Comparing odiff with pixelmatch and jimp

[elesh90]

I have two images to compare. On one of these pictures I changed somehting.
I use these images for odiff, pixelmatch and jimp. And I also used a treshold of 0.1 for every of these.
While jimp and pixelmatch resulting in 0.75% difference, odiff results in 1.07% difference. Can someone explain me why the results are different? Is odiff using somehting else than pixelmatch and jimp which could be the reason for the difference?