Guide to Hair Creation by Alvin Sebastian Hoo

One of most difficult processes in character making is the creation of hair. The process is tedious and most of the time a pain in the ass especially when creating realistic characters.

Basically, hair creation can be divided into 2 methods. The first method is by using transparency mapping and second, by using a 3rd party hair renderer. If you work in big players like Squaresoft, they have software engineers to write propriety plugins to generate realistic hair. Both methods employ tedious hardwork and each has its pros and cons.

Pros:

• Fast to render (Cheap)

Cons:

• Hard to achieve realism
• Hard to Animate

Transparency mapping is the most common method used by 3D CG artists. CG artists spend a lot of time building the mesh of the hair and preparing the textures (alpha mappings, specular etc)

A recommended equipment for creating hair textures is a WACOM tablet, at least a 4"x5". This makes drawing of fine or thick strands of hair easier and more realistic. Do not choose a tablet that is too big! The bigger it is, the more movement your wrist needs to go through to move the cursor.

If you cannot afford a tablet, then use the following method using Photoshop:

Brush:

1. Choose a brush of 1 or 2 px

Define Brush:

2. Make 2 or 3 dots
3. Use the marquee tool to select the draw dots.
4. Define it as a custom brush.

Set Fading:

5. Set fading to 100-200 (depends on how big is your texture)

6. Skip step 2 - 4 if drawing few strands of hair only.

Hair Texture:

Alpha Map:

Specular Map:

The reason why artists want to use this method is merely the cheap cost as the rendering does not take up much time. However, in order to make good looking hair, the artist must spend time to texture the mesh, layer by layer using different textures of different types and thickness of hairstands.

Hair texture is mapped onto a piece of patch plane and is made transparent with an alpha channel, layer by layer. Unless special care is taken during the process, realism is hard to achieve.

Rendering fringe of hair using transparency

The patches of hair posed a great problem in animating. One way to animate the hair using transparency mapping is to use cloth dynamics plugins.

3rd Party Hair Renderer

Pros:

• Realistic
• Realtime Dynamics (animation)
• Ability to "Comb" hair

Cons:

• Slow to render (Expensive)

Using 3rd party hair renderer such as Shag Hair is not only time consuming, but also very expensive. However, this method can achieve the best result in the realism of hair on a character.

CG artists will spend most of their time test-rendering, inputing required parameters of the plugin such as the density of hair, the curliness etc.

Hair is planted 1 strand by 1 strand onto the scalp of the head. Wait, did I say strand by strand!!!?? Yes, but to a certain extend. Because you do need to at least shape out the hair shape using splines or mesh before the plugin can interpolate correctly between the splines or mesh generating hair shaders. However, the more splines you used, the more precise and more natural the hair will look.

This type of hair plugin comes with realtime dynamics so it makes animation easier.

Although I'm using Digimation Shag Hair here, the tips that I'm going to mention do apply to all other 3rd party hair renderers. You can download the Demo version of Shag Hair from www.digimation.com. 

Below is a list of tips that improves and speeds up the process of creating hair using a 3rd party renderer.

1. Do not plant and grow the hair directly on the mesh of the character. Create the scalp using a separate piece of mesh. This will ensure faster rendering as the calculation will be just on the scalp mesh rather than the whole head mesh or worst still, the whole character if it is a single mesh character.

Scalp - Grow hair on scalp instead of on the character mesh to ensure speedy calculation when rendering

2. Use layers of hair to build the volume and density of hair. This will ensure well defined and more realistic looking hair.
   
   As shown below, 4 layers of hair of different parameters of density and colors are used:

Under Layer - Most dense layer and darkest tone color.

Middle Layer - Comparing to underlayer, this layer is of lighter density and lighter tone color.

Over Layer - This layer makes up the overall hairshape and hair color.

Fringe - The fringe layer can also be breakdown into different layers, depending on the type of fringe of the character.

3. Keep hair in a messy or rather in a not too neat manner. Layer hair in different directions on the same area, you will be happy to see the hair building up in volume and 3 dimensionality.

4. Add some noise to bring out the texture of the hair.

5. An artist trying to express a night skyscene, is not going to render the sky with pure black color. He will know that the night is represented by dark shades of blue. Similarly, there is no such thing as true BLACK hair. Even the blackest and darkest shade of hair, should be complemented with shades of grey.

Black hair

Blonde Hair

6. Don't be afraid to test out different parameters and test render. Since it takes hell long to render 1 file, it is advisable to test render with a little window instead of a full 800x600 or bigger window. I myself use a little 160x120 or sometimes 240x180. When I found the correct parameters and am satisfied, I do a full screen render and go to the pantry to get myself a cup of coffee.

Anyway, I hope this tutorial gives you a better idea how hair is created in 3D space. For more details of my works, please visit www.ordix.com and do leave a note in my guestbook.