Use the Filter Hook intermediate_image_sizes_advanced for control the resize function for different sizes. This hook get a array of different sizes and can control your resize with your requirements. Add your logic inside a plugin and remove sizes via this hook.

 // the hook in core
 $sizes = apply_filters( 'intermediate_image_sizes_advanced', $sizes );


A small example to remove the resize for mediumsize.

add_filter( 'intermediate_image_sizes_advanced', 'fb_filter_image_sizes');
function fb_filter_image_sizes( $sizes) {

    unset( $sizes['thumbnail']);

    return $sizes;
}


Stop image resizing in particular case - is that possible?
This question is similar to Is there a TikZ dashed line decorator or some other way to make part of a path dashed?.

What I want to draw: A node with a dashed loop, with a small node on the loop, and the part of the loop from the big node to the small one undashed.

How far I went:

\begin{tikzpicture}[scale=5]
  \draw node (n) [circle,fill] {} edge [dashed,loop above] node
  [fill,circle,minimum size=.4em,inner sep=0pt,pos=0.1] (s) {} ();
  \draw[-&gt;] (n) -- (s);
\end{tikzpicture}


The trouble with it being, of course, that the (n)--(s) path does not match the curvy path.  The solution of the previous question does not seem to help, as I want to work with a path resulting from a clipping (and I'm not sure to know how).
