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미분과 그래디언트

$f' = {df \over dx} = \lim_{\Delta x \to 0} {f(x + \Delta x) - f(x) \over \Delta x}$

https://drive.google.com/uc?id=1r627zU7npUyIrqdcUPrZ26KEVt4BXyye

$I_{x} = {\partial I \over \partial x} \cong {((x+1, y) - I(x-1, y) \over 2}$

$I_{y} = {\partial I \over \partial y} \cong {((x, y+1) - I(x, y-1) \over 2}$

https://drive.google.com/uc?id=11rml4TzHEFPTBxVjXyDOaoPKXB77moSC