How to convert an image from 8-Bit to RGB in ImageJ2 using Java

I'm trying to use ImageJ2 directly from Java to create a binarised image coming from an input image.

A somewhat working version of my code looks like this:

final File file = new File("input.png");

try {
    DefaultDataTypeService dataTypeService = new DefaultDataTypeService();
    Dataset dataset = imageJ.dataset().open(file.getAbsolutePath());
    Img inputImg = dataset.getImgPlus();

    PluginInfo pluginInfo = imageJ.plugin().getPlugin(Binarize.class);
    Binarize binarizeOp = (Binarize) pluginInfo.createInstance();
    binarizeOp.setContext(imageJ.getContext());
    binarizeOp.setChangeInput(true);
    binarizeOp.setFillMaskBackground(true);
    binarizeOp.setFillMaskForeground(true);
    binarizeOp.setInputData(dataset);
    binarizeOp.setInputMask(null);
    binarizeOp.setMaskColor(Binarize.WHITE);
    binarizeOp.setMaskPixels(Binarize.INSIDE);
    binarizeOp.setThresholdEachPlane(false);
    binarizeOp.setDefaultThresholdMethod();
    binarizeOp.run();

    dataset.rgbChange();
    DefaultDatasetService defaultDatasetService = new DefaultDatasetService();
    Img outputImg = dataset.getImgPlus();
    outputImg = outputImg.factory().imgFactory(new UnsignedByteType()).create(outputImg,new UnsignedByteType());
    Dataset outputDataset = defaultDatasetService.create(outputImg);
    imageJ.dataset().save(outputDataset,"input_binary.png");

} catch (IOException e) {
    e.printStackTrace();
} catch (InstantiableException e) {
    e.printStackTrace();
} catch (IncompatibleTypeException e) {
    e.printStackTrace();
}

Running this code I have the problem that "input_binary.png" will be completely black, a behaviour I can reproduce using the ImageJ client application.

What I need to do in the client is to change the image type from "8-bit Color" to "RGB-Color". But I can not figure out how to reproduce that in Java using the current version of the net.imagej library.

I know that it would be possible using the 1.x library but I would like to to it using the 2.x.

Any help would be greatly appreciated.