[sane-devel] Epson perfection 4870 - gamma and brightness in 16bit mode

[Richard Beare]

Hello,

I have an Epson perfection 4870 photo (aka GT-X700). I'm trying to use 
it in what is possibly an unusual way. I seem to be able to get most of 
what I want using xsane, but not using scanimage. I need to use 
something commandline oriented in the end in order to automate some of 
the steps.

Here's the problem at the moment:

I want to scan using 16bit colour mode. I'd like to scan with a gamma of 
1. I'm testing the process at the moment by imaging a set of 4 
reflectance standards (spectralon with 99%, 50%, 25% and 12% reflectance).

When using xsane I can set the gamma to zero and the reduce the 
brightness. This gives a linear response with reflectance (confirmed by 
plotting it). The 99% reflectance region also has pixel values below 
65535 - this is important in order to verify that there is no saturation.

I have no luck trying to reproduce this behaviour using scanimage. Using 
--gamma-correction "User Defined" in isolation gives a close to linear 
response, but doesn't seem the correct thing to do. I can't see any way 
to define 16bit gamma tables to apply through the --red-gamma-table 
option. Am I missing something here?

The other problem is how to explicitly set the "exposure" - I'd like to 
be able to establish some settings that image the reflectance targets 
such that the 99% target is a little bit lower than 65535 and then keep 
these settings while I image other objects. Is this feasable, or is the 
only option to keep the spectral target in the field of view while 
imaging the other objects?

I'm using sane backend version 1.0.15.


Any advice is much appreciated.

Thanks

-- 
Richard Beare, CSIRO Mathematical & Information Sciences
Locked Bag 17, North Ryde, NSW 1670, Australia
Phone: +61-2-93253221 (GMT+~10hrs)  Fax: +61-2-93253200

Richard.Beare@csiro.au