title: convert a greyscale image into rgb image using c#
body: <p>Hi there I have a greyscale jpeg image and I need to open it and convert it in rgb.
  I need the fastest way is possible but I've not been able to find one. 
  For me it's fine to populate the rgb values with the greyscale value. Just doing using setpixel and getpixel takes a while. 
  I'm wondering if there is a fastest way I ignore. </p>
  
  <p>On the web there are a lot of solution to convert rgb to greyscale but it's very hard to find the opposite.</p>
  
  <p>I've tried using FormatConvertedBitmap but I just get error I don't know how to 
  use it correctly. If that is the solution please can anybody write me the code to load the greyscale image from a jpeg file and then create the rgb bitmap?</p>
  
  <p>Thanks in advance!!!</p>