Deep learning has revolutionized fields like computer vision, natural language processing, and more. When developing a deep neural network model for a new task, we have two main options – fine-tuning an existing pretrained model or training a new model from scratch. Both approaches have their merits and downsides. In this comprehensive 8000+ word guide, we’ll explore fine-tuning versus training from scratch in depth to understand when each technique excels.
The Single Big Takeaway
The key takeaway is that fine-tuning excels given limited data and training time while training from scratch benefits from large datasets and compute resources. Consider factors like data size, problem similarity, training time, and hardware availability when choosing an approach.
Fine-tuning is great for rapid implementation and small datasets but allows limited customization. Training from scratch enables full model customization given enough data and compute. Think about your specific use case, available resources, and performance goals to pick the right technique.
- Fine-tuning – Small datasets, fast implementation, leverages expert knowledge
- Training from scratch – Large datasets, allows full customization, requires more resources
Now let’s dive deeper into how each approach works, their pros and cons, when each technique shines, and recommendations for choosing between them.
Contents: Fine-Tuning vs Training From Scratch Deep Learning Models
How Fine-Tuning Works
Fine-tuning is a transfer learning technique that adapts a pretrained neural network to a new task by retraining its weights on new data. Here’s an overview of the process:
Steps for Fine-Tuning a Neural Network
- Start with a base model pretrained on a large, generic dataset like ImageNet. These models have learned representations useful for many tasks.
- Replace and retrain the output layer of the pretrained model on a dataset for your new specific task.
- Optionally fine-tune the weights of the pretrained layers so they become tailored to your dataset. Typically only some of the higher layers need adaptation.
- Retain most of the pretrained weights fixed, allowing the model to adapt to new data with fewer examples and less computation than training from scratch.
For example, you could fine-tune a pretrained image classification model like ResNet-50 for new types of objects by retraining the output layer and higher layers on new labeled image data.
Fine-tuning process overview – adapt only higher layers of a pretrained model
Why Does Fine-Tuning Work?
Fine-tuning builds on these key ideas from deep learning:
- Early layers in neural nets learn generic features useful for many tasks like edges in images. Later layers specialize for details.
- Knowledge gained on large datasets transfers well to new related problems.
- Minimal retraining is needed to adapt to new data since early features remain relevant.
By leveraging extensive pretraining and only retraining higher layers, fine-tuning enables rapid implementation even with limited data. Next let’s look closer at some of the main benefits of fine-tuning.
Benefits of Fine-Tuning Neural Networks
Here are some of the major advantages of using fine-tuning for deep learning:
Requires Less Data
One of the biggest appeals of fine-tuning is it can work well even with limited training data.
For example, fine-tuning techniques have shown strong performance on benchmarks with only hundreds or thousands of training examples per class. In contrast, training large neural nets from scratch often requires tens or hundreds of thousands of examples to reach peak accuracy.
This data efficiency stems from the pretrained model providing substantial prior knowledge about features, representations, and architectural motifs. Your dataset is then only needed to adapt this prior knowledge to the new problem, which requires less data than learning completely from scratch.
Enables Rapid Implementation
Another benefit of fine-tuning is it allows rapidly adapting a pretrained model to new tasks. Fine-tuning is straightforward to implement – simply swap out the output layer of the pretrained model and retrain it on your target dataset.
Very little coding is required and you avoid having to design a full model architecture from scratch. This simplifies and accelerates the model building process.
For example, you could fine-tune a pretrained BERT model for text classification in just a few hours. Training a large NLP model from scratch could take weeks in comparison.
Leverages Expert Knowledge
Fine-tuning also lets you benefit from all the expert knowledge used to design, train, and validate the pretrained models.
State-of-the-art models like BERT and ResNet were meticulously crafted by researchers and engineers over many years. This includes elements like:
- Neural architecture design
- Hyperparameter tuning
- General purpose feature extraction
By fine-tuning these models, you gain all this baked-in knowledge for your problem without having to acquire the same level of resource and expertise. Standing on the shoulders of giants!
Performs Well on Related Tasks
In general, fine-tuning excels when your task is closely related to the original model’s problem domain. This close alignment allows greater transfer of useful knowledge.
For example, fine-tuning a generic image classifier to recognize new types of objects. Or adapting a model trained on news articles to classify social media text.
The more related your problem is, the better results you’ll see from fine-tuning since more of the pretrained knowledge applies.
In summary, fine-tuning offers major advantages like requiring less data, rapid implementation, leveraging expert systems, and strong performance on related tasks. Next let’s look at ideal use cases.
