You've certainly hit the two things I most commonly tweek on all my selected photos - curves and sharpening.
curves - I had not seen the chromasia page you reference, and it looks good. I learned from Dan Margulis' 'Professional Photoshop 5' (found on a gimp recommended reading list once), the key chapter 3 - color correction by the numbers - is downloadable from
http://www.ledet.com/margulis/articles.html. His approach includes correcting colour casts by targeting neutral regions; this is well supported in the gimp with the 'sample points' dialogue and I don't think most people are aware of it or how to use it. search for it on docs.gimp.org for the details, clearly I'm mentioning it because I think you should too
sharpening - I'm lazy and just want to be fed info while I'm reading, and the process is a bit hard to follow. The steps are very clear, but I would like to see some intermediate images of what you are doing with the blurring and layer masks (on the target image). It might be that you can do a (some) put-together image(s) showing what's happening in the different layers/masks, e.g. 1/4 vertical stripe showing background, next stripe showing blurred mask, next stripe showing the inverted mask, 4th stripe showing the working view. This is just from going around your description, probably there are better ways to capture the changes in a few images and the presentation or subject might need some work (perhaps just zoom in) so there is sharpened content in each stripe.
There's also some sharpening approaches working on the L layer after splitting into LAB, but gimp isn't lossless in this conversion so can be done similarly in V layer of HSV.
other stuff :
- I'd like to be more adept at using layer masks to highlight or modify certain regions, e.g. really hammer sharpening a person's eyes but keep all those spots on the forehead a bit blurry. Perhaps a section just about duplicating a layer and merging a portion of it in seamlessly with a layer mask. You might think about factoring some of this out of the sharpening section, and then be able to take it in another direction with a section on merging two completely different images (kitten with dinosaur head etc.).
- seems pretty simple but I was showing someone how to use the clone tool the other day. Don't know how introductory you want to go, but does seem like the docs.gimp.org treatment could be enhanced with some example photos. I know there's lots of tutorials around for this too, depends on your target audience and how you see your contributions being used.
- following on from the above, there are some things I'd like a quick, task-oriented 'cookbook' list for. the other day I was trying to draw a 'smooth curvy line'; I blundered around with the paths dialogue and got good enough for what I was doing at the time, but I wanted a bit better. similarly, drawing basic shapes using the select tool and then stroke isn't very intuitive and I can remember having to search around for this procedure more than once. I love the O'Reilly Perl Cookbook for example, where I can quickly jump to 'how to do this basic task' and then get on with my life. these things aren't big learning essays like using curves, maybe just enough to point to the 'water drop' icon to blur or figure out that 'remove unwanted object/blemish' has an icon like a stamp or pair of plasters and is called 'clone' or 'heal', 1-5 steps if/as needed, and maybe a few links to more in-depth usage tutorials as appropriate. Certainly I can find it all on google, but going off on a tangent to surf around and find what I need isn't always feasible when I am hurrying to get a birthday card done.
so, carry on!
rob.
.
