Title of Invention: Method, apparatus and computer readable recording medium for detecting a location of a face feature point using an Adaboost learning algorithm
Abstract: The present disclosure relates to detecting the location of a face feature point using an Adaboost learning algorithm. According to some embodiments, a method for detecting a location of a face feature point comprises: (a) a step of classifying a sub-window image into a first recommended feature point candidate image and a first non-recommended feature point candidate image using first feature patterns selected by an Adaboost learning algorithm, and generating first feature point candidate location information on the first recommended feature point candidate image; and (b) a step of re-classifying said sub-window image classified into said first non-recommended feature point candidate image, into a second recommended feature point candidate image and a second non-recommended feature point candidate image using second feature patterns selected by the Adaboost learning algorithm, and generating second feature point candidate location information on the second recommended feature point recommended candidate image.
Detailed Description: Part general_description_paragraphs: The present patent application is a continuation application of U.S. application Ser. No. 14/129,356, filed Jan. 28, 2014, pending, which is a U.S. National Phase Application under 35 U.S.C. 371 of International Application No. PCT/KR2012/007843 filed Sep. 27, 2012, which claims priority from Korean Application No. 10-2011-0097794, filed Sep. 27, 2011, the contents of which are incorporated herein in their entirety by reference.
Part TECHNICAL FIELD: The present disclosure relates to a method, apparatus, and computer-readable recording medium for detecting the position of a face feature point by using an Adaboost learning algorithm. More specifically, the present disclosure relates to a method, apparatus, and computer-readable recording medium for more correctly detecting the position of a face feature point in a facial image of an unusual state by using a multi-layer Adaboost classifier.
Part BACKGROUND: Biometrics is the technology for recognizing physical features, such as a fingerprint, a face, an iris, a vein, and the like, which are different from person to person. Such physical features cannot be stolen or copied by others like a key or password and may be utilized in the security field or the like since they are not at the risk of being changed or lost. Face recognition is a type of biometric technology that includes a technique of detecting a face region in a video or a picture image and identifying the identity of a face included in the detected face region. Such face recognition technology can be utilized in not only the security field, but also a variety of applications in line with the progress during the smart phone age.
Specifically, face recognition is a technique for identifying a face in a detected facial image by using positions of feature points. The feature points may include a center point of an eye, both end points of each eye, both end points and a center point of an eyebrow, both end points of a lip or the like.
Techniques such as a histogram, principal component analysis (PCA), and Adaboost learning algorithm are used for detecting positions of such face feature points, and these methods generally provide good results to some extent when they are applied to ordinary facial images (i.e., normal facial images).
However, there is a problem in that considerable degradation in performance is observed in detecting positions of feature points when these methods are applied to unusual facial images (e.g., a facial image of a person wearing glasses, a facial image with a portion of a face hidden behind hairs, a facial image of a person with exaggerated facial expressions, a non-frontal facial image, a partially dark facial image, an image with closed eyes, or the like).
Accordingly, it is necessary to develop a technique that guarantees consistent performance in detecting positions of feature points of unusual facial images as well as ordinary facial images.
Part DETAILED DESCRIPTION: Part Technical Problem: Therefore, an object of the present disclosure is to solve the above-described problems.
In addition, another object of the present disclosure is to guarantee performance in detecting positions of face feature points by accurately detecting positions of candidate feature points in unusual facial images as well as positions of candidate feature points in ordinary facial images, while using an Adaboost learning algorithm to detect positions of face feature points.
Part Technical Solution: The representative configurations of the present disclosure for achieving the above objects are as follows.
According to an aspect of the present disclosure, there is provided a method of detecting a position of a face feature point by using an Adaboost learning algorithm. The method includes (a) classifying a sub-window image into a first feature point candidate recommendation image and a first feature point candidate non-recommendation image using first feature patterns selected through the Adaboost learning algorithm, and generating first feature point candidate position information of the first feature point candidate recommendation image; and (b) re-classifying the sub-window image classified as the first feature point candidate non-recommendation image into a second feature point candidate recommendation image and a second feature point candidate non-recommendation image using second feature patterns selected through the Adaboost learning algorithm, and generating second feature point candidate position information of the second feature point candidate recommendation image.
