Bump map

A material's albedo (left) compared to its bump map.

The above material in-game.

A bump map is an RGB image that can be used to simulate a three-dimensional surface through a process known as normal mapping.

Format

Each color channel in a bump map has a meaning:

1. The red channel defines horizontal facing (X-axis)

   0 = left

   128 = forward (facing viewer)

   255 = right

2. The green channel defines vertical facing (Y-axis)

   0 = up

   128 = forward (facing viewer)

   255 = down

3. The blue channel defines height (Z-axis)

   0 = deepest

   128 = maximum depth capable of receiving dynamic light (it's a bad idea to go under this)

   255 = at the material's surface

The three channels between them allow the engine to calculate a normal vector for every pixel, allowing it to generate shadows and highlights on a two-dimensional surface.

A bump map is largely useless for really flat surfaces like smooth concrete or metal, but even rough concrete sometimes has enough depth to it to make one worthwhile.

Creation

A bump map should:

• Be at the same resolution as the albedo/s it is to be used with.
• Be stored in an uncompressed format (see Conversion).

Programs

Bump maps as created by various programs.

Various programs can automate the creation of bump maps, either by image analysis or by using 3D geometry the user provides.

2D

Photoshop or Paint Shop Pro

The GIMP

3D

XSI

ZBrush2

Lightwave

3D Studio Max

Maya

Blender

NVIDIA Melody

Cinema 4D

NormalMapper

xNormal

Other

CrazyBump: Produces some very good normal maps. Some of them can be argued as almost having the same depth as a parallax map.

ShaderMap: A free alternative to CrazyBump.

Normal2dudv: a third party tool for converting bump maps to Dx8-friendly du/dv maps.

Conversion

In VTFEdit

When converting your texture:

1. Choose BGR8888 or BGRA8888 (if your texture has an alpha channel) as your image format.
   Tip:You can sometimes get away with DXT compression.
2. Check the "Normal map" box in the texture's flags list after the import is complete. It's about 1/5 of the way down the list.

In Vtex

1. Save your normal map as a TGA in the same resolution as the original texture. Give it a name that ends in _normal. The _normal at the end of the name will affect how Vtex converts it. For the brick wall example, we would name the file brickwall_normal.tga.
2. Add nocompress 1 and normal 1 to <texture filename>.txt in the same folder as your texture, then compile.

Implementation

See $bumpmap.

See also

• $ssbump: creation and usage of Valve's new self-shadowing bump maps.
• An old article that explains normal mapping quite well.
• Material Creation