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240 nips-2010-Simultaneous Object Detection and Ranking with Weak Supervision


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Author: Matthew Blaschko, Andrea Vedaldi, Andrew Zisserman

Abstract: A standard approach to learning object category detectors is to provide strong supervision in the form of a region of interest (ROI) specifying each instance of the object in the training images [17]. In this work are goal is to learn from heterogeneous labels, in which some images are only weakly supervised, specifying only the presence or absence of the object or a weak indication of object location, whilst others are fully annotated. To this end we develop a discriminative learning approach and make two contributions: (i) we propose a structured output formulation for weakly annotated images where full annotations are treated as latent variables; and (ii) we propose to optimize a ranking objective function, allowing our method to more effectively use negatively labeled images to improve detection average precision performance. The method is demonstrated on the benchmark INRIA pedestrian detection dataset of Dalal and Triggs [14] and the PASCAL VOC dataset [17], and it is shown that for a significant proportion of weakly supervised images the performance achieved is very similar to the fully supervised (state of the art) results. 1

Reference: text


Summary: the most important sentenses genereted by tfidf model

sentIndex sentText sentNum sentScore

1 In this work are goal is to learn from heterogeneous labels, in which some images are only weakly supervised, specifying only the presence or absence of the object or a weak indication of object location, whilst others are fully annotated. [sent-3, score-1.425]

2 We extend this framework here to weakly annotated images by treating missing information in a latent variable fashion following [2, 40]. [sent-11, score-0.717]

3 Available annotation, such as the presence or absence of an object in an image, constrains the set of values the latent variable can take. [sent-12, score-0.436]

4 We empirically observe that the localization approach of [8] fails in the case that there are many images with no object present, motivating a slight modification of the learning algorithm to optimize detection ranking analogous 1 to [11, 21, 41]. [sent-14, score-1.001]

5 When combined with discriminative latent variable learning, this results in an algorithm similar to multiple instance ranking [6], but we exploit the full generality of structured output learning. [sent-16, score-0.756]

6 The computer vision literature has approached learning from weakly annotated data in many different ways. [sent-17, score-0.496]

7 Search engine results [20] or associated text captions [5, 7, 13, 34] are attractive due to the availability of millions of tagged or captioned images on the internet, providing a weak form of labels beyond unsupervised learning [37]. [sent-18, score-0.518]

8 Alternatively, one may approach the problem of object detection by considering generic properties of objects or their attributes in order to combine training data from multiple classes [1, 26, 18]. [sent-20, score-0.454]

9 learn the common appearance of multiple object categories, which yields an estimate of where in an image an object is without specifying the specific class to which it belongs [15]. [sent-22, score-0.707]

10 This can then be utilized in a weak supervision setting to learn a detector for a specific object category. [sent-23, score-0.679]

11 Here, we consider this latter kind of weak annotation, and will also consider cases where the object center is constrained to a region in the image, but that exact coordinates are not given [27]. [sent-28, score-0.5]

12 Simultaneous localization and classification using a discriminative latent variable model has been recently explored in [29], but that work has not considered mixed annotation, or a structured output loss. [sent-29, score-0.482]

13 In Section 2 we review a structured output learning formulation for object detection that will form the basis of our optimization. [sent-31, score-0.62]

14 We then propose to improve that approach to better handle negative training instances by developing a ranking objective in Section 3. [sent-32, score-0.634]

15 The resulting objective allows us to approach the problem of weakly annotated data in Section 4, and the methods are empirically validated in Section 5. [sent-33, score-0.452]

16 In our case, we would like to learn a mapping f : X → Y where X the space of images and Y is the space of bounding boxes or no bounding box: Y ≡ ∅ (l, t, r, b), where (l, t, r, b) ∈ R4 specifies the left, top, right, and bottom coordinates of a bounding box. [sent-35, score-1.126]

17 It was proposed in [8] to treat images in which there is no instance of the object of interest as zero vectors in the Hilbert space induced by φ, i. [sent-40, score-0.535]

18 φ(x, y− ) = 0 ∀x where y− indicates the label that there is no object in the image (i. [sent-42, score-0.369]

19 For negative images, ∆(y− , y) = 1 if y indicates an ˜∗ object is present, so the maximization corresponds simply to finding the bounding box with highest score. [sent-46, score-0.797]

20 2 which tends to decrease the score associated with all bounding boxes in the image. [sent-49, score-0.457]