According to another aspect of the present disclosure, there is provided an apparatus for detecting a position of a face feature point using an Adaboost learning algorithm. The apparatus includes a classifier for classifying a sub-window image into a first feature point candidate recommendation image and a first feature point candidate non-recommendation image using first feature patterns selected through the Adaboost learning algorithm, and generating first feature point candidate position information of the first feature point candidate recommendation image; and at least one re-classifier for re-classifying the sub-window image classified as the first feature point candidate non-recommendation image into a second feature point candidate recommendation image and a second feature point candidate non-recommendation image using second feature patterns selected through the Adaboost learning algorithm, and generating second feature point candidate position information of the second feature point candidate recommendation image.
The aspects of the present disclosure are characterized in that the first feature patterns are based on features of an ordinary facial image, the second feature patterns are based on features of an unusual facial image, and each of the first feature patterns and the second feature patterns designates one or more dark regions and one or more bright regions.
According to still another aspect of the present disclosure, there is further provided a feature point candidate position generation unit for generating and storing the first feature point candidate position information and the second feature point candidate position information for sub-window images of a facial image; and a feature point candidate position clustering unit for forming clusters by performing clustering for the first feature point candidate position information and the pieces of the second feature point candidate position information, and generating position information of a center point position for the first feature point candidate position information and the second feature point candidate position information forming the largest cluster among the clusters as feature point position information.
In addition, there is further provided a computer-readable recording medium for recording a computer program for executing the above-described methods for implementing the present disclosure.
Part Advantageous Effects: According to the present disclosure, there is obtained an effect of improving performance in detecting positions of feature points by detecting positions of candidate feature points of an unusual facial image as well as positions of candidate feature points of an ordinary facial image.
Part EMBODIMENTS: In the following detailed description of the present disclosure, references are made to the accompanying drawings that show, by way of illustration, specific embodiments in which the present disclosure may be implemented. These embodiments are described in sufficient detail to enable those skilled in the art to implement the present disclosure. It should be understood that various embodiments of the present disclosure, although different, are not necessarily mutually exclusive. For example, specific features, structures, and characteristics described herein, in connection with one embodiment, may be implemented within other embodiments without departing from the spirit and scope of the present disclosure. In addition, it should be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the spirit and scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined only by the appended claims, appropriately interpreted, along with the full range equivalent to what the claims claim. In the drawings, like reference numbers may refer to the same or similar function in many respects.
Hereinafter, various embodiments of the present disclosure will be described in detail with reference to the accompanying drawings in order that those skilled in the art may easily implement the present disclosure.
FIG. 1 is a block diagram 100 showing a configuration of an apparatus for detecting a position of a face feature point in accordance with an embodiment of the present disclosure.
Referring to FIG. 1, the block diagram 100 represents an apparatus for detecting a position of a face feature point may include a normalization unit 110, an image conversion unit 120, a feature point candidate position detection unit 130, a feature point candidate position clustering unit 140, and a feature point position adjustment unit 150.
Functions of each block shown in FIG. 1 are as follows.
The normalization unit 110 may normalize a facial image into a grey image of a predetermined size. The input facial image may be a color image and may be of a variety of sizes. The normalization unit 110 may normalize an input facial image into a grey image of a predetermined size in order to detect positions of feature points in facial images of various sizes.
The image conversion unit 120 may convert a grey image into a multi-scale image by performing modified census transform (MCT). That is, the image conversion unit 120 may convert the grey image into an image having a scale larger than the scale of the grey image. For example, if each pixel of the grey image has 256 scales from 0 to 255, the image conversion unit 120 may convert each pixel of the grey image to have 512 scales from 0 to 511.
The feature point candidate position detection unit 130, when a sub-window image of a multi-scale image is input, classifies the sub-window image as one of a first feature point candidate recommendation image and a first feature point candidate non-recommendation image by using first feature patterns, the first feature patterns having been selected by learning the patterns of an ordinary facial image using an Adaboost learning algorithm. When the sub-window image classified as the first feature point candidate non-recommendation image is input, the feature point candidate position detection unit 130 may classify the sub-window image classified as the first feature point candidate non-recommendation image into a second feature point candidate recommendation image and a second feature point candidate non-recommendation image by using second feature patterns, the second feature patterns having been selected by learning the patterns of an unusual facial image using the Adaboost learning algorithm. The feature point candidate position detection unit 130 may output first feature point position information of the first feature point candidate recommendation image and second feature point position information of the second feature point candidate recommendation image.
