The first thing you have to do when you start to CG a drawing is to clean up the image and prepare it to be colored. There are several ways to get the lineart by itself but before that, you will most likely have to "clean" it by making the lines as crisp and clear as possible. One of the ways to clean up a lineart is to use Brightness and Contrast. Just move the sliders left or right until you get a clean image without any pencil marks. If for some reason your lineart or pencil isn't exactly black, you can use Brightness and Contrast, Hue/Saturation (bring saturaion down to -100) or Colorize or Black & White depending on what software you're using. Note: Your image must be in RGB mode or else you will not be able to color it or make any adjustments.
Brightness & Contrast
GIMP (2.4.2): Colors > Brightness-Contrast (older versions may be under Layer)
Photoshop: Image > Adjustments > Brightness/Contrast
Black & White
GIMP (2.4.2): Colors > Colorize or Hue/Saturation
Photoshop: Image > Adjustments > Black & White or Hue/Saturation
GIMP (2.4.2): Image > Mode > RGB
Photoshop: Image > Mode > RGB Color
If there are lines that still hasn't disappeared from the image, use a brush or eraser to clean it up. Take this time to clean up your lines too or connect them if there are spaces. Here a sample of a properly cleaned pencilwork:
Next, we'll prepare the drawing for coloring. There are two ways to color something, you color atop the lines or you color beneath the lines.
If you're going to color above the lines, then you do not need to follow the remaining steps. Just save your work and stay tuned for the next
tutorial. For those who color beneath the lines, there are several ways of getting the lineart on a layer by itself.
1) Selecting and deleting white spaces
2) Using the alpha channels as in Marie Dillinghams CG Lineart tutorial
3) Selecting the lines and filling it in on a new layer or
4) Tracing your lineart from scratch
Let's start off with the first one. Before we start, make sure you make a duplicate of the original layer. For those using Photoshop, drag and
drop the layer onto the icon that looks like a page. For those using GIMP, drag and drop the layer into the icon with double photo's (next to the
anchor). This will bring up a new layer above the original called Background Copy. Turn off viewing the original layer by clicking on the eye. Now,
make a new layer and place it underneath the copy (Photoshop - hit the page icon; GIMP - hit the page icon to the left). Fill in this new layer with
any color except white. This is so you know which areas have been "cleaned" out. Your layers should look like the image on the left.
Now that's done, lets clean out the white spots by selecting the Magic Wand icon in your tool bar. Click on any white space you see in the image and press delete. To select multiple white spaces at one time, keep your hand down on Shift and click on the spaces you want to select. If there are hard to reach white spots, zoom in at the image and select then delete it or you can use your eraser to get rid of it. Depending on how complex your drawing is, this may be fast or long. To make a nice looking CG, you have to take your time cleaning up your image. The lineart is what holds your drawing together. If it's sloppy, it shows.
GIMP (2.4.2): Shift+Ctrl+A
Now that this cleanup is done, you can do touch up work on the lineart because now it's most likely all jagged looking or not as thick as it was originally. Before you work on it, make sure you make a copy of it and rename it appropriately like original lineart with the new copied layer called cleaned lineart or whatever you prefer. View out of the original lineart and start working on those touchups! Once you're done with that, save your work as a PSD to retain the layer structure(I hope you've saved it before as well!) and you're done!
Using alpha channels will pretty much get you to the same spot as the above method. If you want to do cleanup, follow the instructions as stated above. If not, save your work and stay tuned for the next CG tutorial.
Opening the Layer Palette
GIMP (2.4.2): Ctrl+L or Dialogs > Layers
Photoshop: F7 or Windows > Layers (though usually already open on right)
The third method is a much faster way but works well only if all your lines are mostly connected and are purely black so they are selected
properly. If the lines are not wholly black but have white or other colors in them, selection will be more haphazard. To get your lines black enough,
follow the directions at the beginning of this tutorial. I find using Brightness and Contrast to be the most effective but use what works best.
If you're satisfied with the darkness of your lines, select the line of your drawing using the Magic Wand. Use Shift to select multiple lines
at once. Once you're done selecting, create a new layer and rename it. Make sure you are on this new layer! Hit the Bucket or Fill icon in your
tool bar. Make sure the color is black (or whatever color you want the lines to be) and click where the lines are supposed to be. Ta-dah! Instant
Once you deselect the image, you will see that the lines are jagged (actually, they're aliased). If you prefer smoother lines, run over the lines with a brush or erase using it in brush mode. Make sure you create a duplicate layer and keep one as backup in case you make a mistake. And don't foget to save your work as a PSD!
Last but not least, you can forgo all the other methods and just retrace the lines on a new layer using a brush. Select the original drawing. In the layers palette, you should see something called Opacity. Change the opacity so that you can now see the new lines (pure black) and compare them to the original lines (faded out black). Create a new layer above the original drawing and start tracing! Save your work in PSD format when you're done.
Any of the methods above can be used. It's up to you. Go with what you're most comfortable with. If you have another way of doing things, use that instead if you like it. But don't forget what I said earlier - your lineart is what anchors your CG. If it's sloppy, the whole image will look just as bad so take your time and clean up your lines!