Getting Around in GIMP - Blue Channel Check Layer (Retouching)

In my previous post for the Open Source Portrait (Postprocessing), I had mentioned during the skin retouching in GIMP section that there was a method that I had used in the past for helping to make skin imperfections visible for healing.

The rest of my GIMP tutorials can be found here: 
Getting Around in GIMP

It is a similar method described by Calvin Hollywood (again), that he calls "Check Layers". He explains what they are and how he uses them in the video below:

If you don't want to watch the video, the basic idea came about from my experience when converting images to B&W. That is, the Blue channel of a color image is not flattering at all for skin (unless you have flawless skin). Conversely, the Red channel usually has very pretty skin tones (and hence it's common to overlay a Red channel on your image and set it to Overlay blend mode to enhance this).

What Calvin Hollywood shows in his video is using a Photoshop adjustment layer to turn the image into grayscale, and to turn down the contribution from the Red channel, while increasing the Blue channel. This results in a more contrasty image that favors the blue channels, and will make skin imperfections much more visible.

The problem is that we don't have adjustment layers in GIMP...

Calvin Hollywood Freaky Details in GIMP

This article (possibly updated) is now available on pixls.us:
PIXLS.US: Freaky Details

German photographer/digital artist/photoshop trainer Calvin Hollywood has a rather unique style to his photography. It's a sort of edgy, gritty, hyper-realistic result, almost a blend between illustration and photography.

As part of one of his courses, he talks about a technique for accentuating details in an image that he calls "Freaky Details".

The rest of my GIMP tutorials can be found here: 
Getting Around in GIMP

Here is the original video I saw him describing this technique in from Scott Kelby's blog, Photoshop Insider during a guest appearance:

[Update]
I've been told there are problems loading the page with IE if I include the video I first saw this technique on. So, to make sure everyone can see this tutorial, the original video is on this page towards the end (it's the only video on the page)...

Go check it out, then come back to read the rest of the tutorial!

And here is a more current Youtube video from Calvin that describes this technique using a different image:

In my meandering around different retouching tutorials I came across it a while ago, and wanted to replicate the results in GIMP if possible. There were a couple of problems that I ran into for replicating the exact same workflow:

1. Lack of a "Vivid Light" layer blend mode in GIMP
2. Lack of a "Surface Blur" in GIMP

Those problems have been rectified (and I have more patience these days to figure out what exactly was going on), so let's see what it takes to replicate this effect in GIMP!