Whitening transformation - Wikipedia
[주성분 분석 - 위키백과, 우리 모두의 백과사전](https://ko.wikipedia.org/wiki/주성분_분석#:~:text=주성분 분석(主成分分析,환원시키는 기법을 말한다.)
Normalize data so that all the features are in the same range, and so that they contribute equally. (PCA, whitening)
We don’t need to normalize so much as the data don’t have much deviation. Also, we don’t want our input image to be projected into a lower dimensional space.