Possible Duplicate:
Shrink figure only when necessary?
Consider that you have this:
\includegraphics{some_image_in_pdf.pdf}
This will now take its original width, but if you want it to take up 100% of the text width you do it like this:
\includegraphics[width=\textwidth]{some_image_in_pdf.pdf}
How about if you want to include images and use their original size if they fit, otherwise have it resized?
In this example, the second image should get [width=\textwidth] because it is going to exceed the bounds of the document.
\includegraphics{some_image_in_pdf.pdf}
\includegraphics{some_image_in_pdf_that_is_too_wide.pdf}
twocolumnmode you're probably interested inmax width=\columnwidth. – Werner Nov 22 '15 at 12:24