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:
Kotlin
val imageCapture = ImageCapture.Builder() .setFlashMode(...) .setTargetAspectRatio(...) .build()
Java
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.
CameraXConfig
For simplicity, CameraX has default configurations such as internal executors and handlers that are suitable for most usage scenarios. However, if your application has special requirements or prefers to customize those configurations, CameraXConfig
is the interface for that purpose.
With CameraXConfig
, an application can do the following:
- Optimize startup latency with
setAvailableCameraLimiter()
. - Provide the application's executor to CameraX with
setCameraExecutor()
. - Replace the default scheduler handler with
setSchedulerHandler()
. - Change the logging level with
setMinimumLoggingLevel()
.
Usage Model
The following procedure describes how to use CameraXConfig
:
- Create a
CameraXConfig
object with your customized configurations. - Implement the
CameraXConfig.Provider
interface in yourApplication
, and return yourCameraXConfig
object ingetCameraXConfig()
. - Add your
Application
class to yourAndroidManifest.xml
file, as described here.
For example, the following code sample restricts CameraX logging to error messages only:
Kotlin
class CameraApplication : Application(), CameraXConfig.Provider { override fun getCameraXConfig(): CameraXConfig { return CameraXConfig.Builder.fromConfig(Camera2Config.defaultConfig()) .setMinimumLoggingLevel(Log.ERROR).build() } }
Keep a local copy of the CameraXConfig
object if your application needs to know the CameraX configuration after setting it.
Camera Limiter
During the first invocation of ProcessCameraProvider.getInstance()
, CameraX enumerates and queries characteristics of the cameras available on the device. Because CameraX needs to communicate with hardware components, this process can take a non-trivial amount of time for each camera, particularly on low-end devices. If your application only uses specific cameras on the device, such as the default front camera, you can set CameraX to ignore other cameras, which can reduce startup latency for the cameras your application uses.
If the CameraSelector
passed to CameraXConfig.Builder.setAvailableCamerasLimiter()
filters out a camera, CameraX behaves as if that camera does not exist. For example, the following code limits the application to only use the device's default back camera:
Kotlin
class MainApplication : Application(), CameraXConfig.Provider { override fun getCameraXConfig(): CameraXConfig { return CameraXConfig.Builder.fromConfig(Camera2Config.defaultConfig()) .setAvailableCamerasLimiter(CameraSelector.DEFAULT_BACK_CAMERA) .build() } }
Threads
Many of the platform APIs on which CameraX is built require blocking interprocess communication (IPC) with hardware that can sometimes take hundreds of milliseconds to respond. For this reason, CameraX only calls these APIs from background threads, which ensures the main thread is not blocked and that the UI remains fluid. CameraX internally manages these background threads so that this behavior appears transparent. However, some applications require strict control of threads. CameraXConfig
allows an application to set the background threads that will be used through CameraXConfig.Builder.setCameraExecutor()
and CameraXConfig.Builder.setSchedulerHandler()
.
Camera Executor
The camera executor is used for all internal Camera platform API calls, as well as for callbacks from these APIs. CameraX allocates and manages an internal Executor
to perform these tasks. However, if your application requires stricter control of threads, use CameraXConfig.Builder.setCameraExecutor()
.
Scheduler Handler
The scheduler handler is used to schedule internal tasks at fixed intervals, such as retrying opening the camera when it isn't available. This handler does not execute jobs, and only dispatches them to the camera executor. It is also sometimes used on the legacy API platforms that require a Handler
for callbacks. In these cases, the callbacks are still only dispatched directly to the camera executor. CameraX allocates and manages an internal HandlerThread
to perform these tasks, but you can overridde it with CameraXConfig.Builder.setSchedulerHandler()
.
Logging
CameraX logging allows applications to filter logcat messages, as it may be good practice to avoid verbose messages in your production code. CameraX supports four logging levels, from the most verbose to the most severe:
Log.DEBUG
(default)Log.INFO
Log.WARN
Log.ERROR
Refer to the Android Log documentation for detailed descriptions of these log levels. Use CameraXConfig.Builder.setMinimumLoggingLevel(int)
to set the appropriate logging level for your application.
