Digital ICE

[hart]

I scanned two rolls of film as testing to determine best settings for getting most color information from negative so I could treat TIFF as digital negative and then generate "prints" for specific needs from Photoshop. (I will post my methodology for other newbies to review as one option). During testing, I was getting great results using canned air and static free brush to remove dust. I put plan into action and damn dust showed up on every roll so I took step back.

I scanned two frames with, no Digital ICE, Digital ICE in Speed Mode, and Digital ICE in Quality Mode (discovered Dust Removal mode was a joke from first scans -- it fixed light coming through clouds). The scan speeds got slower (not a problem for me) but I was surprised by tone/color/shift differences in images. When I looked at histograms in PS, differences were obvious. No ICE and ICE in quality mode were very close in tone and histogram but still slightly different (not enough to matter for me). Since the ICE technology for film indicates it uses an IR sensor to detect and map dust and then software to fill in affected area, I expected an occasional bad "fix" of dust spot but not a tone difference.

Did not search, so forgive if already posted, do others see the difference and for knowledge base why does it occur?

[Kevgermany]

Best guess is that ICE is applied before the colour balance. Colour balance, as far as I can tell depends on pure white being present. Dust on negs when inverted to a positive becomes pure white, which would affect the colour balance. Take this away with ICE and you're using a different reference point for the colour balance.

[bez]

How large is the colour shift? AFAIK ICE uses the lower reflective lamp as the IR detector – is it possible (though unlikely) the lamps are different colours? Although I can’t understand why this should affect the colour of the top lamp, coming through the film …

[hart]

Best guess is that ICE is applied before the colour balance. Colour balance, as far as I can tell depends on pure white being present. Dust on negs when inverted to a positive becomes pure white, which would affect the colour balance. Take this away with ICE and you're using a different reference point for the colour balance.

Hadn't reasoned out order of operations but thought the pure white spots may have been factored into color calculations.