Question

我从运行视频捕获一个帧并将其转换为SoftwareBitmap以用于进一步的目的。在此之前，我想将该框架裁剪成矩形。怎么可能？

        var thumbnail = await GetThumbnailAsync(file,seek_position);
        StringBuilder ocr=null;
        InMemoryRandomAccessStream randomAccessStream = new InMemoryRandomAccessStream();
        await RandomAccessStream.CopyAsync(thumbnail, randomAccessStream);
        randomAccessStream.Seek(0);      
        SoftwareBitmap inputBitmap;
        BitmapDecoder decoder = await BitmapDecoder.CreateAsync(randomAccessStream);
        // Get the SoftwareBitmap representation of the file
        inputBitmap = await decoder.GetSoftwareBitmapAsync();
       //crop inputBitmap

  public async Task<IInputStream> GetThumbnailAsync(StorageFile file,int i)
    {
        //int duration_millisecond = i * 1000;
        var mediaClip = await MediaClip.CreateFromFileAsync(file);
        var mediaComposition = new MediaComposition();
        mediaComposition.Clips.Add(mediaClip);
        return await mediaComposition.GetThumbnailAsync(
        TimeSpan.FromMilliseconds(i), 0, 0, VideoFramePrecision.NearestFrame);
    }

Answer 1

BitmapDecoder对象的GetSoftwareBitmapAsync方法有几个重载方法。您可以使用GetSoftwareBitmapAsync(BitmapPixelFormat, BitmapAlphaMode, BitmapTransform, ExifOrientationMode, ColorManagementMode)方法裁剪软件位图。您只需要为它定义一个BitmapTransform对象。

请参阅以下代码示例：

SoftwareBitmap inputBitmap;
BitmapDecoder decoder = await BitmapDecoder.CreateAsync(randomAccessStream);
// Get the SoftwareBitmap representation of the file
inputBitmap = await decoder.GetSoftwareBitmapAsync(decoder.BitmapPixelFormat,BitmapAlphaMode.Ignore,new BitmapTransform() {Bounds=new BitmapBounds() {X=100,Y=200,Width=200,Height=100 } },ExifOrientationMode.IgnoreExifOrientation,ColorManagementMode.DoNotColorManage);

您只需要为其Bounds属性指定一个新的BitmapBounds。

请注意，在此步骤中，您有一个裁剪的软件位图，但如果您想使用它初始化SoftwareBitmapSource并将其显示在Image控件中。您将收到异常“ SetBitmapAsync仅支持具有正宽度/高度，bgra8像素格式和预乘或无alpha 的SoftwareBitmap。”。您需要使用SoftwareBitmap _softbitmap = SoftwareBitmap.Convert()创建一个新的软件位图，如下所示：

SoftwareBitmap _softbitmap = SoftwareBitmap.Convert(inputBitmap,BitmapPixelFormat.Bgra8,BitmapAlphaMode.Premultiplied);
var source = new SoftwareBitmapSource();
await source.SetBitmapAsync(_softbitmap);
image.Source = source; //image is a Image control

如何裁剪矩形的软件位图 - UWP

1 个答案: