VB.NET graphics methods slow compared to VB6

[Clairvoyant1332]

I have this app originally written in VB6 where I loop through each pixel in a picture control and set the color, doing a refresh after each line. When I converted this to .NET it was considerably slower.

Here's a simplified piece of the VB6 code:

mypicture.autoredraw = true   ' set at design time
for x = 1 to 600
  for y = 1 to 400
    mypicture.pset (x,y), vbblack  ' there's more logic going on here, but this is the important part
  next y
  doevents
next x

And here's the VB.NET code

bmap = new bitmap(600,400,system.drawing.imaging.pixelformat.format24bpprgb)
mypicture.image = bmap  ' these two lines done in form.load
for x = 1 to 600
  for y = 1 to 400
    bmap.setpixel(x,y,color.black)  ' again, this is the important part
  next y
  mypicture.refresh()
  system.windows.forms.application.doevents()
next x

Is this the correct approach? Am I missing something?

Thanks,
Dennis