Wittawat Jitkrittum

My research interest is in machine learning. More specifically, I have experience doing research on nonparametric hypothesis testing, kernel methods, Bayesian inference, and model comparison.

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    Preview abstract Many practical settings allow a learner to defer predictions to one or more costly experts. For example, the learning to defer paradigm allows a learner to defer to a human expert, at some monetary cost. Similarly, the adaptive inference paradigm allows a base model to defer to one or more large models, at some computational cost. The goal in these settings is to learn classification and deferral mechanisms to optimise a suitable accuracy-cost tradeoff. To achieve this, a central issue studied in prior work is the design of a coherent loss function for both mechanisms. In this work, we demonstrate that existing losses have two subtle limitations: they can encourage underfitting when there is a high cost of deferring, and the deferral function can have a weak dependence on the base model predictions. To resolve these issues, we propose a post-hoc training scheme: we train a deferral function on top of a base model, with the objective of predicting to defer when the base model's error probability exceeds the cost of the expert model. This may be viewed as applying a partial surrogate to the ideal deferral loss, which can lead to a tighter approximation and thus better performance. Empirically, we verify the efficacy of post-hoc training on benchmarks for learning to defer and adaptive inference. View details
    A Sketch Is Worth a Thousand Words: Image Retrieval with Text and Sketch
    Patsorn Sangkloy
    Diyi Yang
    James Hays
    The European Conference on Computer Vision (ECCV)(2022) (to appear)
    Preview abstract We address the problem of retrieving in-the-wild images with both a sketch and a text query. We present TASK-former (Text And SKetch transformer), an end-to-end trainable model for image retrieval using a text description and a sketch as input. We argue that both input modalities complement each other in a manner that cannot be achieved easily by either one alone. TASK-former follows the late-fusion dual-encoder approach, similar to CLIP, which allows efficient and scalable retrieval since the retrieval set can be indexed independently of the queries. We empirically demonstrate that using an input sketch (even a poorly drawn one) in addition to text considerably increases retrieval recall compared to traditional text-based image retrieval. To evaluate our approach, we collect 5,000 hand-drawn sketches for images in the test set of the COCO dataset. The collected sketches are available a https://janesjanes.github.io/tsbir/. View details
    Preview abstract Negative sampling is a widely adopted technique to enable efficient training in settings with a large number of classes. Typically, negative sampling approaches aim at approximating the value or gradient of the computationally expensive loss function that takes all the negative labels into account. In this work, we study the connection between negative sampling approaches and loss modification techniques for countering label imbalance. We show that different (bias) correction strategies that accompany negative sampling approaches can have unintended consequences on the model's performance on various data sub-populations. We then propose a unified approach to tackle both sampling bias, arising from working with a subset of all negative classes, and labeling bias, which is inherently present in the data due to label-imbalance. Finally, we verify our analysis and demonstrate the utility of our unified approach through empirical evaluation on standard image classification and retrieval benchmarks. View details
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