Here, with regard to the classifying of the sub-window image as one of the first feature point candidate recommendation images or the first feature point candidate non-recommendation image by using the first feature patterns (which were selected by learning the patterns of an ordinary facial image using the Adaboost learning algorithm), the first feature pattern may refer to a pattern included in at least one strong classifier in a first layer (which is described later). In this instance, if a plurality of strong classifiers is included in the first layer, it is apparently understood that the patterns included in the respective strong classifiers of the first layer may be different from one another. In addition, when a sub-window image classified as the first feature point candidate non-recommendation image is input into the feature point candidate position detection unit 130, in classifying the sub-window image classified as the first feature point candidate non-recommendation image into the second feature point candidate recommendation image and the second feature point candidate non-recommendation image by using the second feature patterns, the second feature patterns having been selected by learning the patterns of an unusual facial image using the Adaboost learning algorithm, the second feature patterns may refer to a pattern included in at least one strong classifier in a second or subsequent layer (i.e., the second to k-th layers), which is described later. In this instance, it is apparently understood that the patterns included in the respective strong classifiers may be different from one another between the layers or even within the same layer.
In addition, the various embodiments of the present disclosure is characterized in that the first feature patterns are based on the features of an ordinary facial image, the second feature patterns are based on the features of an unusual facial image, and each of the first feature patterns and the second feature patterns designates one or more dark regions and one or more bright regions. Here, whether or not a facial image is an ordinary facial image may be determined by comparing the facial image with a normal facial image and determining whether or not a difference therebetween exceeds a preset threshold value. Whether a region included in the first and second feature patterns is a dark region or a bright region may be determined based on at least one preset brightness value. More specifically, if a facial image is determined as an unusual facial image, the abnormality may be graded, and to this end, a plurality of preset threshold values may be prepared.
FIG. 2 is a diagram for illustrating a sub-window image to be input into the feature point candidate position detection unit 130 in accordance with an embodiment of the present disclosure. In FIG. 2, reference symbol A may denote an image having a size of 384×288 converted by the image conversion unit 120, and reference symbols a, b, c and d may denote sub-window images each having a size of 24×24 that are sequentially input into the feature point candidate position detection unit 130. That is, the images from the first sub-window image a to the last sub-window image d obtained while moving from the first pixel to the last pixel of the image A by a predetermined pixel unit may be sequentially input into the feature point candidate position detection unit 130.
The feature point candidate position clustering unit 140 may create clusters by performing clustering with reference to feature point position information of the first feature point candidate recommendation images and the second feature point candidate recommendation images obtained from image A and detected by the feature point candidate position detection unit 130 Then, the feature point candidate position clustering unit 140 may output position information of the center point of the largest cluster as final feature point position information.
FIG. 3 is a diagram for illustrating functions of the feature point candidate position clustering unit 140. The black points show feature points according to the first feature point position information and the second feature point position information obtained by the feature point candidate position detection unit 130, and when these feature points form five clusters of e1 to e5, position information of the center point of the largest cluster e1 may be the final feature point position information. As a matter of fact, the present disclosure is not limited thereto, and a variety of modified examples may be assumed. For example, it is not limited to the center point, and a certain representative position that can represent a corresponding cluster may be implemented as information thereon.
The feature point position adjustment unit 150 may receive the final feature point position information and then adjust the information into position information corresponding to the size of the facial image input into the normalization unit 110 to output the feature point position information. That is, since the size of the facial image is changed by the normalization unit 110, the feature point position adjustment unit 150 may perform a function of adjusting the final feature point position information obtained by the feature point candidate position clustering unit 140 into the position information corresponding to the size of the facial image input into the normalization unit 110.
In FIG. 1, when the facial image input into the apparatus 100 for detecting a position of a face feature point is a multi-scale image of a predetermined size for the feature point position detector 130, the normalization unit 110, the image conversion unit 120, and the feature point position adjustment unit 150 may not be required.
FIG. 4 illustrates the feature point candidate position detection unit 130 according to an embodiment of the present disclosure.
