JpegBitmapEncoder.Save() throws exception when wri

问题:

I am trying to set up metadata on JPG image what does not have it. You can't use in-place writer (InPlaceBitmapMetadataWriter) in this case, cuz there is no place for metadata in image.

If I use FileStream as output - everything works fine. But if I try to use MemoryStream as output - JpegBitmapEncoder.Save() throws an exception (Exception from HRESULT: 0xC0000005). After some investigation I also found out what encoder can save image to memory stream if I supply null instead of metadata.

I've made a very simplified and short example what reproduces the problem:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO;

using System.Drawing;
using System.Drawing.Imaging;
using System.Windows.Media.Imaging;

namespace JpegSaveTest
{
    class Program
    {
        public static JpegBitmapEncoder SetUpMetadataOnStream(Stream src, string title)
        {
            uint padding = 2048;
            BitmapDecoder original;
            BitmapFrame framecopy, newframe;
            BitmapMetadata metadata;
            JpegBitmapEncoder output = new JpegBitmapEncoder();
            src.Seek(0, SeekOrigin.Begin);
            original = JpegBitmapDecoder.Create(src, BitmapCreateOptions.PreservePixelFormat, BitmapCacheOption.OnLoad);
            if (original.Frames[0] != null) {
                framecopy = (BitmapFrame)original.Frames[0].Clone();
                if (original.Frames[0].Metadata != null) metadata = original.Frames[0].Metadata.Clone() as BitmapMetadata;
                else metadata = new BitmapMetadata("jpeg");
                metadata.SetQuery("/app1/ifd/PaddingSchema:Padding", padding);
                metadata.SetQuery("/app1/ifd/exif/PaddingSchema:Padding", padding);
                metadata.SetQuery("/xmp/PaddingSchema:Padding", padding);
                metadata.SetQuery("System.Title", title);
                newframe = BitmapFrame.Create(framecopy, framecopy.Thumbnail, metadata, original.Frames[0].ColorContexts);
                output.Frames.Add(newframe);
            }
            else {
                Exception ex = new Exception("Image contains no frames.");
                throw ex;
            }
            return output;
        }

        public static MemoryStream SetTagsInMemory(string sfname, string title)
        {
            Stream src, dst;
            JpegBitmapEncoder output;
            src = File.Open(sfname, FileMode.Open, FileAccess.Read, FileShare.Read);
            output = SetUpMetadataOnStream(src, title);
            dst = new MemoryStream();
            output.Save(dst);
            src.Close();
            return (MemoryStream)dst;
        }

        static void Main(string[] args)
        {
            string filename = "Z:\\dotnet\\gnom4.jpg";
            MemoryStream s;
            s = SetTagsInMemory(filename, "test title");
        }
    }
}

It is simple console application. To run it, replace filename variable content with path to any .jpg file without metadata (or use mine).

Ofc I can just save image to temporary file first, close it, then open and copy to MemoryStream, but its too dirty and slow workaround. Any ideas about getting this working are welcome :)

回答1:

In case someone will encounter same issue, here is the solution:

If you try to .Save() jpeg from main application thread, add [STAThread] before Main().

If not, call .SetApartmentState(ApartmentState.STA) for the thread calling JpegBitmapEncoder.Save()

WinXP and WinVista versions of windowscodecs.dll are not reenterable, so if you will use default MTA model (it is default since .NET framework 2.0) for threads calling JpegBitmapEncoder.Save() function, it can behave strangely and throw described exception. Win7 version of windowscodecs.dll does not have this issue.

回答2:

I ran your code without modifications and it didn't throw an error. I even tried saving the modified data to disk and the image itself was uncorrupted.

string filename = "e:\\a.jpg";
        MemoryStream s;
        s = SetTagsInMemory(filename, "test title");
        FileStream fs = new FileStream("e:\\b.jpg", FileMode.CreateNew, FileAccess.ReadWrite);
        BinaryWriter sw = new BinaryWriter(fs);
        s.Seek(0, SeekOrigin.Begin);
        while (s.Position < s.Length)
       {
            byte[] data = new byte[4096];
            s.Read(data, 0, data.Length);
            sw.Write(data);
       }

        sw.Flush();
        sw.Close();
        fs.Close();

Other than what I added below s = SetTagsInMemory(...) to write to disk, the rest of your code is unmodifed.

Edit: oh and the metadeta definatly ended up in the new file, previous one didn't have any metadata from what I could see.