A web-based image to PTC QR generator for Petit Computer. Choose a file from your computer (again, this is image > GRP, not the other way around) and generate QR codes directly.
This won't suffer from the same problems as PTCUtilities, but it can only be used to edit/create GRP files.
Link: http://www.geocities.jp/obono_kun/storage/petitcom_util/ptcm_grp_exporter.html
Link (Archived): https://web.archive.org/web/20151002235340/http://www.geocities.jp/obono_kun/storage/petitcom_util/ptcm_grp_exporter.html
See also PetitEditor
(Created by OBONO. See http://petitcomputer.wikia.com/wiki/Japanese_User%27s_Link "OBONO's Dairy / Petitcom (by OBONO)" )