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# 显示边界框
Amazon Rekognition Image 操作可以返回在图像中检测到的项目的边界框坐标。例如，[DetectFaces](https://docs.aws.amazon.com/rekognition/latest/APIReference/API_DetectFaces.html) 操作将返回在图像中检测到的每个人脸的边界框 ([BoundingBox](https://docs.aws.amazon.com/rekognition/latest/APIReference/API_BoundingBox.html))。您可以使用边界框坐标围绕检测到的项目显示一个框。例如，下图围绕一张人脸显示一个边界框。
![\[一位戴着眼镜且面带微笑的年轻女子，她周围散布着气泡。\]](http://docs.aws.amazon.com/zh_cn/rekognition/latest/dg/images/face.png)
`BoundingBox` 具有以下属性：
+ 高度 – 边界框的高度（以占整个图像高度的比例显示）。
+ 左侧 – 边界框的左坐标（以占整个图像宽度的比例显示）。
+ 顶部 – 边界框的顶部坐标（以占整个图像高度的比例显示）。
+ 宽度 – 边界框的宽度（以占整个图像宽度的比例显示）。
每个 BoundingBox 属性的值介于 0 和 1 之间。每个属性值都是占整个图像宽度（`Left` 和 `Width`）或高度（`Height` 和 `Top`）的比例。例如，如果输入图像为 700 x 200 像素，而边界框的左上坐标为 350 x 50 像素，则 API 将返回 `Left` 值 0.5 (350/700) 和 `Top` 值 0.25 (50/200)。
下图显示了每个边界框属性覆盖的图像的范围。
![\[该图形描述边界框与图像尺寸之间的关系。\]](http://docs.aws.amazon.com/zh_cn/rekognition/latest/dg/images/bounding-box.png)
要以正确的位置和大小显示边界框，必须将这些 BoundingBox 值乘以图像的宽度或高度（取决于你想要的值）才能得到像素值。使用像素值显示边界框。例如，上一图像的像素大小为 608（宽）x 588（高）。人脸的边界框值为：
```
BoundingBox.Left: 0.3922065
BoundingBox.Top: 0.15567766
BoundingBox.Width: 0.284666
BoundingBox.Height: 0.2930403
```
人脸边界框的位置（以像素为单位）的计算方法如下：
`Left coordinate = BoundingBox.Left (0.3922065) * image width (608) = 238`
`Top coordinate = BoundingBox.Top (0.15567766) * image height (588) = 91`
`Face width = BoundingBox.Width (0.284666) * image width (608) = 173`
`Face height = BoundingBox.Height (0.2930403) * image height (588) = 172`
您可使用这些值围绕人脸显示一个边界框。
**注意**
图像可以通过多种方式定向。您的应用程序可能需要旋转图像才能以正确的方向显示它。边界框坐标受图像方向的影响。您可能需要先转换坐标，然后才能在正确位置显示边界框。有关更多信息，请参阅 [获取图像方向和边界框坐标](images-orientation.md)。
以下示例演示如何围绕通过调用 [DetectFaces](https://docs.aws.amazon.com/rekognition/latest/APIReference/API_DetectFaces.html) 检测到的人脸显示边界框。这些示例假定图像的方向为 0 度。这些示例还演示如何从 Amazon S3 存储桶下载图像。
**显示边界框**
1. 如果您尚未执行以下操作，请：
1. 使用 `AmazonRekognitionFullAccess` 和 `AmazonS3ReadOnlyAccess` 权限创建或更新用户。有关更多信息，请参阅 [步骤 1：设置 AWS 账户并创建用户](setting-up.md#setting-up-iam)。
1. 安装并配置 AWS CLI 和 AWS SDKs。有关更多信息，请参阅 [第 2 步：设置 AWS CLI 和 AWS SDKs](setup-awscli-sdk.md)。
1. 使用以下示例调用 `DetectFaces` 操作。
------
#### [ Java ]
将`bucket`的值更改为包含图像文件的 Amazon S3 存储桶。将 `photo` 的值更改为图像文件（.jpg 或 .png 格式）的文件名。
```
//Loads images, detects faces and draws bounding boxes.Determines exif orientation, if necessary.
