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Author Topic: duck! incoming filmscanner color temp curveball  (Read 13088 times)

carl dw

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duck! incoming filmscanner color temp curveball
« Reply #20 on: April 15, 2009, 01:34:40 PM »

Quote from: lowep
What happens to a scan of a color negative when you change the color temperature and/or the color reproduction of the scanner’s light source, and how can you get the original colors back again?

This is a question I am facing now    after replacing the fluorescent tubes in my Imacon Flextight Precision II negative scanner this morning.

Until recently I have used the original light tubes that came with the scanner when I bought it secondhand a few years ago.  These tubes still function but I decided to change them as it seemed that the scans I was obtaining from my 4x5 negs reproduced less detail in the shadow areas than I had hoped.

To change the tubes is no big deal as the procedure is outlined in the user’s manual. But of course the exact model of the original light tubes specified in the manual (Osram L8W/12-950 Lumilux de luxe Daylight) are no longer available. So I bought a pair of new model tubes (Osram L8W/954 Lumilux de luxe Daylight) that as you can see have very similar specifications. Much to my delight the new tubes fitted in the scanner and produced an almost identical scan to the old tubes.    But the color reproduction was slightly different.  

Concerned by the color change (I have about 400 negatives waiting to be scanned), I wrote to Osram support to ask if there was any difference between the two tubes. This morning I received this thought-provoking reply (which I translate from Danish to English):

Hello Peter
The color temperature and the color reproduction is not the same.
L 8W/12-950 has color temperature 5000K and color reproduction (farvegengivelse) is approx. 98
L 8W/954 has color temperature 5400K and color reproduction (farvegengivelse) Ra > 90, approx. 92
This means that you will probably need to undertake a big calibration job.

Consequently, I am faced with the following questions that I am unable to answer     so would appreciate any insight or suggestions you may be able to offer.

1)   What difference can I expect to see in a scan of a negative if the color temperature (in this case of the scanner’s light source) is increased from 5000K to 5400K?

2)   Does such a change in the color temperature of the scan impose a limit on the output quality of the color reproduction or does it just mean that I have to work a little more on adjustment of each image ( eg in Photoshop) to make it look right (whatever that means!)

3)   What if any significance does a change in color reproduction (farveangivelse) from approx 92 to approx 98 have?

4)   Could these differences in color temperature and color reproduction be corrected by running the scans through a raw conversion software like Capture One that enables adjustment of the color temperature. If so how do I convert my TIFF scans into RAW format (Imacon Flextight uses its own proprietry raw format)

5)   What could be meant by a “big calibration job”? Does this mean I should try to recalibrate the scanner (sounds challenging) or find a way to use software such as Photoshop or Capture One to “recalibrate” the scans?

6)   If you were me and had time to fool around with calibration - but not money to buy a new scanner. What would you do?

Hope this is not too many questions!

Hope you are well into some successful scanning by now.

I also use a Flextight II and have a couple of thoughts on your dilemma having just had the tubes out of mine.

I bought the scanner new a good few years ago and have never had need to change the tubes. Two years after it's purchase I took the digital route for my commercial work and have only used it for scanning personal projects since. I have never scanned reflective originals (as it's such a pain with this model) so the top tube has never been used. They are the same model, they degrade with use as opposed to age, so earlier today a simply swapped them over (after a wipe down with some Isopropanol). This should extend the scanners life for a good few years with no expense or stress.

With regard to your colour change, I usually scan transparency where I take a grey (ish) reading and then adjust to taste. On the few occasions I've had need to scan colour negs I've found the canned 'profiles' able to only get me on the playing field, I always make adjustments in the 'Colour correction panel' and then save them for further use via "File, Setup, New". They then appear in your Setup list to repeat on the same neg type - no need to correct every image individually.

I believe that the scanner does take a 'white balance' before every scan (it is done through that cut-out you see above every frame aperture in your film holders). So the colour shift you're experiencing must be a mismatch between the spiky spectrum of light from your new tubes and the profile Imacon made for your neg type. Again, do colour correction and save a preset.

Though I've read comments to the contrary on this thread, it is my understanding that as much correction as possible should be done in Flexcolor at the scanning end as opposed to Photoshop. This is a high end scanner which cost £9000 back in 2002 (the latest version about the same now), the software is very sophisticated and designed for reprographics and commercial photography. Making changers to the preview image is a little like adjusting the Raw file before outputting a Tif. You can in fact scan to "3F" which is raw data, then do your adjustments later (but the files are huge).

Hope you've sorted things out in the meantime.

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