windows phone 8.1显示PreviewFrame并计算每帧的红色像素的平均值

当前我正在使用Lumia.Imaging获取预览帧并显示它。windows phone 8.1显示PreviewFrame并计算每帧的红色像素的平均值

我创建了新的方法“GetPreview（）”去像素，找到红色像素，比我想计算每帧的红色像素的平均值。

我的问题是，当我经历像素有在app :(

什么是正确的解决方案来计算，每帧红色像素平均值，而不损失性能滞后？

附加如何在闪光灯开启预览启动时？

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); 
    } 
}

来源

2015-07-20 Mati

相反检查的Lumia成像SDK毕竟像素的已处理的图像，但你无效位之前还是可以：

无效可写的位图imidiatelly然后做你的分析步骤中的一个单独的异步任务。这意味着内容将立即显示，您的分析将独立完成。根据您的样本伪代码将是：

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; 
    });

这样分析图像不会阻止在屏幕上的更新任务。当然，如果您需要渲染链本身的分析结果，则此选项可能不可行。

为分析创建自定义过滤器，这样你就可以采取优化的Lumia成像SDK处理的优势。

要开始编写自定义过滤器look at the documentation。

来源

2015-07-20 14:28:32

windows phone 8.1显示PreviewFrame并计算每帧的红色像素的平均值

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