package com.amazonaws.samples;
//Import the basic graphics classes.
import java.awt.*;
import java.awt.image.BufferedImage;
import java.util.List;
import javax.imageio.ImageIO;
import javax.swing.*;
import com.amazonaws.services.rekognition.AmazonRekognition;
import com.amazonaws.services.rekognition.AmazonRekognitionClientBuilder;
import com.amazonaws.services.rekognition.model.BoundingBox;
import com.amazonaws.services.rekognition.model.DetectFacesRequest;
import com.amazonaws.services.rekognition.model.DetectFacesResult;
import com.amazonaws.services.rekognition.model.FaceDetail;
import com.amazonaws.services.rekognition.model.Image;
import com.amazonaws.services.rekognition.model.S3Object;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3ClientBuilder;
import com.amazonaws.services.s3.model.S3ObjectInputStream;
// Calls DetectFaces and displays a bounding box around each detected image.
public class DisplayFaces extends JPanel {
private static final long serialVersionUID = 1L;
BufferedImage image;
static int scale;
DetectFacesResult result;
public DisplayFaces(DetectFacesResult facesResult, BufferedImage bufImage) throws Exception {
super();
scale = 1; // increase to shrink image size.
result = facesResult;
image = bufImage;
}
// Draws the bounding box around the detected faces.
public void paintComponent(Graphics g) {
float left = 0;
float top = 0;
int height = image.getHeight(this);
int width = image.getWidth(this);
Graphics2D g2d = (Graphics2D) g; // Create a Java2D version of g.
// Draw the image.
g2d.drawImage(image, 0, 0, width / scale, height / scale, this);
g2d.setColor(new Color(0, 212, 0));
// Iterate through faces and display bounding boxes.
List faceDetails = result.getFaceDetails();
for (FaceDetail face : faceDetails) {
BoundingBox box = face.getBoundingBox();
left = width * box.getLeft();
top = height * box.getTop();
g2d.drawRect(Math.round(left / scale), Math.round(top / scale),
Math.round((width * box.getWidth()) / scale), Math.round((height * box.getHeight())) / scale);
}
}
public static void main(String arg[]) throws Exception {
String photo = "photo.png";
String bucket = "bucket";
int height = 0;
int width = 0;
// Get the image from an S3 Bucket
AmazonS3 s3client = AmazonS3ClientBuilder.defaultClient();
com.amazonaws.services.s3.model.S3Object s3object = s3client.getObject(bucket, photo);
S3ObjectInputStream inputStream = s3object.getObjectContent();
BufferedImage image = ImageIO.read(inputStream);
DetectFacesRequest request = new DetectFacesRequest()
.withImage(new Image().withS3Object(new S3Object().withName(photo).withBucket(bucket)));
width = image.getWidth();
height = image.getHeight();
// Call DetectFaces
AmazonRekognition amazonRekognition = AmazonRekognitionClientBuilder.defaultClient();
DetectFacesResult result = amazonRekognition.detectFaces(request);
//Show the bounding box info for each face.
List faceDetails = result.getFaceDetails();
for (FaceDetail face : faceDetails) {
BoundingBox box = face.getBoundingBox();
float left = width * box.getLeft();
float top = height * box.getTop();
System.out.println("Face:");
System.out.println("Left: " + String.valueOf((int) left));
System.out.println("Top: " + String.valueOf((int) top));
System.out.println("Face Width: " + String.valueOf((int) (width * box.getWidth())));
System.out.println("Face Height: " + String.valueOf((int) (height * box.getHeight())));
System.out.println();
}
// Create frame and panel.
