script: /* Custom screenshot */ var prev_background = moi.view.viewportBackgroundColor; 
moi.view.viewportBackgroundColor = 0xFFFFFF; 
moi.view.lineWidth = 3; 
moi.grid.display = false; 
moi.grid.showXYAxes = false; 
moi.view.showAxisIcon = false; 
moi.view.meshAngle = 3; 
moi.ui.getActiveViewport().renderToClipboard( 4000, 2500 ); 
moi.view.lineWidth = 1; 
moi.grid.display = true; 
moi.grid.showXYAxes = true; 
moi.view.showAxisIcon = true; 
moi.view.meshAngle = 8; 
moi.view.viewportBackgroundColor = prev_background;

How best to modify above script to save same image as a PNG (preferably a transparent PNG)? Thanks anyone for the help!