DataParameter field 'mean_file' should be deprecated?

[shanyucha]

Issue summary

I wondered, what is the use of mean_file param under data_param. If it is deprecated, I didn't found any comments in the proto file indicating that. Apparently, it didn't work like its literal meaning.

Steps to reproduce

I was using googlenet to do classifications. I got high validation accuracy during training. Unfortunately, I got weird low test accuracy during testing. I tried to many things like adjusting train sets, modifying learning rate, gamma and so on, I got totally different results even if the modifications were very subtle.

At last, I found that I used the 'mean_file' param under 'data_param' in data layer instead of in 'transform_param'. And it was the cause of weird output of testing. In fact, during initialization of network, it didn't load the mean_file param if it was under the data_param.

And I looked into the caffe.proto file and indeed there is a mean_file param in data_param. That's why no error raised. But still it seems that it is of no use.

Your system configuration

Operating system:
Compiler:
CUDA version (if applicable):
CUDNN version (if applicable):
BLAS:
Python or MATLAB version (for pycaffe and matcaffe respectively):

[Noiredd]

Interesting. Initially mean_file and similar parameters were fields of a DataParameter message and the DataLayer handled all preprocessing. Then (#954) the code was refactored into the Transformer class with its own TransformerParameter message that took over mean_file and other preprocessing fields. Later (#963) the fields were brought back for compatibility reasons, and finally (#995) the preprocessing was entirely moved to the Transformer. Legacy proto definitions are upgraded using the upgrade_proto.cpp utility which moves any mean_file passed as data_param into the transform_param - but indeed it seems that caffe.proto is not very clear about this fact:

  // DEPRECATED. See TransformationParameter. For data pre-processing, we can do
  // simple scaling and subtracting the data mean, if provided. Note that the
  // mean subtraction is always carried out before scaling.
  optional float scale = 2 [default = 1];
  optional string mean_file = 3;

(lines 657-661)

@shelhamer Would it be a right thing to do to add // DEPRECATED comment above the mean_file line?