How to create bitmap fonts from .png file

cocos2d-x C++
#1

Hi,
I have a png sprite sheet with letters from A-Z, and I want to create a bitmap fonts. How can I do that?
I tried to use the tool bmfont, but so far it is no possible.
Does anyone has the same issue?
Thanks

#2

try this one.

http://renderhjs.net/shoebox/

#3

Thanks a lot!!!