NetVLAD: CNN architecture for weakly supervised place recognition

Version 1.03 (04 Mar 2016)

• If you used NetVLAD v1.01 or below, you need to upgrade your models using relja_simplenn_tidy

This code implements the NetVLAD layer and the weakly supervised training for place recognition presented in [1]. For the link to the paper, trained models and other data, see our project page: http://www.di.ens.fr/willow/research/netvlad/

NetVLAD is distributed under the MIT License (see the LICENCE file).

Setup

Dependencies

The code is written in MATLAB, and depends on the following libraries:

1. relja_matlab v1.02 or above
2. MatConvNet (requires v1.0-beta18 or above)
3. Optional but highly recommended for speed: Yael_matlab (tested using version 438), and not used for feature extraction (i.e. the feed forward pass)
   • To download it's easiest to go here and download the precompiled yael_matlab binaries for your OS (e.g. yael_matlab_linux64_v438.tar.gz)

Data

Datasets

Visit our project page for information on how to get the datasets. You can also use your custom dataset by creating the appropriate MATLAB object: inherit from datasets/dbBase.m (instructions provided in the file's comments).

Our trained networks

Download them from our project page.

If you want to train your networks

In [1] we always started from networks pretrained on other tasks (ImageNet / Places205), download these from the MatConvNet website. Download imagenet-caffe-ref and imagenet-vgg-verydeep-16 for the AlexNet and VGG-16 experiments, respectively.

However, one can also start from any custom CNN. Change loadNet.m to load your initial network.

Configure the NetVLAD library

Copy localPaths.m.setup into localPaths.m and edit the variables to point to dependencies, dataset locations, pretrained models, etc (detailed information is provided in the file).

Run

See demo.m for examples on how to train and test the networks, as explained below. We use Tokyo as a runnning example, but all is analogous if you use Pittsburgh (just change the dataset setup and use the appropriate networks).

The code samples below use the GPU by default, if you want to use the CPU instead (very slow especially for training!), add 'useGPU', false to the affected function calls (trainWeakly, addPCA, serialAllFeats, computeRepresentation).

Note that if something fails (e.g. you are missing a dependency, your GPU runs out of RAM, you manually stop execution, etc), you should make sure to delete the potentially created corrupt files before rerunning the code. E.g. if you terminate feature extraction, the output file will be incomplete, so trying to perform testing will fail (files are never recomputed if they exist).

Use/Test our networks

You can download our networks from the project page.

Set the MATLAB paths:

setup;

Load our network:

netID= 'vd16_tokyoTM_conv5_3_vlad_preL2_intra_white';
paths= localPaths();
load( sprintf('%s%s.mat', paths.ourCNNs, netID), 'net' );
net= relja_simplenn_tidy(net); % potentially upgrate the network to the latest version of NetVLAD / MatConvNet

Compute the image representation by simply running the forward pass using the network net on the appropriately normalized image (see computeRepresentation.m).

im= vl_imreadjpeg({which('football.jpg')}); im= im{1}; % slightly convoluted because we need the full image path for `vl_imreadjpeg`, while `imread` is not appropriate - see `help computeRepresentation`
feats= computeRepresentation(net, im); % add `'useGPU', false` if you want to use the CPU

To compute representations for many images, use the serialAllFeats function which is much faster as it uses batches and it moves the network to the GPU only once:

serialAllFeats(net, imPath, imageFns, outputFn);

imageFns is a cell array containing image file names relative to the imPath (i.e. [imPath, imageFns{i}] is a valid JPEG image), the representations are saved in binary format (single 4-byte floats). Batch size used for computing the forward pass can be changed by adding the batchSize parameter, e.g. 'batchSize', 10. Note that if your input images are not all of same size (they are in place recognition datasets), you should set batchSize to 1.

