I thought the explanation for why additional noise is added during training was not very clear. So, I asked ChatGPT (3.5) to explain the reasons. This is what is said:
PROMPT:
Can you explain why adding extra noise to a diffusion model produces better results than not adding extra noise?
RESPONSE
Adding extra noise to a diffusion model can improve its results for several reasons:
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Regularization: Diffusion models are generative models that learn to simulate a data distribution by iteratively denoising corrupted samples. By adding extra noise during training, you introduce additional perturbations to the data, which can act as a form of regularization. Regularization helps prevent overfitting and encourages the model to learn more robust and generalizable representations.
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Exploration and Sampling: The additional noise injected into the diffusion model during training allows for better exploration of the data manifold. It helps the model to sample from a wider range of possibilities and increases the diversity of generated samples. This exploration promotes the discovery of novel patterns and modes in the data distribution, leading to more accurate and diverse results.
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Robustness to Imperfections: Real-world data often contains various imperfections, such as missing values, outliers, or noisy measurements. By training a diffusion model with extra noise, the model becomes more robust to these imperfections. It learns to handle and denoise corrupted samples effectively, resulting in improved performance when faced with similar imperfections during inference.
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Implicit Data Augmentation: The additional noise acts as a form of data augmentation, artificially increasing the size of the training dataset. With a larger and more diverse training set, the model can better capture the underlying patterns and structures in the data, leading to enhanced generalization and improved results.
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Training Stability: Diffusion models are trained through a sequence of denoising steps, where noise is progressively reduced over time. This training process can sometimes be challenging, as the model needs to strike a balance between reducing noise and preserving useful information. By injecting extra noise, the training process becomes more stable, making it easier for the model to learn and converge to better solutions.
Overall, the addition of extra noise to a diffusion model helps regularize the training process, improves exploration and sampling, enhances robustness to imperfections, provides implicit data augmentation, and contributes to training stability. These factors collectively contribute to the improved results observed when using extra noise in diffusion models.