how to scale a dataset contains a b&w and Grayscale images
$\hat{p}=2\big(\frac{p}{p_{max}}\big)-1$ so that $\hat{p}\in [-1,1]$ where $p\in[0,p_{max}]$
E.g. with 8-bit channels, $p_{max}=255$, black/white correspond to $-1$ and $1$ respectively, and grayscale is linearly mapped in $[-1,1]$.