To test the network on a place recognition dataset, set up the test dataset:

dbTest= dbTokyo247();

Set the output filenames for the database/query image representations:

paths= localPaths();
dbFeatFn= sprintf('%s%s_%s_db.bin', paths.outPrefix, netID, dbTest.name);
qFeatFn = sprintf('%s%s_%s_q.bin', paths.outPrefix, netID, dbTest.name);

Compute db/query image representations:

serialAllFeats(net, dbTest.dbPath, dbTest.dbImageFns, dbFeatFn, 'batchSize', 10); % adjust batchSize depending on your GPU / network size
serialAllFeats(net, dbTest.qPath, dbTest.qImageFns, qFeatFn, 'batchSize', 1); % Tokyo 24/7 query images have different resolutions so batchSize is constrained to 1

Measure recall@N

[recall, ~, ~, opts]= testFromFn(dbTest, dbFeatFn, qFeatFn);
plot(opts.recallNs, recall, 'ro-'); grid on; xlabel('N'); ylabel('Recall@N'); title(netID, 'Interpreter', 'none');

To test smaller dimensionalities, all that needs to be done (only valid for NetVLAD+whitening networks!) is to keep the first D dimensions and L2-normalize. This is done automatically in testFromFn using the cropToDim option:

recall= testFromFn(dbTest, dbFeatFn, qFeatFn, [], 'cropToDim', 256);

It is also very easy to test our trained networks on the standard object/image retrieval benchmarks, using the same set of steps: load the network, construct the database, compute the features, run the evaluation. See demoRetrieval.m for details.

Train

Set the MATLAB paths:

setup;

Load the train and validation sets, e.g. for Tokyo Time Machine:

dbTrain= dbTokyoTimeMachine('train');
dbVal= dbTokyoTimeMachine('val');

Run the training:

sessionID= trainWeakly(dbTrain, dbVal, ...
    'netID', 'vd16', 'layerName', 'conv5_3', 'backPropToLayer', 'conv5_1', ...
    'method', 'vlad_preL2_intra', ...
    'learningRate', 0.0001, ...
    'doDraw', true);

All arguments of trainWeakly are explained in more details in the trainWeakly.m file, here is a brief overview of the essential ones:

• netID: The name of the network (caffe for AlexNet, vd16 for verydeep-16, i.e. VGG-16)
• layerName: Which layer to crop the initial network at, we always use the last convolutional layer (i.e. conv5 for caffe and conv5_3 for vd16)
• backPropToLayer: Down to which layer to perform the learning. If not specified, the entire network is trained, see [1] for the analysis
• method: Which aggregation method to use for the image representation, default is vlad_preL2_intra (i.e. NetVLAD with input features L2-normalized, and with intra-normalization of the NetVLAD vector). You can also use max for max pooling, avg for average pooling, or other vlad variants (e.g. vlad_preL2 to disable intra-normalization)
• learning rate: The learning rate for SGD
• useGPU: Use the GPU or not
• doDraw: To plot or not some performance curves as training goes along

Other parameters are explained in trainWeakly.m, including SGD parameters (batch size, momentum, weight decay, learning rate schedule, ..), method parameters (margin size, number of negatives, size of the hard negative memory, ..), etc.

The training periodically saves the latest network and performance curves in files which include the sessionID (can be specified, otherwise generated randomly) and the epoch number, e.g.: 0fd5_ep000002_latest.mat , as well as a copy of that file for the latest epoch in 0fd5_latest.mat .

To find the best network, i.e. the one that performs the best on the validation set (we use recall@N here, where N=5, but any value can be used), run:

[~, bestNet]= pickBestNet(sessionID);

Train PCA + whitening

The best performance is achieved if the dimensionality of the image representation is reduced using PCA together with whitening:

finalNet= addPCA(bestNet, dbTrain, 'doWhite', true, 'pcaDim', 4096);

Additional information

More information is available README_more.md and in comments in the code itself.

References

[1] R. Arandjelović, P. Gronat, A. Torii, T. Pajdla, J. Sivic. "NetVLAD: CNN architecture for weakly supervised place recognition", CoRR, abs/1511.07247, 2015

Changes

• 1.03 (04 Mar 2016)

  • Fixed a bug in NetVLAD backprop

• 1.02 (29 Feb 2016)

  • Adapts the code to account for major changes in matconvnet-1.0-beta17's SimpleNN
  • Removed the use of the redundant relja_simplenn since vl_simplenn has sufficient functionality now (from matconvnet-1.0-beta18)

• 1.01 (29 Feb 2016)

  • Easier quick-start with computeRepresentation
  • Standard retrieval benchmarks (Oxford, Paris, Holidays) in demoRetrieval.m
  • Additional examples in demo.m: dimensionality reduction with NetVLAD, construction of off-the-shelf-networks

• 1.00 (04 Dec 2015)

  • Initial public release