Can normal maps be generated from a texture?

Question

If I have a texture, is it then possible to generate a normal-map for this texture, so it can be used for bump-mapping?

Or how are normal maps usually made?

Answer 1

I suggest starting with OpenCV, due to its richness in algorithms. Here's one I wrote that iteratively blurs the normal map and weights those to the overall value, essentially creating more of a topological map.

#define ROW_PTR(img, y) ((uchar*)((img).data + (img).step * y))
cv::Mat normalMap(const cv::Mat& bwTexture, double pStrength)
{
    // assume square texture, not necessarily true in real code
    int scale = 1.0;
    int delta = 127;

    cv::Mat sobelZ, sobelX, sobelY;
    cv::Sobel(bwTexture, sobelX, CV_8U, 1, 0, 13, scale, delta, cv::BORDER_DEFAULT);
    cv::Sobel(bwTexture, sobelY, CV_8U, 0, 1, 13, scale, delta, cv::BORDER_DEFAULT);
    sobelZ = cv::Mat(bwTexture.rows, bwTexture.cols, CV_8UC1);

    for(int y=0; yplanes;

    planes.push_back(sobelX);
    planes.push_back(sobelY);
    planes.push_back(sobelZ);

    cv::Mat normalMap;
    cv::merge(planes, normalMap);

    cv::Mat originalNormalMap = normalMap.clone();

    cv::Mat normalMapBlurred;

    for (int i=0; i<3; i++) {
        cv::GaussianBlur(normalMap, normalMapBlurred, cv::Size(13, 13), 5, 5);
        addWeighted(normalMap, 0.4, normalMapBlurred, 0.6, 0, normalMap);
    }
    addWeighted(originalNormalMap, 0.3, normalMapBlurred, 0.7, 0, normalMap);

    return normalMap;
}