Generative Model with Coordinate Metric Learning for Object Recognition Based on 3D Models

One of the bottlenecks in acquiring a perfect database for deep learning is the tedious process of collecting and labeling data. In this paper, we propose a generative model trained with synthetic images rendered from 3D models which can reduce the burden on collecting real training data and make the bac kground conditions more realistic. Our architecture is composed of two sub-networks: a semantic foreground object reconstruction network based on Bayesian inference, and a classification network based on multi-t riplet cost training for avoiding over-fitting on monotone synthetic object surface and utilizing accurate information of synthetic images like object poses and lightning condi tions which are helpful for recognizing regular photos. Firstly, our generative model with metric learning utilizes additional foreground object channels generated from semantic foreground object reconstruction sub-network for recog nizing the original input images. Multi-triplet cost function based on poses is used for metric learning which makes it possible to train an effective categorical classifier purely based on synthetic data. Secondly, we design a coordinate training strategy with the help of adaptive noise applied on the inputs of both of the concatenated sub-networks to make them benefit from each other and avoid inharmonious parameter tuning due to different convergence speed of two sub-networks. Our architecture achieves the state of the art accuracy of 50.5% on the ShapeNet database with data migration obstacle from synthetic images to real photos. This pipeline makes it applicable to do recognition on real images only based on 3D models.

Copyright (c) 2017, Yida Wang All rights reserved.

Please see our paper for more details about the method and data.

Author info

Yida Wang, Ph.D candidate in Technischen Universität München (TUM), München, Deutschland. read more

Figures in the paper

Pipeline

This is the basic pipeline for Generative Model with Coordinate Metric Learning

Our GM-CML is a concatenated architecture which is shown as reconstruction sub-network and classification sub-network in below:

Samples for the triplet training

Codes Explanation

Training and Testing Strategies

network input / placeholders for train (bn) and dropout

    x_img = tf.placeholder(tf.float32, input_shape, 'x_img')
    x_obj = tf.placeholder(tf.float32, input_shape, 'x_obj')

Input of the reconstruction network

    current_input1 = utils.corrupt(x_img)*corrupt_rec + x_img*(1-corrupt_rec) \
                if (denoising and phase_train is not None) else x_img
    current_input1.set_shape(x_img.get_shape())
    # 2d -> 4d if convolution
    current_input1 = utils.to_tensor(current_input1) \
                if convolutional else current_input1

Encoder

    for layer_i, n_output in enumerate(n_filters):
        with tf.variable_scope('encoder/{}'.format(layer_i)):
            shapes.append(current_input1.get_shape().as_list())
            if convolutional:

    with tf.variable_scope('variational'):
        if variational:

Decoder

    for layer_i, n_output in enumerate(n_filters[1:]):
        with tf.variable_scope('decoder/{}'.format(layer_i)):
            shape = shapes[layer_i + 1]
            if convolutional:

Loss finctions of VAE and softmax

    # l2 loss
    loss_x = tf.reduce_mean(
        tf.reduce_sum(tf.squared_difference(x_obj_flat, y_flat), 1))
    loss_z = 0

    if variational:
        # Variational lower bound, kl-divergence
        loss_z = tf.reduce_mean(-0.5 * tf.reduce_sum(
            1.0 + 2.0 * z_log_sigma -
            tf.square(z_mu) - tf.exp(2.0 * z_log_sigma), 1))

        # Add l2 loss
        cost_vae = tf.reduce_mean(loss_x + loss_z)

    # Alexnet for clasification based on softmax using TensorFlow slim
    if softmax:

There are several optional choices for classification network. Just modify the parameter classifier.

        # The following are optional networks for classification network
        if classifier == 'squeezenet':
            predictions, net = squeezenet.squeezenet(
                        y_concat, num_classes=13)
        if classifier == 'zigzagnet':
            predictions, net = squeezenet.zigzagnet(
                        y_concat, num_classes=13)
        elif classifier == 'alexnet_v2':
            predictions, end_points = alexnet.alexnet_v2(
                        y_concat, num_classes=13)
        elif classifier == 'inception_v1':
            predictions, end_points = inception.inception_v1(
                        y_concat, num_classes=13)
        elif classifier == 'inception_v2':
            predictions, end_points = inception.inception_v2(
                        y_concat, num_classes=13)
        elif classifier == 'inception_v3':
            predictions, end_points = inception.inception_v3(
                        y_concat, num_classes=13)

Here we must set corrupt_rec and corrupt_cls as 0 to find a proper ratio of variance to feed for variable var_prob. We use tanh as non-linear function for ratio of Vars from the reconstructed channels and original channels.

var_prob = sess.run(ae['var_prob'],
            feed_dict={
                ae['x_img']: test_xs_img,
                ae['x_label']: test_xs_label,
                ae['train']: True,
                ae['keep_prob']: 1.0,
                ae['corrupt_rec']: 0,
                ae['corrupt_cls']: 0})

# Here is a fast training process
corrupt_rec = np.tanh(0.25*var_prob)
corrupt_cls = np.tanh(1-np.tanh(2*var_prob))

Main API for training and testing. General purpose training of a (Variational) (Convolutional) Autoencoder.

def train_vae(files_img, files_obj, input_shape):
    """
    Parameters
    ----------
    files : list of strings
        List of paths to images.
    input_shape : list
        Must define what the input image's shape is.
    use_csv = bool, optional
        Use csv files to train conditional VAE or just VAE.
    learning_rate : float, optional
        Learning rate.
    batch_size : int, optional
        Batch size.
    n_epochs : int, optional
        Number of epochs.
    n_examples : int, optional
        Number of example to use while demonstrating the current training
        iteration's reconstruction.  Creates a square montage, so make
        sure int(sqrt(n_examples))**2 = n_examples, e.g. 16, 25, 36, ... 100.
    crop_shape : list, optional
        Size to centrally crop the image to.
    crop_factor : float, optional
        Resize factor to apply before cropping.
    n_filters : list, optional
        Same as VAE's n_filters.
    n_hidden : int, optional
        Same as VAE's n_hidden.
    n_code : int, optional
        Same as VAE's n_code.
    convolutional : bool, optional
        Use convolution or not.
    variational : bool, optional
        Use variational layer or not.
    softmax : bool, optional
        Use the classification network or not.
    classifier : str, optional
        Network for classification.
    filter_sizes : list, optional
        Same as VAE's filter_sizes.
    dropout : bool, optional
        Use dropout or not
    keep_prob : float, optional
        Percent of keep for dropout.
    activation : function, optional
        Which activation function to use.
    img_step : int, optional
        How often to save training images showing the manifold and
        reconstruction.
    save_step : int, optional
        How often to save checkpoints.
    ckpt_name : str, optional
        Checkpoints will be named as this, e.g. 'model.ckpt'
    """

Visualization for Outputs and Parameters

We can visualize filters, reconstruction channels and also outputs according to latent variables.

Plot example reconstructions

recon = sess.run(
    ae['y'], feed_dict={
                ae['x_img']: test_xs_img,
                ae['train']: False,
                ae['keep_prob']: 1.0,
                ae['corrupt_rec']: 0,
                ae['corrupt_cls']: 0})
utils.montage(recon.reshape([-1] + crop_shape),
              'recon_%08d.png' % t_i)

Plot filters

filters = sess.run(
  ae['Ws'], feed_dict={
              ae['x_img']: test_xs_img,
              ae['train']: False,
              ae['keep_prob']: 1.0,
              ae['corrupt_rec']: 0,
              ae['corrupt_cls']: 0})
#for filter_element in filters:
utils.montage_filters(filters[-1],
            'filter_%08d.png' % t_i)