Bump to Normal Map

Simple Python script to convert a bump map to a normal map. Not optimized for performance.

Requirements

• Python 3
• numpy
• opencv-python

Usage / Run

python bumptonormalmap.py <path to bump map> <strength> <output format>

# <path to bump map> : string -> path to the input image (the bump map, i.e. the height map)
#
# <strength> : float > 0 -> "strength" of the normal map
#                           results in smoother (strength -> 0) or sharper (strength -> \infty) features
#                           strength = 1 (recommended to start with)
#                           strength = 2 (more defined features)
#                           strength = 10 (really strong normal mapping effect...)
#                           just experiment a little bit :)
#
# <output format> : string -> "png" or "exr"; output image format. Use "exr" for higher precision.

How does it work?

# Uses horizontal and vertical sobel filters (https://docs.opencv.org/3.4/d2/d2c/tutorial_sobel_derivatives.html)
# to detect edges to determine the gradients in horizontal and vertical direction respectively.
#
# GX = [ -1 0 1] = [1]
#      [ -2 0 2]   [2] * [-1 0 1]
#      [ -1 0 1]   [1]
#
# GY = [ -1 -2 -1] = [-1]
#      [  0  0  0]   [ 0] * [1 2 1]
#      [  1  2  1]   [ 1]
#
# The sobel filter is separable which allows to compute two one-dimensional convolutions instead of one two-dimensional 
# (accelerates computation).
#
# The normals are computed from the gradients in horizontal (dx) and vertical direction (dy) as follows:
# normal = normalize(vec3(dx, dy, 1.0 / strength))
#
# Note that the normals are transformed from [-1,1] space to [0,1] space (normal * vec3(0.5) + vec3(0.5)).
# Remember to undo the transformation (vec3(2.0) * normal - vec3(1.0)) when reading the normals from the normal map.

Example

The bump map is taken from the LPS Head model. The complete model including the bump map can be downloaded from https://casual-effects.com/data/.

python bumptonormalmap.py example/bump_map.png 2 png