Some tricks for coloring drawings in Photoshop
This is an update of sorts to my original cel-style tutorial. Since I wrote the aforementioned tutorial, I have obtained a Wacom graphics tablet, and I now use Photoshop almost exclusively, because of how it supports the pressure-sensitivity of my tablet. As a result, my method has changed a little, although much of the basics remain the same.
One of the main changes to my method as a result of using a tablet, is that most of my drawings now are "paperless" - rather than scanning a drawing, I draw directly on the tablet, and even if I use a scanned image, I now tend to trace over it. As a consequence, my lineart now consists of black lines on a transparent layer, rather than a black-and-white image.
What I describe hereafter is my own method. There are many other ways to achieve similar results, however this is what works for me and what I'm comfortable with.
My method is characterised by the use of layers. I tend to use a fairly limited number of them, typically Background, and then what I call Color, Shading, and Lines. The "Color" layer is a "help" layer, usually invisible in the final result - the use I make of it could be duplicated using masks, or separate layers for each "object".
I usually keep the Background layer plain white until the painting is almost done. The Lines layer contains the finished lineart (there are usually one or two Sketch layers preceding the final trace on Lines, but these are not relevant for the coloring process).
Once I'm satisfied with the lineart, I create a duplicate of Lines, rename it Colors, and move it below Lines.
The next, and crucial step, is a flat coloring of the Colors layer. I try to use colors close to the desired end result, but I also try to make sure that different "objects" have different colors. I usually use the Paintbucket tool to color the drawing. However, because the brushes I draw with are anti-aliased, this leaves some jagged edges.
There are two ways I cope with this: one is to use the magic wand to select the area, and then expand the selection some pixels. For simple drawings, this is sometimes sufficient.
The other way is to use a paintbrush to manually clean up the edges. Because the Lines layer is on top of Colors, there is no risk of erasing the lines, so great precision is not needed.
Note that it is important not to forget filling the "white" areas. It is often useful to Fill the Background layer with a dark and light color alternatively, to better verify that all pixels have been properly filled.
Once the Color layer is finished, I have a flat colored drawing, which - in case of a commission - may be a good thing to show to the client for approval before continuing. I then duplicate the Colors layer, and call this new layer Shading. It is on top of Colors and below Lines.
The rest of this tutorial describes cel-style shading, although my method is not much different for soft shading.
I use the Magic Wand to select an area on the Colors layer- in this case Corin's face, tail and hands.
For soft shading, I'll attack the selected area with brushes. For cel shading, I use the Freehand Lasso tool to modify the selection, subtracting the areas I don't want affected. I then use the Adjust Hue/Saturation/Luminance tool to create shading.
I usually prefer to do this one element at a time, although one could of course select multiple areas or even the entire figure at once in this way. When I select shadow areas, I adjust towards "colder" hue and less luminance, for highlight areas a "warmer" hue and more luminance. Saturation is more for midtones and less for light and shadow areas, usually. This method allows a fairly fast cel shading.
For the banner, I did soft shading using soft brushes, again first selecting the relevant area on the Colors layer so I didn't have to worry about painting within the lines.
Usually this is enough to get a satisfactory result, but in this case I didn't like the prominent black lines on the banner, so I decided to color the lineart. Coloring your lines can produce a quite subtle yet impressive effect. There are various ways to achieve it, what I did in this case was duplicate the Lines layer, select the banner area, and use the Adjust Hue/Saturation/Luminance tool to change the color of the lines there.
I was still not quite satisfied with the banner, so I added a layer on top of the Lines copy to paint out some of the lines I didn't like.
Next, I did a Radial Fill on the Background to have a nice background color.
I added a layer on top of the Background, created a polygonal selection and filled it with black for Corin's shadow, then adjusted the Layer opacity until I was happy with it.
Finally, on top of everything else is an Effects layer, containing highlight effects on the eyes and sword.
Now, the advantage of keeping the Colors layer separate from Shading is that it remains very easy to select and modify related areas. Suppose I am unhappy with Corin's fur color: A simple click of the Magic Wand on the Colors layer selects the relevant area, and I can adjust hue, or contrast, or anything else with a few simple clicks.
Same for making his uniform raspberry-colored.
This is the method I currently use. No doubt it will continue to evolve in the future...