Unable to convert .h5 model to ONNX for inferencing through any means - tensorflow

Question

I built a custom model in .h5 from Matterport's MaskRCNN implementation. I managed to save the full model and not the weights alone using model.keras_model.save(), and assume it worked correctly.
I need to convert this model to ONNX to inference in Unity Barracuda, and I have been hitting several errors along the way.
I tried:
T1. .h5 to ONNX using this tutorial and the keras2onnx package, and I hit an error at:
model = load_model('model.h5')
Error:
ValueError: Unknown layer: BatchNorm
T2. Defining custom layers using this GitHub code:
model = keras.models.load_model(r'model.h5', custom_objects={'BatchNorm':BatchNorm,
'tf':tf, 'ProposalLayer':ProposalLayer,
'PyramidROIAlign1':PyramidROIAlign1, 'PyramidROIAlign2':PyramidROIAlign2,
'DetectionLayer':DetectionLayer}, compile=False)
Error:
ValueError: No model found in config file.
ValueError: Unknown layer: PyramidROIAlign
T3. .h5 to .pb (frozen graph) and .pbtxt, and then from .pb to ONNX using tf2onnx after finding input and output nodes (seems to be only one of each?):
assert d in name_to_node, "%s is not in graph" % d
AssertionError: output0 is not in graph
T4. .h5 to SavedModel using tf-serving code from here and then python -m tf2onnx.convert --saved-model exported_models\coco_mrcnn\3 --opset 15 --output "model.onnx" to convert to ONNX:
ValueError: make_sure failure: variable mrcnn_detection/map/while/Enter already exists as state variable.
TLDR: Is there a way to convert my .h5 model to ONNX through any direct/indirect means? I have been stuck on this for days!
Thanks in advance.
Edit 1:
It seems that keras.models.load_model() throws the first two errors - wondering if there is a way I can work with the .pb/.pbtxt model, or a way around without using load_model(), or a way to solve the load_model() issue?
Edit 2:
Code for T1:
custom dataset modified from Matterport's MaskRCNN implementation
Code for T4

Answer 1

Try converting it to saved model format and then to onnx.
import numpy as np
import tensorflow as tf
from tensorflow import keras
def get_model():
# Create a simple model.
inputs = keras.Input(shape=(32,))
outputs = keras.layers.Dense(1)(inputs)
model = keras.Model(inputs, outputs)
model.compile(optimizer="adam", loss="mean_squared_error")
return model
model = get_model()
# Train the model.
test_input = np.random.random((128, 32))
test_target = np.random.random((128, 1))
model.fit(test_input, test_target)
# Calling `save('my_model.h5')` creates a h5 file `my_model.h5`.
model.save("my_h5_model.h5")
# It can be used to reconstruct the model identically.
model = keras.models.load_model("my_h5_model.h5")
tf.saved_model.save(model, "tmp_model")
Then convert it using tf2onnx.
python3 -m tf2onnx.convert --saved-model tmp_model --output "model.onnx"

Answer 2

this works for me
via anaconda powershell console (execute as admin) :
pip install tf2onnx
pip install onnxmltools
and in a notebook (for example)
from tensorflow.python.keras.models import load_model
import os
os.environ['TF_KERAS'] = '1'
import onnxmltools
model = load_model('[h5 path]')
onnx_model = onnxmltools.convert_keras(model)
onnxmltools.utils.save_model(onnx_model, '[onnx path]')