Camera2 API: 请求提交后4-5秒拍照

Question

目标很简单：只需使用前置相机拍照。图片应在照片请求发送时固定。甚至不需要预览，因此 CameraSession 是使用来自 ImageReader 的单个表面实例化的。但问题是，在某些设备上，图片仅在 4-5 秒后 被捕获 。以下是一些日志：

Photo was requested at 13:47:29.049

Capture was requested on 13:47:29.062

File was written, sending file to the channel on 13:47:33.313

Photo file was received at 13:47:33.339

Photo was requested at 13:47:39.073

Capture was requested on 13:47:39.074

File was written, sending file to the channel on 13:47:43.199

Photo file was received at 13:47:43.215

问题是4秒后抓拍不支持自动对焦功能（小米MI-5测试） ).如何消除捕获或执行焦点锁定之前如此长的延迟？或者这里可能是消除所述问题的另一种解决方案？

值得一提的华硕平板日志：

Photo was requested at 07:07:03.443

Capture was requested on 07:07:03.454

File was written, sending file to the channel on 07:07:03.907

Photo file was received at 07:07:03.944

Photo was requested at 07:07:08.449

Capture was requested on 07:07:08.449

File was written, sending file to the channel on 07:07:08.635

Photo file was received at 07:07:08.651

代码如下：

视图模型：

private fun makePhoto() {
    GlobalScope.launch(Main) {
        Log.i("Photo", "Photo was requested at ${LocalTime.now()}")
        val picture: File = camera.makePhoto()
        Log.i("Photo", "Photo file was received at ${LocalTime.now()}")
        //process the file somehow
    }
}

相机：

//the method is called in onStart of an Activity or Fragment instance
override suspend fun open() {
    val surfaces = listOf(outputSurface) //surface of an ImageReader instance, comes into object's constructor
    cameraDevice =
        suspendCoroutine { cameraManager.openCamera(specification.id, SuspendingCameraStateCallback(it), handler) } //callback just resumes the coroutine with CameraDevice when onOpened method was called.
    session = suspendCoroutine { cameraDevice.createCaptureSession(surfaces, SuspendSessionCallback(it), handler) } //same, just resumes the continuation with the session that comes into onConfigured method
}

override suspend fun makePhoto(): File {
    return suspendCoroutine {
        session.apply {
            stopRepeating()
            abortCaptures()
            Log.i("Photo", "Capture was requested on ${LocalTime.now()}")
            capture(createCaptureRequest(outputSurface), captureAwaitFactory.createListener(it), handler)
        }
    }
}

private fun createCaptureRequest(target: Surface): CaptureRequest {
    val requestBuilder = cameraDevice.createCaptureRequest(CameraDevice.TEMPLATE_STILL_CAPTURE)
    requestBuilder.addTarget(target)
    requestBuilder.set(CaptureRequest.CONTROL_MODE, CameraMetadata.CONTROL_MODE_AUTO)
    requestBuilder.set(CaptureRequest.JPEG_ORIENTATION, orientation.rotation)
    return requestBuilder.build()
}

使用 setOnImageAvailableListener 附加的 ImageReader 侦听器代码：

override fun onImageAvailable(reader: ImageReader) {
    reader.acquireLatestImage().use { image: Image ->
        val byteBuffer = image.planes[0].buffer
        val byteArray = ByteArray(byteBuffer.capacity())
        byteBuffer.get(byteArray)
        val outputFile = createOutputFile()
        FileOutputStream(outputFile).use { stream: FileOutputStream -> stream.write(byteArray) }
        Log.i("Photo", "File was written, sending file to the channel on ${LocalTime.now()}")
        scope.launch {
            fileChannel.send(outputFile)
        }
    }
}

private fun createOutputFile() = //creates a unique file

工厂的 createListener 实施：

override fun createListener(continuation: Continuation<File>): CameraCaptureSession.CaptureCallback {
    return CoroutineCaptureCallback(channel, this, continuation)
}

和CoroutineCaptureCallback的代码：

internal class CoroutineCaptureCallback(
    private val channel: ReceiveChannel<File>,
    private val scope: CoroutineScope,
    private val continuation: Continuation<File>
) : CameraCaptureSession.CaptureCallback() {

    override fun onCaptureCompleted(
        session: CameraCaptureSession,
        request: CaptureRequest,
        result: TotalCaptureResult
    ) {
        super.onCaptureCompleted(session, request, result)
        scope.launch {
            continuation.resume(channel.receive())
        }
    }
}

Answer 1

不包括在创建捕获会话时运行的代码，因此很难说出您此时做了什么。

就是说，您可能应该发出重复拍摄请求以收敛自动曝光和自动对焦，否则您的图像拍摄可能会使用非常糟糕的值。为此，我建议添加第二个 Surface 目标，例如虚拟 SurfaceTexture（使用一些随机纹理 ID 作为参数创建；永远不要对其调用 updateTexImage，并且您不需要 GL 上下文或任何东西）。

这样一来，一旦您发出照片拍摄请求，一切就绪并启动。

Camera2 API: 请求提交后4-5秒拍照

Camera2 API: picture is taken 4-5 seconds after the request was submitted

android

android-camera2