reading note: mask r

TITLE: Mask R-CNN

AUTHOR: Kaiming He, Georgia Gkioxari, Piotr Dollár, Ross Girshick

ASSOCIATION: Facebook AI Research

FROM: arXiv:1703.06870

CONTRIBUTIONS

1. A conceptually simple, flexible, and general framework for object instance segmentation is presented.
2. The method, called Mask R-CNN, extends Faster R-CNN by adding a branch for predicting an object mask in parallel with the existing branch for bounding box recognition.

METHOD

Mask R-CNN is conceptually simple: Faster R-CNN has two outputs for each candidate object, a class label and a bounding-box offset; to this a third branch is added that outputs the object mask. The idea is illustrated in the following image.

In order to avoid competition across classes, the mask branch has a $ Km^{2} $ dimensional output for each ROI, which endoces $ K $ binary masks of resolution $ m times m $, one for each of the $ K $ classes. When training, for an ROI associated with ground-truth class $ k $, loss is only computed on the $k$-th mask.

An $ m times m $ mask from each ROI is predicted using a small FCN network. The input of the small FCN network is an RoIAlign feature, which using bilinear interpolation to compute the exact values of the input feature at four regularly sampled locations in each ROI bin.