long time for the first inference

[alext234]

Hi,
I've bumped into this dataset and think it's pretty cool ! Nice work indeed 👍

I give it a quick try here to measure inference times
https://github.com/alext234/deep-weeds-experiments/blob/master/inference-times.ipynb

I realise the first inference is always much slower. Is there any particular reason why it is so? Perhaps this behaviour might be something very specific to keras/tf