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---
title: Feature extraction with Caffe C++ code.
description: Extract CaffeNet / AlexNet features using the Caffe utility.
category: example
include_in_docs: true
priority: 10
---
Extracting Features
===================
In this tutorial, we will extract features using a pre-trained model with the included C++ utility.
Note that we recommend using the Python interface for this task, as for example in the [filter visualization example](http://nbviewer.ipython.org/github/BVLC/caffe/blob/master/examples/00-classification.ipynb).
Follow instructions for [installing Caffe](../../installation.html) and run `scripts/download_model_binary.py models/bvlc_reference_caffenet` from caffe root directory.
If you need detailed information about the tools below, please consult their source code, in which additional documentation is usually provided.
Select data to run on
---------------------
We'll make a temporary folder to store things into.
mkdir examples/_temp
Generate a list of the files to process.
We're going to use the images that ship with caffe.
find `pwd`/examples/images -type f -exec echo {} \; > examples/_temp/temp.txt
The `ImageDataLayer` we'll use expects labels after each filenames, so let's add a 0 to the end of each line
sed "s/$/ 0/" examples/_temp/temp.txt > examples/_temp/file_list.txt
Define the Feature Extraction Network Architecture
--------------------------------------------------
In practice, subtracting the mean image from a dataset significantly improves classification accuracies.
Download the mean image of the ILSVRC dataset.
./data/ilsvrc12/get_ilsvrc_aux.sh
We will use `data/ilsvrc212/imagenet_mean.binaryproto` in the network definition prototxt.
Let's copy and modify the network definition.
We'll be using the `ImageDataLayer`, which will load and resize images for us.
cp examples/feature_extraction/imagenet_val.prototxt examples/_temp
Extract Features
----------------
Now everything necessary is in place.
./build/tools/extract_features.bin models/bvlc_reference_caffenet/bvlc_reference_caffenet.caffemodel examples/_temp/imagenet_val.prototxt fc7 examples/_temp/features 10 leveldb
The name of feature blob that you extract is `fc7`, which represents the highest level feature of the reference model.
We can use any other layer, as well, such as `conv5` or `pool3`.
The last parameter above is the number of data mini-batches.
The features are stored to LevelDB `examples/_temp/features`, ready for access by some other code.
If you meet with the error "Check failed: status.ok() Failed to open leveldb examples/_temp/features", it is because the directory examples/_temp/features has been created the last time you run the command. Remove it and run again.
rm -rf examples/_temp/features/
If you'd like to use the Python wrapper for extracting features, check out the [filter visualization notebook](http://nbviewer.ipython.org/github/BVLC/caffe/blob/master/examples/00-classification.ipynb).
Clean Up
--------
Let's remove the temporary directory now.
rm -r examples/_temp
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