Thank you for the tool! So I've:

{
    "tile_width": 20, // px
    "tile_height": 25, // px
    "baseline": 19, // px - from top to where letters lie
    "lines": ".!?:,;~*_-=+´`<>/|\\#^%\"'£$¥&()[]{}@0123456789AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZzÇçÃÂÁÀãâáàÉÊÈéêèÍÎÌíîìÕÓÔÒÖõóôòöÚÛÙúûù "
}

I also have an image with varying alpha (due to antialiasing), e.g. alpha=0, alpha=0.5, alpha=1, generated together with the above JSON. Its overall width is 2720x25. I used the HTML5 canvas to generate it, drawing by font size 25px, centering and using top-baseline.

I tried setting BMF to pack texture at fixed size, but I get the error:

Packaging failed, try to increase the size of the package please.