How to trace back to the reasons of this GUIScreenShot's behaviour?

Question

The question I'm going to pose is surely, in some extent, version dependent, however I conjecture that it's rooted in general aspects of video manager architecture in Windows. This, I believe, makes it of overall interest.

Taking a screenshoot of the whole desktop by means of:

"Needs["GUIKit`"];
   fsa = "FullScreenArea" /.Flatten[
       SystemInformation["Devices", ScreenInformation"]
   ];
   saveScreen [fsa_, fileName_] := Export[
     fileName, GUIScreenShot[fsa], "BMP"
   ];
saveScreen [fsa, "e:\\screenshoot.bmp"];"

I get this picture

conversely using a screen grabber (Wisdom Screenhunter free) I obtain this one:

The difference is presumably due by a screen dimming program running on my machine (DimScreen v1.1) and could be easily suppressed setting the dimming factor to zero.

But this isn't the main point; rather, what does this "symptom" uncover (if any) about the way Mathematica reads the video memory ?

May be, pops up something usefully employable ...

( Mathematica 8.0.1.9 , Ms Windows Xp 5.1.2600 )

Answer 1

GUIScreenShot is basically an easy to use wrapper for java.awt.Robot's screen shot functionality. So it's probably that. I haven't looked at that for a while, but I don't think there's a way to .. recognize that some function is changing the screen dimming.