I have a lot of images which has been imported from SQL dump with utf-8 encoding. Thus, instead of "FF D8 FF E0" I see "C3 BF C3 98 C3 BF C3 A0" in the beginning of jpeg images.
I've tried iconv('utf-8', 'iso-8859-1', $data) but it not converts whole file (there is chars in utf-8 which can not be converted to iso-8859-1.
How I can to convert utf-8 simple to one-byte binary with unrespect to encoding?
The problem was because there are some representations of the same character in UTF-8, called "non-shortest" form. That characters can be converted mathematically, but iconv counts them as errorneous and not converts.
I've made a short function, which converts text of any utf-8 character to Unicode (UTF-16) codepoints array. And then remap some non-ASCII values to ASCII by simple table (for example 0x20ac is the same as 0x80, etc). You can found complete code and remapping table here: Converting UTF-8 with non-shortest characters to one-byte encoding