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目前我正在使用 Lumia.Imaging 来获取预览帧并显示它。

我创建了新方法“GetPreview()”来遍历像素，找到红色像素，然后我想计算每一帧的红色像素的平均值。

我的问题是，当我通过像素时，应用程序中有滞后:(

  • 在不损失性能的情况下，计算每一帧的红色像素平均值的正确解决方案是什么？

  • 另外如何在预览开始时打开闪光灯？ 

        private async Task startCameraPreview()
{
    // Create a camera preview image source (from the Lumia Imaging SDK)
    _cameraPreviewImageSource = new CameraPreviewImageSource();

    // Checking id of back camera 
    DeviceInformationCollection devices = await Windows.Devices.Enumeration.DeviceInformation.FindAllAsync(Windows.Devices.Enumeration.DeviceClass.VideoCapture);
    String backCameraId = devices.FirstOrDefault(x => x.EnclosureLocation != null && x.EnclosureLocation.Panel == Windows.Devices.Enumeration.Panel.Back).Id;
    await _cameraPreviewImageSource.InitializeAsync(backCameraId); // use the back camera
    var previewProperties = await _cameraPreviewImageSource.StartPreviewAsync();
    fps = previewProperties.FrameRate.Numerator/previewProperties.FrameRate.Denominator;

    _cameraPreviewImageSource.PreviewFrameAvailable += drawPreview; // call the drawPreview method every time a new frame is available

    // Create a preview bitmap with the correct aspect ratio using the properties object returned when the preview started.
    var width = 640.0;
    var height = (width / previewProperties.Width) * previewProperties.Height;
    var bitmap = new WriteableBitmap((int)width, (int)height);
    _writeableBitmap = bitmap;

    // Create a BitmapRenderer to turn the preview Image Source into a bitmap we hold in the PreviewBitmap object
    _effect = new FilterEffect(_cameraPreviewImageSource);
    _effect.Filters = new IFilter[0]; // null filter for now
    _writeableBitmapRenderer = new WriteableBitmapRenderer(_effect, _writeableBitmap);
}


private async void drawPreview(IImageSize args)
{
    // Prevent multiple rendering attempts at once
    if (_isRendering == false)
    {
        _isRendering = true;
        await _writeableBitmapRenderer.RenderAsync(); // Render the image (with no filter)
        // Draw the image onto the previewImage XAML element
        await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.High,
            () =>
            {
                getPreview();
                previewImage.Source = _writeableBitmap; // previewImage is an image element in MainPage.xaml
                _writeableBitmap.Invalidate(); // force the PreviewBitmap to redraw
            });


        _isRendering = false;
    }
}

private void getPreview()
{
    var pixelBuffer = _writeableBitmap.PixelBuffer;

    for (uint i = 0; i + 4 < pixelBuffer.Length; i += 4)
    {
        var red = pixelBuffer.GetByte(i + 2);
    }
}
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1 回答 1

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在 Lumia Imaging SDK 处理完图像之后，而不是在使位图无效之前检查所有像素，您可以：

  • 立即使可写位图无效，然后在单独的异步任务中执行分析步骤。这意味着内容将立即显示，您的分析将单独完成。基于您的示例的一些伪代码将是：
    await Windows.ApplicationModel.Core.CoreApplication.MainView.CoreWindow.Dispatcher.RunAsync(CoreDispatcherPriority.High, () => {                
    var analysisTask = Task.Run(() => getPreview());

    previewImage.Source = _writeableBitmap; // previewImage is an image element in MainPage.xaml
    _writeableBitmap.Invalidate(); // force the PreviewBitmap to redraw

    await analysisTask;
    });

这样分析图像的任务就不会阻止屏幕上的更新。当然，如果您需要渲染链本身的分析结果，此选项可能不可行。

  • 为分析创建自定义过滤器，这样您就可以利用优化的 Lumia Imaging SDK 处理。

    要开始编写自定义过滤器，请查看文档。

于 2015-07-20T14:28:32.040 回答