svhn的local contrast normalization处理

出处来自：论文：Convolutional Neural Networks Applied toHouse Numbers Digit Classification

https://arxiv.org/pdf/1204.3968.pdf

Samples are pre-processed with a local contrast normalization(with a 7x7 kernel) on the Y channel of theYUV space followed by a global contrast normalizationover each channel. No sample distortions were used toimprove invariance.

但是没有找到具体的实现过程或者数据的处理方法