Photo color boost using GIMP & LAB

furiousBlog

Oct 5: Photo color boost using GIMP & LAB

Note: This entry probably won't be of interest to most of my normal readers. I'm putting it here in hopes that others using the GIMP will find it and find it useful.

I was recently introduced to the idea of using LAB color mode to give a little boost to the colors in a photograph. It really makes a huge difference if your photo looks a little flat. There are a few different ways to do it, but I mostly use the technique described on this page:

Punch Up Those Photos (Gimp Style)

That page has some sample photos, but here's the relevant steps:
  1. Open Image
  2. Go to Image>Mode>Decompose
  3. Check LAB, Check Decompose to Layers, hit OK
  4. Open Layers dialog. Make only the B layer visible.
  5. Duplicate B layer, set "B Copy" to overlay (Opacity is 100%).
  6. Merge both B layers (Image>Merge Visible Layers/CTRL-M) Choose Expand as necessary (though other options don't make a difference in this case) Hit Ok.
  7. Repeat steps #4 through #6 for the "A" layer.
  8. Select "L" layer, apply a slight S curve, mostly adjusted towards the dark end of the curve. (GIMP's overlay is calculated a bit differently)
  9. Image>Mode>Recompose and Make sure you select LAB with the correct layer order.


I find that the results can be a little much, so I usually copy the resulting image into a new layer of the original image and then play with the layer opacity until I like it.

I wanted to work this into my whole photo workflow, so I wrote a GIMP script to perform this action on a directory of images and then save .xcf (GIMP's native format) and .jpg files. It also applies the unsharp mask to the image before saving the jpg.

It seems pretty handy, so I'm releasing it under the GPL:

batch-lab-colorboost.scm

Basic usage:
$: gimp -i -b '(batch-lab-colorboost "PATTERN" RADIUS AMOUNT THRESHOLD OPACITY)' '(gimp-quit 0)'

Example:
$: gimp -i -b '(batch-brp-process "*.ppm" 5.0 0.5 0 30)' '(gimp-quit 0)'

If you just want to apply the effect one image at a time, from within GIMP, you can use this script, which provides a menu item under Script-fu > Decor and lets you set the options in a dialog:

lab-colorboost.scm

To install either, just put the file into you GIMP scripts directory. Mine (Debian Lenny/Sid) is ~/.gimp-2.2/scripts and yours should probably be something similar (maybe ~/.gimp/scripts). I've only tried it on Linux, but I think it should work with GIMP on Windows, too.

p.s. I'm planning on writing an entry on my Linux-and-GIMP-based RAW-to-jpg photo workflow soon.
Posted by ben in Tech on 10/05/07 11:40 | Comments (5) | Trackbacks (0)

Trackbacks
Trackback specific URI for this entry

No Trackbacks

Comments
Display comments as (Linear | Threaded)

I have tried to install this several times but keep getting the same error messages. First it doesn't let me install it directly saying I don't have permission to save it to the scripts file.

Second it gives me this error message when I try to run it on an image

LAB Colorboost Message

Error while executing script-fu-lab-colorboost:

Error: set!: unbound variable: labimage

Can you help me get this working?

Skip
#1 Skip on 2010-03-01 07:23 (Reply)
Hi Skip. I need to update this script for the newer versions of Gimp. I think that Gimp 2.4 & beyond require that all of the variables be declared as opposed to just set on the fly as I've done in this script. This is what is causing the unbound variable error. I'll try to do that and update this entry soon.

I'm not sure about why it won't let you put it in your scripts directory. What OS are you running? What specific directory are you trying to put it in?
#2 Ben (Homepage) on 2010-03-03 14:08 (Reply)
Hi Ben,

I downloaded batch-lab-colorboost.scm today and tried it with Gimp 2.6.7 on Ubuntu 9.10 Linux.

Problems:
Script file is named "batch-lab-colorboost.scm",
but example gives:
gimp -i -b '(batch-brp-process "*.ppm" 5.0 0.5 0 30)' '(gimp-quit 0)'
so I changed this to
gimp -i -b '(batch-lab-colorboost "*.JPG" 5.0 0.5 0 30)' '(gimp-quit 0)'

and run it:

me@ubuntu:~$ cd /home/me/Panorama/colorchange

me@ubuntu:~/Panorama/colorchange$ gimp -i -b '(batch-lab-colorboost "*.JPG" 5.0 0.5 0 30)' '(gimp-quit 0)'

but got this error:

/usr/lib/gimp/2.0/python/gimpui.py:36: Warning: g_set_prgname() called multiple times
from _gimpui import

/usr/lib/gimp/2.0/plug-ins/layerfx.py:5304: Warning: g_set_prgname() called multiple times
gimp.main(self.init, self.quit, self.query, self._run)

/usr/lib/gimp/2.0/python/gimpui.py:36: Warning: g_set_prgname() called multiple times
from _gimpui import

/usr/lib/gimp/2.0/plug-ins/btn4ws.py:1109: Warning: g_set_prgname() called multiple times
gimp.main(self.init, self.quit, self.query, self._run)

GIMP-Error: Opening '/home/me/Panorama/colorchange/(gimp-quit 0)' failed: No such file or directory

(ufraw-gimp:11839): GLib-WARNING **: g_set_prgname() called multiple times
batch command experienced an execution error

And that's it. How to fix?

Thanks,
Jan
#2.1 janmartin (Homepage) on 2010-07-10 04:35 (Reply)
Setting the variables seems to be the problem and I am trying to figure how to do that now. I have never done this so any help would be great.

I am using Windows 7.

Skip
#2.2 Anonymous on 2010-07-10 09:44 (Reply)
Hi Jan and Skip.

I actually haven't run this script in a long time. I've started doing most of my color enhancements in the raw conversion process. But, I'll try to take a look at this this weekend and see if I can get it working. I'll let you know the results.

Ben
#3 Ben (Homepage) on 2010-07-10 10:53 (Reply)

Add Comment

Enclosing asterisks marks text as bold (*word*), underscore are made via _word_.
Standard emoticons like :-) and ;-) are converted to images.
BBCode format allowed
E-Mail addresses will not be displayed and will only be used for E-Mail notifications.
 
 

What I'm Doing (twitter)


    Follow me on Twitter or via RSS

    Categories


    All categories

    Archives

    Syndicate This Blog

    Quicksearch