Colour management

[Antonio Marques]

Hi.

I've come to ask you for advice on colour management.
The context: scanning negatives in AI Studio in HDRI mode, for which I intend the best quality possible, so as to avoid having to scan them again later on. I'll then process them in HDR Studio.

- What's the difference between scanning in RGB and in CIE-LAB? At first sight I'd say CIE-LAB would be better, as it has a wider gamut, but is it? Do I lose anything by using RGB? Do I lose anything by using CIE-LAB? I'm supposing these are the colour models that will be used to interpret the saved data, i.e. CIE-LAB would have the 16 bits spread thinner but the primaries further apart than RGB, which would reduce clipping of the samples - but maybe this is a completely misguided interpretation.

- What should I do regarding AI calibration? These are negatives, not slides. But it would be logical if an exact profile of the scanner were included with the data, wouldn't it? I've also noticed that when I calibrate the scanner (it's an RPS 7200) the results are 1.3, then 1.4 the next time, then 1.3 the next time, then 1.4 again... what could this mean?

- What setting should I use for negafix in AI? I first thought it would be irrelevant, I think you've confirmed that before, but I've noticed that if I select the correct profile for the film in AI, then the image in HDR is shown in brighter colours (actually less natural) than if I had used Other/Other/Standard in AI. And I wonder the same about CCR (colour cast reduction).

- Or should I use AI in 'Positive' mode? Would 'Positive' mode be exactly the same as Other/Other/Standard?

- In my system (w7 x64), I have a few duplicate colour profiles in Silverfast's dialogs - for instance, two 'Adobe RGB (1998)'. I think this is because I have both an ICC and an ICM installed on Windows. I didn't intall them myself, don't know which to use, don't know what's the difference between them, and consequently don't know what to do about this. Can anyone give me some hint?

Thanks,
Antonio

[LSI_Ketelhohn]

- What's the difference between scanning in RGB and in CIE-LAB? At first sight I'd say CIE-LAB would be better, as it has a wider gamut, but is it? Do I lose anything by using RGB? Do I lose anything by using CIE-LAB? I'm supposing these are the colour models that will be used to interpret the saved data, i.e. CIE-LAB would have the 16 bits spread thinner but the primaries further apart than RGB, which would reduce clipping of the samples - but maybe this is a completely misguided interpretation.

This will only have influence on your post-processing.
(e.g. if you woul want to use sharpening filters on the luminance channel.)
For the scanprocess this has negligible differences.
Otherwise I would suggest using RGB which is standard nowadays.
Even most pre-press work is done in RGB today.

- What should I do regarding AI calibration? These are negatives, not slides. But it would be logical if an exact profile of the scanner were included with the data, wouldn't it? I've also noticed that when I calibrate the scanner (it's an RPS 7200) the results are 1.3, then 1.4 the next time, then 1.3 the next time, then 1.4 again... what could this mean?

Calibration has no influence on negative scanning because special film profiles have to be used.
The variation you experience is full normal, it represents the normal statistical dispersion due to variations in each scan.
All values below 2 more-than fulfill the IT8 calibration standard.

- What setting should I use for negafix in AI? I first thought it would be irrelevant, I think you've confirmed that before, but I've noticed that if I select the correct profile for the film in AI, then the image in HDR is shown in brighter colours (actually less natural) than if I had used Other/Other/Standard in AI. And I wonder the same about CCR (colour cast reduction).

The film profile has no influence on the HDR scan.
It is possible the scanner model is already selected and the correct presets are loaded.
Or you are experiencing slight variations in your scans due to scanner temperature/ frame differences/ resolution/etc..

- Or should I use AI in 'Positive' mode? Would 'Positive' mode be exactly the same as Other/Other/Standard?

This makes no difference apart from the possible scanner selection in HDR.

- In my system (w7 x64), I have a few duplicate colour profiles in SilverFast's dialogs - for instance, two 'Adobe RGB (1998)'. I think this is because I have both an ICC and an ICM installed on Windows. I didn't intall them myself, don't know which to use, don't know what's the difference between them, and consequently don't know what to do about this. Can anyone give me some hint?

AdobeRGB is a standard profile.
It should make no difference which one you use.


kind regards,
Arne Ketelhohn.