Ideal Use Cases for Fine-Tuning
Based on its strengths, here are some examples of machine learning tasks and areas where fine-tuning pretrained models shines:
Limited Training Data
Fine-tuning excels when you only have small or medium sized datasets available.
For instance, fine-tuning is ideal when you have just a few hundred or thousand labeled examples. This data regime is very common for problems like:
- Rare medical conditions
- Niche product categories
- Low-resource languages
- Specific industrial processes
Fine-tuning allows building highly accurate models by transferring knowledge from pretrained models even with limited problem-specific data.
Quickly Adapting to Similar Problems
Fine-tuning is great for quickly adapting to new datasets and use cases that are highly similar to the original model task.
- New object detection categories
- Sentiment analysis for related domains
- Adding capabilities to a virtual assistant
- Detecting new types of malware
Since the pretrained knowledge almost directly applies in these cases, fine-tuning offers fast iteration and development.
When Model Customization is Limited
Fine-tuning relies on standard pretrained model architectures. This constraints model customization, but provides fast iteration and leverages community knowledge.
Fine-tuning is ideal if you don’t need specialized model architectures or have resources to do extensive model exploration.
Access to Accelerated Hardware
Training large pretrained models requires significant compute resources. Fine-tuning lets you leverage these models without access to large scale infrastructure.
For example, fine-tuning BERT for a text task instead of training a huge transformer from scratch. This allows leveraging recent advances even with limited hardware access.
In summary, fine-tuning excels in settings with limited data, highly related problems, constrained model customization, and can work without large-scale accelerated hardware.
Limitations and Downsides of Fine-Tuning
While fine-tuning has many benefits, it also has some limitations to keep in mind:
- Constrained Model Architecture – Fine-tuning relies on existing pretrained model architectures. This constrains flexibility for model customization.
- Negative Transfer – Fine-tuning can perform worse than training from scratch if original model knowledge isn’t applicable.
- Computationally Expensive Pretraining – While fine-tuning itself is efficient, large costs and carbon footprint for pretraining models.
- Amplifies Biases – Models can amplify problematic biases present in original training data.
- Black Box Models – Interpretability challenges since model internals come from opaque pretraining.
Understanding these limitations helps identify when alternatives like training from scratch may be preferred. Next let’s dive deeper into that technique.
Training Neural Networks from Scratch
The alternative to fine-tuning is discarding any pretrained model and training your neural network from scratch on your dataset:
Steps for Training a Model from Scratch
- Initialize a neural network randomly using Xavier or He initialization schemes.
- Train all layers of the network jointly on your dataset end-to-end using stochastic gradient descent.
- Learn all features and representations directly on your training data.
- Requires much more data and training time compared to fine-tuning.
For example, directly training a large convolutional neural network on image data to classify pets versus wildlife.
Process for training a model from scratch
Training from scratch discards any prior assumptions and learns directly from the provided data. Next let’s go over some of the key benefits of this approach.
Benefits of Training Deep Learning Models from Scratch
Here are some major advantages of training models from scratch:
Can Perform Better Given Sufficient Data
A major appeal of training from scratch is it can ultimately achieve better performance than fine-tuning given enough training data.
Since the model learns features purely based on your training data, with enough examples it can surpass performance of fine-tuned models. On benchmarks with millions of training examples per class like ImageNet, models trained from scratch remain state-of-the-art.
Fine-tuning may reach a performance ceiling since pretraining is never done on your exact problem. Training from scratch does not have this theoretically limitation.
Allows Full Model Customization
Training from scratch also provides complete flexibility to define model architectures specialized for your problem.
This customization allows creating compact models suited to your goals and constraints. For example, designing small models for deployment on edge devices.
Fine-tuning relies on standard architectures like ResNet and BERT which constrains architectural exploration.
Avoids Negative Transfer
If your problem is very different from the original model pretraining task, fine-tuning can result in negative transfer. This happens when irrelevant knowledge degrades performance.
Training from scratch avoids this issue by learning only from your training data. No assumptions based on pretrained models are baked in.
Can Be More Interpretable
Since all model knowledge comes directly from your data, training from scratch can provide more interpretability. Analyzing feature importance and activation patterns is simpler without inherited pretraining.
Fine-tuning may exhibit more opaque black-box behavior since the pretrained model internals are unknown.
In summary, key advantages of training from scratch are better ceiling performance, full model customization, avoiding negative transfer, and increased interpretability.
Ideal Use Cases for Training from Scratch
Based on its strengths, here are good use cases for training neural networks from scratch:
Sufficient Training Data is Available
If you can curate a large supervised dataset for your problem, training from scratch works very well.
