Added contrastive loss layer, associated tests, and a siamese network…

… example using shared weights and the contrastive loss.

examples/siamese/convert_mnist_siamese_data.cpp

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+//
+// This script converts the MNIST dataset to the leveldb format used
+// by caffe to train siamese network.
+// Usage:
+//    convert_mnist_data input_image_file input_label_file output_db_file
+// The MNIST dataset could be downloaded at
+//    http://yann.lecun.com/exdb/mnist/
+#include <fstream>  // NOLINT(readability/streams)
+#include <string>
+
+#include "glog/logging.h"
+#include "google/protobuf/text_format.h"
+#include "leveldb/db.h"
+#include "stdint.h"
+
+#include "caffe/proto/caffe.pb.h"
+#include "caffe/util/math_functions.hpp"
+
+uint32_t swap_endian(uint32_t val) {
+    val = ((val << 8) & 0xFF00FF00) | ((val >> 8) & 0xFF00FF);
+    return (val << 16) | (val >> 16);
+}
+
+void read_image(std::ifstream* image_file, std::ifstream* label_file,
+        uint32_t index, uint32_t rows, uint32_t cols,
+        char* pixels, char* label) {
+  image_file->seekg(index * rows * cols + 16);
+  image_file->read(pixels, rows * cols);
+  label_file->seekg(index + 8);
+  label_file->read(label, 1);
+}
+
+void convert_dataset(const char* image_filename, const char* label_filename,
+        const char* db_filename) {
+  // Open files
+  std::ifstream image_file(image_filename, std::ios::in | std::ios::binary);
+  std::ifstream label_file(label_filename, std::ios::in | std::ios::binary);
+  CHECK(image_file) << "Unable to open file " << image_filename;
+  CHECK(label_file) << "Unable to open file " << label_file;
+  // Read the magic and the meta data
+  uint32_t magic;
+  uint32_t num_items;
+  uint32_t num_labels;
+  uint32_t rows;
+  uint32_t cols;
+
+  image_file.read(reinterpret_cast<char*>(&magic), 4);
+  magic = swap_endian(magic);
+  CHECK_EQ(magic, 2051) << "Incorrect image file magic.";
+  label_file.read(reinterpret_cast<char*>(&magic), 4);
+  magic = swap_endian(magic);
+  CHECK_EQ(magic, 2049) << "Incorrect label file magic.";
+  image_file.read(reinterpret_cast<char*>(&num_items), 4);
+  num_items = swap_endian(num_items);
+  label_file.read(reinterpret_cast<char*>(&num_labels), 4);
+  num_labels = swap_endian(num_labels);
+  CHECK_EQ(num_items, num_labels);
+  image_file.read(reinterpret_cast<char*>(&rows), 4);
+  rows = swap_endian(rows);
+  image_file.read(reinterpret_cast<char*>(&cols), 4);
+  cols = swap_endian(cols);
+
+  // Open leveldb
+  leveldb::DB* db;
+  leveldb::Options options;
+  options.create_if_missing = true;
+  options.error_if_exists = true;
+  leveldb::Status status = leveldb::DB::Open(
+      options, db_filename, &db);
+  CHECK(status.ok()) << "Failed to open leveldb " << db_filename
+      << ". Is it already existing?";
+
+  char label_i;
+  char label_j;
+  char* pixels = new char[2 * rows * cols];
+  const int kMaxKeyLength = 10;
+  char key[kMaxKeyLength];
+  std::string value;
+
+  caffe::Datum datum;
+  datum.set_channels(2);  // one channel for each image in the pair
+  datum.set_height(rows);
+  datum.set_width(cols);
+  LOG(INFO) << "A total of " << num_items << " items.";
+  LOG(INFO) << "Rows: " << rows << " Cols: " << cols;
+  for (int itemid = 0; itemid < num_items; ++itemid) {
+    int i = caffe::caffe_rng_rand() % num_items;  // pick a random  pair
+    int j = caffe::caffe_rng_rand() % num_items;
+    read_image(&image_file, &label_file, i, rows, cols,
+        pixels, &label_i);
+    read_image(&image_file, &label_file, j, rows, cols,
+        pixels + (rows * cols), &label_j);
+    datum.set_data(pixels, 2*rows*cols);
+    if (label_i  == label_j) {
+      datum.set_label(1);
+    } else {
+      datum.set_label(0);
+    }
+    datum.SerializeToString(&value);
+    snprintf(key, kMaxKeyLength, "%08d", itemid);
+    db->Put(leveldb::WriteOptions(), std::string(key), value);
+  }
+
+  delete db;
+  delete pixels;
+}
+
+int main(int argc, char** argv) {
+  if (argc != 4) {
+    printf("This script converts the MNIST dataset to the leveldb format used\n"
+           "by caffe to train a siamese network.\n"
+           "Usage:\n"
+           "    convert_mnist_data input_image_file input_label_file "
+           "output_db_file\n"
+           "The MNIST dataset could be downloaded at\n"
+           "    http://yann.lecun.com/exdb/mnist/\n"
+           "You should gunzip them after downloading.\n");
+  } else {
+    google::InitGoogleLogging(argv[0]);
+    convert_dataset(argv[1], argv[2], argv[3]);
+  }
+  return 0;
+}

