Antialiased Image Threshold Function

// generates a smooth thresholded image by doing stuff
image_t *img_scalarautothreshold(image_t *img, float thresh, float bias)
{
    float min, max, range, f, *s = (float *)img->data, *d;
    int w = img->w, h = img->h, x, y, o, px, py;
    image_t *ret;

    if(!(ret = img_new(w, h, img->chans, 0)))
        return 0;

    d = (float *)ret->data;

    // for each pixul
    for(y = 0; y < h; y++)
    for(x = 0; x < w; x++)
    {
        min = 99999.0;
        max = -99999.0;

        // find min/max in 3x3 neighbz
        for(o = 0; o < 9; o++)
        {
            px = x + (o % 3) - 1;
            py = y + (o / 3) - 1;

            if(px < 0 || py < 0 || px >= w || py >= h)
                continue;

            // get value for neighborhood pixels
            f = *(float *)&img->data[(px + (py * w)) * sizeof(float)] - thresh;

            if(f < min)
                min = f;

            if(f > max)
                max = f;
        }

        // calc range
        range = max - min;
        f = *s++ - thresh;

        // avoid divzero
        if(m_abs(range) > 0.0000001)
            f /= 0.5 * range;   // double up or boundary is too soft
        else
            f *= 999999;

        *d++ = f + bias;
    }

    return ret;
}
//