Best Way to find Image Resolution?

[Airw0lf]

I am currently finding the resolution of an image as follows:

System::Drawing::Image *img;

img = System::Drawing::Image::FromFile(fn);

I can then make use of img->Width, img->Height etc. The problem is that
this process is really quite slow, especially when traversing a directory
with thousands of very large pictures. (takes several minutes usually) I
think this is because my code actually loads the whole image into memory,
which is unnecessary.

I wonder if there is a more efficient way? For example, if you browse a
directory in windows explorer, you can bring up a column and sort by image
dimensions. Yet it only takes a few seconds to do this in explorer.