Ramblings - Dataset Distillation

What is Dataset Distillation

Dataset Distillation, also called Dataset Condensation in much of the later literature, studies the following problem:

Can we replace a large real training set with a much smaller synthetic set such that training on the small set gives nearly the same downstream performance?

The synthetic dataset is not restricted to being a subset of the original data. The inputs, labels, and sometimes even training schedules can be optimized directly. This makes dataset distillation more general than coreset selection or subset selection.

At a high level, the goal is to compress the task-relevant information in a dataset rather than merely compressing pixels or storing a few representative examples.

Core entry points:

Broad Formal Problem Setup

Let the real dataset be

D={(xi,yi)}i=1N

and let the synthetic distilled dataset be

S={(x~j,y~j)}j=1M,MN.

Let a learning algorithm train model parameters θ from initialization θ0 using some optimizer, augmentation policy, and training schedule. The broad dataset distillation objective is:

minSEθ0p(θ0)[Ltest(θ(S;θ0))]

where θ(S;θ0) is the model obtained after training on the synthetic set.

Papers that are especially useful for formalizing the objective:

Why should we care?

Dataset distillation matters for at least three reasons.

First, it improves efficiency. If a tiny synthetic dataset can stand in for a large real dataset, then training, ablations, architecture search, and hyperparameter sweeps become much cheaper.

Second, it is useful in communication-constrained, storage-constrained, privacy-sensitive, or continual-learning settings where replay buffers or dataset transmission matter.

Third, it is an intriguing scientific problem. A successful distilled dataset is evidence that the original dataset contains a large amount of redundancy. Distillation therefore gives a way to ask: what information does a model really need in order to learn a task? It is about understanding which aspects of learning dynamics are worth preserving

Motivation and use-case papers:

The Evolution of the Field

Origin - The Original Bilevel Optimization Approach

Introduced in Dataset Distillation.
Dataset Distillation gives us a very narrow definition with fixing the evaluation architecture, task, loss function and optimizer. What would happen if we we were to vary each one of the above is something that needs to be explored.

Key papers:

Gradient Matching

While Dataset Distillation optimizes the synthetic data based on the synthetic data effect w.r.t the loss function, Dataset Condensation with Gradient Matching skips that by introducing the idea that both synthetic data and the original data should make the training parameters take similar path. It matches the gradients generated by the distilled data and the synthetic data.

I am not really sold behind the idea that the training parameters should take similar path. Why is that??

Dataset Condensation with Differentiable Siamese Augmentation improved upon Gradient Matching by introducing Siamese Augmentation as a strong regularizer. By applying augmentations to both the training data and the synthetic data, it is forcing the synthetic data to produce similar gradients/be useful not just in one fixed pixel configuration, but under a family of semantic-preserving transformations.

However, they apply it during eval as well, if it truly provides more informative synthetic dataset, the performance should increase even if we don't apply it during eval.

The above methods match the gradients of the same respective classes, however this misses the contrastive signals between classes. Thus in tasks like Fine Grained Classification, the above methods performed poorly. Therefore Dataset Condensation with Contrastive Signals adds all the gradients and then matches the sum. This allows the gradients from the class discriminative features to be prominent.

I do agree with their point and approach. I just wonder how the other methods encode contrastive signals. it does seem to be something that we need to take under consideration. I also believe it is related to intraclass variance in Distribution Matching based methods.

Trajectory Matching

Matching Gradients is short-sighted, and matching the full trajectory is computationally expensive. Therefore, Dataset Distillation by Matching Training Trajectories proposes to store expert training trajectories and then use the distilled data to train the model for a few steps and match the parameters from the training trajectory and those that have been trained using Distilled Data. The student network is trained on all the classes of synthetic data before matching, thus we do learn some form of contrastive signals. However, in individual minibatches, the authors use only synthetic data of the same class. Why is that the case and is it an issue to use all the classes images at once??

