Coloring Tutorial

By Hans Häggström, a.k.a. zzorn.
re"vamped" for Gimp by Kai Blin, a.k.a. nowhere

This tutorial describes the steps used by zzorn and me to color and shade line art. It covers cleaning up scanned images, doing flat coloring, and adding shadows and highlights. It focuses on the technical aspects, and leaves out artistical advice. I'm using Gimp, zzorn used Paintshop Pro but it should apply for any paint program with layers and layer modes such as multiply and screen. Technically speaking, it's entirely zzorn's tutorial. I just added some comments to give Gimp users a better start.

For illustration, I'm using a vampire sketch by Siri Austvik, a.k.a. Alien, that I color and shade.

1. Prepare the line art

We start with a scanned or computer drawn line art sketch. If it was scanned, you need to create a cleaned up version that is purely black and white. You can start by duplicating the scanned art layer.

First, you should close any small holes in lines between different areas in the picture, so that the areas are easy to select with a magic wand or similar selection tool in later steps.

To clean up a scanned picture you use right-click on the image, and choose Image>Colors>Levels, making all pixels brighter than a certain threshold pure white, and the others pure black. Usually you'll set the numbers in three "Input Level" boxes to about 100; 1.0; 200; You'll have to play a bit with the first and last value, but something around this works nicely for me.
A way to get a smoother, rounded look is to apply a smooth filter on the result. You do this by right-clicking the image, selecting Filters>Blur> Gaussian Blur (IIR) and use one to three pixels radius there, and then repeat the former step for the result. That technique is described in a rounded corners tutorial at Gimp User Group.

Vampire picture with line art layers

2. Color the areas

Now create a new layer, and name it "color". This will hold the flat color areas in the picture.

If you don't have the Layers, Channels & Paths window, you can get it by selecting File>Dialogs>Layers, Channels and Paths in the tool bar window, or simply by pressing <Ctrl>+<L>

Use the selection tool to select each garment or item in turn from the cleaned up line art layer. If it consists of multiple disjoint areas select them all by holding down the <Shift> key when clicking. For each area, perform the following steps:

  1. Expand the selection by a few pixels, so that it continues under the line art, and no white seams are left.(right-click, Select>Grow, 2 Pixels are usually enough.)
  2. Pick a suitable base color for each garment or item, select the color layer, and fill the area completely with that color using a large brush or the color bucket tool.

You can edit the color layer by hand to fix any areas that are still uncolored. Now we should have a flat colored picture.

Vampire picture with color layer

3. Add in the line art

We can use either the cleaned up line art drawing or the original scanned drawing to add lines to the picture. We can also use a mixture of both. We don't need to make the white parts in the drawing transparent to show it on top of the color, instead we can just change the mode of the line art and original layers to multiply(burn), and move them on top of the other layers. Then adjust the opacity of the original and/or cleaned up line art as desired. Another method is to select all lines, copy them and paste them in as a new layer.

In the vampire picture I'm only using the original line art, as it was suitably clean already.

Vampire picture with color and line art
layers

4. Create texture layers for some areas

In the vampire picture I'm using a colored gradient for the dress. For this I created two new layers (one for the arms and one for the bottom part of the dress). This way I could use a Hue Color Saturation tool to adjust the colors of them separately. I selected an area using the existing color layer, switched to a dress gradient layer, and used a soft brush to add a stripy gradient from the top.

Material textures could be added to the pictures as additional layers this way. It's important to not disturb the flat color layer, because it is used for selecting areas to work on.

Vampire picture with dress gradient layers

5. Shade and highlight

The next step is to add shadows and highlight.

Personally I use four layers, two shadow layers and two highlight layers. It's possible to use just one shadow and one highlight layer too, and use more varying opacity for the brush. Fewer layers are also easier for slower computers to handle.

Create four new layers, labeling them strong/weak highlight and shadow. Change the layer mode of the shadow layers to multiply, and the mode of the highlight layers to screen. Adjust the opacity of the weak layers to 30% or so, and the strong layers to around 60%. The shadow and highlight layers should be on top of the color layer, and usually the stronger shadow/highlight layers are on top of the weak ones.

Select each color area in turn from the color layer and change to the base color layer, selecting the color with the "pick colors" tool. I used opacity 30% or so for the brush. Then switch to the weak shadow layer, fill in shadows, and repeat for the weak highlight layer. Lastly add the strong shadows and highlighs.

Vampire picture with color and shading

6. Create the background

Draw the background on a separate layer. You may also use a few different background layers, for example to shade over parts of the backgorund picture with darker color to make it more uneven, to add a bit of light to the ground close to the viewer, and to add some shadow directly under the figure. You can also use some existing noise or natural texture for the background if you want to make it more abstract.

Vampire picture background

7. Final details

Then it's time to do a final adjustment of the opacity of the shadow, highlight, and other layers. I tend to shade a bit lightly, so I usually increase the opacity of the shade and highlight layers a bit. Play around until you are satisfied with the balance.

At this step I also added a layer with some white on the teeth of the vampire, credits and signatures, and other details.

Vampire picture with all layers

And here's the final vampire picture:

Full vampire picture

If you want to have a look at the layers, the original Paint Shop Pro picture is also available. It should open in Gimp too.

References

Here's a few sites with useful tutorials: