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Lesson 5 · Diffusion

Denoising, step by step

Generating an image is a series of small denoising steps. Starting from pure noise, the model predicts a little noise to remove, applies it, and repeats — often 20 to 1000 times — until a clear, detailed image emerges. Fewer steps is faster; more steps is sharper.

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Many small steps beat one big guess

Instead of trying to paint the whole image at once, diffusion takes many gentle passes. Step one turns pure noise into a slightly-less-noisy blur. Step two cleans it a little more. By the last step the picture is sharp. Each step only has to make a small improvement, which is much easier than nailing the whole thing in one go — and it's why the results are so detailed.

What happens each step

  1. The model looks at the current noisy image and predicts the noise in it.
  2. It removes a portion of that predicted noise, revealing a slightly clearer image.
  3. Repeat: each pass sharpens the picture until the final step produces the finished image.

The speed–quality dial

The number of steps is a dial you can turn. A few dozen steps is fast and usually good enough; hundreds of steps squeeze out extra detail but take longer. Newer samplers get great results in far fewer steps — which is why image tools that once took a minute now feel almost instant.

Try it

Drag the slider below from pure noise to a finished image and watch the denoising happen — that's exactly what your prompt triggers behind the scenes.

InteractiveDrag the timestep from pure noise (left) to a clear image (right).
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