convert - Converting orthophotomap to .ecw file?

I am looking for a method for convert orthophotomap (.adf files) to ERDAS .ecw file.

Have you got any ideas ?

Or maybe you have got any other idea how i can reduce a size of orthophotomap .adf files? Now i have got 16 GB file I want to compress it to something like 3-4GB- is it even possible?

I read that .ecw is highly compressed for raster formats...