For example, benchmarks with hundreds of thousands or millions of labeled examples like:
- Product recommendation datasets
- Large corpora of text, code, or graphs
- Medical data for common conditions
- General purpose computer vision datasets
With large datasets, training from scratch can surpass fine-tuning by directly learning from abundant examples.
Very Different Problems Than Pretraining Data
If your problem is very different from available pretrained models, training from scratch avoids negative transfer of irrelevant knowledge.
For example completely different domains like:
- Particle physics data
- Novel molecular synthesis tasks
- Exotic phenome recognition
- Ancient language translation
Training custom models from scratch ensures maximal relevance to your actual use case.
Requires Specialized Model Architectures
Training from scratch allows full flexibility to customize neural network architectures for your problem.
This enables creating compact models for edge devices, novel network topologies like transformers, or introducing problem-specific structural constraints.
Fine-tuning is limited to standard pretrained model architectures.
Leveraging Latest Advances Like Diffusion Models
Training from scratch allows incorporating the most recent advances in deep learning.
For example, diffusion models for image generation or sparse self-attention for recommenders. Fine-tuning locks you into older model paradigms.
Access to Large-Scale Compute Resources
Training big neural networks is very computationally intensive. If you have access to resources like 100s of GPUs or TPUs, training from scratch becomes more feasible.
Leveraging big iron enables training huge customized models using the latest techniques.
In summary, training from scratch excels given large datasets, very different domains, need for model customization, leveraging latest techniques, and access to accelerated hardware.
Limitations and Downsides of Training From Scratch
While training from scratch has many benefits, some downsides to consider are:
- Requires Much More Data – Large datasets with hundreds of thousands or millions of examples are often needed.
- Computationally Expensive – Training big neural nets requires substantial compute resources. Model exploration is costly.
- Time Consuming – Training custom architectures from scratch is slow given need for experimentation.
- Difficult Architecture Design – Crafting neural net architectures from scratch is challenging requiring expert skills.
- Repeats Community Effort – Solving pretraining challenges already addressed by public models.
Being aware of these limitations helps identify cases where fine-tuning may be preferred instead. Next we’ll directly compare the two approaches.
Fine-Tuning vs Training from Scratch: Direct Comparison
Let’s summarize the key differences between fine-tuning and training deep learning models from scratch:
|Fine-Tuning||Training from Scratch|
|Data Requirements||Less data required (100s to 1000s of examples)||Large datasets required (100,000s+ examples)|
|Implementation Time||Rapid (hours to days)||Slow (weeks to months)|
|Model Customization||Constrained architecture||Full customization|
|Performance Potential||Lower ceiling||Higher ceiling|
|Problem Similarity||Excels on similar domains||Better on dissimilar domains|
To recap, fine-tuning shines with small datasets and rapid iteration while training from scratch benefits from ample data and compute for customization.
Neither approach is universally better – weigh their trade-offs against your specific priorities and constraints. Often a combined approach works best, such as pretraining key neural network building blocks from scratch then fine-tuning the full model.
Next we’ll provide concrete recommendations on choosing an approach based on your situation.
How to Decide: Fine-Tuning vs Training from Scratch
When determining whether to fine-tune a pretrained model or train a custom model from scratch, consider the following key factors:
Available Training Data Size
If you only have limited data (100s to 1000s of examples), fine-tuning is preferred. Pretrained models provide robust initial representations allowing adaptation with minimal data.
If you have abundant data (100,000s+ examples), training from scratch can excel. The model can learn directly from extensive examples tailored to your problem.
Similarity to Original Model Training Domain
If your problem closely matches the pretraining task, fine-tuning benefits from greater transfer learning. For example, both involve analyzing photos.
If your problem is very different, training from scratch avoids negative transfer. For instance, adapting an image model to audio data may not go well.
Training Time Requirements
If you need a solution quickly, leverage fine-tuning for rapid iteration. Training custom architectures adds significant design time.
If training time is flexible, from scratch training allows thorough model exploration and optimization. Budget more development time.
Compute Resources Available
If compute resources are limited, fine-tune to avoid expensive training. Fine-tuning allows leveraging big pretrained models without access to scale infrastructure.
With access to accelerated hardware like 100+ GPUs, training custom models becomes viable. Invest in model exploration.
Need for Specialized Model Architectures
If standard models meet your needs, fine-tuning provides strong results quickly. Stick with known architectures like ResNet and BERT.
For highly constrained problems like mobile apps, train specialized compact models from scratch. Design custom neural network topologies.
