Niblack algorithm for Document binarization

i've this photo :

and i'm trying to make Document binarization using niblack algorithm
i've implemented the simple Niblack algorithm

T = mean + K* standardDiviation

and that was it's result:

the problem is there's some parts of the image in which the window doesn't contain any objects so it detects the noise as objects and elaborates them .

i tried to apply blurring filter then global thresholding
that was the result :

which wont be solved by any other filter
i guess the only solution is preventing the algorithm from detecting global noise if the window i free from object

i'm interested to do this using niblack algorithm not using other algorithm so any suggestions ?

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