Creates a downscaled copy of an existing image.
Pass -1 as width or height to keep the aspect ratio.
See Also: CreateImage
Example - Create Thumbnail
function OnStart()
{
lay = app.CreateLayout( "absolute" );
img = app.CreateImage( "/Sys/Img/Hello.png" );
lay.AddChild( img );
app.GetThumbnail( "/Sys/Img/Hello.png", "/sdcard/Hello_thmb.png", 100, -1 );
thmb = app.CreateImage( "/sdcard/Hello_thmb.png" );
lay.AddChild( thmb );
app.AddLayout( lay );
}