# PyTorch | Preprocessing images

*Table of Contents:*

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## Three kind of preprocessing

These are:

- normalization
- standardization
- and whitening

Normalization is for the mean, standardization is for the variance and whitening is for the correlation.

## Normalization

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## Standardization

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## Whitening images

The most interesting whitening algorithm is called Zero Component Analysis or ZCA.

**Whitening** also called sphering means we will transform the image so that we get the covariance matrix is the identity matrix.

Identity matrix means all one in the diagonal and 0 else.

Happens to be the white noise has the same covariance matrix as the image after whitening.

Here are more details on the identity matrix.

Whitening is a bit more complicated than the other preprocessing, but we now have all the tools that we need to do it. It involves the following steps:

```
Zero-center the data
Decorrelate the data
Rescale the data
```

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**tags:**

*tricks*&

**category:**

*pytorch*