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:
Kotlin
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() }
Java
@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:
Kotlin
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)
Java
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:
Kotlin
val viewport = findViewById<PreviewView>(R.id.preview_view).viewPort
Java
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 selection
CameraX automatically selects the best camera device for your application’s requirements and use cases. If you wish to use a different device than the one selected for you, there are a few options:
- Request the default front facing camera with
CameraSelector.DEFAULT_FRONT_CAMERA
. - Request the default rear facing camera with
CameraSelector.DEFAULT_BACK_CAMERA
. - Filter the list of available devices by their
CameraCharacteristics
withCameraSelector.Builder.addCameraFilter()
.
The following code sample illustrates how to create a CameraSelector
to influence device selection:
Kotlin
fun selectExternalOrBestCamera(provider: ProcessCameraProvider):CameraSelector? { val cam2Infos = provider.availableCameraInfos.map { Camera2CameraInfo.from(it) }.sortedByDescending { // HARDWARE_LEVEL is Int type, with the order of: // LEGACY < LIMITED < FULL < LEVEL_3 < EXTERNAL it.getCameraCharacteristic(CameraCharacteristics.INFO_SUPPORTED_HARDWARE_LEVEL) } return when { cam2Infos.isNotEmpty() -> { CameraSelector.Builder() .addCameraFilter { it.filter { camInfo -> // cam2Infos[0] is either EXTERNAL or best built-in camera val thisCamId = Camera2CameraInfo.from(camInfo).cameraId thisCamId == cam2Infos[0].cameraId } }.build() } else -> null } } // create a CameraSelector for the USB camera (or highest level internal camera) val selector = selectExternalOrBestCamera(processCameraProvider) processCameraProvider.bindToLifecycle(this, selector, preview, analysis)
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:
Use case | Internal surface resolution | Output data resolution |
---|---|---|
Preview | Aspect Ratio: The resolution that best fits the target to the setting. | Internal surface resolution. Metadata is provided to allow a View to crop, scale, and rotate for the target aspect ratio. |
Default resolution: Highest preview resolution, or highest device-preferred resolution that matches aspect ratio above. | ||
Max resolution: Preview size, which refers to the best size match to the device's screen resolution, or to 1080p (1920x1080), whichever is smaller. | ||
Image analysis | Aspect ratio: The resolution that best fits the target to the setting. | Internal surface resolution. |
Default resolution: The default target resolution setting is 640x480. Adjusting both target resolution and corresponding aspect ratio will result in a best-supported resolution. | ||
Max resolution: The camera device's maximum output resolution of
YUV_420_888 format which is retrieved from
StreamConfigurationMap.getOutputSizes() .
The target resolution is set as 640x480 by default, so if you want a
resolution larger than 640x480, you must use
setTargetResolution()
and
setTargetAspectRatio()
to get the closest one from the supported resolutions.
|
||
Image capture | Aspect ratio: Aspect ratio that best fits the setting. | Internal surface resolution. |
Default resolution: Highest resolution available, or highest device-preferred resolution that matches aspect ratio above. | ||
Max resolution: The camera device's maximum output resolution in
a JPEG format. Use
StreamConfigurationMap.getOutputSizes()
to retrieve this.
|
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:
Kotlin
val imageAnalysis = ImageAnalysis.Builder() .setTargetResolution(Size(1280, 720)) .build()
Java
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 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 camera output
In addition to letting you configure the camera output as-needed for each individual use case, CameraX also implements the following interfaces to support camera operations common to all bound use cases:
CameraControl
lets you configure common camera features.CameraInfo
lets you query the states of those common camera features.
