需要在使用 MLKit 和 Camera2 进行人脸检测期间捕获静止图像

Question

我正在使用 Camera2 和 MLKit 开发人脸检测功能。

在开发者指南的Performance Tips 部分中，他们说如果使用Camera2 API，则以ImageFormat.YUV_420_888 格式捕获图像，这是我的情况。

然后，在Face Detector 部分，他们建议使用尺寸至少为 480x360 像素的图像进行实时人脸识别，这也是我的情况。

好的，我们走吧！这是我的代码，运行良好

private fun initializeCamera() = lifecycleScope.launch(Dispatchers.Main) {

    // Open the selected camera
    cameraDevice = openCamera(cameraManager, getCameraId(), cameraHandler)

    val previewSize = if (isPortrait) {
        Size(RECOMMANDED_CAPTURE_SIZE.width, RECOMMANDED_CAPTURE_SIZE.height)
    } else {
        Size(RECOMMANDED_CAPTURE_SIZE.height, RECOMMANDED_CAPTURE_SIZE.width)
    }

    // Initialize an image reader which will be used to display a preview
    imageReader = ImageReader.newInstance(
            previewSize.width, previewSize.height, ImageFormat.YUV_420_888, IMAGE_BUFFER_SIZE)

    // Retrieve preview's frame and run detector
    imageReader.setOnImageAvailableListener({ reader ->
        lifecycleScope.launch(Dispatchers.Main) {
            val image = reader.acquireNextImage()
            logD { "Image available: ${image.timestamp}" }
            faceDetector.runFaceDetection(image, getRotationCompensation())
            image.close()
        }
    }, imageReaderHandler)

    // Creates list of Surfaces where the camera will output frames
    val targets = listOf(viewfinder.holder.surface, imageReader.surface)

    // Start a capture session using our open camera and list of Surfaces where frames will go
    session = createCaptureSession(cameraDevice, targets, cameraHandler)
    val captureRequest = cameraDevice.createCaptureRequest(
            CameraDevice.TEMPLATE_PREVIEW).apply {
        addTarget(viewfinder.holder.surface)
        addTarget(imageReader.surface)
    }

    // This will keep sending the capture request as frequently as possible until the
    // session is torn down or session.stopRepeating() is called
    session.setRepeatingRequest(captureRequest.build(), null, cameraHandler)
}

现在，我想捕捉一张静止图像……这是我的问题，因为理想情况下，我想要：

• 全分辨率图像，或至少大于 480x360
• 以 JPEG 格式保存

Camera2Basic sample 演示了如何捕获图像（视频和慢动作的示例正在崩溃），MLKit sample 使用了如此古老的相机 API！幸运的是，我成功地混合了这些样本来开发我的功能，但我未能捕捉到具有不同分辨率的静止图像。

我想我必须停止预览会话才能重新创建一个以进行图像捕获，但我不确定...

我所做的是以下，但它是在 480x360 中捕获图像：

session.stopRepeating()

 // Unset the image reader listener
 imageReader.setOnImageAvailableListener(null, null)
 // Initialize an new image reader which will be used to capture still photos
 // imageReader = ImageReader.newInstance(768, 1024, ImageFormat.JPEG, IMAGE_BUFFER_SIZE)

 // Start a new image queue
 val imageQueue = ArrayBlockingQueue<Image>(IMAGE_BUFFER_SIZE)
 imageReader.setOnImageAvailableListener({ reader - >
    val image = reader.acquireNextImage()
    logD {"[Still] Image available in queue: ${image.timestamp}"}
    if (imageQueue.size >= IMAGE_BUFFER_SIZE - 1) {
        imageQueue.take().close()
    }
    imageQueue.add(image)
}, imageReaderHandler)

