使用 Firebase ML 给图片加标签 (Android)

您可以使用 Firebase ML 给图片中识别出的对象加标签。如需了解此 API 的功能，请参阅概览。

准备工作

  1. 将 Firebase 添加到您的 Android 项目（如果尚未添加）。
  2. 在您的模块（应用级）Gradle 文件（通常是 <project>/<app-module>/build.gradle.kts 或 <project>/<app-module>/build.gradle）中，添加 Firebase ML Vision Android 库的依赖项。我们建议使用 Firebase Android BoM 来实现库版本控制。 
    dependencies {
    // Import the BoM for the Firebase platform
    implementation(platform("com.google.firebase:firebase-bom:32.5.0"))

    // Add the dependency for the Firebase ML Vision library
    // When using the BoM, you don't specify versions in Firebase library dependencies
    implementation 'com.google.firebase:firebase-ml-vision'
}

    借助 Firebase Android BoM，可确保您的应用使用的始终是 Firebase Android 库的兼容版本。

    （替代方法） 在不使用 BoM 的情况下添加 Firebase 库依赖项

    如果您选择不使用 Firebase BoM，则必须在每个 Firebase 库的依赖项行中指定相应的库版本。

    请注意，如果您在应用中使用多个 Firebase 库，我们强烈建议您使用 BoM 来管理库版本，从而确保所有版本都兼容。

    dependencies {
    // Add the dependency for the Firebase ML Vision library
    // When NOT using the BoM, you must specify versions in Firebase library dependencies
    implementation 'com.google.firebase:firebase-ml-vision:24.1.0'
}

  3. 如果您尚未为项目启用基于 Cloud 的 API，请立即按照以下步骤启用：

    1. 打开 Firebase 控制台的 Firebase ML API 页面。

    2. 如果您尚未将项目升级到 Blaze 定价方案，请点击升级以执行此操作。（只有在您的项目未采用 Blaze 方案时，系统才会提示您进行升级。）

      只有 Blaze 级项目才能使用基于 Cloud 的 API。

    3. 如果尚未启用基于 Cloud 的 API，请点击启用基于 Cloud 的 API。

现在，您可以给图片加标签了。

1. 准备输入图片

基于图片创建 FirebaseVisionImage 对象。使用 Bitmap 或 JPEG 格式的 media.Image（如果您使用 Camera2 API）时，图片标记器的运行速度最快；建议您尽量使用这两种格式的图片。

  • 如需基于 media.Image 对象创建 FirebaseVisionImage 对象（例如从设备的相机捕获图片时），请将 media.Image 对象和图片的旋转角度传递给 FirebaseVisionImage.fromMediaImage()。

    如果您使用了 CameraX 库，OnImageCapturedListener 和 ImageAnalysis.Analyzer 类会为您计算旋转角度值，因此您只需在调用 FirebaseVisionImage.fromMediaImage() 之前将旋转角度转换为 Firebase ML 的 ROTATION_ 常量：

    Kotlin+KTX

    private class YourImageAnalyzer : ImageAnalysis.Analyzer {
    private fun degreesToFirebaseRotation(degrees: Int): Int = when(degrees) {
        0 -> FirebaseVisionImageMetadata.ROTATION_0
        90 -> FirebaseVisionImageMetadata.ROTATION_90
        180 -> FirebaseVisionImageMetadata.ROTATION_180
        270 -> FirebaseVisionImageMetadata.ROTATION_270
        else -> throw Exception("Rotation must be 0, 90, 180, or 270.")
    }

    override fun analyze(imageProxy: ImageProxy?, degrees: Int) {
        val mediaImage = imageProxy?.image
        val imageRotation = degreesToFirebaseRotation(degrees)
        if (mediaImage != null) {
            val image = FirebaseVisionImage.fromMediaImage(mediaImage, imageRotation)
            // Pass image to an ML Vision API
            // ...
        }
    }
}

    Java

    private class YourAnalyzer implements ImageAnalysis.Analyzer {

    private int degreesToFirebaseRotation(int degrees) {
        switch (degrees) {
            case 0:
                return FirebaseVisionImageMetadata.ROTATION_0;
            case 90:
                return FirebaseVisionImageMetadata.ROTATION_90;
            case 180:
                return FirebaseVisionImageMetadata.ROTATION_180;
            case 270:
                return FirebaseVisionImageMetadata.ROTATION_270;
            default:
                throw new IllegalArgumentException(
                        "Rotation must be 0, 90, 180, or 270.");
        }
    }

    @Override
    public void analyze(ImageProxy imageProxy, int degrees) {
        if (imageProxy == null || imageProxy.getImage() == null) {
            return;
        }
        Image mediaImage = imageProxy.getImage();
        int rotation = degreesToFirebaseRotation(degrees);
        FirebaseVisionImage image =
                FirebaseVisionImage.fromMediaImage(mediaImage, rotation);
        // Pass image to an ML Vision API
        // ...
    }
}