These are the supported camera features with CameraControl:
- Zoom
- Torch
- Focus and Metering (tap-to-focus)
- Exposure Compensation
Get instances of CameraControl and CameraInfo
Retrieve instances of CameraControl
and CameraInfo
using the Camera
object returned by ProcessCameraProvider.bindToLifecyle()
. The following code shows an example:
Kotlin
val camera = processCameraProvider.bindToLifecycle(lifecycleOwner, cameraSelector, preview) // For performing operations that affect all outputs. val cameraControl = camera.cameraControl // For querying information and states. val cameraInfo = camera.cameraInfo
Java
Camera camera = processCameraProvider.bindToLifecycle(lifecycleOwner, cameraSelector, preview) // For performing operations that affect all outputs. CameraControl cameraControl = camera.getCameraControl() // For querying information and states. CameraInfo cameraInfo = camera.getCameraInfo()
For example, you can submit zoom and other CameraControl
operations after calling bindToLifecycle()
. After you stop or destroy the activity used to bind the camera instance, CameraControl
can no longer execute operations and returns a failed ListenableFuture
.
Zoom
CameraControl offers two methods for changing the zoom level:
setZoomRatio()
sets the zoom by the zoom ratio.The ratio must be within the range of
CameraInfo.getZoomState().getValue().getMinZoomRatio()
andCameraInfo.getZoomState().getValue().getMaxZoomRatio()
. Otherwise the function returns a failedListenableFuture
.setLinearZoom()
sets the current zoom with a linear zoom value ranging from 0 to 1.0.The advantage of linear zoom is that it ensures the field of view (FOV) scales with changes in zoom. This makes it ideal for use with a
Slider
view.
CameraInfo.getZoomState()
returns a LiveData of the current zoom state. The value changes when the camera is initialized or if the zoom level is set using setZoomRatio()
or setLinearZoom()
. Calling either method sets the values backing ZoomState.getZoomRatio()
and ZoomState.getLinearZoom()
. This is helpful if you want to display zoom ratio text alongside a slider. Simply observe the ZoomState
LiveData
to update both without needing to do a conversion.
The ListenableFuture
returned by both APIs offers the option for applications to be notified when a repeating request with the specified zoom value is completed. In addition, if you set a new zoom value while the previous operation is still executing, the previous zoom operation's ListenableFuture
fails immediately.
Torch
CameraControl.enableTorch(boolean)
enables or disables the torch (also known as the flashlight).
CameraInfo.getTorchState()
can be used to query the current torch state. You can check the value returned by CameraInfo.hasFlashUnit()
to determine whether a torch is available. If not, calling CameraControl.enableTorch(boolean)
causes the returned ListenableFuture
to complete immediately with a failed result and sets the torch state to TorchState.OFF
.
When the torch is enabled, it remains on during photo and video capture regardless of the flashMode setting. The flashMode
in ImageCapture
works only when the torch is disabled.
Focus and Metering
CameraControl.startFocusAndMetering()
triggers autofocus and exposure metering by setting AF/AE/AWB metering regions based on the given FocusMeteringAction. This is often used to implement the “tap to focus” feature in many camera applications.
MeteringPoint
To begin, create a MeteringPoint
using MeteringPointFactory.createPoint(float x, float y, float size)
. A MeteringPoint
represents a single point on the camera Surface
. It’s stored in a normalized form so that it can be easily converted to sensor coordinates for specifying AF/AE/AWB regions.
The size of the MeteringPoint
ranges from 0 to 1, with a default size of 0.15f. When calling MeteringPointFactory.createPoint(float x, float y, float size)
, CameraX creates a rectangle region centered at (x, y)
for the provided size
.
