searchFacesByImage method

Future<SearchFacesByImageResponse> searchFacesByImage({ required String collectionId, required Image image, double? faceMatchThreshold, int? maxFaces, QualityFilter? qualityFilter, })

For a given input image, first detects the largest face in the image, and then searches the specified collection for matching faces. The operation compares the features of the input face with faces in the specified collection.

You can also call the DetectFaces operation and use the bounding boxes in the response to make face crops, which then you can pass in to the SearchFacesByImage operation. You pass the input image either as base64-encoded image bytes or as a reference to an image in an Amazon S3 bucket. If you use the AWS CLI to call Amazon Rekognition operations, passing image bytes is not supported. The image must be either a PNG or JPEG formatted file.

The response returns an array of faces that match, ordered by similarity score with the highest similarity first. More specifically, it is an array of metadata for each face match found. Along with the metadata, the response also includes a similarity indicating how similar the face is to the input face. In the response, the operation also returns the bounding box (and a confidence level that the bounding box contains a face) of the face that Amazon Rekognition used for the input image.

For an example, Searching for a Face Using an Image in the Amazon Rekognition Developer Guide.

The QualityFilter input parameter allows you to filter out detected faces that don’t meet a required quality bar. The quality bar is based on a variety of common use cases. Use QualityFilter to set the quality bar for filtering by specifying LOW, MEDIUM, or HIGH. If you do not want to filter detected faces, specify NONE. The default value is NONE. This operation requires permissions to perform the rekognition:SearchFacesByImage action.

May throw InvalidS3ObjectException. May throw InvalidParameterException. May throw ImageTooLargeException. May throw AccessDeniedException. May throw InternalServerError. May throw ThrottlingException. May throw ProvisionedThroughputExceededException. May throw ResourceNotFoundException. May throw InvalidImageFormatException.

Parameter collectionId : ID of the collection to search.

Parameter image : The input image as base64-encoded bytes or an S3 object. If you use the AWS CLI to call Amazon Rekognition operations, passing base64-encoded image bytes is not supported.

If you are using an AWS SDK to call Amazon Rekognition, you might not need to base64-encode image bytes passed using the Bytes field. For more information, see Images in the Amazon Rekognition developer guide.

Parameter faceMatchThreshold : (Optional) Specifies the minimum confidence in the face match to return. For example, don't return any matches where confidence in matches is less than 70%. The default value is 80%.

Parameter maxFaces : Maximum number of faces to return. The operation returns the maximum number of faces with the highest confidence in the match.

Parameter qualityFilter : A filter that specifies a quality bar for how much filtering is done to identify faces. Filtered faces aren't searched for in the collection. If you specify AUTO, Amazon Rekognition chooses the quality bar. If you specify LOW, MEDIUM, or HIGH, filtering removes all faces that don’t meet the chosen quality bar. The quality bar is based on a variety of common use cases. Low-quality detections can occur for a number of reasons. Some examples are an object that's misidentified as a face, a face that's too blurry, or a face with a pose that's too extreme to use. If you specify NONE, no filtering is performed. The default value is NONE.

To use quality filtering, the collection you are using must be associated with version 3 of the face model or higher.

Implementation

Future<SearchFacesByImageResponse> searchFacesByImage({
  required String collectionId,
  required Image image,
  double? faceMatchThreshold,
  int? maxFaces,
  QualityFilter? qualityFilter,
}) async {
  ArgumentError.checkNotNull(collectionId, 'collectionId');
  _s.validateStringLength(
    'collectionId',
    collectionId,
    1,
    255,
    isRequired: true,
  );
  ArgumentError.checkNotNull(image, 'image');
  _s.validateNumRange(
    'faceMatchThreshold',
    faceMatchThreshold,
    0,
    100,
  );
  _s.validateNumRange(
    'maxFaces',
    maxFaces,
    1,
    4096,
  );
  final headers = <String, String>{
    'Content-Type': 'application/x-amz-json-1.1',
    'X-Amz-Target': 'RekognitionService.SearchFacesByImage'
  };
  final jsonResponse = await _protocol.send(
    method: 'POST',
    requestUri: '/',
    exceptionFnMap: _exceptionFns,
    // TODO queryParams
    headers: headers,
    payload: {
      'CollectionId': collectionId,
      'Image': image,
      if (faceMatchThreshold != null)
        'FaceMatchThreshold': faceMatchThreshold,
      if (maxFaces != null) 'MaxFaces': maxFaces,
      if (qualityFilter != null) 'QualityFilter': qualityFilter.toValue(),
    },
  );

  return SearchFacesByImageResponse.fromJson(jsonResponse.body);
}