Color Settings for HDR Scans

[braver]

Since there's a lot of options for color management, I'd like to see a concise rundown of what's needed to preserve a scan in HDR with the most information preserved.

E.g. Mark D Segal of Luminous Landscape has,
at http://www.luminous-landscape.com/tutor ... ning.shtml:

Color Model => RGB

In Options/CMS:

Input-Internal => None
Internal-Monitor => Image Colour Matching (ICM)
Internal-Output => RGB

Input => None
INternal => ProPhoto RGB
Grey => None
Printer => None
Rendering intent: rel. colometric

Now I undertstand Mark was doing negatives, and I do slides (non Kodachrome, regular Kodak/Agfa/Fuji/ORWO etc.) I also used to calibrate my Nikon LS4000 with IT8 and will do it again, so I guess I'll have my custom IT8 profile for input, right? For now I see a couple for LS4000, an N-8 and an N-14, so I guess one of these could be used (which one for slides)?

Should the profile be embedded, with the checkbox?

Overall, how should the CMS be done for HDR?

Also, if I did scans where I didn't set Input, so it remained <NONE>, can I reapply a different color profile to those HDR scans post-factum?

Finally, no matter which profile I choose in SilverFast, when the resulting TIFF is opened in Preview by Mac, it's dark. Is it an artifact of HDR TIFF, and can they be made lighter-looking in Finder without sacrificing archival qiality? When I change the Input profile and Apply, the lightness of the Prescan can change significantly. How does it correspond to the final darkness of the TIFF?

Cheers,
Alexy

[LSI_Morales]

Dear Alexy,

Your questions comprise an entire chapter in our instruction manual. I will try to briefly answer them but I recommend you to go over the manual which can be found here: http://www.silverfast.com/download/docu/manual,complete_en_2006-11-27.pdf.
Chapter 8 "Color management" should be of special interest for you.

The first thing you should know is scanning in 48 bits HDR color or 16 bit HDR greyscale create an unmodified raw file of your scanned picture. It means no correction will take place. Also no gamma curve will be applied (pictures will be scanned with a linear gamma), Hence the pictures look dark when viewed with Preview in your Mac. This can not be corrected with finder, you should use an imaging program capable of opening 16 bits TIFF files and then applying a gamma curve.
Or using SilverFast HDR or HDR Studio which are our imaging applications for raw file edition. In this case pictures will open and the gamma curve will automatically be applied to your files.

Now I undertstand Mark was doing negatives, and I do slides (non Kodachrome, regular Kodak/Agfa/Fuji/ORWO etc.) I also used to calibrate my Nikon LS4000 with IT8 and will do it again, so I guess I'll have my custom IT8 profile for input, right? For now I see a couple for LS4000, an N-8 and an N-14, so I guess one of these could be used (which one for slides)?

Exactly, Mark was doing negatives, hence the options you see for the CMS dialogue are different if you change to positive transparency mode.
You should calibrate your scanner relatively often (once a week) if you want to have relatively consistent outcomes.

Should the profile be embedded, with the checkbox?

If you want the editing application to use the same profile used for the scanning process, then yes.

Overall, how should the CMS be done for HDR?

There is not only just one answer for this question, I advice you to go over the chapter 8 and decide which fits better your goals.

Also, if I did scans where I didn't set Input, so it remained <NONE>, can I reapply a different color profile to those HDR scans post-factum?

Well, it is better to put the a profile there, otherwise the scanner color space will not match the color space of your system, editing programs and other devices.

When I change the Input profile and Apply, the lightness of the Prescan can change significantly. How does it correspond to the final darkness of the TIFF?

It is logical, if you are change to a different color profile, colors and lightness will be interpreted differently (because they have different gamma values) and the visualization changes, if you work with mac you should always use ColorSync, if you use windows you should use ICM.

Cheers

[degrub]

Read Ian Lyon's tutorial on CMS and Silverfast.

http://www.computer-darkroom.com/sf5_contents.htm

[braver]

One question I still didn't get is how exactly setting a profile for Internal affects the stored image. Say I picked a ProPhoto profile. Then I bought a custom archival color space from JosephHolmes.com, and decided to store my HDRs in that one. Can I re-apply that without rescanning? I assume that raw data from the scanner is transformed in a known way, and the result of applying a color space is stored in the HDR with the color space itself marked. So theoretically, it should be possible to

-- apply an inverse of the original internal color space transform to the HDR
-- apply a different color space transform
-- store the result in a new HDR

Is this possible in the current HDR? I played with several embedded color spaces, and wonder whether I can replace them by the one I'm going to buy from Joe Holmes, for instance, or by ProPhoto. I also wonder whether I should keep rendering intent as colorimetric if it matters at all for storage.

I've read the manual, and Taz Tally's book chapter, and some tutorials, but there's a variety of material there, so probably getting to the bottom of a few focused questions is the best way to get it right, so I appreciate your help, especially given SilverFast itself changes and HDR gets more capabilities.
Cheers,
Alexy

[LSI_Morales]

Dear Alexy,

One question I still didn't get is how exactly setting a profile for Internal affects the stored image.

When you pick a profile for Internal, you are telling the entire color management to work under this color space. In other words, it is the color space that will be used by the system to match the different devices (scanner to system, system to monitor). So

Say I picked a ProPhoto profile. Then I bought a custom archival color space from JosephHolmes.com, and decided to store my HDRs in that one. Can I re-apply that without rescanning? I assume that raw data from the scanner is transformed in a known way, and the result of applying a color space is stored in the HDR with the color space itself marked.

Well, if you scan a picture in a format different than HDR or HDRi, the resulting file will be affected by this decision and changing the internal color space can not recover the color and details you have trimmed from using the previous color space.
However, with HDR or HDRi or in other words, raw files, no color space is applied, it just stores the information as seen by the scanner and the scanner color space is attached to the raw file.
So, you can always change the internal color space when using HDR or HDRi files without having to rescan the pictures.

So theoretically, it should be possible to

-- apply an inverse of the original internal color space transform to the HDR
-- apply a different color space transform
-- store the result in a new HDR

Yes
Yes
No need to save a new HDR, because you can always change the color spaces at will.

Is this possible in the current HDR? I played with several embedded color spaces, and wonder whether I can replace them by the one I'm going to buy from Joe Holmes, for instance, or by ProPhoto. I also wonder whether I should keep rendering intent as colorimetric if it matters at all for storage.

Again, with HDR files you are creating unmodified raw files with the information as seen by the scanner, no interpretation is made, no color space is applied, no correction is done. You can change the color profiles as needed, note however that the embeded profile from the scanner is needed for the colors to be correctly interpreted.

Cheers