How can I improve the quality of a photographed document?

Question

JavaScript

I am looking for an algorithm that can be ported to js, ​​well or not)

Answer 1

here is the result of processing the upper half according to the algorithm:
1) black&white
2) threshold
3) gauss by 1-pixel
If any of these steps is difficult for you - write ...

Answer 2

white balance and trashhold?
ps: is it possible to see somewhere the real difference between a photo and an iPhonescan?