OpenCV fails to import ONNX model: of type "Where"

[ukoehler]

• OpenCV => Python opencv-python-rolling-5.0.0.20220903
• Operating System / Platform Windows 10 64 bit
• Python =>3.10.4

Detailed description

I converted a model to ONNX and tried to load it with OpenCV 5.6 Windows 10 (Python) and got the same error message. Find the model here:
https://drive.google.com/file/d/15wdXCiS1Yr7a4wFTUb7jQB_GjbkB_a-G/view?usp=sharing
Original model from here: https://github.com/clovaai/rexnet

I checked the ONNX using Pythin and onnx, as well as onnxruntime. Both claim that the model is OK. OpenCV, however, reports:

[ERROR:0@0.104] global D:\a\opencv-python\opencv-python\opencv\modules\dnn\src\onnx\onnx_importer.cpp (1044) cv::dnn::dnn5_v20220821::ONNXImporter::handleNode DNN/ONNX: ERROR during processing node with 3 inputs and 1 outputs: [Where]:(onnx_node!Where_46) from domain='ai.onnx'
Traceback (most recent call last):
  File "d:\Local\devel\Python\OpenCV\image_classification_rexnet_lite\inference.py", line 94, in <module>
    model = cv2.dnn.readNet(model_path)
cv2.error: OpenCV(5.0.0-pre) D:\a\opencv-python\opencv-python\opencv\modules\dnn\src\onnx\onnx_importer.cpp:1063: error: (-2:Unspecified error) in function 'cv::dnn::dnn5_v20220821::ONNXImporter::handleNode'
> Node [Where@ai.onnx]:(onnx_node!Where_46) parse error: OpenCV(5.0.0-pre) d:\a\opencv-python\opencv-python\opencv\modules\dnn\src\layer_internals.hpp:110: error: (-2:Unspecified error) Can't create layer "onnx_node!Where_46" of type "Where" in function 'cv::dnn::dnn5_v20220821::detail::LayerData::getLayerInstance'>

Steps to reproduce

model = cv2.dnn.readNet(model_path)

• Reproducible: yes
• Enforceable: yes

Issue submission checklist

• I report the issue, it's not a question

• I checked the problem with documentation, FAQ, open issues,

• I updated to the latest OpenCV version and the issue is still there

• There is reproducer code and related data files: videos, images, onnx, etc

[fengyuentau]

Thank you for the feedback! You should simplify this model with onnx-simplifier, and the where operator should be eliminated.

rexnet_lite_1.0.simplified.onnx.zip

I can see this model still have some operators not supported in the current version of OpenCV DNN, such as ScatterND. There is a pull request working on the support of ScatterND.

[ukoehler]

Confirmed with opencv-python-rolling 5.0.0.20220903 and a version of the model that I simplified myself. I am left with not supported ScatterND.

[asmorkalov]

OpenCV does not support control-flow onnx operations for now.

• FAQ record: https://github.com/opencv/opencv/wiki/FAQ#dnn

[fengyuentau]

Confirmed with opencv-python-rolling 5.0.0.20220903 and a version of the model that I simplified myself. I am left with not supported ScatterND.

The PR for supporting ScatterND has been merged. Please have a try with latest OpenCV. You need to either compile OpenCV from source for now, or wait for the release of opencv-python-rolling on this Saturday (20221022).

[ukoehler]

Hi @fengyuentau,

fix confirmed with version opencv-python-rolling-4.6.0.20221022.

Many thanks!