Re: convert erroneously returns blank image

>convert -crop 1x2+150+150@ +repage +adjoin img.png img-%d.png
>
>Then I rotate each piece like so:
>
>convert -rotate -90 img-0.png img-0-rotated.png
>convert -rotate -90 img-1.png img-1-rotated.png


Try putting the input image right after convert (in all three 
commands) and the +repage just before the output in the first command.

see  http://www.imagemagick.org/Usage/basics/#why