JFrame frame = new JFrame("RotateImage");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
DisplayFaces panel = new DisplayFaces(result, image);
panel.setPreferredSize(new Dimension(image.getWidth() / scale, image.getHeight() / scale));
frame.setContentPane(panel);
frame.pack();
frame.setVisible(true);
}
}
```
------
#### [ Python ]
将`bucket`的值更改为包含图像文件的 Amazon S3 存储桶。将 `photo` 的值更改为图像文件（.jpg 或 .png 格式）的文件名。将创建 Rekognition 会话的行中的`profile_name`值替换为您的开发人员资料的名称。
```
import boto3
import io
from PIL import Image, ImageDraw
def show_faces(photo, bucket):
session = boto3.Session(profile_name='profile-name')
client = session.client('rekognition')
# Load image from S3 bucket
s3_connection = boto3.resource('s3')
s3_object = s3_connection.Object(bucket, photo)
s3_response = s3_object.get()
stream = io.BytesIO(s3_response['Body'].read())
image = Image.open(stream)
# Call DetectFaces
response = client.detect_faces(Image={'S3Object': {'Bucket': bucket, 'Name': photo}},
Attributes=['ALL'])
imgWidth, imgHeight = image.size
draw = ImageDraw.Draw(image)
# calculate and display bounding boxes for each detected face
print('Detected faces for ' + photo)
for faceDetail in response['FaceDetails']:
print('The detected face is between ' + str(faceDetail['AgeRange']['Low'])
+ ' and ' + str(faceDetail['AgeRange']['High']) + ' years old')
box = faceDetail['BoundingBox']
left = imgWidth * box['Left']
top = imgHeight * box['Top']
width = imgWidth * box['Width']
height = imgHeight * box['Height']
print('Left: ' + '{0:.0f}'.format(left))
print('Top: ' + '{0:.0f}'.format(top))
print('Face Width: ' + "{0:.0f}".format(width))
print('Face Height: ' + "{0:.0f}".format(height))
points = (
(left, top),
(left + width, top),
(left + width, top + height),
(left, top + height),
(left, top)
)
draw.line(points, fill='#00d400', width=2)
# Alternatively can draw rectangle. However you can't set line width.
# draw.rectangle([left,top, left + width, top + height], outline='#00d400')
image.show()
return len(response['FaceDetails'])
def main():
bucket = "bucket-name"
photo = "photo-name"
faces_count = show_faces(photo, bucket)
print("faces detected: " + str(faces_count))
if __name__ == "__main__":
main()
```
------
#### [ Java V2 ]
此代码取自 AWS 文档 SDK 示例 GitHub 存储库。请在[此处](https://github.com/awsdocs/aws-doc-sdk-examples/blob/master/javav2/example_code/rekognition/src/main/java/com/example/rekognition/DisplayFacesFrame.java)查看完整示例。
请注意，`s3` 指的是 AWS 软件开发工具包 Amazon S3 客户端，`rekClient` 指的是 AWS 软件开发工具包 Amazon Rekognition 客户端。
```
//snippet-start:[rekognition.java2.detect_labels.import]
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
import javax.imageio.ImageIO;
import javax.swing.*;
import software.amazon.awssdk.auth.credentials.ProfileCredentialsProvider;
import software.amazon.awssdk.core.ResponseBytes;
import software.amazon.awssdk.core.SdkBytes;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.rekognition.model.Attribute;
import software.amazon.awssdk.services.rekognition.model.BoundingBox;
import software.amazon.awssdk.services.rekognition.model.DetectFacesRequest;
import software.amazon.awssdk.services.rekognition.model.DetectFacesResponse;
import software.amazon.awssdk.services.rekognition.model.FaceDetail;
import software.amazon.awssdk.services.rekognition.model.Image;
import software.amazon.awssdk.services.rekognition.model.RekognitionException;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.rekognition.RekognitionClient;
import software.amazon.awssdk.services.s3.model.GetObjectRequest;
import software.amazon.awssdk.services.s3.model.GetObjectResponse;
import software.amazon.awssdk.services.s3.model.S3Exception;
//snippet-end:[rekognition.java2.detect_labels.import]
/**
* Before running this Java V2 code example, set up your development environment, including your credentials.
