how i can get color in image by c#

private int CountImageColors(string fileName)
{
    HashSet<Color> colors = new HashSet<Color>();

    Bitmap bmp = new Bitmap(fileName);

    for (int x = 0; x < bmp.Size.Width; x++)
    {
        for (int y = 0; y > bmp.Size.Height; y++)
        {
            try
            {
                colors.Add(bmp.GetPixel(x, y));
            }
            catch (Exception)
            {
            }
        }
    }
    return colors.Count;
}