When scanning with (x)sane or similar tools the hp scanners compress their data in order to make the data transfer faster. official support statement
Though this behaviour may make sense in most cases, in some cases you want to use the raw data. (Maybe you just don't want the data to be compressed by the scanner, decompresssed by the driver and compressed again by the user tool.)
So if you want to use better scanner data, you are right here. I have taken the patch from a bug report and compiled it with my distributions' tools.
This is the spec file I used: hplip_enhanced.spec
Unfortunately(1) I'm not so sure wether the actual data transmission is really raw or just JPEG compressed with an extreme high quality setting.
Unfortunately(2) the tools couldn't handle the vast amount of ppd files, so I just deleted most of them (out of the source archive and out of the Makefile/includes). That means that you cannot print using my package and maybe your scanner isn't working either. Maybe it helps to save the ppd files and put them to the right directory manually; I don't know the hardly documented architecture of HPLIP.
Unfortunately(3) I didn't make the spec file as clean as it could be.
Unfortunately(4) this may refuse to work on GNU/Linux distributions other than OpenSUSE 12.2.
For space reasons the package files aren't hosted on this server, but you can donwload them here:
Text from 17 dec 2016, download links updated in October 2018
Document of December 17, 2016, last modification on 12 October 2018. Page source