Adjust line thickness in a bitmap layer

I’ve made a zoom-in to a character made in a bitmap layer, but when I get closer to it the line thickness becomes thicker. I need to retain the original size of the line (or be proportional) but i can’t do it.
Do you know if that its possible?

You can do that with pencil line tool as a vector but not with a brush or bitmap.

THANKS! Can you tell me how to do it?

Go into scripting and look for a script called tb_edit_line_thickness_overtime.

You select all the drawings you want to have impacted, then press it, select edit over time and pick from the dropdown which controller you want (like linethicknes1-9). Then all those pencil lines will be bound to that controller, and you can select any piece and bring up its option and curve and then keyframe it.