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: https://gmicol.greyc.fr/

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