In MTT (Matching Training Trajectories), we match segments of expert trajectories of parameters. Therefore, if there was an error between the student endpoint and the endpoint of expert trajectory's segment, it wouldn't carry over to the next distillation batch, as we again start from the expert trajectory's starting point. However, that is not the case in evaluation. Errors accumulate in evaluation. Therefore Minimizing the Accumulated Trajectory Error to Improve Dataset Distillation employs Sharpness aware Minimization (Currently Reading More Into It)

Distribution Matching

Distribution matching avoids differentiating through long training trajectories by matching statistics or distributions in learned feature spaces. This family is usually cheaper and often more scalable, but its quality depends heavily on the embedding space and diversity constraints.

Introduced in Dataset Condensation with Distribution Matching, the authors match class wise feature distributions over randomly sampled embedding spaces. The authors match the empirical estimate of the MMD. Why do we need many sampled embedding spaces? Each Embedding Function from the family of parametric functions provide a partial interpretation of its input while their combination provides a complete one. This statement is discussed in Deep Neural Networks with Random Gaussian Weights: A Universal Classification Strategy?. (Need to read this paper and discuss about this). They also noticed that trying to make the images look realistic reduce performance. If the images don't look realistic or if they don't lie on the real images manifold, how do expect it to cover all the modes of the real image manifold?
The performance doesn't plateau at higher IPCs and they lead to better generalization performance compared to Gradient Matching.

Kernel and other theoretically grounded methods

Kernel methods are useful because they give a more analyzable version of DD: the model-training map is replaced by kernel ridge regression or neural tangent kernels.

Synthetic Data Parameterization - Latent Space, Generative Priors

This line asks what the synthetic object should be. Instead of raw pixels, DD can optimize labels, latent codes, bases/factors, neural fields, generators, diffusion priors, or quantized representations.

Pixel/label/factor parameterizations:

The idea of distilling knowledge into labels was introduced in Flexible Dataset Distillation: Learn Labels Instead of Images

Generative priors:

Moving beyond Image Classification Task - Different Tasks and Modalities

The original benchmark culture was small image classification. The field now includes language, graphs, video, time series, speech, medical imaging, federated/continual learning, RL, point clouds, object detection, retrieval, recommender systems, and multimodal settings.

Self-supervised, pretrained, and multimodal:

Language and text:

Graphs:

Video, time series, speech, and other structured data:

Applications beyond standard supervised classification:

Continual, federated, medical, and data-sharing contexts:

DD in Different Distributions - Long Tailed, etc.

This cluster covers non-IID data, class imbalance, long-tailed labels, bias/fairness, privacy, robustness, noisy labels, domain shift, and adversarial/backdoor settings. These matter because a distilled set can amplify dataset/model biases even when average accuracy is high.

Long-tailed and imbalanced data:

Bias, fairness, calibration, and robustness:

Privacy, backdoors, and data leakage:

Noisy labels, domain shift, and non-IID data:

Understanding the behavior of Dataset Distillation

Does the Loss Landscape differ for models trained on Real Data vs Distilled Data?

Direct "loss landscape" papers are still sparse, but several lines provide indirect evidence: trajectory matching, curvature matching, flat/stable trajectory objectives, calibration, and architecture-transfer work.

What does Dataset Distillation Learn and Encode?

This is the interpretability/science question: does DD encode prototypes, discriminative shortcuts, training dynamics, class boundaries, model-specific priors, or teacher knowledge?

How far is DD explained theoretically?

Partially. Kernel and convexified settings are much better understood than deep, finite-width, augmentation-heavy, generative, or foundation-model settings. Existing theory explains fragments of DD: approximation, compression, kernels, quantization, and some offline-RL/supervised guarantees.

Open Problems, Research Questions and Future Direction

Open problem clusters and useful starting papers:

Dataset Distillation but we will change the loss when it comes to eval and distillation???

References

[1] T. Wang, J.-Y. Zhu, A. Torralba, and A. A. Efros, “Dataset Distillation,” Feb. 24, 2020, arXiv: arXiv:1811.10959. doi: 10.48550/arXiv.1811.10959.