First of all, im happy that you tried reproduce it)

As for service, they use preprocessing and postprocessing filters, like autowb, autocontrast, histogram equalization, bilateral filtering, etc. so result can be better. You can open Gimp, PS and use this filter to check difference.
And also this pre-trained model is just as an example, if you will train it on your dataset for a week(as it should) you will get much better result.

Here is for example some online filters:



Get the Medium app

A button that says 'Download on the App Store', and if clicked it will lead you to the iOS App store
A button that says 'Get it on, Google Play', and if clicked it will lead you to the Google Play store