The following code demonstrates how to create a MeteringPoint
:
Kotlin
// Use PreviewView.getMeteringPointFactory if PreviewView is used for preview. previewView.setOnTouchListener((view, motionEvent) -> { val meteringPoint = previewView.meteringPointFactory .createPoint(motionEvent.x, motionEvent.y) … } // Use DisplayOrientedMeteringPointFactory if SurfaceView / TextureView is used for // preview. Please note that if the preview is scaled or cropped in the View, // it’s the application's responsibility to transform the coordinates properly // so that the width and height of this factory represents the full Preview FOV. // And the (x,y) passed to create MeteringPoint may need to be adjusted with // the offsets. val meteringPointFactory = DisplayOrientedMeteringPointFactory( surfaceView.display, camera.cameraInfo, surfaceView.width, surfaceView.height ) // Use SurfaceOrientedMeteringPointFactory if the point is specified in // ImageAnalysis ImageProxy. val meteringPointFactory = SurfaceOrientedMeteringPointFactory( imageWidth, imageHeight, imageAnalysis)
startFocusAndMetering and FocusMeteringAction
To invoke startFocusAndMetering()
, applications must build a FocusMeteringAction
, which consists of one or more MeteringPoints
with optional metering mode combinations from FLAG_AF
, FLAG_AE
, FLAG_AWB
. The follow code demonstrates this usage:
Kotlin
val meteringPoint1 = meteringPointFactory.createPoint(x1, x1) val meteringPoint2 = meteringPointFactory.createPoint(x2, y2) val action = FocusMeteringAction.Builder(meteringPoint1) // default AF|AE|AWB // Optionally add meteringPoint2 for AF/AE. .addPoint(meteringPoint2, FLAG_AF | FLAG_AE) // The action will be canceled in 3 seconds (if not set, default is 5s). .setAutoCancelDuration(3, TimeUnit.SECONDS) .build() val result = cameraControl.startFocusAndMetering(action) // Adds listener to the ListenableFuture if you need to know the focusMetering result. result.addListener({ // result.get().isFocusSuccessful returns if the auto focus is successful or not. }, ContextCompat.getMainExecutor(this)
As shown in the code above, startFocusAndMetering()
takes a FocusMeteringAction
consisting of one MeteringPoint
for AF/AE/AWB metering regions and another MeteringPoint for AF and AE only.
Internally, CameraX converts it into Camera2 MeteringRectangles
and sets the corresponding CONTROL_AF_REGIONS
/ CONTROL_AE_REGIONS
/ CONTROL_AWB_REGIONS
parameters to the capture request.
Since not every device supports AF/AE/AWB and multiple regions, CameraX executes the FocusMeteringAction
with best effort. CameraX will use the maximum number of MeteringPoints supported, in the order that points were added. All MeteringPoints added after the maximum count are ignored. For example, if a FocusMeteringAction
is supplied with 3 MeteringPoints on a platform supporting just 2, only the first 2 MeteringPoints are used. The final MeteringPoint
is ignored by CameraX.
Exposure Compensation
Exposure compensation is useful when applications need to fine-tune exposure values (EV) beyond the auto exposure (AE) output result. Exposure compensation values are combined in the following way to determine the necessary exposure for current image conditions:
Exposure = ExposureCompensationIndex * ExposureCompensationStep
CameraX provides the Camera.CameraControl.setExposureCompensationIndex()
function for setting the exposure compensation as an index value.
Positive index values make the image brighter, while negative values dim the image. Applications can query the supported range by CameraInfo.ExposureState.exposureCompensationRange()
described in the next section. If the value is supported, the returned ListenableFuture
completes when the value is successfully enabled in the capture request; if the specified index is out of the supported range, setExposureCompensationIndex()
causes the returned ListenableFuture
to complete immediately with a failed result.
CameraX keeps only the latest outstanding setExposureCompensationIndex()
request, and calling the function multiple times before the previous request gets executed results in its cancellation.
The following snippet sets an exposure compensation index and registers a callback for when the exposure change request has been executed:
Kotlin
camera.cameraControl.setExposureCompensationIndex(exposureCompensationIndex) .addListener({ // Get the current exposure compensation index, it may be // different from the asked value in case this request was // canceled by a newer setting request. val currentExposureIndex = camera.cameraInfo.exposureState.exposureCompensationIndex … }, mainExecutor)
Camera.CameraInfo.getExposureState()
retrieves the currentExposureState
including:- The supportability of exposure compensation control.
- The current exposure compensation index.
- The exposure compensation index range.
- The exposure compensation step used in exposure compensation value calculation.
For example, the following code initializes the settings for an exposure SeekBar
with current ExposureState
values:
Kotlin
val exposureState = camera.cameraInfo.exposureState binding.seekBar.apply { isEnabled = exposureState.isExposureCompensationSupported max = exposureState.exposureCompensationRange.upper min = exposureState.exposureCompensationRange.lower progress = exposureState.exposureCompensationIndex }
Additional resources
To learn more about CameraX, consult the following additional resources.
Codelab
Code sample
Developer community
Android CameraX Discussion Group