 // Creates list of Surfaces where the camera will output frames
 val targets = listOf(viewfinder.holder.surface, imageReader.surface)
 val captureRequest = createStillCaptureRequest(cameraDevice, targets)
 session.capture(captureRequest, object: CameraCaptureSession.CaptureCallback() {
    override fun onCaptureCompleted(
        session: CameraCaptureSession,
        request: CaptureRequest,
        result: TotalCaptureResult) {
        super.onCaptureCompleted(session, request, result)
        val resultTimestamp = result.get(CaptureResult.SENSOR_TIMESTAMP)
        logD {"Capture result received: $resultTimestamp"}
        // Set a timeout in case image captured is dropped from the pipeline
        val exc = TimeoutException("Image dequeuing took too long")
        val timeoutRunnable = Runnable {
            continuation.resumeWithException(exc)
        }
        imageReaderHandler.postDelayed(timeoutRunnable, IMAGE_CAPTURE_TIMEOUT_MILLIS)
        // Loop in the coroutine's context until an image with matching timestamp comes
        // We need to launch the coroutine context again because the callback is done in
        //  the handler provided to the `capture` method, not in our coroutine context
        @ Suppress("BlockingMethodInNonBlockingContext")
        lifecycleScope.launch(continuation.context) {
            while (true) {
                // Dequeue images while timestamps don't match
                val image = imageQueue.take()
                if (image.timestamp != resultTimestamp)
                  continue
                logD {"Matching image dequeued: ${image.timestamp}"}

                // Unset the image reader listener
                imageReaderHandler.removeCallbacks(timeoutRunnable)
                imageReader.setOnImageAvailableListener(null, null)

                // Clear the queue of images, if there are left
                while (imageQueue.size > 0) {
                    imageQueue.take()
                        .close()
                }
                // Compute EXIF orientation metadata
                val rotation = getRotationCompensation()
                val mirrored = cameraFacing == CameraCharacteristics.LENS_FACING_FRONT
                val exifOrientation = computeExifOrientation(rotation, mirrored)
                logE {"captured image size (w/h): ${image.width} / ${image.height}"}
                // Build the result and resume progress
                continuation.resume(CombinedCaptureResult(
                    image, result, exifOrientation, imageReader.imageFormat))
                // There is no need to break out of the loop, this coroutine will suspend
            }
        }
    }
}, cameraHandler)
}

如果我取消注释新的 ImageReader 实例，我有这个例外：

java.lang.IllegalArgumentException: CaptureRequest 包含 未配置的输入/输出表面！

谁能帮帮我？

Answer 1

这个IllegalArgumentException：

java.lang.IllegalArgumentException：CaptureRequest 包含未配置的输入/输出表面！

...显然是指imageReader.surface。

---

Meanhile（使用 CameraX）这会有所不同，请参阅 CameraFragment.kt ...

问题 #197：Firebase Face Detection Api issue while using cameraX API;

可能很快就会有一个与您的用例相匹配的示例应用程序。

Answer 2

ImageReader 对格式的选择和/或使用标志的组合很敏感。 documentation 指出某些格式组合可能不受支持。对于某些 Android 设备（可能是一些较旧的手机型号），您可能会发现 IllegalArgumentException 不是使用 JPEG 格式抛出的。但这并没有多大帮助——你想要多才多艺的东西。

我过去所做的是使用ImageFormat.YUV_420_888 格式（这将得到硬件和ImageReader 实现的支持）。此格式不包含阻止应用程序通过内部平面阵列访问图像的预优化。我注意到您已经在 initializeCamera() 方法中成功使用了它。

然后你可以从你想要的帧中提取图像数据

Image.Plane[] planes = img.getPlanes();
byte[] data = planes[0].getBuffer().array();

然后通过位图使用 JPEG 压缩、PNG 或您选择的任何编码创建静止图像。

ByteArrayOutputStream out = new ByteArrayOutputStream();
YuvImage yuvImage = new YuvImage(data, ImageFormat.NV21, width, height, null);
yuvImage.compressToJpeg(new Rect(0, 0, width, height), 100, out);
byte[] imageBytes = out.toByteArray();
Bitmap bitmap= BitmapFactory.decodeByteArray(imageBytes, 0, imageBytes.length);
ByteArrayOutputStream out2 = new ByteArrayOutputStream();
bitmap.compress(Bitmap.CompressFormat.JPEG, 75, out2);