2009-10-18 23:17:11 UTC
I'm no expert but I've researched some of the same questions. Here's what I found.
1) Wolf Faust suggested to me to create CLUT 33 profiles. You end up with much larger profile files (668KB) but the colours, specially the mid tones, are much more accurate. Your dE seem very good too (less than 1.0). The values do tend to vary a lot depending on the target. I don't expect anything near perfection with profiling. We're dealing with scanned slides anyway. Even with a good profile, you'll get variable results due to your slide exposures and its color balance (daylight film used in non "daylight" conditions).
At the end of the day, I do use my profiled display to judge of the accuracy of the scanner profiles I create. The main things to look for are color cast and clipped highlights or shadows, and that's easy to see from a good display. Have a look at this scanning tip document.
http://www.hutchcolor.com/PDF/Scanning_Guide.pdf
It's mainly for high end drum scanners but it has some really good tips for extending the range of the profile (I'm getting clipped highlights and shadows with my LProf generated profiles).
2) Good question, although I suspect that the improvement over 33 CLUT would not be noticeable.
3) Do not blur the scan of your IT8 target. The noise is apparently needed to get an accurate profile. I can't remember where I read this but it was a knowledgeable source.
4) My version (using the latest code from CVS) doesn't show "Output colorspace" but "Input colorspace". It is simply the profile to use to display the IT8 scan within LProf. It has no bearing on the produced profile. I simply just leave it at Adobe98 (my display nearly covers the Adobe98 gamut).
5) I don't know
6) The advantage of an embedded profile is that you can assign another (better) profile later on without potentially throwing away colour data. In other words, it's a non-destructive process. In my book, this more than compensates for the increased size of each image. 668KB extra isn't much when you're dealing with scans that take up 148MB (16bit with Infrared channel). Disk space is already cheap.
Of course, I convert my scans to sRGB or Adobe 1998 when sending to a printer or publishing on the web.
6a) Yes. Assigning a profile is non destructive on the image data. The image data only gets affected when you convert to a particular profile.
Assign and convert is the terminology used by Photoshop.
6b) Yes, disable the scanner software color management. Scans created that way will be in the color space of the scanner, which is what you obtain when you profile your scanner.
By default, when you open images in Photoshop that have no profile, it will assume that they are in the sRGB colorspace. You need to make sure that Photoshop doesn't convert the image to your working colorspace when you open images without profile. Go in the Edit menu -> Color Settings and specify RGB: Preserve Embedded Profiles.
Use the Edit -> Assign Profile to assign the profile you've created in LProf.
Something else. Wolf Faust told me to use the current version of LProf. They've apparently made important improvements on the generated profiles since 2006. Unfortunately, the pre-built version are all outdated so you need to build from scratch from CVS. It's quite a chore due to all the extra libraries that also need to be built, specially the Qt lib used for the graphical user interface. I've built mine on a mac so I can't share with you my resulting application.