examples/siamese/create_mnist_siamese.sh

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+#!/usr/bin/env sh
+# This script converts the mnist data into leveldb format.
+
+EXAMPLES=../../build/examples/siamese
+DATA=../../data/mnist
+
+echo "Creating leveldb..."
+
+rm -rf mnist-siamese-train-leveldb
+rm -rf mnist-siamese-test-leveldb
+
+$EXAMPLES/convert_mnist_siamese_data.bin \
+    $DATA/train-images-idx3-ubyte \
+    $DATA/train-labels-idx1-ubyte \
+    mnist-siamese-train-leveldb
+$EXAMPLES/convert_mnist_siamese_data.bin \
+    $DATA/t10k-images-idx3-ubyte \
+    $DATA/t10k-labels-idx1-ubyte \
+    mnist-siamese-test-leveldb
+
+echo "Done."

examples/siamese/mnist_siamese.prototxt

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+name: "mnist_siamese"
+input: "data"
+input_dim: 10000
+input_dim: 1
+input_dim: 28
+input_dim: 28
+
+layers {
+  name: "conv1"
+  type: CONVOLUTION
+  bottom: "data"
+  top: "conv1"
+  blobs_lr: 1
+  blobs_lr: 2
+  convolution_param {
+    num_output: 20
+    kernel_size: 5
+    stride: 1
+  }
+}
+layers {
+  name: "pool1"
+  type: POOLING
+  bottom: "conv1"
+  top: "pool1"
+  pooling_param {
+    pool: MAX
+    kernel_size: 2
+    stride: 2
+  }
+}
+layers {
+  name: "conv2"
+  type: CONVOLUTION
+  bottom: "pool1"
+  top: "conv2"
+  blobs_lr: 1
+  blobs_lr: 2
+  convolution_param {
+    num_output: 50
+    kernel_size: 5
+    stride: 1
+  }
+}
+layers {
+  name: "pool2"
+  type: POOLING
+  bottom: "conv2"
+  top: "pool2"
+  pooling_param {
+    pool: MAX
+    kernel_size: 2
+    stride: 2
+  }
+}
+layers {
+  name: "ip1"
+  type: INNER_PRODUCT
+  bottom: "pool2"
+  top: "ip1"
+  blobs_lr: 1
+  blobs_lr: 2
+  inner_product_param {
+    num_output: 500
+  }
+}
+layers {
+  name: "relu1"
+  type: RELU
+  bottom: "ip1"
+  top: "ip1"
+}
+layers {
+  name: "ip2"
+  type: INNER_PRODUCT
+  bottom: "ip1"
+  top: "ip2"
+  blobs_lr: 1
+  blobs_lr: 2
+  inner_product_param {
+    num_output: 10
+  }
+}
+
+layers {
+  name: "feat"
+  type: INNER_PRODUCT
+  bottom: "ip2"
+  top: "feat"
+  blobs_lr: 1
+  blobs_lr: 2
+  inner_product_param {
+    num_output: 2
+  }
+}

examples/siamese/mnist_siamese_solver.prototxt

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+# The train/test net protocol buffer definition
+net: "mnist_siamese_train.prototxt"
+# test_iter specifies how many forward passes the test should carry out.
+# In the case of MNIST, we have test batch size 100 and 100 test iterations,
+# covering the full 10,000 testing images.
+test_iter: 100
+# Carry out testing every 500 training iterations.
+test_interval: 500
+# The base learning rate, momentum and the weight decay of the network.
+base_lr: 0.01
+momentum: 0.9
+weight_decay: 0.0000
+# The learning rate policy
+lr_policy: "inv"
+gamma: 0.0001
+power: 0.75
+# Display every 100 iterations
+display: 100
+# The maximum number of iterations
+max_iter: 100000
+# snapshot intermediate results
+snapshot: 5000
+snapshot_prefix: "mnist_siamese"
+# solver mode: CPU or GPU
+solver_mode: GPU