Portrait of Reyhane Askari Hemmat is unavailable

Reyhane Askari Hemmat

reyhane.askari.hemmat@mila.quebec
Collaborating researcher - Université de Montréal
Supervisor
Adriana Romero Soriano
Research Topics
Diffusion Models
Generative Models
GitHub

Publications

Increasing the Utility of Synthetic Images through Chamfer Guidance
Nicola Dall'Asen
Xiaofeng Zhang
Reyhane Askari Hemmat
Melissa Hall
Jakob Verbeek
Adriana Romero Soriano
Michal Drozdzal
Conditional image generative models hold considerable promise to produce infinite amounts of synthetic training data. Yet, recent progress i… (see more)n generation quality has come at the expense of generation diversity, limiting the utility of these models as a source of synthetic training data. Although guidance-based approaches have been introduced to improve the utility of generated data by focusing on quality or diversity, the (implicit or explicit) utility functions oftentimes disregard the potential distribution shift between synthetic and real data. In this work, we introduce Chamfer Guidance: a training-free guidance approach which leverages a handful of real exemplar images to characterize the quality and diversity of synthetic data. We show that by leveraging the proposed Chamfer Guidance, we can boost the diversity of the generations w.r.t. a dataset of real images while maintaining or improving the generation quality on ImageNet-1k and standard geo-diversity benchmarks. Our approach achieves state-of-the-art few-shot performance with as little as 2 exemplar real images, obtaining 96.4\% in terms of precision, and 86.4\% in terms of distributional coverage, which increase to 97.5\% and 92.7\%, respectively, when using 32 real images. We showcase the benefits of the Chamfer Guidance generation by training downstream image classifiers on synthetic data, achieving accuracy boost of up to 15\% for in-distribution over the baselines, and up to 16\% in out-of-distribution. Furthermore, our approach does not require using the unconditional model, and thus obtains a 31\% reduction in FLOPs w.r.t. classifier-free-guidance-based approaches at sampling time.
2025-08-14
ArXiv (preprint)
arxiv.org
arxiv.org
Improving the Scaling Laws of Synthetic Data with Deliberate Practice
Reyhane Askari Hemmat
Mohammad Pezeshki
Elvis Dohmatob
Florian Bordes
Pietro Astolfi
Melissa Hall
Jakob Verbeek
Michal Drozdzal
Adriana Romero Soriano
2025-05-01
ICML.cc/2025/Conference (oral)
doi.org
openreview.net
Multi-Modal Language Models as Text-to-Image Model Evaluators
Jiahui Chen
Candace Ross
Reyhane Askari Hemmat
Koustuv Sinha
Melissa Hall
Michal Drozdzal
Adriana Romero Soriano
2025-05-01
arXiv (published)
doi.org
arxiv.org
Multi-Modal Language Models as Text-to-Image Model Evaluators
Jiahui Chen
Candace Ross
Reyhane Askari Hemmat
Koustuv Sinha
Melissa Hall
Michal Drozdzal
Adriana Romero Soriano
2025-05-01
ArXiv (preprint)
arxiv.org
arxiv.org
Improving the Scaling Laws of Synthetic Data with Deliberate Practice
Reyhane Askari Hemmat
Mohammad Pezeshki
Elvis Dohmatob
Florian Bordes
Pietro Astolfi
Melissa Hall
Jakob Verbeek
Michal Drozdzal
Adriana Romero Soriano
Inspired by the principle of deliberate practice in human learning, we propose Deliberate Practice for Synthetic Data Generation (DP), a nov… (see more)el framework that improves sample efficiency through dynamic synthetic data generation. Prior work has shown that scaling synthetic data is inherently challenging, as naively adding new data leads to diminishing returns. To address this, pruning has been identified as a key mechanism for improving scaling, enabling models to focus on the most informative synthetic samples. Rather than generating a large dataset and pruning it afterward, DP efficiently approximates the direct generation of informative samples. We theoretically show how training on challenging, informative examples improves scaling laws and empirically validate that DP achieves better scaling performance with significantly fewer training samples and iterations. On ImageNet-100, DP generates 3.4x fewer samples and requires six times fewer iterations, while on ImageNet-1k, it generates 8x fewer samples with a 30 percent reduction in iterations, all while achieving superior performance compared to prior work.
