How to get ONNX input/output class from signature file?

[zydjohnHotmail]

Hello:
I have installed Lobe Application in my Windows 10 PC, from this URL: https://www.lobe.ai/
I used a small dataset to train and get an ONNX model. This model is an image converter, it is not a classifier.

The following is the signature JSON file:
{
"doc_id": "2cc072ae-dbda-43c5-8db7-4c2515e0548d",
"doc_name": "model",
"doc_version": "9c8be1ab541b4591f46bb01fc60116cf",
"format": "onnx",
"version": 5,
"inputs": {
"Image": {
"dtype": "float32",
"shape": [null, 224, 224, 3],
"name": "Image:0"
}
},
"outputs": {
"Confidences": {
"dtype": "float32",
"shape": [null, 2],
"name": "2cc072ae-dbda-43c5-8db7-4c2515e0548d.9554adfa-5d26-484f-88d3-dea9f2f46f01/dense_2/Softmax:0"
}
},
"tags": [],
"classes": {
"Label": ["test_A", "test_B"]
},
"filename": "model.onnx",
"export_model_version": 1
}

I also use mlgen for Visual Studio 2019 from this URL, to generate some C# wrapper class, like this:
public sealed class ModelInput
{
public TensorFloat Image00; // shape(-1,224,224,3)
}

public sealed class ModelOutput
{
    public TensorFloat output2cc072ae0dbda043c508db704c2515e0548d09554adfa05d260484f088d30dea9f2f46f010dense_20Softmax00; // shape(-1,2)
}

public sealed class ModelModel
{
    private LearningModel model;
    private LearningModelSession session;
    private LearningModelBinding binding;
    public static async Task<ModelModel> CreateFromStreamAsync(IRandomAccessStreamReference stream)
    {
        ModelModel learningModel = new ModelModel();
        learningModel.model = await LearningModel.LoadFromStreamAsync(stream);
        learningModel.session = new LearningModelSession(learningModel.model);
        learningModel.binding = new LearningModelBinding(learningModel.session);
        return learningModel;
    }
    public async Task<ModelOutput> EvaluateAsync(ModelInput input)
    {
        binding.Bind("Image:0", input.Image00);
        var result = await session.EvaluateAsync(binding, "0");
        var output = new ModelOutput();
        output.output2cc072ae0dbda043c508db704c2515e0548d09554adfa05d260484f088d30dea9f2f46f010dense_20Softmax00 = result.Outputs["2cc072ae-dbda-43c5-8db7-4c2515e0548d.9554adfa-5d26-484f-88d3-dea9f2f46f01/dense_2/Softmax:0"] as TensorFloat;
        return output;
    }

But I don’t quite understand the meaning of the above class.
If I want to use an input image and generate an output image from the ONNX model.
How I can write an OnnxInput and OnnxOutputClass?
I have no idea about the input shape [null, …] means what and output shape [null, 2] means what?

By the way, the input/output name seems to be very long and meaningless.
Can I use python code to change the ONNX model, so it will show some meaningful names for input/output? For example, if I want to use output name like: Iamge2Sketch, not like this one:
"name": "2cc072ae-dbda-43c5-8db7-4c2515e0548d.9554adfa-5d26-484f-88d3-dea9f2f46f01/dense_2/Softmax:0"

I am using Visual Studio 2022 and 2019 on Windows 10, I also installed Python 3.9.
Please advise,
Thanks,