[scikit-learn] Should we standardize data before PCA?

[James Melenkevitz]

 https://stats.stackexchange.com/questions/69157/why-do-we-need-to-normalize-data-before-principal-component-analysis-pca
    On Thursday, May 24, 2018, 4:41:07 PM PDT, Shiheng Duan <shiduan at ucdavis.edu> wrote:  
 
 Hello all,
I wonder is it necessary or correct to do z score transformation before PCA? I didn't see any preprocessing for face image in the example of Faces recognition example using eigenfaces and SVMs, link:http://scikit-learn.org/stable/auto_examples/applications/plot_face_recognition.html#sphx-glr-auto-examples-applications-plot-face-recognition-py
I am doing on a similar dataset and got a weird result if I standardized data before PCA. The components figure will have a strong gradient and it doesn't make any sense. Any ideas about the reason? 
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