Performance issues in the program

[DLPerf]

Hello,I found a performance issue in the definition of val_generator , titu1994/neural-image-assessment/blob/master/utils/data_loader.py, val_dataset = val_dataset.map was called without num_parallel_calls. I think it will increase the efficiency of your program if you add this.

Here is the documemtation of tensorflow to support this thing.

Looking forward to your reply. Btw, I am very glad to create a PR to fix it if you are too busy.

[titu1994]

Yes please send a PR

[DLPerf]

Hello,could you please tell me the version of tensorflow that you use in your program? Actually,different version has different way to solve,so please.Thank you.