上载具有ftp松散透明度的png图片

Question

In my c# application, I'm trying to upload an png image using ftp, the problem is I loose transparency (the transparent area turn to black!).

PS : The image I send is stored in an Sql Server database, and they look fine in my application. Here is the code I use :

private const int defultbuffersize = 1024 * 60;

public void UploadImage(Image image, string uri, string filename)
{
    var request = WebRequest.Create(String.Format(@"{0}/{1}", uri, filename)) as FtpWebRequest;

    if (request == null)
        return;

    request.Method = WebRequestMethods.Ftp.UploadFile;
    request.Credentials = new NetworkCredential("userName", "password");
    request.UsePassive = true;
    request.UseBinary = true;
    request.KeepAlive = true;

    using (var writer = request.GetRequestStream())
    {
        var bytesData = image.ToByteArray();
        var position = 0;

        while (position < bytesData.Length)
        {
            var buffer = readData(bytesData, position);
            writer.Write(buffer, 0, buffer.Length);
            position += buffer.Length;
        }
    }
}

private static byte[] readData(byte[] bytesData, int position)
{
    var buffer = new byte[defultbuffersize];
    var lenght = position + defultbuffersize > bytesData.Length ?
        bytesData.Length - position : defultbuffersize;

    Array.Copy(bytesData.ToArray(), position, buffer, 0, lenght);
    return buffer;
}

Extension method in an other class

public static byte[] ToByteArray(this Image image)
{
    var stream = new MemoryStream();
    image.Save(stream, ImageFormat.Jpeg);
    return stream.ToArray();
}

Thanks in advance

Answer 1

The reason you lose transparency is found in your extension method

public static byte[] ToByteArray(this Image image)
{
    var stream = new MemoryStream();
    image.Save(stream, ImageFormat.Jpeg);
    return stream.ToArray();
}

You are trying to serialize an png image using jpeg format

Change the extension method to this.

public static byte[] ToByteArray(this Image image)
{
    var stream = new MemoryStream();
    image.Save(stream, ImageFormat.Png);
    return stream.ToArray();
}

This should fix your transparency problem.