Re: scanner profiling (again)
Re: scanner profiling (again)
- Subject: Re: scanner profiling (again)
- From: Jim Rich <email@hidden>
- Date: Tue, 16 Dec 2003 15:42:38 -0500
On 12/16/03 3:12 PM, "Armand Rosenberg" <email@hidden>
wrote:
>
Jim,
>
>
At 1:01 PM -0500 12/16/03, Jim Rich wrote:
>
> So one question to consider is why does each image I photograph have a
>
> different white and black point?
>
>
That's THE question.
>
>
> As I pointed out in my last post factors like exposure, the scenes content,
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> and film processing cause the wp and bp to vary. It is just that simple.
>
>
Let me repeat my starting assumptions, in case they were not clear: I
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have a correct exposure and processing is reasonably consistent (with
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positive film). That is the case I am interested in. Then wp and bp
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should be reasonably consistent between target and image. I can
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understand small deviations, but not major changes.
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>
I don't understand why scene content would matter in this case. As I
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said, the target contains patches corresponding to highlight and
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shadow. So any scene's content should be covered by the target
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patches.
>
>
> It is the nature of light striking objects and then reflecting back on to
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> film or a sensor.
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> It is not perfect.
>
>
What is "not perfect" about this phenomenon? How is it going to
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result in a properly exposed image that has areas with OD higher than
>
the GS23 patch or areas with OD less than the GS0 patch?
>
>
If this can happen and is a frequent occurrence, then the concept of
>
using that target to profile a scanner is flawed.
>
>
> So a savvy operator then intervenes
>
> to set the correct wp and bp for that situation.
>
>
OK. But that's outside a true ColorSync (ie, ICC) workflow, isn't it?
>
>
> As for when to adjust the wp and bp. I adjust wp and bp after I have used
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> one pair of profiles. That is to Assgin and then Convert to my WS.
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>
OK. Makes sense.
>
>
> I am not sure how else it can be a Photoshop ICC based workflow that uses
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> non ICC savvy scanner software.
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>
The scanner sw need not be "ICC savvy" itself -- all it has to do is
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capture a raw scan with locked scanner settings. The profile can be
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assigned later (eg, in PS.) Isn't that all that's required of an ICC
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workflow?
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It's the same idea as printing with a printer driver that isn't "ICC
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savvy" itself: you can still use custom profiles just by letting PS
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handle all profile conversions.
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>
> If you adjust the raw image before you
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> Assign the profile you are altering the raw state in which you created a
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> scanner profile. This makes the scanner profile invalid and is illogical in
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> an ICC workflow.
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>
I agree.
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>
(clip)
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> If the scanner and software allows you to set up all of the image
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> processing parameters before the scan then you are ahead of the curve when
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> it comes to being paranoid about quantization errors that Photoshop image
>
> processing might or might not introduce.
>
>
It's true that you can set up the parameters in the scanner sw based
>
on preview, before clicking "scan," but really the adjustments are
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done by the scanner driver sw AFTER the data is captured... The
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capture itself seems unaffected by these parameters.
>
>
So I repeat once more: even if you do these settings in the scanner
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software, they are still applied only after the data is captured, as
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far as I can tell -- then it just does not matter whether you do this
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in the scanner software or in PS, as long as you have a true 16-bit
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data path.
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>
(clip)
>
>
So back to THE question: with a correct exposure and consistent
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processing, and using the same film as the target (nominally), why
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should each image have drastically different wp and bp? To me, it
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seems like the differences, if any, should be small.
>
>
Armand
Armand,
I am not sure what you are all wound up about and if you want to start an
argument please leave me out of it.
You asked for the technical reasons why you need to set wp and bp. I gave
them to you twice. And on one of the things that can go wrong with
photography, I have never seen a photographic process line that is perfect
so things do change from the time the scanner target was created (say at
Kodak) and the time any new film that is being scanned is used. So things
are not perfect. If you have a perfect photographic process line then I
guess you don9t need to set the wp and bp. But I have never seen that in my
35 years of doing this kind of work.
And then of course what about hi-key and low-key shots and subjective
judgements. The point is there are reasons to adjust wp and bp no matter how
good your profiles are.
As for being outside of a perfect ColorSync workflow...well the world is
not perfect. The Photoshop image processing steps I sent in the last post
described a Photoshop workflow that uses profiles. How many folks use
Photoshop with profiles? More than the 50 people on this list? Are they
wrong because it does not fit the definition of a perfect Colorsync
workflow. I doubt it.
Good luck
Jim Rich
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