I see more and more tutorials springing up across the net advising people to only use the 'multiply' function on their base lineart to color under it. How about having the lineart truly isolated from its original plain background? Just a layer itself with nothing else but the pre-existing image before color :)

FOR: Adobe Photoshop 5.0-CS. I'm not too familiar with 4.0 and later. I'm sure some of them dont have channel pallate or transparency options :/

Advantages to this method:
-extremley mallable. Methods used to enhance lineart via filters and by hand are easy and convenient to do.
-Strengthening your lineart. Able to copy the layer of lineart under the original to bold, highlight, perfect, etc.
-Access to the 'preserve transparency' option; enabling the artist to brush over certain parts of the lineart with other colors, gradients, and patterns.

Disadvantages to this method:
-Any color gradiation pre-existing in the image's lineart will be lost in the conversion. This can be sometimes remedied just by using the 'preserve transparency' option
-Not much else :P

(Sorry, I dont have any images for this, but hopefully you'll know what I'm talking about. I might come back in later and add images to help)

- Start off with your basic lineart, pencil art, a photo, whatever you want! Just an image in general :) Make sure the image itself is in 'Greyscale' or 'RBG Color' mode. You can remedy this by going to Window > Image > Mode and selecting your color mode of choice.

- In your layer's pallate (F7 or Window > Window > Layers ), Create a new layer. Leave that alone for now.

- In the channel's pallate (Window > Window > Channels ) and click the button farthest to the left. It should be shaped like a dotted circle. This function selects all of the white parts of your image.

- Select Window > Select > Inverse (Ctrl + Shift + I) to inverse your selection. Now this has selected all the dark/colored parts of your image.

- Keeping your selection, trash or throw away your 'background' image (your original image layer). You wont need it :)

- On your new layer, select Window > Edit > Fill (Shit + F5 ) to open your fill option. Depending on your version, the fill will automatically be selected as your foreground or background color on your toolbar. In newer versions you can select your color fill inside the pallate or a pattern t o fill with... Or just click 'black' :D Press OK.

- Deselect your selection.

Tadah! Isolated art! You can manipulate the color of the lineart or image without ruining it by either locking or 'preserving' transparency and running your brushes or gradients over it
.
Hope this helps someone :)
-TRIP

This is just to preserve/convert all lineart into 100% opaque right? If I'm thinking about this correctly (and I like to think I am) you don't preserve any transparency since you're inverting the selection. It seems that checking the 'preserve transparency' option still wouldn't "preserve" the transparency this way, but you'd probably know more about this. Anyway, nice tutorial.

preserving transparency only reguards to the final outcome of the image. Say you had color gradiation in your original image. Say, like.. A sunrise. Where a sun is, the bright light yellow there will be less color (less dense) than a part that had a darker color like orange. It keeps almost a sort of 'shadow' of images like photos and keeps solid color like black cartoon lineart. Every color that isnt white in the inversed selection is preserved as dense or partially transparent shades of the new single color. You don't use the 'preserve transparency' feature until you are actually coloring with the lineart, you dont need to during the lineart's conversion :) sorry if that wasnt very clear