21 The primary problem with this approach is that it optimizes a regularized risk functional for which negative images are treated equally with positive images. [sent-50, score-0.399]

22 In the case of imbalances in the training data where a large majority of images do not contain the object of interest, the objective function may be dominated by the terms in i ξi for which there is no bounding box present. [sent-51, score-1.097]

23 The learning procedure may focus on decreasing the score of candidate detections in negative images rather than on increasing the score of correct detections. [sent-52, score-0.508]

24 We show empirically in Section 5 that this treatment of negative images is in fact detrimental to localization performance. [sent-53, score-0.436]

25 The results presented in [8] were achieved by training only on images with an instance of the object present, ignoring large quantities of negative training data. [sent-54, score-0.767]

26 Although one may attempt to address this problem by adjusting the loss function, ∆, to penalize negative images less than positive images, this approach is heuristic and requires searching over an additional parameter during training (the relative size of the loss for negative images). [sent-55, score-0.645]

27 3 Learning to Rank We propose to remedy the shortcomings outlined in the previous section by modifying the objective in Equation (1) to simultaneously localize and rank object detections. [sent-57, score-0.369]

28 The following constraints applied to the test set ensure a perfect ranking, that is that every true detection has a higher score than all false detections: ∀i, j, yj ∈ Y \ {yj }. [sent-58, score-0.396]

29 ˜ w, φ(xi , yi ) > w, φ(xj , yj ) ˜ (5) We modify these constraints, incorporating a structured output loss, in the following structured output ranking objective 1 w 2 min w,ξ 2 +C 1 n · n+ ξij (6) i,j w, φ(xi , yi ) − w, φ(xj , yj ) ≥ ∆(yj , yj ) − ξij ˜ ˜ ξij ≥ 0 ∀i, j s. [sent-59, score-1.629]

30 As compared with Equations (1)-(3), we now compare each positive instance to all bounding boxes in all images in the training set instead of just the bounding boxes from the image it comes from. [sent-62, score-1.257]

31 The constraints attempt to give all positive instances a score higher than all negative instances, where the size of the margin is scaled to be proportional to the loss achieved by the negative instance. [sent-63, score-0.458]

32 We note that one can use this same approach to optimize related ranking objectives, such as precision at a given detection rate, by extending the formulations of [11, 41] to incorporate our structured output loss function, ∆. [sent-64, score-0.775]

33 ij ∆(yj , yj ) − ξ ˜ ij ξ≥0 ∀˜ ∈ y Y \ {yj } (10) j (11) where y is a vector with jth element yj . [sent-68, score-0.48]

34 If w, φ(xj , yj ) ≥ w, φ(xi , yi ) and ı ˜∗ 3 Algorithm 1 1-slack structured output ranking – maximally violated constraint. [sent-75, score-1.008]

35 Ensure: Maximally violated constraint is δ − w, ψ ≤ ξ for all i do s+ = w, φ(xi , yi ) i end for for all j do yj = argmaxy w, φ(xj , y) + ∆(yj , y) ˜∗ s− = w, φ(xj , yj ) + ∆(yj , yj ) ˜∗ ˜∗ j end for (s+ , p+ ) = sort(s+ ) {p+ is a vector of indices specifying a given score’s original index. [sent-76, score-0.871]

36 In˜∗ stead, we sort the instances of the class by their score, and sort the negative instances by their score as well. [sent-78, score-0.368]

37 We iterate through each violated region, ordered by score, and sum the violated constraints into ψ and δ, yielding the maximally violated 1-slack constraint. [sent-80, score-0.409]

38 4 Weakly Supervised Data Now that we have developed a structured output learning framework that is capable of appropriately handling images from the background class, we turn our attention to the problem of learning with weakly annotated data. [sent-81, score-0.839]

39 We will consider the problem in full generality by assuming that we have bounding box level annotation for some training images, but only binary labels or weak location information for others. [sent-82, score-0.917]

40 For negatively labeled images, we know that no bounding box in the entire image contains an instance of the object class, while for positive images at least one bounding box belongs to the class of interest. [sent-83, score-1.619]

41 We approach this issue by considering the location of a bounding box to be a latent variable to be inferred during training. [sent-84, score-0.578]

42 In the case that we have only a binary image-level label, we constrain the latent variable to indicate that some region of the image corresponds to the object of interest. [sent-86, score-0.528]

43 In a more constrained case, such as annotation indicating the object center, we constrain the latent variable to belong to the set of bounding boxes that have a center consistent with the annotation. [sent-87, score-0.932]

