Add ImageColumn

Question

I should like to use an image in a column.

FastReportBuilder drb = new FastReportBuilder();
drb.addImageColumn("Example", expression, 20, true, ImageScaleMode.NO_RESIZE, myStyle);
CustomExpression iexpressionr = new CustomExpression() {

    String ok = "http://....//ok.png";
    String ko = "http://....//error.png";

    public String getClassName() {
        return String.class.getName();
    }

    public Object evaluate(Map fields, Map variables, Map parameters) {
        String result = (String) fields.get("result");
        if (result.equals("true")) {
            return ok;
        } else {
            return ko;
        }
    }
};

My problem is the following: the style of the header is the default. How Can I insert the header style in this case?

I try

ImageColumn d = new ImageColumn();
d.setExpression(imgExpr);
d.setTitle("Example");
d.setWidth(20);        
d.setHeaderStyle(myHeaderStyle);        
d.setStyle(myStyle);

but the method "addColumn" for the object FastReportBuilder it is not good.