Configuration options

You configure each CameraX use case to control different aspects of the use case's operations.

For example, with the image capture use case, you can set a target aspect ratio and a flash mode. The following code shows one example:

val imageCapture = ImageCapture.Builder()
    .setFlashMode(...)
    .setTargetAspectRatio(...)
    .build()

ImageCapture imageCapture =
    new ImageCapture.Builder()
        .setFlashMode(...)
        .setTargetAspectRatio(...)
        .build();

In addition to configuration options, some use cases expose APIs to dynamically alter settings after the use case has been created. For information on configuration that is specific to the individual use cases, see Implement a preview, Analyze images, and Image capture.

Automatic selection

CameraX automatically provides functionality that is specific to the device that your app is running on. For example, CameraX will automatically determine the best resolution to use if you don't specify a resolution, or if the resolution you specify is unsupported. All of this is handled by the library, eliminating the need for you to write device-specific code.

CameraX's goal is to successfully initialize a camera session. This means CameraX compromises on resolution and aspect ratios based on device capability. The compromise may happen because:

• The device doesn't support the requested resolution.
• The device has compatibility issues, such as legacy devices that require certain resolutions to operate correctly.
• On some devices, certain formats are only available at certain aspect ratios.
• The device has a preference for a "nearest mod16" for JPEG or video encoding. See SCALER_STREAM_CONFIGURATION_MAP for more information.

Although CameraX creates and manages the session, you should always check the returned image sizes on the use case output in your code and adjust accordingly.

Rotation

By default, the camera rotation is set to match the default display's rotation during the creation of the use case. In this default case, CameraX produces outputs to allow the app to easily match what you would expect to see in the preview. You can change the rotation to a custom value to support multi-display devices by passing in the current display orientation when configuring use case objects or dynamically after they have been created.

Your app can set the target rotation using configuration settings. It can then update rotation settings by using the methods from the use case APIs (such as ImageAnalysis.setTargetRotation()), even while the lifecycle is in a running state. You might use this when the app is locked to portrait mode—and so no reconfiguration occurs on rotation—but the photo or analysis use case needs to be aware of the current rotation of the device. For example, rotation awareness may be needed so faces are oriented correctly for face detection, or photos are set to landscape or portrait.

Data for captured images might be stored without rotation information. Exif data contains rotation information so that gallery applications can show the image in the correct orientation after saving.

To display preview data with the correct orientation, you can use the metadata output from Preview.PreviewOutput() to create transforms.

The following code sample shows how to set the rotation on an orientation event:

override fun onCreate() {
    val imageCapture = ImageCapture.Builder().build()

    val orientationEventListener = object : OrientationEventListener(this as Context) {
        override fun onOrientationChanged(orientation : Int) {
            // Monitors orientation values to determine the target rotation value
            val rotation : Int = when (orientation) {
                in 45..134 -> Surface.ROTATION_270
                in 135..224 -> Surface.ROTATION_180
                in 225..314 -> Surface.ROTATION_90
                else -> Surface.ROTATION_0
            }

            imageCapture.targetRotation = rotation
        }
    }
    orientationEventListener.enable()
}

@Override
public void onCreate() {
    ImageCapture imageCapture = new ImageCapture.Builder().build();

    OrientationEventListener orientationEventListener = new OrientationEventListener((Context)this) {
       @Override
       public void onOrientationChanged(int orientation) {
           int rotation;

           // Monitors orientation values to determine the target rotation value
           if (orientation >= 45 && orientation < 135) {
               rotation = Surface.ROTATION_270;
           } else if (orientation >= 135 && orientation < 225) {
               rotation = Surface.ROTATION_180;
           } else if (orientation >= 225 && orientation < 315) {
               rotation = Surface.ROTATION_90;
           } else {
               rotation = Surface.ROTATION_0;
           }

           imageCapture.setTargetRotation(rotation);
       }
    };

    orientationEventListener.enable();
}

Based on the set rotation, each use case will either rotate the image data directly or provide rotation metadata to the consumers of the non-rotated image data.

