Q:

'System.ArgumentException' when trying to use SetPixel (x, y, Color)

I am trying to create a white picture (greyscale format).
So here is the code I use:
Bitmap bmp = new Bitmap(1, 1,        
System.Drawing.Imaging.PixelFormat.Format16bppGrayScale);
bmp.SetPixel(0, 0, Color.FromArgb(255, 255, 255));
bmp = new Bitmap(bmp, i.Width, i.Height);

"I" is an existing Bitmap image. I am playing with its channels.
The principle is to create a 1 pixel image in greyscale, give this pixel the white color and then enlarge it to the good size.
But I have this as a result:

"An unhandled exception of type 'System.ArgumentException' occurred in
  System.Drawing.dll"

I tried Color.White but it isn't allowed for greyscale or indexed formats.
What are my other options to fix this?

A:

Why not to do it without converting to greyscale?
Bitmap A = new Bitmap(i.Width, i.Height);
for (int x = 0; x < i.Width; x++)
    for (int y = 0; y < i.Height; y++)
    {
        Color C = i.GetPixel(x, y);
        Color WD = Color.FromArgb(C.R, 255, C.G, 0);
        A.SetPixel(x, y, WD);
    }

Simply done by placing colour channels in the desired order