2025-02-21
ArXiv (preprint)
arxiv.org
arxiv.org
EvalGIM: A Library for Evaluating Generative Image Models
Melissa Hall
Oscar Mañas
Reyhane Askari Hemmat
Mark Ibrahim
Candace Ross
Pietro Astolfi
Tariq Berrada
Marton Havasi
Yohann Benchetrit
Karen Ullrich
Carolina Braga
Abhishek Charnalia
Maeve Ryan
Michael Rabbat
Michal Drozdzal
Jakob Verbeek
Adriana Romero Soriano
As the use of text-to-image generative models increases, so does the adoption of automatic benchmarking methods used in their evaluation. Ho… (see more)wever, while metrics and datasets abound, there are few unified benchmarking libraries that provide a framework for performing evaluations across many datasets and metrics. Furthermore, the rapid introduction of increasingly robust benchmarking methods requires that evaluation libraries remain flexible to new datasets and metrics. Finally, there remains a gap in synthesizing evaluations in order to deliver actionable takeaways about model performance. To enable unified, flexible, and actionable evaluations, we introduce EvalGIM (pronounced ''EvalGym''), a library for evaluating generative image models. EvalGIM contains broad support for datasets and metrics used to measure quality, diversity, and consistency of text-to-image generative models. In addition, EvalGIM is designed with flexibility for user customization as a top priority and contains a structure that allows plug-and-play additions of new datasets and metrics. To enable actionable evaluation insights, we introduce ''Evaluation Exercises'' that highlight takeaways for specific evaluation questions. The Evaluation Exercises contain easy-to-use and reproducible implementations of two state-of-the-art evaluation methods of text-to-image generative models: consistency-diversity-realism Pareto Fronts and disaggregated measurements of performance disparities across groups. EvalGIM also contains Evaluation Exercises that introduce two new analysis methods for text-to-image generative models: robustness analyses of model rankings and balanced evaluations across different prompt styles. We encourage text-to-image model exploration with EvalGIM and invite contributions at https://github.com/facebookresearch/EvalGIM/.
2024-12-13
ArXiv (preprint)
doi.org
arxiv.org
Improving Geo-diversity of Generated Images with Contextualized Vendi Score Guidance
Reyhane Askari Hemmat
Melissa Hall
Alicia Sun
Candace Ross
Michal Drozdzal
Adriana Romero Soriano
2024-11-21
Lecture Notes in Computer Science (published)
doi.org
arxiv.org
On Improved Conditioning Mechanisms and Pre-training Strategies for Diffusion Models
Tariq Berrada
Pietro Astolfi
Melissa Hall
Reyhane Askari Hemmat
Yohann Benchetrit
Marton Havasi
Matthew J. Muckley
Karteek Alahari
Adriana Romero Soriano
Jakob Verbeek
Michal Drozdzal
Large-scale training of latent diffusion models (LDMs) has enabled unprecedented quality in image generation. However, the key components of… (see more) the best performing LDM training recipes are oftentimes not available to the research community, preventing apple-to-apple comparisons and hindering the validation of progress in the field. In this work, we perform an in-depth study of LDM training recipes focusing on the performance of models and their training efficiency. To ensure apple-to-apple comparisons, we re-implement five previously published models with their corresponding recipes. Through our study, we explore the effects of (i)~the mechanisms used to condition the generative model on semantic information (e.g., text prompt) and control metadata (e.g., crop size, random flip flag, etc.) on the model performance, and (ii)~the transfer of the representations learned on smaller and lower-resolution datasets to larger ones on the training efficiency and model performance. We then propose a novel conditioning mechanism that disentangles semantic and control metadata conditionings and sets a new state-of-the-art in class-conditional generation on the ImageNet-1k dataset -- with FID improvements of 7% on 256 and 8% on 512 resolutions -- as well as text-to-image generation on the CC12M dataset -- with FID improvements of 8% on 256 and 23% on 512 resolution.
