# How do I get a negative orange mask *back*?

Manuel Panea (mpd@rzg.mpg.de)
Fri, 26 Nov 1999 17:11:07 +0100

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Hi. Here is a question to the experts.

I'm developing the Canon backend. The backend works with some Canon
flatbed scanner models and with my 35mm-film scanner model 2700F. This
model can scan negatives and slides.

When scanning negatives, there is a SCSI command to set the scanning
speed. In this way, dark photos can be scanned at a lower speed, exposing
the film to more light so that the scanned image looks good. Alas, this
speed setting command works only for negatives, not for slides (that's
what the specs say and it's true, I've tried it). Unfortunately, the only
available and fixed scanning speed for slides is invariably too fast.
Almost all slides get scanned too dark. What to do?

I thought I could try to outsmart the scanner and tell it to scan a
negative at a low speed when in fact I am feeding it a slide. Inverting
the colors is then an easy problem. The difficult problem is that, when
scanning negatives, the scanner automatically removes the orange color of
negative films. Slide films do not have this orange color, so if I try
this trick, the scanner gives me an image where all information about
orange-like colors is missing.

Does anyone know of a good way to get this orange back? Just "adding" it
with e.g. the Gimp doesn't help, the image still doesn't look good. With
some other operations, specially "equalize" I can get the image to look
almost good, but not quite, and worst of all, the histogram is then "full
of holes".

I have put on my Web-page a sample image scanned as a negative and as a
slide, in case someone wants to see the effects and maybe experiment with
the images. Find them at: http://www.rzg.mpg.de/~mpd/sane/blueslides

Any help would be very much appreciated.

Manuel Panea Tel. +49 89 3299 1133
Rechenzentrum Garching Fax +49 89 3299 1301
Postfach 1533 E-mail: mpd@rzg.mpg.de
85740 Garching Germany http://www.rzg.mpg.de/~mpd

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