Negafix off (Kodak Portra and Ektar)

Problems with HiRePP®, NegaFix or profiles

AndreasResch
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Scanner: Epson Perfection V800
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Negafix off (Kodak Portra and Ektar)

Postby AndreasResch » Fri Mar 18, 2016 1:12 pm

Hello,

I'm not very happy with the Negafix Profiles for Kodak Portra and Ektar. The colors and brightness are off quite a bit. After trying several things I stumbled over a weird situation. When I make a prescan with the correct Negafix profile selected (in this case Kodak Ektar) the colors are off (here too red) and the brightness is a bit too high. If I go to Edit->Preferences->CMS and switch the internal profile from ProPhoto to AdobeRGB, the colors of the prescan instantly change to a better, more correct version. If I switch the profile back to ProPhoto afterwards (while still being in the dialog) nothing changes with the prescan.

Here's a comparison. On the left is the bad looking scan with ProPhoto selected in the CMS options. On the right is the prescan after I changed the profile to AdobeRGB in the Options dialog.

Image

Thanks,
Andreas Resch

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LSI_Ketelhohn
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Re: Negafix off (Kodak Portra and Ektar)

Postby LSI_Ketelhohn » Fri Mar 18, 2016 5:40 pm

Dear Mr Resch,

AdobeRGB is a little smaller than ProPhoto. It is possible that the colorspace rendering masks the effect when using a different colorspace.
There is always some calculation invloved because the Scanner colorspace is always bigger than even ProPhoto.

Also of cause there can be variations in the way certain films are produced, exposed or processed.
The NegaFix tool tries to compensate that through the CCR shown in the tool as a checkbox.
You can test how switching it on and off influences the image.

There are also several tools in SilverFast for handling such casts.
The easiest one to use is the Neutral Pipette in the Pipette tool.
Using it on a neutral (grey) area will remove a cast based on the values found there.
The stones in the image should work good for that.

In Ai Studio it is also possible to create individual Profiles for your films through the curves tab in the experts dialog.


Kind regards,
Arne Ketelhohn.


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