""" This file contains different utility functions that are not connected
in anyway to the networks presented in the tutorials, but rather help in
processing the outputs into a more understandable way.
For example ``tile_raster_images`` helps in generating a easy to grasp
image from a set of samples or weights.
"""
import numpy
def scale_to_unit_interval(ndar, eps=1e-8):
""" Scales all values in the ndarray ndar to be between 0 and 1 """
ndar = ndar.copy()
ndar -= ndar.min()
ndar *= 1.0 / (ndar.max() + eps)
return ndar
def tile_raster_images(X, img_shape, tile_shape, tile_spacing=(0, 0),
scale_rows_to_unit_interval=True,
output_pixel_vals=True):
"""
Transform an array with one flattened image per row, into an array in
which images are reshaped and layed out like tiles on a floor.
This function is useful for visualizing datasets whose rows are images,
and also columns of matrices for transforming those rows
(such as the first layer of a neural net).
:type X: a 2-D ndarray or a tuple of 4 channels, elements of which can
be 2-D ndarrays or None;
:param X: a 2-D array in which every row is a flattened image.
:type img_shape: tuple; (height, width)
:param img_shape: the original shape of each image
:type tile_shape: tuple; (rows, cols)
:param tile_shape: the number of images to tile (rows, cols)
:param output_pixel_vals: if output should be pixel values (i.e. int8
values) or floats
:param scale_rows_to_unit_interval: if the values need to be scaled before
being plotted to [0,1] or not
:returns: array suitable for viewing as an image.
(See:`Image.fromarray`.)
:rtype: a 2-d array with same dtype as X.
"""
assert len(img_shape) == 2
assert len(tile_shape) == 2
assert len(tile_spacing) == 2
# The expression below can be re-written in a more C style as
# follows :
#
# out_shape = [0,0]
# out_shape[0] = (img_shape[0]+tile_spacing[0])*tile_shape[0] -
# tile_spacing[0]
# out_shape[1] = (img_shape[1]+tile_spacing[1])*tile_shape[1] -
# tile_spacing[1]
out_shape = [
(ishp + tsp) * tshp - tsp
for ishp, tshp, tsp in zip(img_shape, tile_shape, tile_spacing)
]
if isinstance(X, tuple):
assert len(X) == 4
# Create an output numpy ndarray to store the image
if output_pixel_vals:
out_array = numpy.zeros((out_shape[0], out_shape[1], 4),
dtype='uint8')
else:
out_array = numpy.zeros((out_shape[0], out_shape[1], 4),
dtype=X.dtype)
#colors default to 0, alpha defaults to 1 (opaque)
if output_pixel_vals:
channel_defaults = [0, 0, 0, 255]
else:
channel_defaults = [0., 0., 0., 1.]
for i in range(4):
if X[i] is None:
# if channel is None, fill it with zeros of the correct
# dtype
dt = out_array.dtype
if output_pixel_vals:
dt = 'uint8'
out_array[:, :, i] = numpy.zeros(
out_shape,
dtype=dt
) + channel_defaults[i]
else:
# use a recurrent call to compute the channel and store it
# in the output
out_array[:, :, i] = tile_raster_images(
X[i], img_shape, tile_shape, tile_spacing,
scale_rows_to_unit_interval, output_pixel_vals)
return out_array
else:
# if we are dealing with only one channel
H, W = img_shape
Hs, Ws = tile_spacing
# generate a matrix to store the output
dt = X.dtype
if output_pixel_vals:
dt = 'uint8'
out_array = numpy.zeros(out_shape, dtype=dt)
for tile_row in range(tile_shape[0]):
for tile_col in range(tile_shape[1]):
if tile_row * tile_shape[1] + tile_col < X.shape[0]:
this_x = X[tile_row * tile_shape[1] + tile_col]
if scale_rows_to_unit_interval:
# if we should scale values to be between 0 and 1
# do this by calling the `scale_to_unit_interval`
# function
this_img = scale_to_unit_interval(
this_x.reshape(img_shape))
else:
this_img = this_x.reshape(img_shape)
# add the slice to the corresponding position in the
# output array
c = 1
if output_pixel_vals:
c = 255
out_array[
tile_row * (H + Hs): tile_row * (H + Hs) + H,
tile_col * (W + Ws): tile_col * (W + Ws) + W
] = this_img * c
return out_array