Add translate and RandomTranslate

[ekagra-ranjan]

This PR adds translate and RandomTranslate as a separate transformation like the rotation transformation.

[codecov-io]

Codecov Report

Merging #806 into master will decrease coverage by 22.04%.
The diff coverage is 88.57%.

@@             Coverage Diff             @@
##           master     #806       +/-   ##
===========================================
- Coverage   60.03%   37.98%   -22.05%     
===========================================
  Files          64       33       -31     
  Lines        5054     3296     -1758     
  Branches      754      526      -228     
===========================================
- Hits         3034     1252     -1782     
- Misses       1817     1964      +147     
+ Partials      203       80      -123

Impacted Files	Coverage Δ
torchvision/transforms/functional.py	71.2% <100%> (+0.08%)	⬆️
torchvision/transforms/transforms.py	83.51% <85.18%> (+0.97%)	⬆️
torchvision/models/inception.py	14.41% <0%> (-71.87%)	⬇️
torchvision/models/vgg.py	18.18% <0%> (-71.38%)	⬇️
torchvision/models/resnet.py	17.29% <0%> (-70.53%)	⬇️
torchvision/models/densenet.py	18.8% <0%> (-66.43%)	⬇️
torchvision/models/squeezenet.py	27.45% <0%> (-59.09%)	⬇️
torchvision/models/googlenet.py	15.87% <0%> (-57.51%)	⬇️
torchvision/models/alexnet.py	38.09% <0%> (-48.27%)	⬇️
torchvision/datasets/utils.py	35.1% <0%> (-13.32%)	⬇️
... and 54 more

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[surgan12]

@ekagra-ranjan would be nice if you add some tests.

[ekagra-ranjan]

@surgan12 Yup! Will add them.

[ekagra-ranjan]

@fmassa Please have a look at the PR.

[fmassa]

Hi,

What's the difference between translate and a random crop?

[ekagra-ranjan]

If the user needs to randomly translate the image by some pixels then I think using RandomTranslate with its parameters will be more intuitive for the users (due to the straight forward naming of function and its parameter) rather than using RandomCrop. I agree that RandomCrop can get the same results but it is just that RandomCrop's main function is cropping and not translate. Being able to give translated image as well is a sort of extension with the padding argument.

@fmassa Your views on this?

[fmassa]

So, there was a PR in the past that already added a similar functionality #363

I was not convinced by then, because both performed the same thing in the end.

[ekagra-ranjan]

I think it is the connotation of RandomCrop that can get people confused about its application.

Maybe we can add translation as a use case in the docs of RandomCrop just like there is a mention about whitening in the LinearTransformation (now AffineTransformation)?

[ekagra-ranjan]

@fmassa What are your views on addition of translation as a use case in RandomCrop?