ProposalLayer

Table Of Contents

• Description
  • Structure
• Parameters
• Additional resources
• License
• Changelog
• Known issues

Description

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 sampleUffMaskRCNN.

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. object_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 refers to the 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 refers to coordinates of ROI candidates [y1, x1, y2, x2]

The default anchors are generated in this plugin during initialization method. For ResNet101 with 1024*1024 input image, 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.
int[3]	image_size	Input image size in CHW. Only supports C=3 and defaults to [3,1024,1024].

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

July 2020: Add (optional) plugin parameter for specifying image size. June 2019: First release of proposeLayerPlugin.

Known issues

There are no known issues in this plugin.