Referring to FIG. 4, the feature point candidate position detection unit 130 according to an embodiment of the present disclosure may include a classifier 210-1, re-classifiers 210-2 to 210-k, and a feature point candidate position generator 220. Here, the classifier 210-1 may be a classifier corresponding to a so-called first layer, and the re-classifiers 210-2 to 210-k may be classifiers respectively corresponding to a so-called second to k-th layers. For reference, the first layer may include at least one strong classifier including patterns acquired by learning from an ordinary facial image, and the second to k-th layers may include at least one strong classifier including patterns acquired by learning from an unusual facial image, with the degree of abnormality increasing as k increases. The classifier 210-1, which is a classifier of the first layer, may include strong classifiers 230-11 to 230-1n; the re-classifier 210-2, which is a classifier of the second layer, may include strong classifiers 230-21 to 230-2m; and the re-classifier 210-k, which is a classifier of the k-th layer, may include strong classifiers 230-k1 to 230-kl. The classifier 210-1 and the re-classifiers 210-2 to 210-k may include one or more strong classifiers respectively having configurations different from one another.
Functions of each block shown in FIG. 4 are as follows.
The classifier 210-1 may classify an input sub-window image as one of the first feature point candidate recommendation image and the first feature point candidate non-recommendation image by using first feature patterns, the first feature patterns having been selected among the patterns of an ordinary facial image by learning using the Adaboost learning algorithm, and may generate position information for the first feature point candidate recommendation image.
Each of the re-classifiers 210-2 to 210-k may reclassify the sub-window image classified as a feature point candidate non-recommendation image by the classifier 210-1, which is a classifier of the first layer, and the re-classifiers 210-2 to 210-k, which are classifiers of the second layer, as one of the second feature point candidate recommendation image and the second feature point candidate non-recommendation image by using the second feature patterns, the second feature patterns having been selected among the patterns of an unusual facial image by learning using the Adaboost learning algorithm, and may generate feature point position information for the second feature point candidate recommendation image.
According to the above, the classifier 210-1 may generate first feature point candidate positions of the first feature point candidate recommendation image for an ordinary facial image, and each of the re-classifiers 210-2 to 210-k may generate second feature point candidate positions of the second feature point candidate recommendation image for an unusual facial image.
The strong classifiers 230-11 to 230-1n included in the first layer are configured to classify into the first feature point candidate recommendation image and the first feature point candidate non-recommendation image by using the first feature pattern, the first feature pattern having been selected by learning using the Adaboost learning algorithm, and output first feature point candidate position information. Here, in order to output the first feature point candidate position information, all the strong classifiers 230-11 to 230-1n included in the first layer should be determined as the first feature point candidate recommendation image.
In addition, the strong classifiers 230-21 to 230-2m included in the second layer are configured to classify into the second feature point candidate recommendation image and the second feature point candidate non-recommendation image by using the second feature pattern, the second feature pattern having been selected by learning using the Adaboost learning algorithm, and output second feature point candidate position information. Here, in order to output the second feature point candidate position information through the second layer, all the strong classifiers 230-21 to 230-2m included in the second layer should be determined as the second feature point candidate recommendation image.
In addition, the strong classifiers 230-k1 to 230-kl included in the k-th layer classify into the second feature point candidate recommendation image and the second feature point candidate non-recommendation image by using the second feature pattern (which may be different from the second feature pattern used by the strong classifiers 230-21 to 230-2m), the second feature pattern having been selected by learning using the Adaboost learning algorithm, and output second feature point candidate position information. Here, in order to output the second feature point candidate position information through the k-th layer, the input sub-window image should be determined as the second feature point candidate recommendation image by all the strong classifiers 230-k1 to 230-kl included in the k-th layer.
