SANE EPSON Backend - Negative Scanning

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These instructions were provided by Mike Porter:

Hi,

As you have noticed, it is critical to use a 'user specified gamma
curve' when scanning negatives or slides.  So, always select 'user
specified...' as the gamma curve type.  After this, you must get
proper gamma curves set up.

Color correction is best done using xsane, and just hitting the
color correction button.  On the main window, there are three or
four buttons near the buttom with strange icons on them.  Auto
color correct is the third one, I think (Not writing from a
location I can run xsane).  If you are using xscanimage, you might
want to consider a switch to xsane.

If, after color correcting, your previews look good, but your scans
come out mostly white, then you have an old sane-epson driver.  I
fixed this bug a few months ago...get a new(er) version.

If you want to do color correction manually, you need to bring up
the xsane dialog that shows the color histograms.  The raw
histogram will probably show the three curves tightly crunched to
around 1/3 the total length of the X axis, with each curve somewhat
offset from each other.  Use the buttons to display just one color
at a time to see what I mean.

You now have to play with the gamma, brightness and contrast
sliders to expand the curve and shape it properly.  Gamma moves the
'hump'?  Brightness adds to all values and contrast basically
multiplies each value, with 0 set to the middle of the curve (I
think).  When you are done, you will have three curves that cover
the X axis, and nicely overlap each other.

Or, you could just hit the auto button I mentioned above, which
does the same thing!

A trick:  When using auto, select, on the preview, the area you
want to make your exposure for.  For instance, an outside flash
picture taken at night will likely have a black background and a
well lit subject.  Select just the subject and hit auto.  The color
correction will then only take into account the subject area you
have selected.  Then reselect the area you want to scan and make
your scan.

There are plans to add manual gamma curve correction to xsane.
This will allow you to fine tune the gamma curve.  I find this is
needed about %10 of the time, and only for 'special' prints.

Let me know if you have any more questions.  I've done a fair
amount of transparency scanning using sane.

Also:  I have never figured out anything useful with the actual
color correction sliders.  I used to think they were broken, but
the actual problem was my technique and then there was the error I
mentioned above that I fixed a couple of months ago.  Hmmm...I'll
have to re-investigate those sliders.

Mike