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

[Karl Heinz Kremer]

Richard,

the Perfection 4870 does not have an exposure setting, and only 
supports 8bit Gamma tables. I suspect that you see the combined gamma 
applied by the scanner and xsane, whereas scanimage only gives you 
access to the scanners gamma setting. Have you tried xscanimage?

Karl Heinz


On Jan 17, 2005, at 2:58 AM, Richard Beare wrote:

> 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
>
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