A question of calibration

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drm
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A question of calibration

Postby drm » Mon Jun 21, 2010 10:47 pm

Hi,

I recalibrated my scanner this evening, and out of curiosity I compared the Auto IT8 calibration with the stock profile that shipped with the scanner (Minolta Dimage Scan MultiPro). I was surprised to see that there is a really big difference in colour space - in this XYZ plot the Auto IT8 is the reference, outline space, the Minolta is the solid:

Image

Actually, Silverfast AI Studio gives me scans which are as close as I could ever reasonably ask for to my transparencies, but even so I'm curious. Does this difference indicate a wildly optimistic calibration by the manufacturer ? Or a deterioration of my scanner over time (it is at least 8 years old) ? Or some specific attribute of the Silverfast calibration process ... or that I have no idea what I'm talking about :-) ?

Just curious...

Oh, and another thing: does the film stock of the target make a big difference ? I generally shoot on Fuji Velvia 100F - would using the Provia target rather than the Ekta make any noticeable difference ?

David

LSI_Morales
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Re: A question of calibration

Postby LSI_Morales » Tue Jun 22, 2010 8:13 am

Dear David,

Your graphic is hard to interpret because is hard to tell if the outer thin lines are what you meant by IT8 calibration reference or the bigger color solid. I see another white solid contained within.

There is also the question whether you compared two color profiles or you used any information delivered by the scanner manufacturer and compare it to the color profile obtained after the calibration?
drm wrote:Oh, and another thing: does the film stock of the target make a big difference ? I generally shoot on Fuji Velvia 100F - would using the Provia target rather than the Ekta make any noticeable difference ?

Not really, because you are calibrating the color response of the scanner and not specific films.

However if you are to scan Kodachromes, it is important to use a Kodachrome specific IT8 target.

Cheers
Alejandro Morales

LaserSoft Imaging
Media manager, Software testing

drm
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Re: A question of calibration

Postby drm » Tue Jun 22, 2010 9:06 am

Hi Alejandro,

The Silverfast-generated profile is the outer, thin lines (set as reference profile in the Apple ColorSync Utility) - so the smaller colorspace. The solid shows the Minolta factory profile. So what I've done is to simply load the most recent Auto IT8 profile, and then the factory profile to compare.

When I compare Auto IT8 profiles made over several years, I see very little difference, none significant I think.

It is VERY likely that I'm doing something stupid :-) In any case, it's just curiosity....

Cheers
David

LSI_Morales
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Re: A question of calibration

Postby LSI_Morales » Tue Jun 22, 2010 9:56 am

Dear David,

I am assuming, what you call thin lines is what I see as white solid (included within the bigger color solid).

So, you are comparing two different color profiles and this is showing the differences. Different color profiles are usually different.

drm wrote:Does this difference indicate a wildly optimistic calibration by the manufacturer ? Or a deterioration of my scanner over time (it is at least 8 years old) ? Or some specific attribute of the Silverfast calibration process ... or that I have no idea what I'm talking about :-) ?


The manufacturer profile is regularly a generic profile created for all scanners of the same model, the IT8 profile was created for your scanner specifically.

All scanners have different responses to light and color(even if they are the same brand and model) and also time as well as external conditions influence the operation of these devices (e.g. temperature and humidity).

This differences are reflected in the graphic.

drm wrote:When I compare Auto IT8 profiles made over several years, I see very little difference, none significant I think.


That little difference you observe between these profiles is the one that happens either to your scanner or even the calibration target over time.

drm wrote:It is VERY likely that I'm doing something stupid :-) In any case, it's just curiosity....


What do you mean by "stupid"?

Actually color space comparison can be used to determine whether one specific color will be reproductible or not on other color space or by a specific medium.

Cheers
Alejandro Morales

LaserSoft Imaging
Media manager, Software testing

LSI_Luebker
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Re: A question of calibration

Postby LSI_Luebker » Tue Jun 22, 2010 10:01 am

Dear David,

the generic manufacturer profile is covering all scanners thats why it can not be that accurate. A scanner contains several different parts that are responsible for the actual colorspace the scanner can "see" so the manufacturer profile is really just very genreric . The custom IT8 calibration therefore is creating the ICC profile for your acutal Scanner.
We do not tweak the ICC profile created by using the Auto IT8 calibration it is the same ICC profile that you would get doing a manual calibration.

I
best regards,

Thomas Luebker,
LaserSoft Imaging AG

drm
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Re: A question of calibration

Postby drm » Tue Jun 22, 2010 12:12 pm

Hi Thomas, Alejandro,

Thanks for explaining it to me! By "something stupid" I just mean that I don't really claim to understand much about colour management - fortunately with Silverfast, I don't need to - it looks after it all for me :-)

Best wishes
David

degrub
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Re: A question of calibration

Postby degrub » Tue Jun 22, 2010 1:37 pm

also, your fluorescent light source is likely to have aged and may give you a different spectral output from what it had new.

LSI_Morales
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Re: A question of calibration

Postby LSI_Morales » Tue Jun 22, 2010 2:02 pm

Dear David,

Great things are working!

Cheers
Alejandro Morales

LaserSoft Imaging
Media manager, Software testing


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