I noticed that a lot of tutorials will use what are, in my opinion, two of the most powerful modifiers for gimp photo-editors, but it's hard to find a good tutorial that explains how these two tools work.

I'm talking about layer masks, and layer modes of course. I'd say approximately 90% of my technique falls within using a combination of these two tools, and I think anyone who is serious about learning GIMP (or photoshop, or any decent photo-editor) should have a firm grasp on the principals behind these two tools.

I explain how it's done by teaching everyone a more-powerful way to do the oh-so-popular "make a part of an image in color while the rest is in black and white" effect. Check out the video below, hope it helps you.

I keep telling myself to make a list of the layer modes and what they do, as they are very important to achieve certain effects...but I'm a bit lazy. I wish I knew more about layer masks, would love a tutorial on that, too! I have used them following tutorials, but am not very good with going out on my own with them.

Gimp's tutorial page really explains it in quite possibly too much detail here http://docs.gimp.org/en/gimp-concepts-layer-modes.html

All-in-all, I think I use overlay, color, saturation, multiply, and on rare occasion dissolve the most.

PS: Yes! Definitely get comfortable with layer masks...In my tutorials, that's the only way I teach. I never delete, just mask.

the document is way to complicated ... too much information! I just want to know in layman's terms. What I usually do is experiment, but it's hard to plan ahead that way.

Agreed. I think that's why Gimp's tutorials are never referenced...they just have too much information. (I guess it has to exist somewhere for developers though.)

I really, really love this tutorial. It is very easy to understand and the method is simple. I like the fact that the original image is still intact and without changes. I think this is a place where having a video tutorial is superior to a text + pictures tutorial. Original image here: http://www.sxc.hu/photo/1334759

I lowered the opacity of the black layer just a little to give a faint pink, almost porcelain-like quality to the hands and arms.

that is awesome, one of the best spot color pics I have seen! The slightly colored background really works!!!

Fantastic! I'm very glad you thought the tutorial taught well. I really love the image you got out of it.

i made this a while back.

very nice tutorial, I must start using layer masks more as I like the non-destructive editing. Oh, that hummingbird looks great in the b&w pic.
oops, what happened to my pic?

The only issue I have with that method is if you decide to edit the image (curves, contrast, etc) you have to duplicate those changes on the duplicated layer (which sometimes can mess things up in more involved edits.)

using a layer mode removes that concern.

@ tstandiford excellent tutorial.very clear

Rod i don't find the info on layer modes in gimp help overwelming, on the contrary are even a bit incomplete :
Maybe clear for who has a very mathematical mind but for other know the mode math formula doesn't help much to imagine the results
For that are needed visual examples...several not just one (as example i seldom saw a example of what i found a very interesting use of several modes as overlay ,multiply ,grain merge , that is merge over a duplicate )

Agreed. Unfortunately, I believe in order to ever truly use layer modes to their full potential, you have to force yourself into the layer mode mindset, which mostly happens with tinkering around with each layer mode.

Thank you for the compliment. I'm happy to see my explanation was clear. It's really hard to put a layer mask in layman's terms, haha.

a real quick try using your video, saved it as a png other wise i would have to merge layers for jpg..right, also i used paths to select the tractor but couldn't i have just used the eraser instead
i'm just here to learn..

First off, great job. Looks like you used the pen tool really well.

Yes, you could have just erased the spot inside of the mask, but getting into the habit of always using a mask instead of erasing will give you an extra layer of depth for more interesting edits in the future.

Plus, it's a lot faster to switch between "erase mode" and "draw mode" by setting your foreground and background colors to black and white, and pressing the x button on your keyboard to switch between the two.

Example, I'm "brushing the color" off of the grass around Noah's shoe in my video above by brushing in the color white in the layer mask. Notice that my background color is black and my foreground color is white at that point. If you press the X key on your keyboard, it would switch the foreground and background colors, turning your brush into a black brush. Brushing a layer mask with black would "brush the color back on."

This is especially handy when you're doing any sort of shading with transparent brushes.

old habits and all..i do like using the x to switch back and forth
wish it would've been that easy to paint my old tractor

I can imagine so. Take a look at some of my other tutorials, maybe that will show you my theory of the "mask" vs "erase" thinking.

i will look at them later today, i've had gimp on my computers since windows 98 but never really spent as much time with it as i have this summer, learned a lot since joining gimpchat

AH! I got it! Do this to your tractor image:

Click on your layer mask
Click colors>>>invert - this will make everything but the tractor in color.
Now take the bucket tool, and fill the layer (not the mask, the layer) with red. That will turn the tractor into a red one. You could fill this layer with green, blue, purple, a rainbow gradient, it doesn't matter - it will give your tractor a paint job in any color you want.

See how easy it is to change that?

One thing I do take exception to is breaking the path with the Shift key. It starts a new path in the same path window rather than making a sharp corner. You may be able to get by with one break in the path, but not more than that.

This shows a path I broke in several places with the Shift key. Then, when the path is activated, there are separate areas that will fill with color, rather than one large area.