# Reducing the REAL size of an image (compressing) when using \includegraphics

I know when downscaling images we can just use the scale option. But as far as I know, this doesn't change the size of the overall output (let's say the PDF file).

\begin{figure}
\centering
\includegraphics[trim=1cm 6.1cm 6cm 14.0cm, clip=true, scale=0.3]{figs3.pdf}
\caption{The averaging blocks with $W=2$.}
\label{fig:theAvgBlock}
\end{figure}

1. Is there anyway to compress the figure when we downscale using scale option?
2. When we trim the figure, and clip=true, does it through away the extra parts? In other words, does it decrease the size of the figure?
3. Is there anyway to compress images inside Latex ?

The original problem is that I am using zoombox to include magnified subfigures of a BIG image, but I want to put a figure with smaller size instead of the full high-quality figure. (because of size limitation) At the same time, I want the magnified figures to be from the high-quality figure. Any ideas how to do this?

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I suppose that technically you could use \DeclareGraphicsRule to do this if, say, you had a bunch of .gif files which were twice the size you needed. You could set up your conversion command to not only convert the images to a format latex could use but also to reduce their size to 50%. This would be a pretty unusual kind of situation, though, and it would be far easier and far more transparent to just handle it as part of your pre-processing than to try running it as part of your tex code. –  cfr Jan 5 '14 at 0:07
Can you give me a pointer to a sample code? –  Daniel Jan 5 '14 at 0:11
It was really just a wild idea. I don't know of anybody who has done it. I wouldn't recommend it either. However, if you want I can probably post something if that would really be useful. At least, something which would work on GNU/Linux or OS X. I don't know if conversion is done in the same way on Windows so it would likely need to be adapted in that case. –  cfr Jan 5 '14 at 0:14
Also, for some reason I can't figure out how to adapt DeclareGraphicsRule to GNU/Linux although it seems to me it should work just the same as on OS X! –  cfr Jan 5 '14 at 1:03