private static void alterRasterY2Gray(WritableRaster wr, int bitsPerComponent,
                                          Vector decode) {
        int[] values = new int[1];
        int width = wr.getWidth();
        int height = wr.getHeight();
        boolean defaultDecode = (0.0f == ((Number) decode.elementAt(0)).floatValue());

        int Y;
        for (int y = 0; y < height; y++) {
            for (int x = 0; x < width; x++) {
                wr.getPixel(x, y, values);
                Y = values[0];
                Y = defaultDecode ? 255 - Y : Y;
                Y = (Y < 0) ? (byte) 0 : (Y > 255) ? (byte) 0xFF : (byte) Y;
                values[0] = Y;
                wr.setPixel(x, y, values);
            }
        }
    }