The results might be caused by poor (or no) CIS calibration being done by the backend. You could try getting a trace of the device in action with the windows driver, and investigate adding the calibration steps to the backend.
generally this involves doing several small scans of a white area under the shell of the scanner, with and without the lamp on. this is usually pretty easy to identify in the logs. interpreting it is a different matter... :) allan On 5/12/08, Ekkehard Morgenstern <ekkehard at ekkehardmorgenstern.de> wrote: > > It's the ma1509 backend. > > I've already seen that there's a possibility to provide gamma correction > tables and such to SANE from within a backend. How does it work? > > I'm not sure whether the poor results of my scanner are the result of > hardware aging, or if it's just because the backend seems to pass on the > data from the scanner chipset unchanged. > > It's an LED scanner, so there must be a set of photo diodes or photo > transistors somewhere. It appears as if the scanner sends the data in > raw form, unadapted to the characteristics of the semiconductors. > > Distribution of RGB values across their channels suggest that the data > should be scaled or transformed somehow. I spent a whole night this > weekend trying to figure out some formula that would solve the problem, > but I didn't find a solution. > > Instead, I wrote this program to simply compute the difference between a > blank page and the color white. The program generates one line of > averaged out scaling data, which is stored in the file "white.shape". > I'm not sure whether the data can be made constant. If it were to be > included in the backend driver, it has to be fairly constant over all > scanners of that type. > > After all, the Windows driver must do the same thing somehow! ;) > > > > On Sun, 2008-05-11 at 15:42 -0400, m. allan noah wrote: > > > Ekkehard- another choice might be to do this sort of calibration > > inside the driver in sane, but that would require becoming familiar > > with the code of the sane backend which drives the scanner.... > > > > > -- "The truth is an offense, but not a sin"
