title: Invalidate a single Pixel?
body: <p>I'm working on some image processing and for debug I'm overlaying colours on the original bitmap.</p>
  
  <p>The problem is the image is rendered in a picture box with SizeMode set to Zoom and invalidating every time I update a pixel is Really slow and just gets slower the larger picturebox is (for the same size image)</p>
  
  <p>What I think might help is if I only invalidate the pixel(s) I've changed but I don't know how convert the co-ordinates of the pixel I've changed into a rectangle rendered on the control.  Obviously if the image is being drawn larger than the original image then the rectangle I'm invalidating is going to be more than one pixel</p>