• Preview: Metadata output is provided so that the rotation of the target resolution is known using Preview.getTargetRotation().
• ImageAnalysis: Metadata output is provided so that image buffer coordinates are known relative to display coordinates.
• ImageCapture: The image Exif metadata, buffer, or both the buffer and metadata will be altered to note the rotation setting. The value altered depends upon the HAL implementation.

Crop rect

By default, the crop rect is the full buffer rect. You can customize it with ViewPort and UseCaseGroup. By grouping use cases and setting the viewport, CameraX guarantees that the crop rects of all the use cases in the group point to the same area in the camera sensor.

The following code snippet shows how to use these two classes:

val viewPort =  ViewPort.Builder(Rational(width, height), display.rotation).build()
val useCaseGroup = UseCaseGroup.Builder()
    .addUseCase(preview)
    .addUseCase(imageAnalysis)
    .addUseCase(imageCapture)
    .setViewPort(viewPort)
    .build()
cameraProvider.bindToLifecycle(lifecycleOwner, cameraSelector, useCaseGroup)

ViewPort viewPort = new ViewPort.Builder(
         new Rational(width, height),
         getDisplay().getRotation()).build();
UseCaseGroup useCaseGroup = new UseCaseGroup.Builder()
    .addUseCase(preview)
    .addUseCase(imageAnalysis)
    .addUseCase(imageCapture)
    .setViewPort(viewPort)
    .build();
cameraProvider.bindToLifecycle(lifecycleOwner, cameraSelector, useCaseGroup);

ViewPort defines the buffer rect visible to end users. Then CameraX calculates the largest possible crop rect based on the properties of the viewport and the attached use cases. Usually, to achieve a WYSIWYG effect, you should configure the viewport based on the preview use case. A simple way to get the viewport is to use PreviewView.

The following code snippets shows how to get the ViewPort object:

val viewport = findViewById<PreviewView>(R.id.preview_view).viewPort

ViewPort viewPort = ((PreviewView)findViewById(R.id.preview_view)).getViewPort();

In the preceding example, what the app gets from ImageAnalysis and ImageCapture matches what the end user sees in PreviewView, assuming the PreviewView's scale type is set to the default, FILL_CENTER. After applying the crop rect and rotation to the output buffer, the image from all use cases will be the same, though possibly with different resolutions. For more information on how to apply the transformation info, see transform output.

Camera resolution

You can choose to allow CameraX to set image resolution based on a combination of the device capabilities, device’s supported hardware level, use case, and provided aspect ratio. Alternatively, you can set a specific target resolution or a specific aspect ratio in use cases that support that configuration.

Automatic resolution

CameraX can automatically determine the best resolution settings based on the use cases specified in cameraProcessProvider.bindToLifecycle(). Whenever possible, specify all the use cases needed to run concurrently in a single session in a single bindToLifecycle() call. CameraX will determine resolutions based on the set of use cases bound by considering the device’s supported hardware level and by accounting for device-specific variance (where a device may exceed or not meet the stream configurations available). The intent is to allow the application to run on a wide variety of devices while minimizing device-specific code paths.

The default aspect ratio for image capture and image analysis use cases is 4:3.

Use cases have a configurable aspect ratio to allow the application to specify the desired aspect ratio based on UI design. CameraX output will be produced to match the aspect ratios requested as closely as the device supports. If there is no exact-match resolution supported, the one that fulfills the most conditions is selected. Thus the application dictates how the camera should appear in the app, and CameraX determines the best camera resolution settings to satisfy that on different devices.