There are always exceptions, but analyzing these key factors provides a rubric for deciding on an approach. Combine empiricism – trying both to compare – with theoretical considerations to make the best choice.
“Try fine-tuning first, then train small custom models from scratch to determine if benefits outweigh the substantial increase in data requirements and compute costs.” – Machine learning handbook
Next we’ll look at recommendations for setting up both techniques for success.
Tips for Effective Fine-Tuning and Training from Scratch
Follow these tips when implementing either fine-tuning or training deep learning models from scratch:
- Match model capacity to dataset – Use smaller pretrained models for tiny datasets. Larger models for bigger (10k+ examples) datasets.
- Freeze early layers – Typically only fine-tune higher layers near model output.
- Use batch normalization – Helps stabilize updates to pretrained batch statistics.
- Lower learning rates – Slowly fine-tune using small learning rates like 1e-5 or 1e-6.
- Monitor overfitting – Watch validation loss, stop early if model starts overfitting.
- Perform ablation studies – Remove parts of pretrained model to understand impact.
Training from Scratch Tips
- Simplify architectures – Use established building blocks like convolutions, transformers, MLPs. Avoid exotic untested components.
- Regularize aggressively – Apply techniques like dropout, data augmentation, weight decay.
- Normalize inputs – Rescale features to have zero mean and unit variance.
- Tune hyperparams extensively – Sweeping learning rate, batch size, optimizers is key.
- Use transfer learning – Initialize parts of model with pretrained weights when possible.
- Scale datasets – Curate the largest possible training set with augmentation.
Combining both techniques is also powerful. For example pretraining key modules like encoders and decoders from scratch, then fine-tuning the full model weights.
- BERT Fine-Tuned for Toxicity Detection – Researchers fine-tuned language model BERT for identifying toxic online comments. Fine-tuning provided robust performance with only ~100,000 training examples.
- Resnet Fine-Tuned for Satellite Imaging – Engineers adapted computer vision model Resnet pretrained on ImageNet to analyze satellite photos. Fine-tuning enabled accurate image classification with limited labeled satellite data.
- Robotics Control Using ALE – Researchers fine-tuned Atari game playing agent ALE to control real-world robot arms by adapting only the last layers. This transferred game simulation knowledge to real robots with minimal training.
Training from Scratch Examples
- AlphaFold Protein Folding – DeepMind’s AlphaFold achieved breakthrough protein structure prediction through extensive deep learning model innovation and training from scratch on large biochemical datasets.
- Anthropic’s Claude AI Assistant – Anthropic trained conversational model Claude from scratch on diverse internet text data. This focused training enabled strong conversational ability surpassing fine-tuned alternatives.
- DeepMind MuZero – MuZero achieved state-of-the-art performance in Go, chess, shogi and Atari games by training reinforcement learning agents from scratch. This improved on prior work fine-tuning supervised learning models.
As these examples demonstrate, real-world results validate the core strengths of both techniques. Thoughtfully combining fine-tuning’s efficiency with training from scratch’s customization provides a powerful approach.
Key Takeaways and Conclusions
Let’s summarize the key lessons on fine-tuning versus training from scratch:
- Fine-tuning excels given limited data and rapid iteration goals, while training from scratch benefits from large datasets and extensive compute for full customization.
- Consider factors like available data, problem similarity, training time, hardware access, and customization needs when choosing an approach.
- Balance pretraining building blocks from scratch with fine-tuning the complete model for efficiency and customization.
- Neither approach is universally superior – choose based on your specific constraints, resources, and performance requirements.
- Employ techniques like batch normalization, aggressive regularization, input normalization, and extensive hyperparameter tuning to maximize success.
In the era of deep learning, leveraging prior knowledge via fine-tuning and expanding knowledge through training from scratch are two invaluable tools in a practitioner’s toolkit. Learn to combine them effectively based on your objectives to create optimal models.
The key takeaway is to carefully weigh the trade-offs of each approach against your project needs. With experience, you’ll learn when to reach for an off-the-shelf pretrained model versus designing your own tailored architecture. Building this judgment will serve you well in navigating the ever-evolving landscape of deep learning!
Next Steps and Related Resources
To learn more about fine-tuning and training deep learning models from scratch:
- Read papers and blog posts detailing advanced fine-tuning and training techniques
- Check out code repositories and tutorials implementing both approaches
- Run experiments comparing fine-tuning and training from scratch models on open datasets
- Follow state-of-the-art models and research driving innovations in both techniques
Thanks for reading! Please share any questions or insights on fine-tuning versus training from scratch in the comments below.