(05-02-2022, 06:39 PM)Chemist116 Wrote: My second doubt is, does it exist some filter to make a color image to be black and white?. No I don't mean to make it grayscale I mean a black and white image like the one you get with a xerox copy so that the letters and formulas and sketches like found in geometry can be seen more clearly or have more contrast and can be later reprinted.
Actually a bad idea. You can definitely increase contrast to make the page background white, perhaps after equalizing the lighting over it, and the characters black. But a pure threshold is going to make pixellated edges and specks all over.
Btw, this is what you get with at scanner app on an Android phone (Xiaomi Note7). Metal ruler included so you can ascertain how small some characters are (like the exponent "θ").
Otherwise, as they say: cheap, fast, good quality: pick any two...