Convert List<Bitmap> to byte array and store in xml c#

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I have a class of objects which I store in an xml file, a bitmap list is an object in this class. I'm trying to avoid having to store the bitmap list separately from the other objects. Hence, I convert the bitmap list into bytes (showed in code below) and want to read the byte array from the xml and send it to a list of Bitmaps. First I convert the list of bitmaps into bytes by:

C#

private byte[] BitmapToByteArray(List<Bitmap> bmp)
{
   MemoryStream ms = new MemoryStream();
   foreach(Bitmap item in bmp)
   {
    item.Save(ms, ImageFormat.Bmp);
   }
return ms.ToArray();
}

Now i am trying to create a function which does the reversal but I'm stuck:

C#

private List<Bitmap> ByteToBitmapList(byte[] byteArrayIn)
{
   MemoryStream ms = new MemoryStream(byteArrayIn);
   List<Bitmap> returnList = (List<Bitmap>)Image.FromStream(ms); //this is where I get an error
   return returnList;

How can I return the byte array to the bitmap list? Thanks in advance.

BTW: I'm also storing the bytes in xml because apparently you can't save Images/Bitmaps in xml. So I'm trying to read the byte[] from the xml file and convert it to a list of bitmaps

Posted 13-Nov-15 3:13am

Member 11971544

Updated 13-Nov-15 7:04am

v3

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BillWoodruff 13-Nov-15 9:34am

If your bitmaps are in some compressed format, have you considered using WCF to serialize them directly ?

Member 11971544 13-Nov-15 9:39am

I just updated the question. I'm actually storing the bitmaps(converted to byte[]) in an xml file

BillWoodruff 13-Nov-15 9:44am

Why would you want to store them in such an "expensive" (memory, computation time) format ? To transmit them "over the wire" ?

Member 11971544 13-Nov-15 9:53am

Just for clarity, what do you mean by "expensive"? I have a class of objects I store in the xml file, this bitmap list is part of it....trying to avoid having to store the list separately from the others.

BillWoodruff 13-Nov-15 11:52am

" I have a class of objects I store in the xml file, this bitmap list is part of it....trying to avoid having to store the list separately from the others."

That's important information; I suggest you edit your post to include that information; remember, the more we understand the context you are working in, the clearer our response can be.

I think if there's any way you can store the actual bitmap content "outside" the XML, that will be a win. Storing pointers to files is an idea comes to mind.

pietvredeveld 13-Nov-15 9:49am

What error do you get?

[no name] 13-Nov-15 10:07am

I understood above your question like you want to store the bitmap object in xml with help of converting bitmap to byte right

BillWoodruff 13-Nov-15 12:08pm

The code here by Marc Gravell (StackOverFlow principal) for using WCF to save Bitmap => Byte[] may interest you.

http://stackoverflow.com/a/9014624/133321

Member 11971544 13-Nov-15 13:06pm

Thanks Bill

2 solutions

Solution 2

I'll expect you get an InvalidCastException. FromStream returns an Image (just one) and you cast to an List<Bitmap>.

Furtermore you must dispose the memorystream like this:

C#

private Image ByteToBitmap(byte[] byteArrayIn)
{
   using (MemoryStream ms = new MemoryStream(byteArrayIn))
   {
       return Image.FromStream(ms); 
   }
}

Posted 13-Nov-15 3:56am

pietvredeveld

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jimmson · Accepted Answer · 2015-11-13T03:46:00

Hi,

you saving multiple bitmaps into one MemoryStream. If you want to work this, you need to create byte[][] instead of byte[]. Image.FromStream returns only one image.

C#

private byte[][] BitmapToByteArray(List<Bitmap> bmp)
{
    var res = new List<byte[]>();
    foreach (Bitmap item in bmp)
    {
        using (var ms = new MemoryStream())
        {
            item.Save(ms, ImageFormat.Bmp);
            res.Add(ms.ToArray());
        }
    }
    return res.ToArray();
}

C#

private List<Bitmap> ByteToBitmapList(byte[][] byteArrayIn)
{
    var res = new List<Bitmap>();
    foreach (byte[] img in byteArrayIn)
    {
        using (var ms = new MemoryStream(img))
        {
            var bitmap = (Bitmap)Image.FromStream(ms);
            res.Add(bitmap);
        }
    }
    return res;
}

Hope this helps,
Michal