HDR Scanning and gamma gradation?

[harry shin]

Hi:

1. I use silverfast ai (within photoshop), and I usually make 48 bit HDR Color scans (color negatives).

2. Question: Does it matter what the "gamma gradation" is, when making 48 bit HDR scans?

3. I've done some basic tests, scanning the same negative with gamma
gradations of 1.00, 1.80 (default) and 2.00--> opened the scans via HDR and really couldn't notice any difference.

IF it does matter what the gamma gradation is when scanning a 48 bit HDR scan, how do I save the new gamma gradation? The reason I ask this is because when I change the gamma gradation to 2.00 and click ok, make a scan and then the next day make another scan, silverfast reverts back to the default gamma of 1.80.


Thanks for the information. Harry Shin

[RAG]

Hello Harry Shin,

Are you making this setting under options on the general tab as shown below?

<img src="/img/forum/gamma.gif">

[degrub]

dumb question. you did check off the "for HDR output" box ?

Are you using a CRT or an LCD display ?

[RAG]

I don't have it checked because I'm not using HDR in PS at this point in time.

I believe Harry, if this is where he has been setting Gamma did check the box though, right Harry?

[Ogando]

As far as I know Silverfast Ai has a default setting of Gamma 2.00, which has just to do with silverfasts midtone interpretation of an avarage scanner lightsource.

This setting has no influence on the rest of your workflow calibration according to colormanagement and so on.

It?s just the midtone position by default for the prescan. Anyway you can change it by moving the midtone button in the curves dialog.

You may check out by yourself which is the best setting for the best prescan result nearest to your final scan settings.

I use for Colornegative scans with a scanner Nikon LS 8000 (LED light source) and a scanner Epson 4870 (fluorescent light source) for sheet films a Silverfast preset Gamma of 1.8.

(As said above the Gamma setting in Silverfast?s option dialogue hasn?t anything to do with workflow calibration on D50 with Gamma 1.8. Also it doesn?t have any influence on the IT8 calibration inside Silverfast.)

For transparencies I use a Gamma preset of 2.00 as the software suggests by installation. You can make a test just by scanning the transparency for the IT8 calibration without any adjustements in the tool bar.

As already mentioned Gamma 2.0 here isn?t just the difference between Gamma 1.8 and 2.2. , the native Gammas of the common color spaces. Gamma 2.0 correspond to the character of a scanner light source - for transparencies. For scanning prints I use a Gamma preset of 1.6.

In Silverfast HDR I use the standard preset of Gamma 1.8 and have preview results in fine correspondance.

There are different explaining versions around in the Silverfast literature according to this issue in course of time. So you may get confused in this point.

Together with a collegue we explored this section of the software and this is my version of the truth checked in my personal reality.

Getting deeper into the issue you?ll discover more open questions but I?m quite shure the customer can "sleep well" with a quite simple calming answer in this point.

Ogando

[RAG]

Ogando,

If I understand you correctly, you are saying that you have done some experimentation and found the Gamma setting has no effect on your images, correct?


When you changed the setting was is saved, or did it revert to the previous setting like it did for Harry?

[Ogando]

RAG,
the gamma setting in the options dialog has influence on the midtone interpretation in the prescan of Silverfast ai or "preloading" (how shall I say in english) of Silverfast HDR.

Inside certain limits as from 2.00 to 1.8 or from 2.00 to 2.2 you can conter-correct easily the difference caused by different gamma setting as well in the gradtiation dialogue of the software-tools. That means, if you use a "wrong" gamma setting in the options dialogue, what means not the best one you could choose for your kind of scanning task, you are optimizing your prescan in the tool-dialogue without noticing it.

By the gamma setting in Silverfast?s option dialogue there is no influence on the colormanagement, if you pass the file to Photoshop using a color space with another native gamma and wether you?re using a CRT or LCD Monitor. Of course it makes sense to run software, color spaces and Monitor Gamma at the same level to minimize the operations from the CMM module. But the look-up-tables by the profile connection space in the computer?s?graphic card aren?t involved here. Silverfast?s preset Gamma isn?t written into the ICC-Profile of the scan.

If opening your file in Photoshop you sometimes notice some little difference in the highest highlights to your densitometer numbers in Silverfast (with CMYK preview although you?re using corresponding profiles in SF and PS) shurely its because of the perceptive rendering intent passing a CMM twice while changing between the programms.

I remember somewhere in the younger Silverfast literature some advice from theory considering the best gamma setting in correspondance to the native gamma of the internal colorspace activated in the SilverFast?s CMS dialogue, Adobe RGB, sRGB Gamma 2.2, ECI-RGB Gamma 1.8 .

I couldn?t verify it in my real life.

Of course I use the same colorspace in Silverfast as in Photoshop, but for the correspondance of the Monitor preview.

According other advices in the SilverFast literature the Gamma setting in the option?s dialogue is just a suggestion by the software for the midtone range in the prescan. This is also my experience. I use different settings according to different film material as described in the first reply.

So at this level in the software architecture you can?t do any colormanagement mistakes using different settings from the color space native gamma in SF or PS.

If the software is working correct the gamma setting shouldn?t change, if you don?t change it.

Ogando

[RAG]

Ogando,

I agree that it is possible to use the gradation tool in SilverFast or the levels or curves adjustments in Photoshop to correct image tonality problems in general.

Thank you for the information!

[Ogando]

Thanks a lot for Sonny Noack?s reply and instruction
according how to use the HDR output checkbox
beside the gamma gradiation in the option?s dialogue sensfully.

Imho one of the last few blanks in the Silverfast manuals and special user pdfs.

Have a look at Support Nikon Filmscanners:

topic: 612 and 617 film support on Nikon 9000ED

viewtopic.php?t=3708

Ogando