LaTeX: leave image size as is?

Currently, if neither width nor height is given the image will scale to *texwidth* x 0.75% *textheight*:

\includegraphics[keepaspectratio,width=\textwidth,height=0.75\textheight]{/path/to/image.png}

That's good for big images. On the other hand, small images scale up.

**Suggestion**: if the image has no size given leave it as is.