Convert an image to black and white with some thresholding - Convert an image to black and white with some thresholding

//Setting desired threshold
int threshold = 170;
Aurigma.GraphicsMill.Bitmap bitmap = new Aurigma.GraphicsMill.Bitmap(@"input.jpg");
for(int i = 0; i < bitmap.Palette.Count; i++)
{
     // RGB-to-brightness calculation taken from https://stackoverflow.com/a/596243
     var brightness = (0.299 * bitmap.Palette[i].R + 0.587 * bitmap.Palette[i].G + 0.114 * bitmap.Palette[i].B);
     if (brightness > threshold)
     {
          bitmap.Palette[i] = Aurigma.GraphicsMill.RgbColor.White;
     }
     else
     {
          bitmap.Palette[i] = Aurigma.GraphicsMill.RgbColor.Black;
     }
}
bitmap.ColorManagement.Convert(PixelFormat.Format1bppIndexed);
bitmap.Save(@"output.tif");