Rendering Output Extremely High Size images from nXt 3.0 to 5.5

I’ve been getting familiar with nXt 5.5, using the same model and settings, when rendering with nXt 3.0 the result is a 2.3 MB size image, with nXt 5.5 I got a 20.3 MB size image, why is this happening?

Thank you.


Sounds like an other image compression. Is it PNG or JPG?