recent versions of Imagemagick's convert won't auto-recognize the xwd format from a pipe, hence the xwd:- helper.
The beauty is that you can screenshot remote displays, can do the entire screen, windows, or regions, have the entire image-editing power of Imagemagick available, and can end up with any supported image format.
xwd | convert xwd:- somename.someformat
recent versions of Imagemagick's convert won't auto-recognize the xwd format from a pipe, hence the xwd:- helper.
The beauty is that you can screenshot remote displays, can do the entire screen, windows, or regions, have the entire image-editing power of Imagemagick available, and can end up with any supported image format.