c# - JpegBitmapEncoder.Save() 在使用元数据写入图像时抛出异常

Question

我正在构建一个 WPF 桌面应用程序来帮助我组织照片以发布到 Facebook。这是我在新位置创建照片副本并添加了标题 (EXIF + IPTC + XMP) 的代码:

    private void SaveImageAs(string currPath, string newPath, bool setCaption = false, string captionToSet = "")
    {
        System.IO.FileStream stream = new System.IO.FileStream(currPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
        JpegBitmapDecoder decoder = new JpegBitmapDecoder(stream, BitmapCreateOptions.None, BitmapCacheOption.None);
        BitmapFrame bitmapFrame = decoder.Frames[0];
        BitmapMetadata metadata = bitmapFrame.Metadata.Clone() as BitmapMetadata;
        stream.Close();

        if (setCaption)
        {
            // if we want to set the caption, do it in EXIF, IPTC, and XMP

            metadata.SetQuery("/app1/ifd/{uint=270}", captionToSet);
            metadata.SetQuery("/app13/irb/8bimiptc/iptc/Caption", captionToSet);
            metadata.SetQuery("/xmp/dc:description/x-default", captionToSet);
        }

        MemoryStream memstream = new MemoryStream();   // create temp storage in memory
        JpegBitmapEncoder encoder = new JpegBitmapEncoder();
        encoder.Frames.Add(BitmapFrame.Create(bitmapFrame, bitmapFrame.Thumbnail, metadata, bitmapFrame.ColorContexts));
        encoder.Save(memstream);   // save in memory
        stream.Close();

        stream = new FileStream(newPath, FileMode.OpenOrCreate, FileAccess.Write, FileShare.ReadWrite);
        memstream.Seek(0, System.IO.SeekOrigin.Begin);    // go to stream start
        byte[] bytes = new byte[memstream.Length + 1];
        memstream.Read(bytes, 0, (int)memstream.Length);
        stream.Write(bytes, 0, bytes.Length);
        stream.Close();
        memstream.Close();
    }

运行它，我得到一个“COMException was unhandled”异常突出显示这一行:

encoder.Save(memstream);

An unhandled exception of type 'System.Runtime.InteropServices.COMException' occurred in PresentationCore.dll

Additional information: The handle is invalid. (Exception from HRESULT: 0x80070006 (E_HANDLE))

我看到了here这可能是由于线程问题，所以我没有直接从应用程序调用 SaveImageAs，而是添加了这个，但没有效果:

        private void _SaveImageAs(string currPath, string newPath, bool setCaption = false, string captionToSet = "")
    {
        Thread saveThread = new Thread(() => SaveImageAs(currPath, newPath, setCaption, captionToSet));
        saveThread.SetApartmentState(ApartmentState.STA);
        saveThread.IsBackground = false;
        saveThread.Start();
    }

我还尝试将 MemoryStream 换成 FileStream，创建一个本地临时文件——这并没有改变任何东西:

FileStream memstream = new FileStream(System.IO.Path.GetDirectoryName(newPath) + @"\" + "temp.jpg", System.IO.FileMode.OpenOrCreate);

有什么想法吗？

Answer 1

您的代码中有一些错误。

1. 源流必须保持打开状态，直到将 BitmapFrame 写入目标流。

2. 来自 BitmapDecoder 的 BitmapFrame 的图像元数据是只读的。当您想要修改元数据时，您必须从原始的 BitmapFrame 创建一个新的 BitmapFrame。

3. 第三个查询似乎已损坏。异常显示“找不到属性”。

这段代码对我有用:

public static void SaveImageAs(string sourcePath, string targetPath, string caption)
{
    using (var sourceStream = new FileStream(sourcePath, FileMode.Open, FileAccess.Read, FileShare.Read))
    {
        var decoder = new JpegBitmapDecoder(sourceStream, BitmapCreateOptions.None, BitmapCacheOption.None);
        var frame = decoder.Frames[0];

        if (!string.IsNullOrWhiteSpace(caption))
        {
            frame = BitmapFrame.Create(frame);
            var metadata = (BitmapMetadata)frame.Metadata;

            metadata.SetQuery("/app1/ifd/{uint=270}", caption);
            metadata.SetQuery("/app13/irb/8bimiptc/iptc/Caption", caption);
            //metadata.SetQuery("/xmp/dc:description/x-default", caption);
        }

        var encoder = new JpegBitmapEncoder();
        encoder.Frames.Add(frame);

        using (var targetStream = new FileStream(targetPath, FileMode.Create))
        {
            encoder.Save(targetStream);
        }
    }
}