this.setLocationRelativeTo(null);
//crea el fondo
SubstanceImageWatermark watermark = new SubstanceImageWatermark("grafico/admin.jpg");
watermark.setKind(SubstanceConstants.ImageWatermarkKind.APP_TILE);
watermark.setOpacity(0.9f);
SubstanceSkin skin = new SaharaSkin().withWatermark(watermark);
SubstanceLookAndFeel.setSkin(skin);
}