44 There is an asymmetry in the image level labeling in that negative labels can be considered to be full annotation (i. [sent-88, score-0.409]

45 all bounding boxes do not contain an instance of the object), while positive labels are incomplete. [sent-90, score-0.502]

46 4 where Ym is the set of bounding boxes consistent with the weak annotation for image m. [sent-94, score-0.851]

47 Viewed another way, we treat the location of the hypothesized bounding box as a latent variable. [sent-97, score-0.55]

48 In order to use this in our discriminative optimization, we will try to put a large margin between the maximally scoring box and all bounding boxes with high loss. [sent-98, score-0.733]

49 Though our algorithm does not have direct information about the true location of the object of interest, it tries to learn a discriminant function that can distinguish a region in the positively labeled images from all regions in the negatively labeled images. [sent-99, score-0.749]

50 We first illustrate the performance of the ranking objective developed in Section 3 and subsequently show the performance of learning with weakly supervised data using the latent variable approach of Section 4. [sent-102, score-0.885]

51 1 Experimental Setup We have implemented variants of two popular object detection systems in order to show the generalization of the approaches developed in this work to different levels of supervision and feature descriptors. [sent-104, score-0.527]

52 Inference of maximally violated constraints and object detection was performed using Efficient Subwindow Search (ESS) branch-and-bound inference [24, 25]. [sent-106, score-0.589]

53 The joint kernel map, φ, was constructed using a concatenation of the bounding box visual words histogram (the restriction kernel) and a global image histogram, similar to the approach described in [9]. [sent-107, score-0.552]

54 We first show results for the cat class in which 10% of negative images are included in the training set (Figure 1(a)), and subsequently results for which all negative images are used for training (Figure 1(b)). [sent-121, score-0.938]

55 While the ranking objective can appropriately handle varying amounts of negative training data, the objective in Equation (1) fails, resulting in worse performance as the amount of negative training data increases. [sent-122, score-0.902]

56 These results empirically show the shortcomings of the treatment of negative images proposed in [8], but the ranking objective by contrast is robust to large imbalances between positive and negative images. [sent-123, score-0.986]

57 Mean AP increases by 69% as a result of using the ranking objective when 10% of negative images are included during training, and mean AP improves by 71% when all negative images are used. [sent-124, score-1.132]

58 4 Ranking objective Standard objective Ranking objective Standard objective 0. [sent-127, score-0.38]

59 Figure 1: Precision-recall curves for the structured output ranking objective proposed in this paper (blue) vs. [sent-155, score-0.681]

60 the structured output objective proposed in [8] (red) for varying amounts of negative training data. [sent-156, score-0.522]

61 Results are shown on the cat class from the PASCAL VOC 2007 data set for 10% of negative images (1(a)) and for 100% of negatives (1(b)). [sent-157, score-0.474]

62 The structured output objective proposed in [8] performs worse with increasing amounts of negative training data, and the algorithm completely fails in 1(b). [sent-159, score-0.522]

63 Three cost functionals are compared: a simple binary SVM, the structural SVM model of (1), and the ranking SVM model of (6). [sent-163, score-0.408]

64 3 Learning with Weak Annotations To evaluate the objective in the case of weak supervision, we have additionally performed experiments in which we have varied the percentage of bounding box annotations provided to the learning algorithm. [sent-176, score-0.816]

65 Figure 3 contrasts the performance on the VOC dataset of our proposed discriminative latent variable algorithm with that of a fully supervised algorithm in which weakly annotated training data are ignored. [sent-177, score-0.777]

66 We have run the algorithm for 10% of images having full bounding box annotations (with the other 90% weakly labeled) and for 50% of images having complete annotation. [sent-178, score-1.176]

67 In the fully supervised case, we ignore all images that do not have full bounding box annotation and train the fully supervised ranking objective developed in Section 3. [sent-179, score-1.575]

68 For 10% of images fully annotated, mean AP increases by 64%, and with 50% of images fully annotated, mean AP increases by 83%. [sent-181, score-0.652]

69 (b) reports the performance of the latent variable ranking model (8) for the HOG-based detector on the INRIA pedestrian dataset. [sent-183, score-0.647]

70 Only one positive image is fully labeled with the pedestrian bounding boxes while the remaining positive images are weakly labeled. [sent-184, score-1.345]

