Combed histograms when using Negafix?

Problems with HiRePP®, NegaFix or profiles

petru
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Combed histograms when using Negafix?

Postby petru » Wed Oct 09, 2002 8:46 pm

Hi all,

I noticed that when I'm using Negafix the output has a combed histogram. The histo displayed in SF looks smooth, but I assume that SF displays the histo of the image before the Negafix corrections are applied. When I open the output file in Photoshop however, the histo looks pretty bad esp in the mid to low range. It looks almost as if a second histo curve (made from many discrete spikes) was artificially placed on top of the old one.

Is this normal?

I'm using SF Ai and HDR 5.5.2r<latest>, WinXP, Polaroid SS4000.

Thanks,
Petru.

petru
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Re: Combed histograms when using Negafix?

Postby petru » Mon Oct 14, 2002 5:19 pm

petru wrote:I noticed that when I'm using Negafix the output has a combed histogram.


Okay, no one from LSI has replied so far. I guess they're busy fixing the SF 6.0 bugs. I am therefore replying to my own message because I see that quite a few people have read it and they might be interested to find out why this happens.

I posted the same question on the filmscanners mailing list and the list owner, Tony Sleep, suggested that the combed histogram could happen if SF (or the NegaFix module) was cheating by handling the images internally in 8bit mode, even though the output is set to 16bit mode. Tony says that this used to be the case with Polaroid's scanning software (Polacolor Insight). To me this sounds like a credible explanation.

I guess I should take a second look at v**s**n, after all.

LSI_Ingraham
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Postby LSI_Ingraham » Tue Oct 15, 2002 2:08 pm

Dear Petru,

I am investigating the comb histogram issue, and I currently only notice the problem with images scanned at 8 bits and not 16. Are you finding the problem with 16 bit scans?

petru
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Postby petru » Wed Oct 16, 2002 3:46 am

LSI_Ingraham wrote:Dear Petru,

I am investigating the comb histogram issue, and I currently only notice the problem with images scanned at 8 bits and not 16. Are you finding the problem with 16 bit scans?


Hi,

First of all, I'm using SFE-5.5.2r12(HDR).exe and SFE-5.5.2r20(Polaroid).exe, Win XP, Polaroid SprintScan 4000.

If I scan in AI in "48bit HDR color" mode at 4000dpi and then scan the resulting file in HDR in "48bit color" mode at 4000dpi => comb histo. If I scan from the same file in HDR at 1600, 3200, 3999 or 4001 dpi I get the same histograms as the ones displayed in HDR (which are decent).

If I scan in AI in "48bit color" mode at 4000dpi I once again get a bad histo, but if I scan at 3200dpi => ok.

The negative is a Fuji Superia 400. With the exception of Negafix and I'm not making any other corrections (levels, curves etc).

Many thanks,
Petru.

petru
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is this fixed yet?

Postby petru » Thu Nov 21, 2002 4:50 pm

More than a month has passed since the last message was posted. Is this issue still under investigation? When can we expect to have it fixed?

Thanks,
Petru.

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Gregory C
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Postby Gregory C » Sun Dec 08, 2002 5:20 am

This is an interesting problem, so please excuse me if I join in. ;-)

I would be interested to know two things:
  1. When using SF with the Polaroid scanners, there is an LGS (Limit Gamma Slope) option. It is probably in the Options dialog. In your case, is it On or Off? If it is On, what happens if you turn it off?
  2. SF by default uses interpolation when scanning. To see the hardware resolution in the Resolution field, hold down the Control key. To see the interpolated resolution in the Resolution field, hold down the Control and Shift keys. At 3200 dpi, 3999 dpi and 4000 dpi, what are the hardware and interpolation values?
regards
Gregory

ilyons
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Postby ilyons » Sun Dec 08, 2002 10:22 am


I would be interested to know two things:
[list=1][*]When using SF with the Polaroid scanners, there is an LGS (Limit Gamma Slope) option. It is probably in the Options dialog. In your case, is it On or Off? If it is On, what happens if you turn it off?


OFF - In really simply terms the shadow end of the scale will NOT be clipped - that is to say SilverFast will NOT toss away a large amount of shadow data to hide noise. Whilst ON is the defualt setting for the SS4000 and MicroTek equivalent it is BAD for most images - turn it OFF.
[/quote]


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