Normalization of an image in MATLAB
First, shift: put the minimum to $0$, by compensating the actual minimum $m=−18.3667⋅10^5$ for every pixel: $p\to p - m$. Now your pixels are between $0$ and a new maximum $M = 9.3127 - m$. Finally you want the final image in $[0,255]$. The second operation is scale: multiply by something, so that $0$ remains at $0$, and $M$ is cast to $255$. So you have to multiply by $255/M$.