Ah, I don't know. But I can tell you that ImageMagick is going to be a better tool for that. You'll want to look into the convert or mogrify utilities that are part of that package.
cbell@circe:~$ dpkg -s imagemagick
Status: install ok installed
Replaces: geomview (<= 1.8.0), imagemagick-doc
Depends: libbz2-1.0, libc6 (>= 2.7-1), libfontconfig1 (>= 2.4.0), libfreetype6 (>= 2.3.5), libice6 (>= 1:1.0.0), libjpeg62, liblcms1 (>= 1.15-1), libmagick10, libsm6, libtiff4, libx11-6, libxext6, libxt6, zlib1g (>= 1:1.1.4)
Description: image manipulation programs
Imagemagick is a set of programs to manipulate various image formats
(JPEG, TIFF, PhotoCD, PBM, XPM, etc...). All manipulations can
be achieved through shell commands as well as through an X11 graphical
Possible effects: colormap manipulation, channel operations, thumbnail
creation, image annotation, limited drawing, image distortion, etc...