Anyhoo (yes "anyway" was already taken).

[Probably superseded]
Wrong place for this, but I'm not sure where the right place is. Basically I've been trying to use GIMP 2.6 to replicate a process I use in Paint Shop Pro 6 (why? Because Flickr penalises any image without EXIF data [digital cameras include EXIF, so no EXIF means it's not a photography, just art or advertising], which this ancient version of PSP strips out).

The process is extrapolated from Stairs's technique:

I run it through a couple of adjustment layers - I blend a 70% grayscale (to desaturate non destructively) with a 58% inversion layer above (to increase contrast but reduce depth of shadow) - then a couple of masks to burn and dodge the highlights and shadows. It picks out every little imperfection, so it works better for men than for women.

My take on this is in PSP6 is:
- Open image.
- Take out gunk, hot pixels, straighten.
- Add Hue/Saturation layer, using saturation of -80 with a layer opacity of 25%.
- Add Inversion layer, using a layer opacity of 40% [it's looking pretty grey by this stage].
- Add Curves layer and dump the contrast back in, leaving the shadows a little off absolute-zero.

Yes, I know this veers wildly off-course from Stairs's route, but if I do what I think he says it sort of does the opposite of what I think he says it'll do. Also my version, although it feels desaturated is a lot less so than Stairs's [No. 8 in his Camera folder].

Basically it's a way of damping the shadows while encouraging contrast in the midtones, while avoiding the super-saturated look that is a little frequent on Flickr (I believe it's technically known as 'punchy').

And trying to replicate it in GIMP* just turned the sky pink (seriously, how can an inverted layer with opacity at less than 50% invert the colours? Setting the opacity to 50 shows a slight negative image amid the grey. According to my take on maths +50 + -50 = 0, not somewhere a bit below freezing. PSP with an upper invert layer opacity of 50 becomes one big block of middle-C grey, so it's not just me. So if the mid-point in GIMP is below 50%, what's).

* Which I did by:
- Duplicating the base image to provide the right number of layers.
- Leaving the base as is.
- Desaturating the next (20% opacity should equal my -80x25%opacity, Stairs says 70%).
- Inverting the third and applying 40% opacity.
- Merging the visible layers.
- Applying curves.
- Abandoning it in the preview because the sky is pink.
- Going back and tweaking.
- Getting the same result.

Interestingly turning off the visibility of the desaturated layer stops the 50% inversion layer from being anything but the purest grey. Which is kind of weird.

You'd think that makes it sound like I've applied the the inversion to two layer, except I've reverted and repeated the steps a couple of times to get the same pink result. Most, most weird.

So anyone have the foggiest idea what's going wrong? What am I doing in a really absurd way? What have I forgotten?
---
So it turns out closing everything and starting again but this time using Hue/Sat within gimp to desaturate works better. Using the same settings still desaturates more in GIMP than it does in PSP though (and inventing layers and then applying non-editable changes to them [you can undo, but you can't tweak] is mighty cumbersome).

Guess who's reverted to the old way.

Anyhoo,

PS. The image above is not one the technique has been applied to. It's simply one that shows what happens when I don't have some idea of what I'm trying to do.