    如果您没有使用可提供图片旋转角度的相机库，可以根据设备的旋转角度和设备中相机传感器的朝向来计算旋转角度：

    Kotlin+KTX

    private val ORIENTATIONS = SparseIntArray()

init {
    ORIENTATIONS.append(Surface.ROTATION_0, 90)
    ORIENTATIONS.append(Surface.ROTATION_90, 0)
    ORIENTATIONS.append(Surface.ROTATION_180, 270)
    ORIENTATIONS.append(Surface.ROTATION_270, 180)
}
/**
 * Get the angle by which an image must be rotated given the device's current
 * orientation.
 */
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
@Throws(CameraAccessException::class)
private fun getRotationCompensation(cameraId: String, activity: Activity, context: Context): Int {
    // Get the device's current rotation relative to its "native" orientation.
    // Then, from the ORIENTATIONS table, look up the angle the image must be
    // rotated to compensate for the device's rotation.
    val deviceRotation = activity.windowManager.defaultDisplay.rotation
    var rotationCompensation = ORIENTATIONS.get(deviceRotation)

    // On most devices, the sensor orientation is 90 degrees, but for some
    // devices it is 270 degrees. For devices with a sensor orientation of
    // 270, rotate the image an additional 180 ((270 + 270) % 360) degrees.
    val cameraManager = context.getSystemService(CAMERA_SERVICE) as CameraManager
    val sensorOrientation = cameraManager
        .getCameraCharacteristics(cameraId)
        .get(CameraCharacteristics.SENSOR_ORIENTATION)!!
    rotationCompensation = (rotationCompensation + sensorOrientation + 270) % 360

    // Return the corresponding FirebaseVisionImageMetadata rotation value.
    val result: Int
    when (rotationCompensation) {
        0 -> result = FirebaseVisionImageMetadata.ROTATION_0
        90 -> result = FirebaseVisionImageMetadata.ROTATION_90
        180 -> result = FirebaseVisionImageMetadata.ROTATION_180
        270 -> result = FirebaseVisionImageMetadata.ROTATION_270
        else -> {
            result = FirebaseVisionImageMetadata.ROTATION_0
            Log.e(TAG, "Bad rotation value: $rotationCompensation")
        }
    }
    return result
}
    VisionImage.kt

    Java

    private static final SparseIntArray ORIENTATIONS = new SparseIntArray();
static {
    ORIENTATIONS.append(Surface.ROTATION_0, 90);
    ORIENTATIONS.append(Surface.ROTATION_90, 0);
    ORIENTATIONS.append(Surface.ROTATION_180, 270);
    ORIENTATIONS.append(Surface.ROTATION_270, 180);
}

/**
 * Get the angle by which an image must be rotated given the device's current
 * orientation.
 */
@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
private int getRotationCompensation(String cameraId, Activity activity, Context context)
        throws CameraAccessException {
    // Get the device's current rotation relative to its "native" orientation.
    // Then, from the ORIENTATIONS table, look up the angle the image must be
    // rotated to compensate for the device's rotation.
    int deviceRotation = activity.getWindowManager().getDefaultDisplay().getRotation();
    int rotationCompensation = ORIENTATIONS.get(deviceRotation);

    // On most devices, the sensor orientation is 90 degrees, but for some
    // devices it is 270 degrees. For devices with a sensor orientation of
    // 270, rotate the image an additional 180 ((270 + 270) % 360) degrees.
    CameraManager cameraManager = (CameraManager) context.getSystemService(CAMERA_SERVICE);
    int sensorOrientation = cameraManager
            .getCameraCharacteristics(cameraId)
            .get(CameraCharacteristics.SENSOR_ORIENTATION);
    rotationCompensation = (rotationCompensation + sensorOrientation + 270) % 360;

    // Return the corresponding FirebaseVisionImageMetadata rotation value.
    int result;
    switch (rotationCompensation) {
        case 0:
            result = FirebaseVisionImageMetadata.ROTATION_0;
            break;
        case 90:
            result = FirebaseVisionImageMetadata.ROTATION_90;
            break;
        case 180:
            result = FirebaseVisionImageMetadata.ROTATION_180;
            break;
        case 270:
            result = FirebaseVisionImageMetadata.ROTATION_270;
            break;
        default:
            result = FirebaseVisionImageMetadata.ROTATION_0;
            Log.e(TAG, "Bad rotation value: " + rotationCompensation);
    }
    return result;
}
    VisionImage.java

    然后，将 media.Image 对象及旋转角度值传递给 FirebaseVisionImage.fromMediaImage()：

    Kotlin+KTX

    val image = FirebaseVisionImage.fromMediaImage(mediaImage, rotation)
    VisionImage.kt

    Java

    FirebaseVisionImage image = FirebaseVisionImage.fromMediaImage(mediaImage, rotation);
    VisionImage.java
  • 如需基于文件 URI 创建 FirebaseVisionImage 对象，请将应用上下文和文件 URI 传递给 FirebaseVisionImage.fromFilePath()。如果您使用 ACTION_GET_CONTENT Intent 提示用户从图库应用中选择图片，这一操作会非常有用。