71 Since most positive images contain multiple pedestrians, the weak annotations carry a minimal amount of information that is still sufficient to distinguish the different pedestrian instances. [sent-185, score-0.743]

72 Specifically, the bounding boxes are discarded and only their centers are kept. [sent-186, score-0.402]

73 8 1 recall Figure 2: (a) Precision-recall curves for different formulations: binary and structural SVMs, balanced binary and structural SVMs, ranking SVM. [sent-216, score-0.569]

74 The ranking formulation is slightly better than the other balanced costs for this dataset. [sent-218, score-0.363]

75 (b) Precision-recall curves for increasing amounts of weakly supervised data for the ranking formulation. [sent-219, score-0.704]

76 For all curves, only one image is fully labeled with bounding boxes around pedestrians, while the other images are labeled only by the pedestrian centers. [sent-220, score-1.115]

77 The first curve (AP 32%) corresponds to the case in which only the fully supervised image is used; the last curve (AP 75%) to the case in which all the other training images are added with weak annotations. [sent-221, score-0.789]

78 45 (a) cat class trained with 10% of bounding (b) cat class trained with 50% of bounding boxes. [sent-259, score-0.728]

79 Figure 3: Precision-recall curves for the structured output ranking objective proposed in this paper trained with a linear bag of words image representation and weak supervision (blue) vs. [sent-261, score-1.19]

80 Results are shown for 10% of bounding boxes (left) and for 50% of bounding boxes (right), the remainder of the images were provided with weak annotation indicating the presence or absence of an object in the image, but not the object location. [sent-263, score-1.972]

81 In both cases, the latent variable model (blue) results in performance that is substantially better than discarding weakly annotated images and using a fully supervised setting (red). [sent-264, score-0.899]

82 all object locations and scales for which the corresponding bounding box center is within a given bound of the labeled center (the bound is set to 25% of the length of the box diagonal). [sent-265, score-0.899]

83 In other words, a weak annotation contains only approximate location information. [sent-266, score-0.405]

84 The figure shows how the model performs when, in addition to the singly fully annotated image, an increasing number of weakly annotated images are added. [sent-268, score-0.823]

85 First, using the learning formulation developed in [8], negative images are not handled properly, resulting in the undesired behavior that additional negative images in the training data decrease performance. [sent-271, score-0.865]

86 The special case of the objective in Equations (1)-(3), for which no negative training data are incorporated, can be viewed roughly as an estimate of the log probability of an object being present at a location conditioned on that an object is present in the image. [sent-272, score-0.872]

87 In fact, the results presented in [8] were computed by training the objective function only on positive images, and then using a separate non-linear ranking function based on global image statistics. [sent-276, score-0.612]

88 Using only positively labeled images in the objective presented in Section 2 only incorporates a subset of the constraints in Equation (7) corresponding to i = j. [sent-277, score-0.442]

89 Reweighting the loss corresponding to positive and negative examples resulted in similar performance to the ranking objective on the INRIA pedestrian data set, but requires a search across an additional parameter. [sent-279, score-0.767]

90 From the perspective of regularized risk, subsampling negative images can be viewed as a noisy version of this reweighting, and experiments on PASCAL VOC using the objective in (1) showed poor performance over a wide range of sampling rates. [sent-280, score-0.489]

91 The ranking objective by contrast weights loss from the negative examples appropriately (Algorithm 1) according to their contribution to the loss for the precision-recall curve. [sent-281, score-0.612]

92 By using the ranking objective to treat negative images, learning with weak annotations was made directly applicable using a discriminative latent variable model. [sent-283, score-1.05]

93 Results showed consistent improvement across different proportions of weakly and fully supervised data. [sent-284, score-0.399]

94 Our formulation handled different ratios of weakly annotated and fully annotated training data without additional parameter tuning in the loss function. [sent-285, score-0.746]

95 The discriminative latent variable approach has been able to achieve performance within a few percent of that achieved by a fully supervised system using only one fully supervised label. [sent-286, score-0.548]

96 That this is consistent across the data sets reported here indicates that discriminative latent variable models are a promising strategy for treating weak annotation in general. [sent-288, score-0.538]

97 Weak hypotheses and boosting for generic object detection and recognition. [sent-518, score-0.364]

98 Object localization with boosting and weak supervision for generic object recognition. [sent-523, score-0.711]

99 Implicit color segmentation features for pedestrian and object detection. [sent-528, score-0.42]

100 A framework for learning to recognize and segment object classes using weakly supervised training data. [sent-533, score-0.633]


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