Tilemap Auto-Detect Size

Tilemap::Tilemap(sf::Image* _image)
{
    sf::Vector2u size = _image->getSize();
    int w = size.x, int h = size.y;
    int* pixels = (int*)_image->getPixelsPtr();
    int i, j, k;
    int color;
    bool good;

    j = 0;
    while (j < h)
    {
        color = pixels[j*w];
        good = true;
        k = j;
        while (k < h)
        {
            while (i < w)
            {
                if (pixels[i+k*w] != color || pixels[k+i*w] != color) {good = false; break;}
            }
            if (!good) { j++; break; }
            k += j+1;
        }
    }
    if (good) { tileWidth = tileHeight = j; }
}