An MPEG encoder performs, in compliance with the MPEG-2 standard, intra-image coding compression on thumbnail images, selected by an image selector, whose data amount has been reduced by a data reducing unit. Specifically, a polyamide acid containing a chlorine atom and a fluorine atom and comprising a repeating unit represented by the following formula : } bonded to the relevant benzene ring, representing an integer of 0-3; q and q\u2032 independently denote an integer of 0-3; and p+q total 3, and p\u2032+q\u2032 total 3). Protection typically embodies the safe distribution of ESD current to ground during user printhead installation.