Deep Active Learning for Joint Classification & Segmentation with Weak Annotator

CNN visualization and interpretation methods, like class activation maps (CAMs), are typically used to highlight the image regions linked to the class predictions. These models allow to simultaneously classify images and yield pixel-wise localization scores, without the need for costly pixel-level annotations. However, they are prone to high false positive localization, and thus poor visualisations when processing challenging images, such as histology images for cancer grading and localization. In this paper, an active learning (AL) framework is proposed to alleviate this issue by progressively integrating pixel-wise annotation during training. Given training data with global class-level labels, our deep weakly-supervised learning (WSL) model simultaneously allows for supervised learning for classification, and active learning for segmentation of images selected for pixel-level annotation by an oracle. Unlike traditional AL methods that focus on acquisition method, we also propose leveraging the unlabeled images to improve model accuracy with less oracle-annotation. To this end, self-learning is considered where the model is used to pseudo-annotate a large number of relevant unlabeled samples, which are then integrated during the learning process with oracle-annotated samples. Our extensive experiments are conducted on complex high resolution medical and natural images from two benchmark datasets -- GlaS for colon cancer, and CUB-200-2011 for bird species. Results indicate that by using simply random acquisition, our approach can significantly outperform segmentation obtained with state-of the-art CAMs and AL methods, using an identical oracle-supervision budget. Our method provides an efficient solution to improve the regions of interest (ROI) segmentation accuracy for real-world visual recognition applications.