Upon some investigation I managed to find the reason of scanned image artifacts. It was indeed JPEG compression, which occured before transferring image to computer, in order to speed up process. I also discovered that JPEG compression became default setting for hpio backend only recenty.
A [working, but ugly] solution is to tweak file ~/.sane/.xsane/your-super-scanner.drc, changing the value of "compression" parameter. I have set it to "none", and artifacts gone. Note however, that it a) works for only one user and b) works only if you use xsane frontend. I sometimes use scanimage frontend, so it's crucial that I do not forget to specify --compression=none option. That's real PITA. Also note that xsane GUI has no control for the option (you have to edit drc file). I'm absolutely sure there must be a way to specify compression type on backend level. The information on compression parameter should be clearly stated in backend manual. Andrey -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]