Weird binary formatter behaviour

Question

I have a struct with an array of images :

public struct ObjectImages
{

    public System.Drawing.Image[] _images;
    public ObjectImages(System.Drawing.Image[] images)
    {
          _images = images; 
    }

}

If I put two images of 10 kb in the object and then try to serialize, I found that my memory stream target have 160kb. I verified,each image have ~10-11kb.

ObjectImages o = new ObjectImages(x); // where x is an array of images from my webcam
MemoryStream ms = new MemoryStream();
BinaryFormatter formatter = new BinaryFormatter();
formatter.Serialize(ms, o); 

I found that really strange! Can you please tell me if you know where is the problem?

Answer 1

Well, when you see the image on your hard disk, it is compressed - for example as PNG or JPEG file. When you load the image in C#, it is decompressed, so the pixels can be rendered. So in reality, the image consists of more bytes than are stored on your hard disk.

The C# object contains the uncompressed data, so roughly (for RGBA images), the size in memory should be (4 * width * height) + further data needed by .NET. The binary formatter does not save the image (as PNG or JPEG), it saves the object that represents the image.