Difference between Bitmap.FromFile(path) and new Bitmap(path)

Question

I woud like to know the difference between these two:

Bitmap bitmap1 = new Bitmap("C:\\test.bmp");
Bitmap bitmap2 = (Bitmap) Bitmap.FromFile("C:\\test.bmp");

Is one option better than the other one? Does Bitmap.FromFile(path) fills in any additional data to the bitmap image or is it just a delegate to new Bitmap(path)?

Answer 1

The 'FromFile' method comes from the abstract base class Image, which returns an Image object. Whereas the Bitmap class inherits the Image class, and the Bitmap constructor allows you to initialize Bitmap object directly.

In your second line of code, what you are trying to do is call FromFile() and get an Image object, and then type cast it to Bitmap. There's not really a good reason to do this manually, when the bitmap constructor can do it for you.

Answer 2

Both methods get a handle to the image via the path argument. Image.FromFile will return the superclass Image, while the former will simply return the Bitmap so you can avoid the cast.

Internally, they pretty much do the same:

public static Image FromFile(String filename,
                                     bool useEmbeddedColorManagement)
{

    if (!File.Exists(filename)) 
    {
        IntSecurity.DemandReadFileIO(filename);
        throw new FileNotFoundException(filename);
    }

    filename = Path.GetFullPath(filename);

    IntPtr image = IntPtr.Zero;
    int status;

    if (useEmbeddedColorManagement) 
    {
        status = SafeNativeMethods.Gdip.GdipLoadImageFromFileICM(filename, out image);
    }
    else 
    {
        status = SafeNativeMethods.Gdip.GdipLoadImageFromFile(filename, out image);
    }

    if (status != SafeNativeMethods.Gdip.Ok)
        throw SafeNativeMethods.Gdip.StatusException(status);

    status = SafeNativeMethods.Gdip.GdipImageForceValidation(new HandleRef(null, image));

    if (status != SafeNativeMethods.Gdip.Ok)
    {
        SafeNativeMethods.Gdip.GdipDisposeImage(new HandleRef(null, image));
        throw SafeNativeMethods.Gdip.StatusException(status);
    }

    Image img = CreateImageObject(image);
    EnsureSave(img, filename, null);

    return img;
}

And:

public Bitmap(String filename) 
{
    IntSecurity.DemandReadFileIO(filename);
    filename = Path.GetFullPath(filename);

    IntPtr bitmap = IntPtr.Zero;

    int status = SafeNativeMethods.Gdip.GdipCreateBitmapFromFile(filename, out bitmap);

    if (status != SafeNativeMethods.Gdip.Ok)
        throw SafeNativeMethods.Gdip.StatusException(status);

    status = SafeNativeMethods.Gdip.GdipImageForceValidation(new HandleRef(null, bitmap));

    if (status != SafeNativeMethods.Gdip.Ok) 
    {
        SafeNativeMethods.Gdip.GdipDisposeImage(new HandleRef(null, bitmap));
        throw SafeNativeMethods.Gdip.StatusException(status);
    }

    SetNativeImage(bitmap);

    EnsureSave(this, filename, null);
}