 # HeightMap to NormalMap

Hey guys.
I sort of have a problem when trying to do this…
First of all my engine uses deferred lighting(still it shouldn’t make any difference).
So I made a really nice terrain but give the way it works I have to use a normal map for it. I only have a height map so I have to convert the heightmap into a normalmap.
Currently I have this code for converting:

``````for(int Y=1;Y<image->sizeX-1;Y++)
{
for(int X=1;X<image->sizeY-1;X++)
{
float v1 = image->GetImageHeight(X,Y-1)*scale;
float v2 = image->GetImageHeight(X-1,Y)*scale;
float v3 = image->GetImageHeight(X+1,Y+1)*scale;

CVector3 n1 = (CVector3(1,v3,1)-CVector3(0,v1,-1)).cross(CVector3(1,v3,1)-CVector3(-1,v2,0));

CVector3 normal = n1;

normal.normalize();

unsigned char r, g, b;
r = (BYTE)(255.0 * (normal.x * 0.5 + 0.5));
g = (BYTE)(255.0 * (normal.y * 0.5 + 0.5));
b = (BYTE)(255.0 * (normal.z * 0.5 + 0.5));
norm->data[Y*image->sizeX*3+X*3] = r;
norm->data[Y*image->sizeX*3+X*3+1] = g;
norm->data[Y*image->sizeX*3+X*3+2] = b;

}
}
``````

It basically takes 3 near adjacent pixels transforms them into 3 3d points with the height(y value) being the height from the heightmap as a float multiplied by the maximum height in the terrain so that all the vertexes will be just like in the terrain.
Interesting problem is that when I run it my normal map looks chunky. I really can’t figure this out.
I guess it’s something from my function but I can’t understand what.
Could anyone be so nice to help me please?
Thank you very much.

Maybe you can quickly find-out if simply sampling more and doing some filtering would be nicer:

Some nice sync here! I am trying to solve the same (or a very similar) issue.

In my experience, running a 3x3 sobel filter yields better results:

``````
Vector3 CalculateNormal(int u, int v)
{
// Value from trial & error.
// Seems to work fine for the scales we are dealing with.
float strength = scale.Y / 16;

float tl = Math.Abs(this[u - 1, v - 1]);
float l = Math.Abs(this[u - 1, v]);
float bl = Math.Abs(this[u - 1, v + 1]);
float b = Math.Abs(this[u, v + 1]);
float br = Math.Abs(this[u + 1, v + 1]);
float r = Math.Abs(this[u + 1, v]);
float tr = Math.Abs(this[u + 1, v - 1]);
float t = Math.Abs(this[u, v - 1]);

// Compute dx using Sobel:
//           -1 0 1
//           -2 0 2
//           -1 0 1
float dX = tr + 2 * r + br - tl - 2 * l - bl;

// Compute dy using Sobel:
//           -1 -2 -1
//            0  0  0
//            1  2  1
float dY = bl + 2 * b + br - tl - 2 * t - tr;

Vector3 N = new Vector3(dX, dY, 1.0f / strength);
N.Normalize();

//convert (-1.0 , 1.0) to (0.0 , 1.0), if necessary
//Vector3 scale = new Vector3(0.5f, 0.5f, 0.5f);
//Vector3.Multiply(ref N, ref scale, out N);
//Vector3.Add(ref N, ref scale, out N);

return N;
}

``````

For best results, your normalmap should be at least 4x bigger than the heightmap (i.e. generate the heightmap at a higher resolution and downsample when you construct the vertex buffer). 16x bigger is even better.

``````
for(int Y=1;Y<image->sizeX-1;Y++)
for(int X=1;X<image->sizeY-1;X++)

``````

that’s a little bit incorrect However, I don’t see any other major mistakes…
Maybe the problem lies aside the code you provided.