If anyone try to generate a png with 896 x 640 instead of 927 x 656, that can chop 16x16 character prefectly, you can open the generator.html with txt and find this two line:
canvas.width = this.naturalWidth;
canvas.height = this.naturalHeight;
change it to:
canvas.width = 896 ;
canvas.height = 640;
save it and open it again, you can save your png file as 896 x 640 instead of 927 x 656 which you should manuly chop each of the character and cannot directly chop it to 56 col x 20 row. This not the best way to do it but it work for me.
I also change this line
ctx.clearRect(0, 0, canvas.width, canvas.height);
to
ctx.clearRect(0, 0, 896 , 640);
for trying, but just change this does not work. I am too lazy to test the result with and without this line, so if not work change this too.