theano_backend.py

from theano import tensor as T
from theano.sandbox.neighbours import images2neibs

try:
    import theano.sparse as th_sparse_module
except ImportError:
    th_sparse_module = None
try:
    from theano.tensor.nnet.nnet import softsign as T_softsign
except ImportError:
    from theano.sandbox.softsign import softsign as T_softsign
from keras.backend import theano_backend as KTH
from keras.backend.common import image_data_format
from keras.backend.theano_backend import _preprocess_conv2d_input
from keras.backend.theano_backend import _postprocess_conv2d_output

py_all = all


def conv2d(x, kernel, strides=(1, 1), padding='valid', data_format='channels_first',
           image_shape=None, filter_shape=None):
    '''
    padding: string, "same" or "valid".
    '''
    if data_format not in {'channels_first', 'channels_last'}:
        raise Exception('Unknown data_format ' + str(data_format))

    if data_format == 'channels_last':
        # TF uses the last dimension as channel dimension,
        # instead of the 2nd one.
        # TH input shape: (samples, input_depth, rows, cols)
        # TF input shape: (samples, rows, cols, input_depth)
        # TH kernel shape: (depth, input_depth, rows, cols)
        # TF kernel shape: (rows, cols, input_depth, depth)
        x = x.dimshuffle((0, 3, 1, 2))
        kernel = kernel.dimshuffle((3, 2, 0, 1))
        if image_shape:
            image_shape = (image_shape[0], image_shape[3],
                           image_shape[1], image_shape[2])
        if filter_shape:
            filter_shape = (filter_shape[3], filter_shape[2],
                            filter_shape[0], filter_shape[1])

    if padding == 'same':
        th_padding = 'half'
        np_kernel = kernel.eval()
    elif padding == 'valid':
        th_padding = 'valid'
    else:
        raise Exception('Border mode not supported: ' + str(padding))

    # Theano might not accept long type
    def int_or_none(value):
        try:
            return int(value)
        except TypeError:
            return None

    if image_shape is not None:
        image_shape = tuple(int_or_none(v) for v in image_shape)

    if filter_shape is not None:
        filter_shape = tuple(int_or_none(v) for v in filter_shape)

    conv_out = T.nnet.conv2d(x, kernel,
                             border_mode=th_padding,
                             subsample=strides,
                             input_shape=image_shape,
                             filter_shape=filter_shape)

    if padding == 'same':
        if np_kernel.shape[2] % 2 == 0:
            end = (x.shape[2] + strides[0] - 1) // strides[0]
            conv_out = conv_out[:, :, :end, :]
        if np_kernel.shape[3] % 2 == 0:
            end = (x.shape[3] + strides[1] - 1) // strides[1]
            conv_out = conv_out[:, :, :, :end]

    if data_format == 'channels_last':
        conv_out = conv_out.dimshuffle((0, 2, 3, 1))
    return conv_out


def extract_image_patches(X, ksizes, strides,
                          padding='valid',
                          data_format='channels_first'):
    '''
    Extract the patches from an image
    Parameters
    ----------
    X : The input image
    ksizes : 2-d tuple with the kernel size
    strides : 2-d tuple with the strides size
    padding : 'same' or 'valid'
    data_format : 'channels_last' or 'channels_first'
    Returns
    -------
    The (k_w,k_h) patches extracted
    TF ==> (batch_size,w,h,k_w,k_h,c)
    TH ==> (batch_size,w,h,c,k_w,k_h)
    '''
    patch_size = ksizes[1]
    if padding == 'same':
        padding = 'ignore_borders'
    if data_format == 'channels_last':
        X = KTH.permute_dimensions(X, [0, 3, 1, 2])
    # Thanks to https://github.com/awentzonline for the help!
    batch, c, w, h = KTH.shape(X)
    xs = KTH.shape(X)
    num_rows = 1 + (xs[-2] - patch_size) // strides[1]
    num_cols = 1 + (xs[-1] - patch_size) // strides[1]
    num_channels = xs[-3]
    patches = images2neibs(X, ksizes, strides, padding)
    # Theano is sorting by channel
    new_shape = (batch, num_channels, num_rows * num_cols, patch_size, patch_size)
    patches = KTH.reshape(patches, new_shape)
    patches = KTH.permute_dimensions(patches, (0, 2, 1, 3, 4))
    # arrange in a 2d-grid (rows, cols, channels, px, py)
    new_shape = (batch, num_rows, num_cols, num_channels, patch_size, patch_size)
    patches = KTH.reshape(patches, new_shape)
    if data_format == 'channels_last':
        patches = KTH.permute_dimensions(patches, [0, 1, 2, 4, 5, 3])
    return patches


def depth_to_space(input, scale, data_format=None):
    """Uses phase shift algorithm to convert
    channels/depth for spatial resolution
    """
    if data_format is None:
        data_format = image_data_format()
    data_format = data_format.lower()
    input = _preprocess_conv2d_input(input, data_format)

    b, k, row, col = input.shape
    out_channels = k // (scale ** 2)
    x = T.reshape(input, (b, scale, scale, out_channels, row, col))
    x = T.transpose(x, (0, 3, 4, 1, 5, 2))
    out = T.reshape(x, (b, out_channels, row * scale, col * scale))

    out = _postprocess_conv2d_output(out, input, None, None, None, data_format)
    return out


def moments(x, axes, shift=None, keep_dims=False):
    ''' Calculates and returns the mean and variance of the input '''

    mean_batch = KTH.mean(x, axis=axes, keepdims=keep_dims)
    var_batch = KTH.var(x, axis=axes, keepdims=keep_dims)

    return mean_batch, var_batch