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Author Topic: SilverFast Ai IT8 observations  (Read 499 times)

saiguy

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SilverFast Ai IT8 observations
« on: August 20, 2017, 11:48:27 AM »

Using MBP retina, Nikon LS9000, SF 8.8 Studio, Ektachrome measured target dated 2013.

After running the IT8 with a dE 0.4. I pre-scan the target with the new profile, normalize the Histogram, and read patch #11 on the gray scale ramp.

It reports R103  G107  B111. I get the same results on an Epson 11000XL. Same when measured on my EIZO. Both displays recently calibrated.

Import the scan to LR. The histogram there reports R57.3  G57.4  B57.0 %

Some other darker gray patches were showing up to 7 points off from neutral.

Doesn't seem right. If I click the gray pipette on patch 11 it will go to RGB 127. But we don't have gray cards in our old film.

Any thoughts on this?

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saiguy

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Re: SilverFast Ai IT8 observations
« Reply #1 on: August 20, 2017, 12:22:25 PM »

I forgot to mention the Densitometer was set to 3 pixel radius and Picture Settings at zero.
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Mark D Segal

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Re: SilverFast Ai IT8 observations
« Reply #2 on: August 20, 2017, 12:26:55 PM »

What do you mean exactly by "normalize the histogram"?
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml

saiguy

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Re: SilverFast Ai IT8 observations
« Reply #3 on: August 20, 2017, 08:16:59 PM »

Hi Mark.

By normalize the histogram I mean pulling the black & white ends just to where the data starts or ends, respectively, on the graph. This is for each color channel.
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Mark D Segal

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Re: SilverFast Ai IT8 observations
« Reply #4 on: August 20, 2017, 08:54:44 PM »

OK, that's what I thought but needed to confirm. Once you do that, you are remapping values, so what you read AFTER remapping is a mixture of the profile and the remapping. Gamma also remaps data unless it is linear. It's been quite a while since I've done this, but if I remember correctly, to "round-trip" the profile to check for accuracy you would prescan the target in linear gamma, make no changes and read the patch values to verify whether they conform with the target file reference values.   
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml

saiguy

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Re: SilverFast Ai IT8 observations
« Reply #5 on: August 21, 2017, 09:21:40 AM »

Mark,

I ran IT8 again. With the new profile showing at the bottom of the GUI. In Preferences General changed the gamma to 1.0. Did a prescan of the target.
Patch 11 now reads R27  G32  B32.
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Mark D Segal

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Re: SilverFast Ai IT8 observations
« Reply #6 on: August 21, 2017, 09:31:18 AM »

What is the reference file value for patch 11? (Preferably in L*a*b* for both the reference file and your patch reading).
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml

saiguy

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Re: SilverFast Ai IT8 observations
« Reply #7 on: August 21, 2017, 10:59:30 AM »

Think I'm in over my head. Read your Appendix 3 in the SF8 book. The spread sheet part is beyond my ability.

Ran the IT8 again with dE 0.5. After that, and no prescan yet, patch 11 read  L 38,  A -2,  B 0

Did a prescan with gamma 1.0. Patch 11 reads  L 12,  A -2,  B -1

Downloaded LSI reference, same number as on the target. Assuming GS11 is the correct line,  it says;  L 45.15,  A -3.75,  B -2.59

thanks for your interest,
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Mark D Segal

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Re: SilverFast Ai IT8 observations
« Reply #8 on: August 21, 2017, 11:15:40 AM »

If the dE from the SilverFast Auto IT8 profile creation process is as low as 0.4~0.5, you are doing well - just use that profile. There is no perfection in this business. Any scan will usually need some post-scan editing. The better the profiling the less post-scan editing will be needed; but especially with the average quality of an IT8 target, something will always be needed.
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml

saiguy

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Re: SilverFast Ai IT8 observations
« Reply #9 on: August 21, 2017, 12:52:58 PM »

Thank you Mark,

In Appendix 3 of your book you state that the gray patches are not necessarily neutral, nor designed to be so. Must be some kind of LSI Secret Sauce.

After your informed replies I'll not worry about my uninformed observations.

Hope others may also benefit.
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Mark D Segal

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Re: SilverFast Ai IT8 observations
« Reply #10 on: August 21, 2017, 01:48:57 PM »

Thank you Mark,

In Appendix 3 of your book you state that the gray patches are not necessarily neutral, nor designed to be so. Must be some kind of LSI Secret Sauce.

The file numbers are the file numbers and they are transparent (i.e. not hidden, not secret); if they don't indicate neutrality it could only mean they were not meant to be. Now, why that should be I don't know, and if that's what you mean by "Secret Sauce", perhaps. :-)
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Mark D Segal (formerly MarkDS)
Author: "Scanning Workflows with SilverFast 8....." http://www.luminous-landscape.com/reviews/film/scanning_workflows_with_silverfast_8.shtml
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