This article investigates a data-driven approach for semantic scene understanding, without pixelwise annotation or classifier training. The proposed framework parses a target image in two steps: first, retrieving its exemplars (that is, references) from an image database, where all images are unsegmented but annotated with tags; second, recovering its pixel labels by propagating semantics from the references. The authors present a novel framework making the two steps mutually conditional and bootstrapped under the probabilistic Expectation-Maximization (EM) formulation. In the first step, the system selects the references by jointly matching the appearances as well as the semantics (that is, the assigned labels) with the target. They process the second step via a combinatorial graphical representation, in which the vertices are superpixels extracted from the target and its selected references. Then they derive the potentials of assigning labels to one vertex of the target, which depend upon the graph edges that connect the vertex to its spatial neighbors of the target and to similar vertices of the references. The proposed framework can be applied naturally to perform image annotation on new test images. In the experiments, the authors validated their approach on two public databases, and demonstrated superior performance over the state-of-the-art methods in both semantic segmentation and image annotation tasks.
Several weakly supervised methods are proposed to indicate the classes presented in the images with only image-level labels. For example, @cite_16 proposed to learn object classes based on unsupervised image segmentation. @cite_8 learned classification models for all scene labels by selecting representative training samples, and multiple instance learning was utilized in @cite_7 . Some nonparametric approaches have been also studied that solve the problems by searching and matching with an auxiliary image database. For example, an efficient structure-aware matching algorithm was discussed in @cite_6 to transfer labels from the database to the target image, but the pixelwise annotation was required for the auxiliary images.
@cite_16 @cite_6 @cite_7 @cite_8
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We address the problem of learning object class models and object segmentations from unannotated images. We introduce LOCUS (learning object classes with unsupervised segmentation) which uses a generative probabilistic model to combine bottom-up cues of color and edge with top-down cues of shape and pose. A key aspect of this model is that the object appearance is allowed to vary from image to image, allowing for significant within-class variation. By iteratively updating the belief in the object's position, size, segmentation and pose, LOCUS avoids making hard decisions about any of these quantities and so allows for each to be refined at any stage. We show that LOCUS successfully learns an object class model from unlabeled images, whilst also giving segmentation accuracies that rival existing supervised methods. Finally, we demonstrate simultaneous recognition and segmentation in novel images using the learned models for a number of object classes, as well as unsupervised object discovery and tracking in video. In this paper we propose a novel nonparametric approach for object recognition and scene parsing using dense scene alignment. Given an input image, we retrieve its best matches from a large database with annotated images using our modified, coarse-to-fine SIFT flow algorithm that aligns the structures within two images. Based on the dense scene correspondence obtained from the SIFT flow, our system warps the existing annotations, and integrates multiple cues in a Markov random field framework to segment and recognize the query image. Promising experimental results have been achieved by our nonparametric scene parsing system on a challenging database. Compared to existing object recognition approaches that require training for each object category, our system is easy to implement, has few parameters, and embeds contextual information naturally in the retrieval alignment procedure. We propose a novel method for weakly supervised semantic segmentation. Training images are labeled only by the classes they contain, not by their location in the image. On test images instead, the method predicts a class label for every pixel. Our main innovation is a multi-image model (MIM) - a graphical model for recovering the pixel labels of the training images. The model connects superpixels from all training images in a data-driven fashion, based on their appearance similarity. For generalizing to new test images we integrate them into MIM using a learned multiple kernel metric, instead of learning conventional classifiers on the recovered pixel labels. We also introduce an “objectness” potential, that helps separating objects (e.g. car, dog, human) from background classes (e.g. grass, sky, road). In experiments on the MSRC 21 dataset and the LabelMe subset of [18], our technique outperforms previous weakly supervised methods and achieves accuracy comparable with fully supervised methods. We propose a novel approach to semantic segmentation using weakly supervised labels. In traditional fully supervised methods, superpixel labels are available for training; however, it is not easy to obtain enough labeled superpixels to learn a satisfying model for semantic segmentation. By contrast, only image-level labels are necessary in weakly supervised methods, which makes them more practical in real applications. In this paper we develop a new way of evaluating classification models for semantic segmentation given weekly supervised labels. For a certain category, provided the classification model parameter, we firstly learn the basis superpixels by sparse reconstruction, and then evaluate the parameters by measuring the reconstruction errors among negative and positive superpixels. Based on Gaussian Mixture Models, we use Iterative Merging Update (IMU) algorithm to obtain the best parameters for the classification models. Experimental results on two real-world datasets show that the proposed approach outperforms the existing weakly supervised methods, and it also competes with state-of-the-art fully supervised methods.