调整图像大小并保存图像，同时保留元数据

Question

我正在尝试调整图像大小并保存图像，这相当简单（例如，查看此示例外部示例不再有效）。

但是，使用此代码会从图像中剥离元数据信息。我似乎不太清楚如何保留 jpeg 图像的元数据。

编辑：示例代码

public static void ResizeMethodThree(string sourceFile, string targetFile)
{
    byte[] baSource = File.ReadAllBytes(sourceFile);

    PropertyItem[] propertyItems = new Bitmap(sourceFile).PropertyItems;

    using (Stream streamPhoto = new MemoryStream(baSource))
    {
        BitmapFrame bfPhoto = ReadBitmapFrame(streamPhoto);
        BitmapMetadata metaData = (BitmapMetadata)bfPhoto.Metadata;
        int nNewPictureSize = 200;
        int nWidth = 0;
        int nHeight = 0;

        if (bfPhoto.Width > bfPhoto.Height)
        {
            nWidth = nNewPictureSize;
            nHeight = (int)(bfPhoto.Height * nNewPictureSize / bfPhoto.Width);
        }
        else
        {
            nHeight = nNewPictureSize;
            nWidth = (int)(bfPhoto.Width * nNewPictureSize / bfPhoto.Height);
        }        

        BitmapFrame bfResize = ResizeHelper(bfPhoto, nWidth, nHeight, BitmapScalingMode.HighQuality);

        byte[] baResize = ToByteArray(bfResize);

        File.WriteAllBytes(targetFile, baResize);

        Image targetImage = new Bitmap(targetFile);
        foreach (var propertyItem in propertyItems)
        {
            targetImage.SetPropertyItem(propertyItem);
        }

        targetImage.Save(targetFile);
    }
}

public static BitmapFrame ResizeHelper(BitmapFrame photo, int width, 
                                       int height, BitmapScalingMode scalingMode)
{

    var group = new DrawingGroup();
    RenderOptions.SetBitmapScalingMode(
        group, scalingMode);
    group.Children.Add(
        new ImageDrawing(photo,
            new Rect(0, 0, width, height)));
    var targetVisual = new DrawingVisual();
    var targetContext = targetVisual.RenderOpen();
    targetContext.DrawDrawing(group);
    var target = new RenderTargetBitmap(
        width, height, 96, 96, PixelFormats.Default);
    targetContext.Close();
    target.Render(targetVisual);
    var targetFrame = BitmapFrame.Create(target);
    return targetFrame;
}

private static byte[] ToByteArray(BitmapFrame bfResize)
{
    using (MemoryStream msStream = new MemoryStream())
    {
        JpegBitmapEncoder jpgEncoder = new JpegBitmapEncoder();
        jpgEncoder.Frames.Add(bfResize);
        jpgEncoder.Save(msStream);
        return msStream.ToArray();
    }
}

private static BitmapFrame ReadBitmapFrame(Stream streamPhoto)
{
    BitmapDecoder bdDecoder = 
        BitmapDecoder.Create(streamPhoto, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.None);
    return bdDecoder.Frames[0];
}

Answer 1

使用源图像上的 Image.PropertyItems 属性来获取元数据项的列表。循环列表，在目标图像上调用 Image.SetPropertyItem。通常应避免调整 jpeg 图像的大小和重新压缩，使用未压缩的原始图像最好保持质量并避免伪影。