In each of the cascaded strong classifiers 230-11 to 230-1n, 230-21 to 230-2m, . . . , and 230-k1 to 230-kl, a strong classifier in a former stage may classify the sub-window images into the first and second feature point candidate recommendation images and the first and second feature point candidate non-recommendation images by using a smaller number of first and second feature patterns, the first and second feature patterns having been selected by learning using the Adaboost learning algorithm, as compared with a strong classifier in a latter stage. For example, the strong classifier 230-11 may use two first feature patterns, the strong classifier 230-12 may use ten first feature patterns, and the strong classifier 230-1n may use thirty first feature patterns. The reason is to lightly filter the sub-window images using a small number of patterns at the strong classifiers in the front stage of each layer, in view of the fact that most of the sub-window images are determined as “negative” (i.e., successively determined as the feature point candidate non-recommendation image up to the k-th layer), since the number of points in a single image determined as positions of face feature points is small. Accordingly from the example, although one hundred sub-window images that are sequentially input are classified as the first and second feature point candidate recommendation images at the strong classifier in the former stage, only fifty sub-window images may be classified as the first and second feature point candidate recommendation images (i.e., accepted) at the strong classifier of the next stage, and the first and second feature point candidate recommendation images that pass (i.e., are accepted) the n-th strong classifier of the final stage may be reduced to ten. Accordingly, the feature point position information of the first and second feature point candidate recommendation images generated at the strong classifiers 230-1n, 230-2m and 230-kl of the final stages of the classifier 210-1 and the re-classifiers 210-2 to 210-k may be position information with a high probability of including a feature point.
The feature point candidate position generator 220 may store and output pieces of the first and second feature point candidate position information respectively output from the classifier 210-1 and the re-classifiers 210-2 to 210-n. The feature point candidate position generator 220 may store and then output the pieces of the first and second feature point candidate position information for all the sub-window images of the image A of FIG. 2.
FIG. 5 illustrates an example strong classifier of the feature point candidate position detector 130 shown in FIG. 4.
Referring to FIG. 5, the strong classifier 230 according to an embodiment may include weak classifiers 240-1 to 240-p and a determination unit 250.
Functions of each block shown in FIG. 5 are as follows.
If a sub-window image is input, each of the weak classifiers 240-1 to 240-p may generates a feature value indicating whether the sub-window image is a feature point candidate recommendation image or a feature point candidate non-recommendation image using feature patterns different from one another.
The determination unit 250 combines the results from the weak classifiers 240-1 to 240-p, outputs feature point candidate position information and the sub-window image to the strong classifier in the latter stage (if there is no strong classifier in the latter stage, a “positive” state is recorded in the feature point candidate position generator 220) when the sub-window image is the feature point candidate recommendation image, and outputs feature point candidate non-recommendation position information and the sub-window image to the re-classifiers 210-2 to 210-k in the latter stage when the sub-window image is the feature point candidate non-recommendation image.
FIG. 6 shows feature patterns selected by learning using an Adaboost learning algorithm according to an embodiment of the present disclosure. When three weak classifiers 240-1 to 240-3 form one strong classifier, feature patterns shown in FIGS. 6 (a), (b), and (c) may be used for weak classifiers different from one another. The feature pattern shown in FIG. 6 (a) denote a pattern including two squares disposed at corresponding positions in a sub-window 10, the feature pattern FIG. 6 (b) denote a pattern including three squares disposed at corresponding positions in the sub-window 10, and the feature pattern FIG. 6 (c) denote a pattern including four squares disposed at corresponding positions in the sub-window 10. In addition, a dark image may exist in a shaded square f of the feature patterns shown in FIGS. 6 (a), (b), and (c), and a bright image may exist in a square g. That is, the feature patterns may designate one or more regions f where a dark image exists and one or more regions g where a bright image exists within the sub-window 10. In addition, each of the feature patterns shown in FIGS. 6 (a), (b), and (c) is learned using an Adaboost learning algorithm, and a weighting factor may be set to be high if the probability of finding a feature point position is high and set to be low if the probability is low, and weighting factors of the weak classifiers 240-1 to 240-3 forming one strong classifier may be set to make a sum of 1. In addition, a threshold value for classifying the input sub-window image into the feature point candidate recommendation image and the feature point candidate non-recommendation image may be set in each of the weak classifiers and the strong classifiers by learning using an Adaboost learning algorithm.
A method in which the weak classifiers 240-1 to 240-p of FIG. 5 classifies a sub-window image into the feature point candidate recommendation image and the feature point candidate non-recommendation image by using FIG. 6, will be described as follows.
Each of the weak classifiers 240-1 to 240-p of FIG. 5 may generate a feature value indicating whether a sub-window image is the feature point candidate recommendation image or the feature point candidate non-recommendation image by comparing a set threshold value with a difference between a total sum of pixels in the sub-window image existing within the square g and a total sum of pixels in the sub-window image existing within the square f of one selected pattern of the sub-window 10. The feature value may have a value of 1 when the sub-window image is the feature point candidate recommendation image and may have a value of 0 when the sub-window image is the feature point candidate non-recommendation image.
