Round Corners via UI
You round the corners by showing the round corners dialog and set the Radius, the Border Thickness and their colors.
Round Corners Programmatically
The following snippet shows how you can round the corners with the RoundCorners method.
Round Corners in code.
radImageEditor1.ImageEditorElement.RoundCorners(100, Color.Red, 2, Color.Green);
radImageEditor1.ImageEditorElement.SaveState();
radImageEditor1.ImageEditorElement.RoundCorners(100, Color.Red, 2, Color.Green)
radImageEditor1.ImageEditorElement.SaveState()