[sane-devel] Re: Re: Re: epson 3490 - transparency unit problem

[patrick deflandre]

Levente Novák a écrit :
>>>- dirt on the calibration stripe or windows. Even a small dark spot on
>>>  the area where shading correction is done could have a big impact, as
>>>  it gets applied over and over for the whole scan height.
>>>
>>
>>This is a possibility. I will check this as soon as possible : in few hours...
>>
>>Could you explain the calibration process with much details. Is it possible that
>>the calibration process be different whith snapscan backend than with the epson
>>software ?
>>I mean : the position of the calibration is done under the controle of the
>>firmware, or under the controle of the backend ?
> 
> 
> I don't know for the Epson, but previously I had a Microtek Phantom
> 636CX and there calibration was done in software, by the backend. And
> yes, it happened that I had a speck of dust on the calibration stripe
> (it had an impact on the scan, although the dust was small and did not
> completely occlude light).
> 

So this was the problem : a fine particule of dust on the backlight of 
the tpu. But at the wrong place : ie at the calibration position (which 
is not at the same place with the epson software !).

It's necessary to clean not only the glass, but also the backlight !

Now, the scanner work very well until the 1200 dpi.
But at a higher level (2400 and 3600) it seems there is a shake of the line.
Is it what it is expected ?

Nevertheless, thank for all your help and advice :-)