Creating an image LMDB for Caffe2

Question

In the original Caffe framework, there was an executable under caffe/build/tools called convert_imageset, which took a directory of JPEG images and a text file with labels for each image, and output an LMDB that could be fed to a Caffe model to train, test, etc.

What is the best way to convert raw JPEG images and labels to an LMDB that Caffe2 can ingest using the AddInput() function from this MNIST tutorial on the Caffe2 website?

According to my research, you cannot simply create an LMDB file using this tool and feed a Caffe2 model.

The tutorial script just downloads two LMDBs (mnist-train-nchw-lmdb and mnist-test-nchw-lmdb) and passes them to AddInput(), but gives no insight as to how the LMDBs were created.

You can look at [this answer](https://stackoverflow.com/a/37149186/1714410) to see how to create lmdb in python. — Shai, Jan 17 '18 at 06:26

Steve Cruz · Answer 1 · 2018-02-14T21:41:52.713

There is a binary called make_image_db.cc which does precisely what you are describing. It is located in caffe2/build/bin/make_image_db:

// This script converts an image dataset to a database.
//
// caffe2::FLAGS_input_folder is the root folder that holds all the images
//
// caffe2::FLAGS_list_file is the path to a file containing a list of files
// and their labels, as follows:
//
//   subfolder1/file1.JPEG 7
//   subfolder1/file2.JPEG 7
//   subfolder2/file1.JPEG 8
//   ...

As described in https://github.com/caffe2/caffe2/issues/1755 you can use the binary in the following way (also with fewer parameters):

caffe2/build/bin/make_image_db -color -db lmdb -input_folder ./some_input_folder
-list_file ./labels_file -num_threads 10 -output_db_name ./some_output_folder -raw -scale 256 -shuffle

A full Caffe2 example on how to create and read a lmdb database (for random images) can be found in the official github repository and can be used as a skeleton to adapt to your own images https://github.com/caffe2/caffe2/blob/master/caffe2/python/examples/lmdb_create_example.py. Since I have not used this method yet, I will simply copy the example. In order to create the database, one can use:

import argparse
import numpy as np

import lmdb
from caffe2.proto import caffe2_pb2
from caffe2.python import workspace, model_helper

def create_db(output_file):
    print(">>> Write database...")
    LMDB_MAP_SIZE = 1 << 40   # MODIFY
    env = lmdb.open(output_file, map_size=LMDB_MAP_SIZE)

    checksum = 0
    with env.begin(write=True) as txn:
        for j in range(0, 128):
            # MODIFY: add your own data reader / creator
            label = j % 10
            width = 64
            height = 32

            img_data = np.random.rand(3, width, height)
            # ...

            # Create TensorProtos
            tensor_protos = caffe2_pb2.TensorProtos()
            img_tensor = tensor_protos.protos.add()
            img_tensor.dims.extend(img_data.shape)
            img_tensor.data_type = 1

            flatten_img = img_data.reshape(np.prod(img_data.shape))
            img_tensor.float_data.extend(flatten_img)

            label_tensor = tensor_protos.protos.add()
            label_tensor.data_type = 2
            label_tensor.int32_data.append(label)
            txn.put(
                '{}'.format(j).encode('ascii'),
                tensor_protos.SerializeToString()
            )

            checksum += np.sum(img_data) * label
            if (j % 16 == 0):
                print("Inserted {} rows".format(j))

    print("Checksum/write: {}".format(int(checksum)))
    return checksum

The database can then by loaded by:

def read_db_with_caffe2(db_file, expected_checksum):
    print(">>> Read database...")
    model = model_helper.ModelHelper(name="lmdbtest")
    batch_size = 32
    data, label = model.TensorProtosDBInput(
        [], ["data", "label"], batch_size=batch_size,
        db=db_file, db_type="lmdb")

    checksum = 0

    workspace.RunNetOnce(model.param_init_net)
    workspace.CreateNet(model.net)

    for _ in range(0, 4):
        workspace.RunNet(model.net.Proto().name)

        img_datas = workspace.FetchBlob("data")
        labels = workspace.FetchBlob("label")
        for j in range(batch_size):
            checksum += np.sum(img_datas[j, :]) * labels[j]

    print("Checksum/read: {}".format(int(checksum)))
    assert np.abs(expected_checksum - checksum < 0.1), \
        "Read/write checksums dont match"

Last but not least, there is also a tutorial on how to create a minidb database: https://github.com/caffe2/caffe2/blob/master/caffe2/python/tutorials/create_your_own_dataset.ipynb. For this, one could use the following function:

def write_db(db_type, db_name, features, labels):
    db = core.C.create_db(db_type, db_name, core.C.Mode.write)
    transaction = db.new_transaction()
    for i in range(features.shape[0]):
        feature_and_label = caffe2_pb2.TensorProtos()
        feature_and_label.protos.extend([
            utils.NumpyArrayToCaffe2Tensor(features[i]),
            utils.NumpyArrayToCaffe2Tensor(labels[i])])
        transaction.put(
            'train_%03d'.format(i),
            feature_and_label.SerializeToString())
    # Close the transaction, and then close the db.
    del transaction
    del db

Features would be a tensor containing your images as numpy arrays. Labels are the corresponding true labels for the features. You would then simply call the function as

write_db("minidb", "train_images.minidb", train_features, train_labels)

Finally, you would load the images from the database by

net_proto = core.Net("example_reader")
dbreader = net_proto.CreateDB([], "dbreader", db="train_images.minidb", db_type="minidb")
net_proto.TensorProtosDBInput([dbreader], ["X", "Y"], batch_size=16)

Welcome to StackOverflow. Instead of just posting a link, you should post the relevant parts in your answer. This creates a more complete answer, and would ensure your answer is still relevant if that link ever breaks — AfroThundr, Feb 13 '18 at 19:07

score -1 · Answer 2 · edited May 17 '18 at 06:12

for create database in lmbd: create the train data folder create train.txt file conataining filename label create validation data folder create val.txt file contatining filename and label

edit this file

gedit examples/imagenet/create_imagenet.sh

EXAMPLE= path to where *.lmbd folder wil be stored
DATA= path where val.txt and train.txt is present
TOOLS=build/tools

TRAIN_DATA_ROOT=test/make_caffe_data/train/ # path to trainfiles
VAL_DATA_ROOT=test/make_caffe_data/val/ # path to test_files

Set RESIZE=true to resize the images to 256x256. Leave as false if images have already been resized using another tool. RESIZE=true

./examples/imagenet/create_imagenet.sh

Creating an image LMDB for Caffe2

2 Answers2