For example an app can do any of the following:

• Specify a target resolution of 4:3 or 16:9 for a use case
• Specify a custom resolution, which CameraX will attempt to find the closest match to
• Specify a cropping aspect ratio for ImageCapture

CameraX will choose the internal Camera2 surface resolutions automatically. The following table shows the resolutions:

Specify a resolution

You can set specific resolutions when building use cases using the setTargetResolution(Size resolution) method, as shown in the following code sample:

val imageAnalysis = ImageAnalysis.Builder()
    .setTargetResolution(Size(1280, 720))
    .build()

ImageAnalysis imageAnalysis =
  new ImageAnalysis.Builder()
    .setTargetResolution(new Size(1280, 720))
    .build();

You can't set both target aspect ratio and target resolution on the same use case. Doing so will throw an IllegalArgumentException when building the config object.

Express the resolution Size in the coordinate frame after rotating the supported sizes by the target rotation. For example, a device with portrait natural orientation in natural target rotation requesting a portrait image may specify 480x640, and the same device, rotated 90 degrees and targeting landscape orientation may specify 640x480.

The maximum available resolution that you can select for an ImageAnalysis is 1080p. The limitation of 1080p for ImageAnalysis considers both performance and quality factors so that users can obtain reasonable quality and a smooth output stream.

The target resolution attempts to establish a minimum bound for the image resolution. The actual image resolution will be the closest available resolution in size that is not smaller than the target resolution, as determined by the Camera implementation. However, if no resolution exists that is equal to or larger than the target resolution, the nearest available resolution smaller than the target resolution will be chosen. Resolutions with the same aspect ratio of the provided Size are given higher priority than resolutions of different aspect ratios.

CameraX will apply the best suitable resolution based on the requests. If the primary need is to satisfy aspect ratio, specify only setTargetAspectRatio, and CameraX will determine a specific resolution suitable based on the device. If the primary need of the app is to specify a resolution in order to make image processing more efficient (for example a small or mid-sized image based on device processing capability), use setTargetResolution(Size resolution).

If your app requires an exact resolution, see the table within createCaptureSession() to determine what maximum resolutions are supported by each hardware level. To check for the specific resolutions supported by the current device, see StreamConfigurationMap.getOutputSizes(int).

If your app is running on Android 10 or higher, you can use isSessionConfigurationSupported() to verify a specific SessionConfiguration.

Control focus

The CameraControl API offers Tap-to-Focus capabilities. Start by getting a CameraControl object, as shown in the following code:

val camera = processCameraProvider.bindToLifecycle(...)
val cameraControl = camera.getCameraControl()

Camera camera = processCameraProvider.bindToLifecycle(...);
CameraControl cameraControl = camera.getCameraControl();

Use MeteringPointFactory, MeteringPoint, MeteringMode, and FocusMeteringAction to run Tap-to-Focus:

val factory = SurfaceOrientedMeteringPointFactory(width, height)
val point = factory.createPoint(x, y)
val action = FocusMeteringAction.Builder(point, FocusMeteringAction.FLAG_AF)
    .addPoint(point2, FocusMeteringAction.FLAG_AE) // could have many
    // auto calling cancelFocusAndMetering in 5 seconds
    .setAutoCancelDuration(5, TimeUnit.SECONDS)
    .build()

val future = cameraControl.startFocusAndMetering(action)
future.addListener( Runnable {
    val result = future.get()
    // process the result
} , executor)

MeteringPointFactory factory = new SurfaceOrientedMeteringPointFactory(width, height);
MeteringPoint point = factory.createPoint(x, y);
FocusMeteringAction action = new FocusMeteringAction.Builder(point, FocusMeteringAction.FLAG_AF)
        .addPoint(point2, FocusMeteringAction.FLAG_AE) // could have many
        // auto calling cancelFocusAndMetering in 5 seconds
        .setAutoCancelDuration(5, TimeUnit.SECONDS)
        .build();

ListenableFuture future = cameraControl.startFocusAndMetering(action)
future.addListener( () -> {
    try {
        FocusMeteringResult result = future.get();
        // process the result
    } catch (Exception e) {
    }
} , executor);

Additional resources

To learn more about CameraX, consult the following additional resources.

Codelab

Code sample

Developer community

Android CameraX Discussion Group