of the face authentication unit 5 is a method using template matching using density gradient direction values. In this case, the density gradient direction value determined by the magnitude of the difference value between adjacent pixels is used as the density gradient direction value as shown in the following equation. Therefore, in order to perform highly reliable template matching, a highly reliable density gradient direction value is required, and for this purpose, a facial part image having a high contrast between adjacent pixels is required in this example.

dx = (c + 2f + ia + 2d + g)
dy = (g + 2h + ia−2b + c)
θ = tan ⁻¹ (dy / dx)
| G (i, j) | = [dx ² (i, j) + dy ² (i, j)] ^1/2
In the above equation, a Sobel filter having a mask size of 3 × 3 is used, dx and dy are differential values in the x direction and y direction of the pixel, and a to i are pixel values of the pixel of interest and its neighboring eight pixels ( Represents the density gradient direction, and | G (i, J) | represents the differential intensity value at the pixel (i, j).

  Next, after determining the white part indicating the facial part in the differential intensity binarized image output from the facial part extraction unit 4 as a part to be template-matched, correlation of template matching in the face authentication unit 5 when performing face authentication An example of a value calculation method will be briefly described.

Example 1
Both the input image A (I, J) input from the image input unit 2 through the image data buffer 2a by the face authentication unit 5 and the template image B (I, J) made up of face images registered for authentication. Assuming 256 gradations, pixel difference value C (I, J) = | A (I, J) −B (I, J) |, and assuming that the total number of pixels for which correlation values are to be calculated is N, template matching The correlation value is calculated as correlation value = 1− (ΣC (I, J)) / N / 256.

Example 2
This example is an example of a calculation method with different weights, and the face authentication unit 5 registers the input image A (I, J) input from the image input unit 2 through the image data buffer 2a for authentication. The template image B (I, J) made up of the face image has 256 gradations and is multiplied by a coefficient α when calculating the pixel-specific difference value C (I, J). This α is a specified value of 0 or more and less than 1 for the area subjected to the expansion processing as described above, and 1 for the area to be calculated from the beginning. Therefore, the pixel-by-pixel difference value C (I, J) is
C (I, J) = α × | A (I, J) −B (I, J) |

  Further, the total number N of pixels for which correlation values are to be calculated is a value (N = n + m) obtained by adding the number of pixels n before expansion and the number of pixels m when expanded.

And the correlation value of template matching is
Correlation value = 1− (ΣC (I, J)) / K / 256 (where K = n + α × m)
Is calculated.

  In the calculation method of this example, it is reasonable to weight the correlation value calculation as much as it lacks reliability (weighting so as not to affect the correlation value compared to the pixel to be calculated from the beginning). I can say that.

  For example, the difference value in the calculation target pixel from the beginning before expansion is C (I, J) = 64, the total number of pixels is N = n = 100, and the difference value in the calculation target pixel after expansion is C (I, J). = 32 and the total number is m = 100, the correlation value before expansion is 0.75, and the correlation value after expansion (by calculation without weighting) is 0.8125.

  On the other hand, when the weight coefficient α is 0.1, the correlation value after expansion is 0.7614 (rounded to the fifth decimal place), and when the weight coefficient α is 0.8, 0,8056 ( Rounded to the fifth decimal place).

  That is, in the calculation method of this example, by setting the coefficient α to a small value, a correlation value close to the value before expansion can be calculated while taking into account the expansion.

It is a whole block diagram of the face authentication apparatus using one Embodiment. (A) is a flowchart for explaining the operation of the face authentication apparatus using one embodiment, and (b) is a flowchart for explaining the operation of the face part extraction unit in the face authentication apparatus. It is explanatory drawing of grouping of the face image in one Embodiment. In one embodiment, it is explanatory drawing of the example of extraction of the face component image when the predetermined area | region which rearranges differential intensity | strength is made into the left and right of a face image. It is explanatory drawing of the example of extraction of the face component image in a comparative example. In one Embodiment, it is explanatory drawing of the face image of appropriate contrast used for face component extraction, Comprising: (a) is a face image example figure, (b) is a luminance distribution histogram, (c) is a differential intensity distribution histogram. In one embodiment, it is explanatory drawing of the face image with insufficient contrast used for face component extraction, Comprising: (a) is a face image example figure, (b) is a luminance distribution histogram, (c) is a differential intensity distribution histogram. In one Embodiment, it is explanatory drawing at the time of making the predetermined area | region which rearranges differential intensity | strength into eyes and a mouth. In one embodiment, it is explanatory drawing of the example of extraction of the face component image in case the predetermined area | region which rearranges differential intensity | strength is made into the eyes and the mouth. In one embodiment, it is explanatory drawing of the example of extraction of the face component image in case the predetermined area | region which performs an expansion process and rearranges differential intensity | strength is made into eyes and a mouth.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging camera 2 Image data input part 2a Image data buffer 3 Face position search part 4 Face component extraction part 4a Memory | storage part 5 Face authentication part X Face authentication apparatus

Claims (10)

After searching for a facial part from a gray image captured by a person, the pixel having a large density change in the gray image of the facial part and its neighboring pixels including information indicating a facial part in the neighboring pixel and its neighboring pixels A face part extraction method for selecting a pixel and extracting a binarized image as a face part image,
After searching for a facial part, the grayscale image of the facial part is differentiated into a differential intensity image, and in this differential intensity image, the pixels are rearranged in the order of the differential intensity within a predetermined area including the facial part to be extracted. Select only the specified number of pixels associated with the facial part based on the order of the differential intensity, and extract the differential intensity binarized image obtained by binarizing the selected part and other parts as a facial part image. Feature facial part extraction method. Sort the differential intensities in descending order of the differential intensity, select the specified number of pixels corresponding to the face part from the one with the highest differential intensity, and place the selected part where the change in density is severe, otherwise 2. The facial part extraction method according to claim 1, wherein the part is binarized as a flat part where the density does not change drastically. Reorder the differential intensities in the order of decreasing differential intensities, and select from the smaller differential intensities the specified number of pixels associated with the facial part, and select the selected part as a flat part where the density does not change drastically 2. The method of extracting facial parts according to claim 1, wherein the other parts are binarized as parts having a sharp density change. The number of pixels constituting a face part is obtained in advance from a reference face image, and the specified number of pixels is determined according to the size of a face to be extracted based on the number of reference pixels. Item 4. The facial part extraction method according to any one of Items 1 to 3. 5. The face component extraction method according to claim 1, wherein the number of pixels necessary for face authentication is determined in advance separately from the designated number of pixels for a part that is effective for face authentication and has a large individual difference. . 6. The face component extraction method according to claim 1, wherein a region extracted as a differential intensity binarized image is expanded. 7. The face part extraction method according to claim 1, wherein the predetermined area is an area grouped for each area that is similarly affected by the illumination direction. After the rearrangement, when the differential intensity near the lowest position at the specified number of pixels does not satisfy a predetermined differential intensity value, the imaging parameter of the imaging camera is controlled to exceed the predetermined differential intensity value. The face part extracting method according to any one of claims 1 to 7. The imaging parameter of the imaging camera is controlled so that the density value distribution satisfies a predetermined range of distribution when the density value distribution of the grayscale image does not satisfy a predetermined range of distribution. 9. The facial part extraction method according to any one of 1 to 8. A facial part extracting unit that extracts a facial part as a binarized image by the facial part extracting method according to claim 1, and a binarized image from the facial part extracting unit A face authentication apparatus that performs face authentication determination processing by grayscale matching or density gradient direction matching using pixel values.