Scanner gamma for profiling [was: Re: maclife.de]
Scanner gamma for profiling [was: Re: maclife.de]
- Subject: Scanner gamma for profiling [was: Re: maclife.de]
- From: Marco Ugolini <email@hidden>
- Date: Sat, 06 Sep 2008 00:01:28 -0700
- Thread-topic: Scanner gamma for profiling [was: Re: maclife.de]
In a message dated 8/4/08 10:16 PM, Uli Zappe wrote:
> The most remarkable test result for me was that the profile quality
> depends very much on the scanner gamma used. This is true for all
> profiling software, but to a different degree.
Hi Uli.
Sorry for the late reply. I'm catching up only know with some older
messages.
This reminds me of an exchange I had with the late Bruce Fraser on the
ColorSync forum in early 2006.
Here is the thread in its entirety:
******
In a message dated 3/10/06 10:20 AM, Bruce Fraser wrote:
> Here's a simple objective test for evaluating scanner profiles AND
> for determining the ideal scanner tone curve. (Andrew alluded in an
> earlier message to the fact that I use the Imaco 848 at gamma
> =3.0-this is how I found the gamma value.)
>
> Scan the target.
>
> Build a profile.
>
> Assign the profile to the target.
>
> Convert to Lab
>
> Compare the difference between the Lab values in the scan and those
> in the target reference file.
>
> Repeat with different tone curves until the minimum delta-e is achieved.
>
> Bruce
-------------
In a message dated 3/10/06 10:34 PM, Marco Ugolini wrote:
> Hi Bruce.
>
> You mean to say that one ought to keep setting different gamma values in the
> scanner software when scanning the target, then create a profile for each of
> those gamma values and assign it to the raw scan of the target, until one
> achieves the lowest Delta E values compared to the reference file: is that
> correct?
>
> It's been a while since I last used an Imacon, and I forget whether it
> allows the user to specify precise increments in gamma values (e.g., 2.1,
> 2.2, 2.3, etc.): I seem to remember that it does, or am I mistaken?
>
> Thank you, and best regards.
>
> Marco Ugolini
-------------
In a message dated 3/11/06 9:47 AM, Bruce Fraser wrote:
> At 10:34 PM -0800 3/10/06, Marco Ugolini wrote:
>>
>>
>> Hi Bruce.
>>
>> You mean to say that one ought to keep setting different gamma values in the
>> scanner software when scanning the target, then create a profile for each of
>> those gamma values and assign it to the raw scan of the target, until one
>> achieves the lowest Delta E values compared to the reference file: is that
>> correct?
>
> Yes, exactly.
>
>> It's been a while since I last used an Imacon, and I forget whether it
>> allows the user to specify precise increments in gamma values (e.g., 2.1,
>> 2.2, 2.3, etc.): I seem to remember that it does, or am I mistaken?
>
> The Imacon lets you specify a gamma value, as do many other CCD
> scanners. Most drum scanners let you specify a tone curve. In either
> case, the principle is the same.
>
> The best-fit tone curve typically produces scans that are a little
> flat, but with very accurate hue and saturation relationships. It's
> easy to tweak the tonality to get great results.
>
> Bruce
******
Marco Ugolini
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