*
* For more information, see the following documentation topic:
*
* https://docs.aws.amazon.com/sdk-for-java/latest/developer-guide/get-started.html
*/
public class DisplayFaces extends JPanel {
static DetectFacesResponse result;
static BufferedImage image;
static int scale;
public static void main(String[] args) throws Exception {
final String usage = "\n" +
"Usage: " +
" \n\n" +
"Where:\n" +
" sourceImage - The name of the image in an Amazon S3 bucket (for example, people.png). \n\n" +
" bucketName - The name of the Amazon S3 bucket (for example, amzn-s3-demo-bucket). \n\n";
if (args.length != 2) {
System.out.println(usage);
System.exit(1);
}
String sourceImage = args[0];
String bucketName = args[1];
Region region = Region.US_EAST_1;
S3Client s3 = S3Client.builder()
.region(region)
.credentialsProvider(ProfileCredentialsProvider.create("profile-name"))
.build();
RekognitionClient rekClient = RekognitionClient.builder()
.region(region)
.credentialsProvider(ProfileCredentialsProvider.create("profile-name"))
.build();
displayAllFaces(s3, rekClient, sourceImage, bucketName);
s3.close();
rekClient.close();
}
// snippet-start:[rekognition.java2.display_faces.main]
public static void displayAllFaces(S3Client s3,
RekognitionClient rekClient,
String sourceImage,
String bucketName) {
int height;
int width;
byte[] data = getObjectBytes (s3, bucketName, sourceImage);
InputStream is = new ByteArrayInputStream(data);
try {
SdkBytes sourceBytes = SdkBytes.fromInputStream(is);
image = ImageIO.read(sourceBytes.asInputStream());
width = image.getWidth();
height = image.getHeight();
// Create an Image object for the source image
software.amazon.awssdk.services.rekognition.model.Image souImage = Image.builder()
.bytes(sourceBytes)
.build();
DetectFacesRequest facesRequest = DetectFacesRequest.builder()
.attributes(Attribute.ALL)
.image(souImage)
.build();
result = rekClient.detectFaces(facesRequest);
// Show the bounding box info for each face.
List faceDetails = result.faceDetails();
for (FaceDetail face : faceDetails) {
BoundingBox box = face.boundingBox();
float left = width * box.left();
float top = height * box.top();
System.out.println("Face:");
System.out.println("Left: " + (int) left);
System.out.println("Top: " + (int) top);
System.out.println("Face Width: " + (int) (width * box.width()));
System.out.println("Face Height: " + (int) (height * box.height()));
System.out.println();
}
// Create the frame and panel.
JFrame frame = new JFrame("RotateImage");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
DisplayFaces panel = new DisplayFaces(image);
panel.setPreferredSize(new Dimension(image.getWidth() / scale, image.getHeight() / scale));
frame.setContentPane(panel);
frame.pack();
frame.setVisible(true);
} catch (RekognitionException | FileNotFoundException e) {
System.out.println(e.getMessage());
System.exit(1);
} catch (IOException e) {
e.printStackTrace();
}
}
public static byte[] getObjectBytes (S3Client s3, String bucketName, String keyName) {
try {
GetObjectRequest objectRequest = GetObjectRequest
.builder()
.key(keyName)
.bucket(bucketName)
.build();
ResponseBytes objectBytes = s3.getObjectAsBytes(objectRequest);
return objectBytes.asByteArray();
} catch (S3Exception e) {
System.err.println(e.awsErrorDetails().errorMessage());
System.exit(1);
}
return null;
}
public DisplayFaces(BufferedImage bufImage) {
super();
scale = 1; // increase to shrink image size.
image = bufImage;
}
// Draws the bounding box around the detected faces.
public void paintComponent(Graphics g) {
float left;
float top;
int height = image.getHeight(this);
int width = image.getWidth(this);
Graphics2D g2d = (Graphics2D) g; // Create a Java2D version of g.
// Draw the image
g2d.drawImage(image, 0, 0, width / scale, height / scale, this);
g2d.setColor(new Color(0, 212, 0));
// Iterate through the faces and display bounding boxes.
List faceDetails = result.faceDetails();
for (FaceDetail face : faceDetails) {
BoundingBox box = face.boundingBox();
left = width * box.left();
top = height * box.top();
g2d.drawRect(Math.round(left / scale), Math.round(top / scale),
Math.round((width * box.width()) / scale), Math.round((height * box.height())) / scale);
}
}
// snippet-end:[rekognition.java2.display_faces.main]
}
```
------