ImageReader

acquireLatestImage

public Image acquireLatestImage ()

Acquire the latest Image from the ImageReader's queue, dropping older images. Returns null if no new image is available.

This operation will acquire all the images possible from the ImageReader, but close() all images that aren't the latest. This function is recommended to use over acquireNextImage() for most use-cases, as it's more suited for real-time processing.

Note that maxImages should be at least 2 for acquireLatestImage() to be any different than acquireNextImage() - discarding all-but-the-newest Image requires temporarily acquiring two Images at once. Or more generally, calling acquireLatestImage() with less than two images of margin, that is (maxImages - currentAcquiredImages < 2) will not discard as expected.

This operation will fail by throwing an IllegalStateException if maxImages have been acquired with acquireLatestImage() or acquireNextImage(). In particular a sequence of acquireLatestImage() calls greater than getMaxImages() without calling Image.close in-between will exhaust the underlying queue. At such a time, IllegalStateException will be thrown until more images are released with Image.close.

acquireNextImage

public Image acquireNextImage ()

Acquire the next Image from the ImageReader's queue. Returns null if no new image is available.

Warning: Consider using acquireLatestImage() instead, as it will automatically release older images, and allow slower-running processing routines to catch up to the newest frame. Usage of acquireNextImage() is recommended for batch/background processing. Incorrectly using this function can cause images to appear with an ever-increasing delay, followed by a complete stall where no new images seem to appear.

This operation will fail by throwing an IllegalStateException if maxImages have been acquired with acquireNextImage() or acquireLatestImage(). In particular a sequence of acquireNextImage() or acquireLatestImage() calls greater than maxImages without calling Image.close in-between will exhaust the underlying queue. At such a time, IllegalStateException will be thrown until more images are released with Image.close.

close

public void close ()

Free up all the resources associated with this ImageReader.

After calling this method, this ImageReader can not be used. Calling any methods on this ImageReader and Images previously provided by acquireNextImage() or acquireLatestImage() will result in an IllegalStateException, and attempting to read from ByteBuffers returned by an earlier Plane#getBuffer call will have undefined behavior.

discardFreeBuffers

public void discardFreeBuffers ()

Discard any free buffers owned by this ImageReader.

Generally, the ImageReader caches buffers for reuse once they have been allocated, for best performance. However, sometimes it may be important to release all the cached, unused buffers to save on memory.

Calling this method will discard all free cached buffers. This does not include any buffers associated with Images acquired from the ImageReader, any filled buffers waiting to be acquired, and any buffers currently in use by the source rendering buffers into the ImageReader's Surface.

The ImageReader continues to be usable after this call, but may need to reallocate buffers when more buffers are needed for rendering.

getDataSpace

public int getDataSpace ()

The default dataspace of Images.

Use this function if the ImageReader instance is created by builder pattern ImageReader.Builder and Builder.setDefaultDataSpace.

getHardwareBufferFormat

public int getHardwareBufferFormat ()

The default HardwareBuffer format of Images.

Use this function if the ImageReader instance is created by builder pattern ImageReader.Builder and using Builder.setDefaultHardwareBufferFormat and Builder.setDefaultDataSpace.

getHeight

public int getHeight ()

The default height of Images, in pixels.

The height may be overridden by the producer sending buffers to this ImageReader's Surface. If so, the actual height of the images can be found using Image.getHeight.

getImageFormat

public int getImageFormat ()

The default image format of Images.

Some color formats may be overridden by the producer sending buffers to this ImageReader's Surface if the default color format allows. ImageReader guarantees that all Images acquired from ImageReader (for example, with acquireNextImage()) will have a "compatible" format to what was specified in newInstance(int, int, int, int). As of now, each format is only compatible to itself. The actual format of the images can be found using Image.getFormat.

Use this function if the ImageReader instance is created by factory method newInstance function or by builder pattern ImageReader.Builder and using Builder.setImageFormat.

getMaxImages

public int getMaxImages ()

Maximum number of images that can be acquired from the ImageReader by any time (for example, with acquireNextImage()).

An image is considered acquired after it's returned by a function from ImageReader, and until the Image is closed to release the image back to the ImageReader.

Attempting to acquire more than maxImages concurrently will result in the acquire function throwing a IllegalStateException. Furthermore, while the max number of images have been acquired by the ImageReader user, the producer enqueueing additional images may stall until at least one image has been released.

getSurface

public Surface getSurface ()

Get a Surface that can be used to produce Images for this ImageReader.

Until valid image data is rendered into this Surface, the acquireNextImage() method will return null. Only one source can be producing data into this Surface at the same time, although the same Surface can be reused with a different API once the first source is disconnected from the Surface.

