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Help Center/ Face Recognition Service/ API Reference/ APIs/ Face Retrieval

Face Retrieval

Updated on 2023-04-25 GMT+08:00

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Function

This API is used to search an existing facial image library for one or more faces similar to the input face, and return corresponding confidence levels.

You can input an image or face ID to retrieve faces. If multiple facial images are input, the largest face detected in the images is used for retrieval.

Prerequisites:

Ensure that you have enabled FRS. For detailed operations, see Applying for FRS.

Restrictions:

Only images in JPG, PNG, JPEG, or BMP format can be recognized.
Use standard JSON format in the body of the application/json request.
Do not use carriage return characters in Base64 code.
The system does not save images of users.
The image size must be less than 8 MB. If the image is too large, the latency is long and the image information volume is small. It is recommended that the image size be less than 1 MB.
The image resolution must be less than 4,096 x 2,160. The face resolution in an image must be greater than 80 x 80. It is recommended that the face resolution be greater than 120 x 120.
To ensure the recognition effect, facial images need to meet the following requirements:
1. The illumination should be greater than 200 lux and there is no light reflection or shadow caused by strong light.
2. The overall image is clear without obvious motion blur and the face in it is not blocked.
3. The side face angle does not exceed 30°, and the tilt angle and horizontal angle do not exceed 15°. The face in an image must be a vertically placed front face.
For details about other restrictions, see Restrictions and Limitations.

Suggestions:

A larger image does not significantly improve the recognition algorithm precision but will cause a long latency. Therefore, you are advised to upload an image smaller than 1 MB. Generally, 500 KB is enough.
It is recommended that the size of an image stored on OBS be less than 1 MB.
It is recommended that the face resolution in an image be greater than 120 x 120.

URI

POST /v2/{project_id}/face-sets/{face_set_name}/search

**Table 1** Path parameters
Parameter	Type	Mandatory	Description
project_id	String	Yes	Project ID. For details about how to obtain the ID, see Obtaining the Project ID/Account Name/AK/SK.
face_set_name	String	Yes	Name of a facial image library.

Request Parameters

**Table 2** Request header parameters
Parameter	Mandatory	Type	Description
X-Auth-Token	Yes	String	User token. During API authentication using a token, the token is added to requests to obtain permissions for calling the API. The value of X-Subject-Token in the response header is the obtained token.
Content-Type	Yes	String	MIME type of the request body. The value is application/json.

**Table 3** Request body parameters
Parameter	Type	Mandatory	Description
image_url	String	Either image_url, image_file, image_base64, or face_id is mandatory.	Image URL. Currently, only the URL of an OBS bucket on Huawei Cloud is supported and FRS must have the permission to read data in the OBS bucket. For details about how to enable the read permission, see Service Authorization.
image_file	File	Either image_file, image_url, image_base64, or face_id is mandatory.	Local image file, whose size cannot exceed 8 MB. It is recommended that the image size be less than 1 MB. The request format is Multipart.
image_base64	String	Either image_base64, image_url, image_file, or face_id is mandatory.	Image data (Base64-encoded). The value must meet the following requirements: The image size after Base64 encoding cannot exceed 8 MB. It is recommended that the image size be less than 1 MB. The image is in JPG, JPEG, BMP, or PNG format.
face_id	String	Either face_id, image_url, image_file, or image_base64 is mandatory.	Face ID returned by the system after a face is imported
top_n	Integer	No	N faces returned that are most similar to the input one. The default value of N is 10. The returned faces are sorted by confidence in descending order.
threshold	Double	No	Face similarity threshold. If the similarity degree of a face is lower than the threshold, the face is not returned. The value ranges from 0 to 1. The recommended value is 0.93. The default value is 0.
sort	JSONArray	No	Field sorting. For details, see Sort Syntax.
filter	String	No	Filtering criteria. For details, see Filter Syntax.
return_fields	JsonArray	No	Returned customized field.

Response Parameters

Status code: 200

**Table 4** Response body parameter
Parameter	Type	Description
faces	Array of SearchFace objects	Face set to be retrieved. For details, see SearchFace.

