issue met when try to load mask rcnn model with dnn module

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Hi guys, When tried to load mask rcnn model(Mask-RCNN Inception v2 from tensorflow model zoo, also listed on OpenCV github wiki), I've met this issue: msk_net = dnn.readNet(msknet_model, msknet_config) cv2.error: OpenCV(3.4.2) /io/opencv/modules/dnn/src/tensorflow/tf_graph_simplifier.cpp:659: error: (-215:Assertion failed) !field.empty() in function 'getTensorContent'

i thought it could be caused by *.pbtxt not right, so re-generate that config file as follow: python3 tf_text_graph_mask_rcnn.py --input ./mask_rcnn_inception_v2_coco_2018_01_28/frozen_inference_graph.pb --config ./mask_rcnn_inception_v2_coco_2018_01_28/pipeline.config --output ./mask_rcnn_inception_v2_coco_2018_01_28/graph.pbtxt

Number of classes: 90 Scales: [0.25, 0.5, 1.0, 2.0] Aspect ratios: [0.5, 1.0, 2.0] Width stride: 16.000000 Height stride: 16.000000 Features stride: 16.000000 2018-09-20 11:49:14.170689: I tensorflow/tools/graph_transforms/transform_graph.cc:318] Applying sort_by_execution_order

but still the same issue is there.

then I noticed that there is another might-be options: to simplify the *.pb file or fuse constant nodes, like below, even though i am not sure it could fix my issue or not: python ~/tensorflow/tensorflow/python/tools/optimize_for_inference.py \ --input frozen_inference_graph.pb \ --output opt_graph.pb \ --input_names image_tensor \ --output_names "num_detections,detection_scores,detection_boxes,detection_classes" \ --placeholder_type_enum 4 \ --frozen_graph

yet i have some confusion on that output_names argument: for mask rcnn, would those 4 output names be enough? if not, what those should be?

Could any buddy please help me on this? Thank you so much~~~