Hi, I think the discussion is of general interest so I Cc: sane-devel.
On Sat, Jul 26, 2003 at 10:18:23PM +0200, Stefan Schlörholz wrote: > > > Let me explain my suggestion: > > > The software for my scanner under windows offers a dialog where you > > > scan a reference target, tell the programm which target standard > > > you used and mark the positions of the reference marks. > > > > So it does a preview scan and you must select where the target is > > positioned on the glass? Or does the software find out the position > > automatically ? > > You make a preview scan of the target and then mark the calibration > marks. This is necessary since you may end up with diffrent visible > areas or tilted targets. I think an automatism could be possible but > then you need some image processing. Ok. > > files to backends or the SANE API. For me it looks like it can be > > included in the frontends without the help of the backends. Or a > > special "frontend" could be created that just does the calibration > > and other frontends could just use the .icm files. > > agree > > > If I understand the method correctly, the frontends then use the .icm > > files to adjust the gamma tables. What I don't really understand is > > could be. I do not know what gamma correction really does. But does the > gamma correction compensate for when only a single color is affected > (say if the scanner bulp is missing some red)? The .icm would do that. > I thought gamma applies a transfer function whereas the .icm file is > more or less a look-up table for color transformation. In SANE terms, gamma tables are look-up tables. For color mode, there could be one table (total), three tables (RGB) or four tables (RGB + total). If the scanner provides a mean to set gamma tables in hardware, the backends usually provide these tables and send them to the scanner. Otherwise the correction is done in the frontend. > > how that corresponds to the other scanner settings like exposure, > > gain and offset which have influence on the brightness/gamma of the > > image, too. So the .icm profile is only valid for one scanner with > > one setting of these values? > > correct, the .icm file compensates for the color in raw (no other > correction) mode. Other methods like histogram and gamma should be > applied afterwards. Ok. > > driver uses other settings (e.g. exposure, gain etc)? Generally > > speaking, the images scanned by SANE are NOT always worse than with > > Windows, so this may be a backend/scanner-specific problem. > > I do not doubt that. When having said Windows I meant including the use > of the .icm File. Scans in raw (no correction applied) modes do not > differ from Linux to Windows. > > > But the profile muste be created with the help of the frontend > > anyway. So I don't see what role the backend plays here. Keep in mind > > Is this a mailing list for the backends anly then? Sorry I did nor know > that. Where can I bring up this isuue correctly? It's the correct list here. This comment was directed to the previous discussion on this list. > On the other side I see that the functionality should be available for > any scanner. Why not bringing it in the backend (again, due to lack of > programming know how i do not know if possible at all) making it easier > for frontend developers to take advantage of it? The backens should support all the functions the hardware provides. As that type of calibration is not a harware feature, I don't think they can do anything to help it. Especially if a feature is needed for all devices, it's better to put it in the frontend because that means to change one (or some) frontends instead of > 50 backends. The only thing I could think about is that the backend could provide the .icm file over the SANE API once that file was generated and written to the hard disc. > > Ok, then these users should propose the details on how to do it and > > send patches :-) > > Maybe it would be best to involve some developers of the existing > projects like "lcms" projects. They know all the details of gamma, > histogram and the difference to color management using .icm files. Well, go ahead :-) Bye, Henning
