There is a limitation with the wrapper TeeChart uses, a limitation documented here: http://bugs.teechart.net/show_bug.cgi?id=356
As suggested, the workaround is to use the GDI+ canvas for image exportation, e.g.
private void InitializeChart()
{
tChart1.Graphics3D = new Graphics3DDirect2D(tChart1.Chart);
tChart1.Aspect.View3D = false;
FastLine series = new FastLine(tChart1.Chart);
series.FillSampleValues(1000);
}
TChart tChart2;
private void button1_Click(object sender, EventArgs e)
{
if(tChart2 == null) tChart2 = new TChart();
MemoryStream ms = new MemoryStream();
tChart1.Export.Template.Save(ms);
ms.Position = 0;
tChart2.Import.Template.Load(ms);
tChart2.Export.Image.PNG.Width = tChart1.Width;
tChart2.Export.Image.PNG.Height = tChart1.Height;
tChart2.Export.Image.PNG.Save(@"C:\tmp\direct2d.png");
}