如何调整一个SoftwareBitmap的大小？

Question

SoftwareBitmap是UWP中的新功能。以下是简单介绍：

var softwareBitmap = EXTERNALVALUE;

// do I even need a writeable bitmap?
var writeableBitmap = new WriteableBitmap(softwareBitmap.PixelWidth, softwareBitmap.PixelHeight);
softwareBitmap.CopyToBuffer(writeableBitmap.PixelBuffer);

// maybe use BitmapDecoder?

我感到困惑。谢谢。

请注意，我指的不是 BitmapImage，而是 SoftwareBitmap。

- Jerry Nixon

---

那可以是任何语言。调整图像大小并不简单。这里有一些C语言算法：https://github.com/MalcolmMcLean/babyxrc/tree/master/src - Malcolm McLean

我过去使用过ImageMagick来完成这个任务。这是相当简单的 https://magick.codeplex.com/ - big_water

也许可以查看BitmapTransform的ScaledHeight和ScaledWidth方法？https://msdn.microsoft.com/library/windows/apps/br226254#methods 我不是很懂这个领域，只是猜测一下。 - JohnLBevan

请注意，我指的不是BitmapImage，而是SoftwareBitmap。 - Jerry Nixon

你有看过ScaleEffect吗？我想我在某个地方有一个样例，不过得去找找。 - Romasz

不行，如果你想在内存中调整图像大小，ScaleEffect 似乎无法帮助，但如果你想显示调整大小后的图像，它可能会起作用。保持图像原始大小，然后通过 CanvasControl 显示时进行缩放。 - Romasz

Answer 1

我尝试使用ScaleEffect，并得出了以下扩展方法。实际上这个方法还需要更多的工作，但也许它能帮助你在某种程度上更进一步。

public static SoftwareBitmap Resize(this SoftwareBitmap softwareBitmap, float newWidth, float newHeight)
{
    using (var resourceCreator = CanvasDevice.GetSharedDevice())
    using (var canvasBitmap = CanvasBitmap.CreateFromSoftwareBitmap(resourceCreator, softwareBitmap))
    using (var canvasRenderTarget = new CanvasRenderTarget(resourceCreator, newWidth, newHeight, canvasBitmap.Dpi))
    using (var drawingSession = canvasRenderTarget.CreateDrawingSession())
    using (var scaleEffect = new ScaleEffect())
    {
        scaleEffect.Source = canvasBitmap;
        scaleEffect.Scale = new System.Numerics.Vector2(newWidth / softwareBitmap.PixelWidth, newHeight / softwareBitmap.PixelHeight);
        drawingSession.DrawImage(scaleEffect);
        drawingSession.Flush();
        return SoftwareBitmap.CreateCopyFromBuffer(canvasRenderTarget.GetPixelBytes().AsBuffer(), BitmapPixelFormat.Bgra8, (int)newWidth, (int)newHeight, BitmapAlphaMode.Premultiplied);
    }
}

- Romasz

Answer 2

看起来像是一个支架，但它可能会解决你的问题：

    private async Task<SoftwareBitmap> ResizeSoftwareBitmap(SoftwareBitmap softwareBitmap, double scaleFactor)
    {
        var resourceCreator = CanvasDevice.GetSharedDevice();
        var canvasBitmap = CanvasBitmap.CreateFromSoftwareBitmap(resourceCreator, softwareBitmap);
        var canvasRenderTarget = new CanvasRenderTarget(resourceCreator, (int)(softwareBitmap.PixelWidth * scaleFactor), (int)(softwareBitmap.PixelHeight * scaleFactor), 96);

        using (var cds = canvasRenderTarget.CreateDrawingSession())
        {
            cds.DrawImage(canvasBitmap, canvasRenderTarget.Bounds);
        }

        var pixelBytes = canvasRenderTarget.GetPixelBytes();

        var writeableBitmap = new WriteableBitmap((int)(softwareBitmap.PixelWidth * scaleFactor), (int)(softwareBitmap.PixelHeight * scaleFactor));
        using (var stream = writeableBitmap.PixelBuffer.AsStream())
        {
            await stream.WriteAsync(pixelBytes, 0, pixelBytes.Length);
        }

        var scaledSoftwareBitmap = new SoftwareBitmap(BitmapPixelFormat.Bgra8, (int)(softwareBitmap.PixelWidth * scaleFactor), (int)(softwareBitmap.PixelHeight * scaleFactor));
        scaledSoftwareBitmap.CopyFromBuffer(writeableBitmap.PixelBuffer);

        return scaledSoftwareBitmap;
    }

您需要从Nuget获取Win2D包。

- Jet Chopper

Answer 3

这里我将一个图像文件缩小为100x100的SoftwareBitmap，并将其作为ImageSource返回。

既然你已经拥有了一个SoftwareBitmap，我认为你的任务会更容易。但希望这能给你一些想法。

我们只需要WritableBitmap的PixelBuffer来初始化我们新缩放的SoftwareBitmap实例。如果你可以直接从我们拥有的字节数组像素数据（本地变量pixels）创建一个IBuffer，则可以直接将其提供给SoftwareBitmap.CreateCopyFromBuffer()方法。在那种情况下，就不需要WritableBitmap了。

以下是代码：

private async Task<ImageSource> ProcessImageAsync(StorageFile ImageFile)
    {
        if (ImageFile == null)
            throw new ArgumentNullException("ImageFile cannot be null.");

        //The new size of processed image.
        const int side = 100;

        //Initialize bitmap transformations to be applied to the image.
        var transform = new BitmapTransform() { ScaledWidth = side, ScaledHeight = side, InterpolationMode = BitmapInterpolationMode.Cubic };

        //Get image pixels.
        var stream = await ImageFile.OpenStreamForReadAsync();
        var decoder = await BitmapDecoder.CreateAsync(stream.AsRandomAccessStream());
        var pixelData = await decoder.GetPixelDataAsync(BitmapPixelFormat.Bgra8, BitmapAlphaMode.Premultiplied, transform, ExifOrientationMode.RespectExifOrientation, ColorManagementMode.ColorManageToSRgb);
        var pixels = pixelData.DetachPixelData();

        //Initialize writable bitmap.
        var wBitmap = new WriteableBitmap((int)decoder.PixelWidth, (int)decoder.PixelHeight);
        await wBitmap.SetSourceAsync(stream.AsRandomAccessStream());

        //Create a software bitmap from the writable bitmap's pixel buffer.
        var sBitmap = SoftwareBitmap.CreateCopyFromBuffer(wBitmap.PixelBuffer, BitmapPixelFormat.Bgra8, side, side, BitmapAlphaMode.Premultiplied);

        //Create software bitmap source.
        var sBitmapSource = new SoftwareBitmapSource();
        await sBitmapSource.SetBitmapAsync(sBitmap);

        return sBitmapSource;
    }

我知道这句话不应该成为答案的一部分，但我必须说，我从你的MVA和Channel9视频中学到了很多关于XAML/C#和开发Windows Store应用程序的知识！ :)

- Vijay Chavda

---

这个贵吗？ - Jerry Nixon

虽然我最初的做法也行，但后来我发现有更直截了当的方法。我又问了一个关于调整大小和灰度化 SoftwareBitmap 的问题。你可以看看这个（https://stackoverflow.com/a/45393902/4062881）回答，从性能上来说比我的好。 - Vijay Chavda

@JerryNixon-MSFT 你也可以使用Lumia Imaging SDK - https://msdn.microsoft.com/zh-cn/library/mt598502.aspx。它很棒！ - Vijay Chavda