Introduction
So far, every example belonged to exactly one class: a digit is a 5 or a 3, never both. But many real problems aren't like that:
- A photo can contain a dog and a cat and a person at the same time.
- A news article can be about politics and economics.
- A film can be tagged comedy, romance and drama.
This topic covers two more general kinds of classification:
| Type | Each example has… | Example |
|---|---|---|
| binary | one of 2 classes | spam / not spam |
| multiclass | one of many classes | which digit |
| multilabel | several yes/no labels at once | which people appear in a photo |
| multioutput | several labels, each with many classes | the colour of every pixel in a cleaned-up image |