How do I reliably get an image dimensions in .NET without loading the image?

Question

I know how to get the size (x,y) of an image

Image.FromFile(\"cat.jpg\").Size

BUT that requires loading the image from memory.

When

Answer 1

Doing this usually involves actually opening the file and reading only its header (the first few bytes) to find its format and the size. You don't need to read the whole file to find out it's size. Sometimes the size is even in a specific offset in the file so finding the size is only reading 8 bytes.

You can use filemon.exe to actually find out what windows explorer itself does to find the size.