2024-11-05
ArXiv (preprint)
doi.org
arxiv.org
Deliberate Practice with Synthetic Data
Reyhane Askari Hemmat
Mohammad Pezeshki
Pietro Astolfi
Melissa Hall
Florian Bordes
Jakob Verbeek
Michal Drozdzal
Adriana Romero Soriano
2024-10-10
NeurIPS.cc/2024/Workshop/AFM (poster)
openreview.net
openreview.net
On improved Conditioning Mechanisms and Pre-training Strategies for Diffusion Models
Tariq Berrada
Pietro Astolfi
Melissa Hall
Reyhane Askari Hemmat
Yohann Benchetrit
Marton Havasi
Matthew J. Muckley
Karteek Alahari
Adriana Romero Soriano
Jakob Verbeek
Michal Drozdzal
Large-scale training of latent diffusion models (LDMs) has enabled unprecedented quality in image generation. However, large-scale end-to-e… (see more)nd training of these models is computationally costly, and hence most research focuses either on finetuning pretrained models or experiments at smaller scales. In this work we aim to improve the training efficiency and performance of LDMs with the goal of scaling to larger datasets and higher resolutions. We focus our study on two points that are critical for good performance and efficient training: (i) the mechanisms used for semantic level (\eg a text prompt, or class name) and low-level (crop size, random flip, \etc) conditioning of the model, and (ii) pre-training strategies to transfer representations learned on smaller and lower-resolution datasets to larger ones. The main contributions of our work are the following: we present systematic experimental study of these points, we propose a novel conditioning mechanism that disentangles semantic and low-level conditioning, we obtain state-of-the-art performance on CC12M for text-to-image at 512 resolution.
2024-09-25
NeurIPS.cc/2024/Conference (poster)
doi.org
openreview.net
Improving Geo-diversity of Generated Images with Contextualized Vendi Score Guidance
Reyhane Askari Hemmat
Melissa Hall
Alicia Sun
Candace Ross
Michal Drozdzal
Adriana Romero Soriano
With the growing popularity of text-to-image generative models, there has been increasing focus on understanding their risks and biases. Rec… (see more)ent work has found that state-of-the-art models struggle to depict everyday objects with the true diversity of the real world and have notable gaps between geographic regions. In this work, we aim to increase the diversity of generated images of common objects such that per-region variations are representative of the real world. We introduce an inference time intervention, contextualized Vendi Score Guidance (c-VSG), that guides the backwards steps of latent diffusion models to increase the diversity of a sample as compared to a"memory bank"of previously generated images while constraining the amount of variation within that of an exemplar set of real-world contextualizing images. We evaluate c-VSG with two geographically representative datasets and find that it substantially increases the diversity of generated images, both for the worst performing regions and on average, while simultaneously maintaining or improving image quality and consistency. Additionally, qualitative analyses reveal that diversity of generated images is significantly improved, including along the lines of reductive region portrayals present in the original model. We hope that this work is a step towards text-to-image generative models that reflect the true geographic diversity of the world.
2024-06-06
ArXiv (preprint)
doi.org
arxiv.org
An Introduction to Vision-Language Modeling
Florian Bordes
Richard Yuanzhe Pang
Anurag Ajay
Alexander C. Li
Adrien Bardes
Suzanne Petryk
Oscar Mañas
Zhiqiu Lin
Anas Mahmoud
Bargav Jayaraman
Mark Ibrahim
Melissa Hall
Yunyang Xiong
Jonathan Lebensold
Candace Ross
Srihari Jayakumar
Chuan Guo
Diane Bouchacourt
Haider Al-Tahan
Karthik Padthe … (see 21 more)
Vasu Sharma
Huijuan Xu 0001
Xiaoqing Ellen Tan
Megan Richards
Samuel Lavoie
Pietro Astolfi
Reyhane Askari Hemmat
Jun Chen
Kushal Tirumala
Rim Assouel
Mazda Moayeri
Arjang Talattof
Kamalika Chaudhuri
Zechun Liu
Xilun Chen
Quentin Garrido
Karen Ullrich
Aishwarya Agrawal
Kate Saenko
Asli Celikyilmaz
Vikas Chandra
Following the recent popularity of Large Language Models (LLMs), several attempts have been made to extend them to the visual domain. From h… (see more)aving a visual assistant that could guide us through unfamiliar environments to generative models that produce images using only a high-level text description, the vision-language model (VLM) applications will significantly impact our relationship with technology. However, there are many challenges that need to be addressed to improve the reliability of those models. While language is discrete, vision evolves in a much higher dimensional space in which concepts cannot always be easily discretized. To better understand the mechanics behind mapping vision to language, we present this introduction to VLMs which we hope will help anyone who would like to enter the field. First, we introduce what VLMs are, how they work, and how to train them. Then, we present and discuss approaches to evaluate VLMs. Although this work primarily focuses on mapping images to language, we also discuss extending VLMs to videos.
2024-05-27
ArXiv (preprint)
doi.org
arxiv.org