    Kotlin+KTX

    val image: FirebaseVisionImage
try {
    image = FirebaseVisionImage.fromFilePath(context, uri)
} catch (e: IOException) {
    e.printStackTrace()
}
    VisionImage.kt

    Java

    FirebaseVisionImage image;
try {
    image = FirebaseVisionImage.fromFilePath(context, uri);
} catch (IOException e) {
    e.printStackTrace();
}
    VisionImage.java
  • 如需基于 ByteBuffer 或字节数组创建 FirebaseVisionImage 对象，请先按上述 media.Image 输入的说明计算图片旋转角度。

    然后，创建一个包含图片的高度、宽度、颜色编码格式和旋转角度的 FirebaseVisionImageMetadata 对象：

    Kotlin+KTX

    val metadata = FirebaseVisionImageMetadata.Builder()
    .setWidth(480) // 480x360 is typically sufficient for
    .setHeight(360) // image recognition
    .setFormat(FirebaseVisionImageMetadata.IMAGE_FORMAT_NV21)
    .setRotation(rotation)
    .build()
    VisionImage.kt

    Java

    FirebaseVisionImageMetadata metadata = new FirebaseVisionImageMetadata.Builder()
        .setWidth(480)   // 480x360 is typically sufficient for
        .setHeight(360)  // image recognition
        .setFormat(FirebaseVisionImageMetadata.IMAGE_FORMAT_NV21)
        .setRotation(rotation)
        .build();
    VisionImage.java

    使用缓冲区或数组以及元数据对象来创建 FirebaseVisionImage 对象：

    Kotlin+KTX

    val image = FirebaseVisionImage.fromByteBuffer(buffer, metadata)
// Or: val image = FirebaseVisionImage.fromByteArray(byteArray, metadata)
    VisionImage.kt

    Java

    FirebaseVisionImage image = FirebaseVisionImage.fromByteBuffer(buffer, metadata);
// Or: FirebaseVisionImage image = FirebaseVisionImage.fromByteArray(byteArray, metadata);
    VisionImage.java
  • 如需基于 Bitmap 对象创建 FirebaseVisionImage 对象，请运行以下代码：

    Kotlin+KTX

    val image = FirebaseVisionImage.fromBitmap(bitmap)
    VisionImage.kt

    Java

    FirebaseVisionImage image = FirebaseVisionImage.fromBitmap(bitmap);
    VisionImage.java
    以 Bitmap 对象表示的图片必须保持竖直，不需要额外的旋转。

2. 配置并运行图片标记器

如需给图片中的对象加标签，请将 FirebaseVisionImage 对象传递给 FirebaseVisionImageLabeler 的 processImage 方法。

  1. 首先，获取 FirebaseVisionImageLabeler 的一个实例。

    Kotlin+KTX 

    val labeler = FirebaseVision.getInstance().getCloudImageLabeler()

// Or, to set the minimum confidence required:
// val options = FirebaseVisionCloudImageLabelerOptions.Builder()
//     .setConfidenceThreshold(0.7f)
//     .build()
// val labeler = FirebaseVision.getInstance().getCloudImageLabeler(options)

    Java 

    FirebaseVisionImageLabeler labeler = FirebaseVision.getInstance()
    .getCloudImageLabeler();

// Or, to set the minimum confidence required:
// FirebaseVisionCloudImageLabelerOptions options =
//     new FirebaseVisionCloudImageLabelerOptions.Builder()
//         .setConfidenceThreshold(0.7f)
//         .build();
// FirebaseVisionImageLabeler labeler = FirebaseVision.getInstance()
//     .getCloudImageLabeler(options);

  2. 然后，将图片传递给 processImage() 方法：

    Kotlin+KTX 

    labeler.processImage(image)
    .addOnSuccessListener { labels ->
      // Task completed successfully
      // ...
    }
    .addOnFailureListener { e ->
      // Task failed with an exception
      // ...
    }

    Java 

    labeler.processImage(image)
    .addOnSuccessListener(new OnSuccessListener<List<FirebaseVisionImageLabel>>() {
      @Override
      public void onSuccess(List<FirebaseVisionImageLabel> labels) {
        // Task completed successfully
        // ...
      }
    })
    .addOnFailureListener(new OnFailureListener() {
      @Override
      public void onFailure(@NonNull Exception e) {
        // Task failed with an exception
        // ...
      }
    });

3. 获取已加标签的对象的相关信息

如果为图片添加标签的操作成功完成，系统会向成功监听器传递一组 FirebaseVisionImageLabel 对象。每个 FirebaseVisionImageLabel 对象代表图片中加了标签的某个事物。对于每个标签，您可以获取标签的文本说明、其知识图谱实体 ID（如果有）以及匹配的置信度分数。例如：

Kotlin+KTX 

for (label in labels) {
  val text = label.text
  val entityId = label.entityId
  val confidence = label.confidence
}

Java 

for (FirebaseVisionImageLabel label: labels) {
  String text = label.getText();
  String entityId = label.getEntityId();
  float confidence = label.getConfidence();
}

后续步骤