is there an image package that doesn't require Tk ?

I'd like it to open a .png file (screenshot from an android
phone) extract five rectangular regions from it, and convert
them to something similar to Tk's [$image data] - e.g. a list
of lists of colors

For now, I use "image photo" to scrape(simple ocr) some numbers
from it, but it only works with Tk.  In the end I want to do
the processing of the image in the same cron-script that gets
the screenshot from the phone.

If nothing else, I'd "convert" (from Imagemagick) the png to
something I can easier parse in Tcl.