Please note that holding on to the Surface object returned by this method is not enough to keep its parent ImageReader from being reclaimed. In that sense, a Surface acts like a weak reference to the ImageReader that provides it.

getUsage

public long getUsage ()

The usage flag of images that can be produced by the ImageReader.

getWidth

public int getWidth ()

The default width of Images, in pixels.

The width may be overridden by the producer sending buffers to this ImageReader's Surface. If so, the actual width of the images can be found using Image.getWidth.

newInstance

public static ImageReader newInstance (int width, 
                int height, 
                int format, 
                int maxImages, 
                long usage)

Create a new reader for images of the desired size, format and consumer usage flag.

The maxImages parameter determines the maximum number of Image objects that can be be acquired from the ImageReader simultaneously. Requesting more buffers will use up more memory, so it is important to use only the minimum number necessary for the use case.

The valid sizes and formats depend on the source of the image data.

The format and usage flag combination describes how the buffer will be used by consumer end-points. For example, if the application intends to send the images to MediaCodec or MediaRecorder for hardware video encoding, the format and usage flag combination needs to be PRIVATE and HardwareBuffer.USAGE_VIDEO_ENCODE. When an ImageReader object is created with a valid size and such format/usage flag combination, the application can send the images to an ImageWriter that is created with the input Surface provided by the MediaCodec or MediaRecorder.

If the format is PRIVATE, the created ImageReader will produce images that are not directly accessible by the application. The application can still acquire images from this ImageReader, and send them to the camera for reprocessing, or to the MediaCodec / MediaRecorder for hardware video encoding via ImageWriter interface. However, the getPlanes() will return an empty array for PRIVATE format images. The application can check if an existing reader's format by calling getImageFormat().

PRIVATE format ImageReaders are more efficient to use when application access to image data is not necessary, compared to ImageReaders using other format such as YUV_420_888.

Note that not all format and usage flag combinations are supported by the ImageReader. Below are the supported combinations by the ImageReader (assuming the consumer end-points support the such image consumption, e.g., hardware video encoding).

If the ImageReader is used as an output target for a CameraDevice, and if the usage flag contains HardwareBuffer.USAGE_VIDEO_ENCODE, the timestamps of the images produced by the ImageReader won't be in the same timebase as SystemClock.elapsedRealtimeNanos(), even if CameraCharacteristics.SENSOR_INFO_TIMESTAMP_SOURCE is CameraMetadata.SENSOR_INFO_TIMESTAMP_SOURCE_REALTIME. Instead, the timestamps will be roughly in the same timebase as in SystemClock.uptimeMillis(), so that A/V synchronization could work for video recording. In this case, the timestamps from the ImageReader with HardwareBuffer.USAGE_VIDEO_ENCODE usage flag may not be directly comparable with timestamps of other streams or capture result metadata.

newInstance

public static ImageReader newInstance (int width, 
                int height, 
                int format, 
                int maxImages)

Create a new reader for images of the desired size and format.

The maxImages parameter determines the maximum number of Image objects that can be be acquired from the ImageReader simultaneously. Requesting more buffers will use up more memory, so it is important to use only the minimum number necessary for the use case.

The valid sizes and formats depend on the source of the image data.

If the format is PRIVATE, the created ImageReader will produce images that are not directly accessible by the application. The application can still acquire images from this ImageReader, and send them to the camera for reprocessing via ImageWriter interface. However, the getPlanes() will return an empty array for PRIVATE format images. The application can check if an existing reader's format by calling getImageFormat().

PRIVATE format ImageReaders are more efficient to use when application access to image data is not necessary, compared to ImageReaders using other format such as YUV_420_888.

setOnImageAvailableListener

public void setOnImageAvailableListener (ImageReader.OnImageAvailableListener listener, 
                Handler handler)

Register a listener to be invoked when a new image becomes available from the ImageReader.

finalize

protected void finalize ()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the finalize method to dispose of system resources or to perform other cleanup.

The general contract of finalize is that it is invoked if and when the Java virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized. The finalize method may take any action, including making this object available again to other threads; the usual purpose of finalize, however, is to perform cleanup actions before the object is irrevocably discarded. For example, the finalize method for an object that represents an input/output connection might perform explicit I/O transactions to break the connection before the object is permanently discarded.

The finalize method of class Object performs no special action; it simply returns normally. Subclasses of Object may override this definition.

The Java programming language does not guarantee which thread will invoke the finalize method for any given object. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked. If an uncaught exception is thrown by the finalize method, the exception is ignored and finalization of that object terminates.

After the finalize method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, including possible actions by other objects or classes which are ready to be finalized, at which point the object may be discarded.

The finalize method is never invoked more than once by a Java virtual machine for any given object.

Any exception thrown by the finalize method causes the finalization of this object to be halted, but is otherwise ignored.