Multicrop - missing feature

[edouardoyallon]

Hi!

I think the transforms could be improved by adding a multicrop transform for the test.
Thanks

E

[soumith]

do you mean, like 5-crop and 10-crop?

[edouardoyallon]

Hi, yes. It can be implemented by using a custom transform for the input and the class. I'm trying to do one. Hopefully it will be nice enough to be PR

[catalystfrank]

@edouardoyallon have you done an implementation of multi-crop? If so where can I find it ? Many thanks.

[penguinshin]

Has anyone done the multi-crop implementation yet?

[alykhantejani]

I can implement this but I have a few comments/questions:

1. I think we should only implement 5-crop as the 10-crop version is the flipped 5-crops and after Refactor of transforms  #240 is merged this will be trivial to do with just the 5-crop version.
2. should we call it Oversample following the caffe standard? Or do you have a better name?
3. This transform wont be useful for training (at least easily) as if your transform emits multiple images/tensors you would need to have a custom collate function to put them all into a batch as far as I can tell. I think the same problem occurs if you want to batch these 5/10 crops for fast evaluation using the pytorch DataLoader?

[fmassa]

About your points:

1. While I agree that it would be a simple extension to have the 10-crop from the 5-crop, I think that the 10-crop is common enough so that having the 10 crops would be the most used case, so I'd rather keep it.
2. oversample is not a representative name to me. In fb-resnet-torch, they called it TenCrop, what do you think? Or maybe MultiCrop?
3. I believe this transform is only used for testing, in order to improve results during evaluation, so I think this shouldn't be a concern. We could eventually just concatenate over the 1st dimension, for example, but that might indeed need a different collate function.

[alykhantejani]

1 - makes sense
2 - I think FiveCrop and TenCrop are pretty good, MultiCrop wouldn't accept any other number so might be misleading?
3 - yeah I think even for testing you will need a special collate function (unless you want to test one image at a time (10-cropped)).

Ok great, I think that's enough to go on. Will send a PR soon.

[alykhantejani]

This has now been merged into master

[wlnirvana]

Could anyone elaborate on how are FiveCrop and TenCrop supposed to be used? It seems they return plain Python list, which fails ToTensor as it is neither an ndarray nor PIL.Image.