[Leica] Scanning Kodachrome

[tgray at 125px.com (Tim Gray)]

On Mar 13, 2011 at 09:08 PM -0700, Peter Klein wrote:
> But one thing that drives me crazy is that even with VueScan's Kodachrome
> profile, my old 1970s slides scan a bit green/cyan in the shadows, and a 
> bit
> magenta in the mid to upper midtones.  Fixing either color makes the other
> worse.

A couple things.

1. If you've got a lot of Kodachrome to scan, think about shelling out the 
$50 and get a Kodachrome target from Lasersoft.  Profile your scanner with 
it.  I didn't particularly like the target I got using Vuescan's built in 
profiling routine.  I find the one I got from ArgyllCMS (free but a command 
line utility) a lot more.  We can discuss this offline if you want - I can 
generate a profile for you if you'd like.  I got best results from using raw 
scans...

2. Don't know much about the software you are using.  I also don't know what 
the original slide of your example looks like.  But, the color casts you 
talk about can be corrected.  It's a shame you don't have Photoshop, because 
there is a nifty little command called Auto Color, accessible through a 
Curves adjustment layer.  When you put it on 'Find Dark & Light colors' mode 
with the 'Snap to neutral midtones' option, it often gives you a great 
starting place for color correction.  Your software sounds like it has a 
similar function (see point 4 below).

3. That being said, try adding a curves or levels adjustment to your image. 
Play around with adjusting the gammas (or midpoints) of the R, G, and B 
channels.  Again, I'm working from no references, but to me, boosting the R 
midpoint and pulling the B midpoint down seems to give a better result from 
your sample.  Also, your black point is seems a bit low, especially on the G 
and B channels.  You might play around with moving up the shadow end of 
those two channels.

4. This document on the Picture Window Pro looks like it has some 
interesting pointers on color correction.  I apologize if you already know 
this stuff.

<http://ftp2.bmtmicro.com/dlc/Color_Balance.pdf>