**Table 5** SearchFace
Parameter	Type	Description
bounding_box	BoundingBox object	Position of a face in an image
similarity	Double	Similarity degree in Face Retrieval
external_fields	Object	Additional field a user customizes
external_image_id	String	ID of the external image to which a face belongs
face_id	String	Face ID, which is a unique ID generated by the system

**Table 6** BoundingBox
Parameter	Type	Description
width	Integer	Width of a rectangle
top_left_y	Integer	Vertical coordinate of the upper-left corner of a rectangle
top_left_x	Integer	Horizontal coordinate of the upper-left corner of a rectangle
height	Integer	Height of a rectangle

Status code: 400

**Table 7** Response body parameters
Parameter	Type	Description
error_code	String	Error code when calling the API failed. This parameter is not included when the API is successfully called.
error_msg	String	Error message returned after the API fails to be called. This parameter is not included when the API is successfully called.

Example Requests

For details about how to obtain the value of X-Auth-Token, see Authentication.

Example request (Method 1: Use a Base64-encoded image.)

POST https://{endpoint}/v2/{project_id}/face-sets/showFaceSet/search
Request Header:
Content-Type: application/json
X-Auth-Token: MIINRwYJKoZIhvcNAQcCoIINODCCDTQCAQExDT...

Request Body:
{
  "image_base64": "/9j/4AAQSkZJRgABAgEASABIAAD",
  "sort" : [
    {
      "timestamp" : "asc"
    } 
  ],
  "return_fields" : ["timestamp", "id"],
  "filter" : "timestamp:12"
}

Example request (Method 2: Use an image file.)

POST https://{endpoint}/v2/{project_id}/face-sets/showFaceSet/search
Request Header:
X-Auth-Token: MIINRwYJKoZIhvcNAQcCoIINODCCDTQCAQExDT...

Request Body:
image_file: File (image file)
return_fields: ["timestamp","id"]
filter: timestamp:12

Example request (Method 3: Use the image URL.)

POST https://{endpoint}/v2/{project_id}/face-sets/showFaceSet/search
Request Header:
Content-Type: application/json
X-Auth-Token: MIINRwYJKoZIhvcNAQcCoIINODCCDTQCAQExDT...

Request Body:
{
  "image_url":"/BucketName/ObjectName",
  "sort" : [
    {
      "timestamp" : "asc"
    } 
  ],
  "return_fields" : ["timestamp", "id"],
  "filter" : "timestamp:12"
}

Example request (Method 4: Use the face ID.)

POST https://{endpoint}/v2/{project_id}/face-sets/showFaceSet/search
Request Header: 
Content-Type: application/json 
X-Auth-Token: MIINRwYJKoZIhvcNAQcCoIINODCCDTQCAQExDT... 

Request Body: 
{ 
  "face_id":"6KLB1Ktu", 
  "sort" : [ 
    { 
      "timestamp" : "asc" 
    }  
  ], 
  "return_fields" : ["timestamp", "id"], 
  "filter" : "timestamp:12" 
}

Example Responses

Status code: 200

Response example (successful request)

{
  "faces": [
    {
      "bounding_box": {
        "width": 170,
        "top_left_y": 37,
        "top_left_x": 20,
        "height": 170
      },
      "similarity": 0.996146,
      "external_image_id": "123",
      "external_fields": {
        "id": "home",
        "timestamp": 12
      },
      "face_id": "6KLB1Ktu"
    },
    {
      "bounding_box": {
        "width": 170,
        "top_left_y": 37,
        "top_left_x": 20,
        "height": 170
      },
      "similarity": 0.996146,
      "external_image_id": "12",
      "external_fields": {
        "id": "home1",
        "timestamp": 12
      },
      "face_id": "PexOpqRj"
    }
  ]
}

Status code: 400

Example response (failed request)

{
  "error_code": "FRS.0018",
  "error_msg": "The service inner error."
}

Status Code

For details about the status code, see Status Codes.

Error Code

For details about the error code, see Error Codes.

Parent topic: APIs

Previous topic: Face LiveDetect

Next topic: Facial Image Library Management

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