How Can I Extract Bitplanes Of A Gray Image?

public static Bitmap MakeGrayscale(Image original)
{
    //create a blank bitmap the same size as original image
    Bitmap newBitmap = new Bitmap(original.Width, original.Height);

    //get a graphics object from the new image
    Graphics g = Graphics.FromImage(newBitmap);

    //create the grayscale ColorMatrix
    ColorMatrix colorMatrix = new ColorMatrix(
        new float[][] 
{
    new float[] {.3f, .3f, .3f, 0, 0},
    new float[] {.59f, .59f, .59f, 0, 0},
    new float[] {.11f, .11f, .11f, 0, 0},
    new float[] {0, 0, 0, 1, 0},
    new float[] {0, 0, 0, 0, 1}
});

    //create some image attributes
    ImageAttributes attributes = new ImageAttributes();

    //set the color matrix attribute
    attributes.SetColorMatrix(colorMatrix);

    //draw the original image on the new image
    //using the grayscale color matrix
    g.DrawImage(original, new Rectangle(0, 0, original.Width, original.Height),
        0, 0, original.Width, original.Height, GraphicsUnit.Pixel, attributes);

    //dispose the Graphics object
    g.Dispose();
    return newBitmap;
}

private void button1_Click(object sender, EventArgs e)
{
    //get a graphics object
    Graphics graph = CreateGraphics();

    // load you bitmap image  =>  change the name Image.jpg below to your image
    // Don't forget full path if file isn't in exe directory
    // the function supports  BMP, JPG, PNG, TIFF or GIF formats
    Image img = Image.FromFile("Image.jpg"); 

    // Makes a greyscale version of the bitmap by calling above function
    Bitmap b = MakeGrayscale(img);
    
    // draw bitmap to 0,0 on form
    graph.DrawImage(b, 0, 0);
}