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I have an image classification task to solve, but based on quite simple/good terms:

  • There are only two classes (either good or not good)
  • The images always show the same kind of piece (either with or w/o fault)
  • That piece is always filmed from the same angle & distance
  • I have at least 1000 sample images for both classes

So I thought it should be easy to come up with a good CNN solution - and it was. I created a VGG16-based model with a custom classifier (Keras/TF). Via transfer learning I was able to achieve up to 100% validation accuracy during model training, so all is fine on that end.

Out of curiosity and because the VGG-based approach seems a bit "slow", I also wanted to try it with a more modern model architecture as base, so I did with ResNet50v2 and Xception. I trained both similar to the VGG-based model, tried it with several hyperparameter modifications etc. However, I was not able to achieve a better validation accuracy than 95% - so much worse than with the "old" VGG architecture.

Hence my question is: Given these "simple" (always the same) images and only two classes, is the VGG model probably a better base than a modern network like ResNet or Xception? Or is it more likely that I messed something up with my model or simply got the training / hyperparameters not right?

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VGG is a more basic architecture which uses no residual blocks. Reset usually perform better then VGG due to it's more layers and residual approach. Given that resnet-50 can get 99% accuracy on MNIST and 98.7% accuracy on CIFAR-10, it probably should achieve better than VGG network. Also, the validation accuracy should not be 100%. You could try increasing the size of your validation set to improve accuracy on validation. VGG network should perform worst than ResNet in most scenario, but experimenting is the way to go. Try and experiment more to get a method that works for your data. Hope that I can help you and have a nice day!

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