A method in which the determination unit 250 of FIG. 5 classifies a sub-window image into the feature point candidate recommendation image and the feature point candidate non-recommendation image by combining feature values output from the weak classifiers 240-1 to 240-p by using FIG. 6 will be described as follows.
The determination unit 250 may calculate a total sum of values obtained by multiplying feature values output from the respective weak classifiers 240-1 to 240-p with weighting factors set in the respective weak classifiers 240-1 to 240-p and determine whether the sub-window image is the feature point candidate recommendation image or the feature point candidate non-recommendation image by comparing the total sum with a threshold value set in the strong classifier 230.
Then, the strong classifier 230 may calculate and output a confidence value for the feature point candidate position information of the feature point candidate recommendation image. In this case, the determination unit 250 may output a total sum of values obtained by multiplying feature values output from the respective weak classifiers 240-1 to 240-p by weighting factors of the respective weak classifiers 240-1 to 240-p as the confidence value.
In addition, using the confidence value, the feature point candidate position clustering unit 140 may determine final feature point candidate position information with reference to a total sum of values obtained by multiplying respective pieces of the feature point candidate position information of the largest cluster created through clustering by the confidence values of the respective pieces of the feature point candidate position information.
As an example of the Adaboost learning algorithm used in the present disclosure, a paper entitled “Robust Real-Time Face Detection” developed by Paul Viola and Michael J. Jones and published in International Journal of Computer Vision, Volume 57, Issue 2 dated May, 2004 may be referred to. All the descriptions used for detecting positions of feature points included in this paper (including a technique of selecting feature patterns from the patterns of a facial image by learning using the Adaboost learning algorithm and a technique of detecting positions of feature points by cascading strong classifiers and the like) are hereby incorporated by reference in the method of detecting a face feature point of the present disclosure.
Although not shown, the face recognition system according to an embodiment of the present disclosure may identify an input facial image by comparing feature point position information extracted from a registered facial image with feature point position information extracted from an input facial image and determining similarity therebetween.
The embodiments according to the present disclosure described above can be implemented in the form of program commands that can be executed through various computer components and recorded in a computer-readable recording medium. The computer-readable recording medium may include a program command, a data file, a data structure and the like solely or in a combined manner. The program command recorded in the computer-readable recording medium may be a program command specially designed and configured for the present disclosure or a program command known to be used by those skilled in the art of the computer software field. The computer-readable recording medium includes, for example, a magnetic medium, such as a hard disk, a floppy disk and a magnetic tape, an optical recording medium, such as a CD-ROM and a DVD, a magneto-optical medium, such as an optical disk, and a hardware device specially configured to store and execute program commands, such as a ROM, a RAM, a flash memory and the like. The program command includes, for example, a high-level language code that can be executed by a computer using an interpreter or the like, as well as a machine code generated by a compiler. The hardware devices can be configured to operate using one or more software modules in order to perform the processing according to the present disclosure, and vice versa. In the foregoing discussion, although the present disclosure has been described in connection with the specific matters, such as the specific components, the exemplary embodiments, and the drawings, they are provided only for assisting in the understanding of the present disclosure, and the present disclosure is not limited to the embodiments. It will be apparent that those skilled in the art can make various modifications and changes thereto from these descriptions.
Therefore, the spirit of the present disclosure should not be limited to the above-described embodiments, and the appended claims and what are modified equally or equivalently thereto will be considered to fall within the scopes of the present disclosure.
Part EXPLANATION OF REFERENCE NUMERALS: 

    
    
        100: Apparatus for Detecting Position of Face Feature Point
        110: Normalization Unit
        120: Image Conversion Unit
        130: Feature Point Candidate Position Detection Unit
        140: Feature Point Candidate Position Clustering Unit
        150: Feature Point Position Adjustment Unit
        210-1: Classifier
        210-2 to 210-k: Re-Classifier
        220: Feature Point Candidate Position Generator
        230-11 to 230-kl: Strong Classifier
        240-1 to 240-p: Weak Classifier
        250: Determination Unit
    
    




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