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.