**EfficientDet** is a type of object detection model, which utilizes several optimization and backbone tweaks, such as the use of a [BiFPN](https://paperswithcode.com/method/bifpn), and a compound scaling method that uniformly scales the resolution,depth and width for all backbones, feature networks and box/class prediction networks at the same time.

**Region of Interest Align**, or **RoIAlign**, is an operation for extracting a small feature map from each RoI in detection and segmentation based tasks. It removes the harsh quantization of [RoI Pool](https://paperswithcode.com/method/roi-pooling), properly *aligning* the extracted features with the input. To avoid any quantization of the RoI boundaries or bins (using $x/16$ instead of $[x/16]$), RoIAlign uses bilinear interpolation to compute the exact values of the input features at four regularly sampled locations in each RoI bin, and the result is then aggregated (using max or average).

RoIAlign

Mask R-CNN

EfficientDet

EfficientDet: Scalable and Efficient Object Detection

**HITNet** is a framework for neural network based depth estimation which overcomes the computational disadvantages of operating on a 3D volume by integrating image warping, spatial propagation and a fast high resolution initialization step into the network architecture, while keeping the flexibility of a learned representation by allowing features to flow through the network. The main idea of the approach is to represent image tiles as planar patches which have a learned compact feature descriptor attached to them. The basic principle of the approach is to fuse information from the high resolution initialization and the current hypotheses using spatial propagation. The propagation is implemented via a [convolutional neural network](https://paperswithcode.com/methods/category/convolutional-neural-networks) module that updates the estimate of the planar patches and their attached features. 

In order for the network to iteratively increase the accuracy of the disparity predictions, the network is provided a local cost volume in a narrow band (±1 disparity) around the planar patch using in-network image warping allowing the network to minimize image dissimilarity. To reconstruct fine details while also capturing large texture-less areas we start at low resolution and hierarchically upsample predictions to higher resolution. A critical feature of the architecture is that at each resolution, matches from the initialization module are provided to facilitate recovery of thin structures that cannot be represented at low resolution.

Source	EfficientDet: Scalable and Efficient Object Detection
Year	2000
Data Source	CC BY-SA - https://paperswithcode.com