The ProposalLayer plugin generates the first-stage detection (ROI candidates) out of the scores, refinement info from RPN(Region Proposal Network) and pre-defined anchors. It is used in sampleMaskRCNN.

Structure

This plugin supports the NCHW format. It takes two input tenosrs: object_score and object_delta

object_score is the objectness score from RPN. objetc_score's shape is [N, anchors, 2, 1] where N is the batch_size, anchors is the total number of anchors and 2 means 2 classes of objectness --- foreground and background .

object_delta is the refinement info from RPN of shape [N, anchors, 4, 1]. 4 means 4 elements of refinement information --- [dy, dx, dh, dw]

This plugin generates one output tensor of shape [N, keep_topk, 4] where keep_topk is the maximum number of detections left after NMS and 4 means coordinates of ROI candidates [y1, x1, y2, x2]

Instead of fed as input in Keras, the default anchors are generated in this plugin during initialization.
For resnet101 + 1024*1024 input shape, the number of anchors can be computed as

Anchors in feature map P2: 256*256*3 
Anchors in feature map P3: 128*128*3
Anchors in feature map P4: 64*64*3
Anchors in feature map P5: 32*32*3
Anchors in feature map P6(maxpooling): 16*16*3  

total number of anchors: 87296*3 = 261888

Parameters

This plugin has the plugin creator class ProposalLayerPluginCreator and the plugin class ProposalLayer.

The following parameters were used to create ProposalLayer instance:

Type	Parameter	Description
`int`	`prenms_topk`	The number of ROIs which will be kept before NMS.
`int`	`keep_topk`	Number of detections will be kept after NMS.
`float`	`iou_threshold`	IOU threshold value used in NMS.

Additional resources

The following resources provide a deeper understanding of the ProposalLayer plugin:

MaskRCNN

License

For terms and conditions for use, reproduction, and distribution, see the TensorRT Software License Agreement documentation.

Changelog

June 2019 This is the first release of this README.md file.

Known issues

There are no known issues in this plugin.