**Faster R-CNN** is an object detection model that improves on [Fast R-CNN](https://paperswithcode.com/method/fast-r-cnn) by utilising a region proposal network ([RPN](https://paperswithcode.com/method/rpn)) with the CNN model. The RPN shares full-image convolutional features with the detection network, enabling nearly cost-free region proposals. It is a fully convolutional network that simultaneously predicts object bounds and objectness scores at each position. The RPN is trained end-to-end to generate high-quality region proposals, which are used by [Fast R-CNN](https://paperswithcode.com/method/fast-r-cnn) for detection. RPN and Fast [R-CNN](https://paperswithcode.com/method/r-cnn) are merged into a single network by sharing their convolutional features: the RPN component tells the unified network where to look.

As a whole, Faster R-CNN consists of two modules. The first module is a deep fully convolutional network that proposes regions, and the second module is the Fast R-CNN detector that uses the proposed regions.

**Depthwise Convolution** is a type of convolution where we apply a single convolutional filter for each input channel. In the regular 2D [convolution](https://paperswithcode.com/method/convolution) performed over multiple input channels, the filter is as deep as the input and lets us freely mix channels to generate each element in the output. In contrast, depthwise convolutions keep each channel separate. To summarize the steps, we:

1. Split the input and filter into channels.
2. We convolve each input with the respective filter.
3. We stack the convolved outputs together.

Image Credit: [Chi-Feng Wang](https://towardsdatascience.com/a-basic-introduction-to-separable-convolutions-b99ec3102728)

Depthwise Convolution

Faster R-CNN

Faster R-CNN: Towards Real-Time Object Detection with Region Proposal Networks

**BlendMask** is an [instance segmentation framework](https://paperswithcode.com/methods/category/instance-segmentation-models) built on top of the[ FCOS](https://paperswithcode.com/method/fcos) object detector. The bottom module uses either backbone or [FPN](https://paperswithcode.com/method/fpn) features to predict a set of bases. A single [convolution](https://paperswithcode.com/methods/category/convolutions) layer is added on top of the detection towers to produce attention masks along with each bounding box prediction. For each predicted instance, the [blender](https://paperswithcode.com/method/blender) crops the bases with its bounding box and linearly combine them according the learned attention maps. Note that the Bottom Module can take features either from ‘C’, or ‘P’ as the input.

Source	Faster R-CNN: Towards Real-Time Object Detection with Region Proposal Networks
Year	2000
Data Source	CC BY-SA - https://paperswithcode.com