forked from rykov8/ssd_keras
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ssd_layers.py
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ssd_layers.py
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"""Some special pupropse layers for SSD."""
import keras.backend as K
from keras.engine.topology import InputSpec
from keras.engine.topology import Layer
import numpy as np
import tensorflow as tf
class Normalize(Layer):
"""Normalization layer as described in ParseNet paper.
# Arguments
scale: Default feature scale.
# Input shape
4D tensor with shape:
`(samples, channels, rows, cols)` if dim_ordering='th'
or 4D tensor with shape:
`(samples, rows, cols, channels)` if dim_ordering='tf'.
# Output shape
Same as input
# References
http://cs.unc.edu/~wliu/papers/parsenet.pdf
#TODO
Add possibility to have one scale for all features.
"""
def __init__(self, scale, **kwargs):
if K.image_dim_ordering() == 'tf':
self.axis = 3
else:
self.axis = 1
self.scale = scale
super(Normalize, self).__init__(**kwargs)
def build(self, input_shape):
self.input_spec = [InputSpec(shape=input_shape)]
shape = (input_shape[self.axis],)
init_gamma = self.scale * np.ones(shape)
self.gamma = K.variable(init_gamma, name='{}_gamma'.format(self.name))
self.trainable_weights = [self.gamma]
def call(self, x, mask=None):
output = K.l2_normalize(x, self.axis)
output *= self.gamma
return output
class PriorBox(Layer):
"""Generate the prior boxes of designated sizes and aspect ratios.
# Arguments
img_size: Size of the input image as tuple (w, h).
min_size: Minimum box size in pixels.
max_size: Maximum box size in pixels.
aspect_ratios: List of aspect ratios of boxes.
flip: Whether to consider reverse aspect ratios.
variances: List of variances for x, y, w, h.
clip: Whether to clip the prior's coordinates
such that they are within [0, 1].
# Input shape
4D tensor with shape:
`(samples, channels, rows, cols)` if dim_ordering='th'
or 4D tensor with shape:
`(samples, rows, cols, channels)` if dim_ordering='tf'.
# Output shape
3D tensor with shape:
(samples, num_boxes, 8)
# References
https://arxiv.org/abs/1512.02325
#TODO
Add possibility not to have variances.
Add Theano support
"""
def __init__(self, img_size=(300.0, 300.0), min_size=30.0, max_size=None, aspect_ratios=None,
flip=True, variances=[0.1], clip=True, **kwargs):
if K.image_dim_ordering() == 'tf':
self.waxis = 2
self.haxis = 1
else:
self.waxis = 3
self.haxis = 2
self.img_size = img_size
if min_size <= 0:
raise Exception('min_size must be positive.')
self.min_size = min_size
self.max_size = max_size
self.aspect_ratios = [1.0]
if max_size:
if max_size < min_size:
raise Exception('max_size must be greater than min_size.')
self.aspect_ratios.append(1.0)
if aspect_ratios:
for ar in aspect_ratios:
if ar in self.aspect_ratios:
continue
self.aspect_ratios.append(ar)
if flip:
self.aspect_ratios.append(1.0 / ar)
self.variances = np.array(variances)
self.clip = True
super(PriorBox, self).__init__(**kwargs)
def get_output_shape_for(self, input_shape):
num_priors_ = len(self.aspect_ratios)
layer_width = input_shape[self.waxis]
layer_height = input_shape[self.haxis]
num_boxes = num_priors_ * layer_width * layer_height
return input_shape[0], num_boxes, 8
# support for Keras 2.0
def compute_output_shape(self, input_shape):
return self.get_output_shape_for(input_shape)
def call(self, x, mask=None):
if hasattr(x, '_keras_shape'):
input_shape = x._keras_shape
elif hasattr(K, 'int_shape'):
input_shape = K.int_shape(x)
layer_width = input_shape[self.waxis]
layer_height = input_shape[self.haxis]
img_width = self.img_size[0]
img_height = self.img_size[1]
# define prior boxes shapes
box_widths = []
box_heights = []
for ar in self.aspect_ratios:
if ar == 1 and len(box_widths) == 0:
box_widths.append(self.min_size)
box_heights.append(self.min_size)
elif ar == 1 and len(box_widths) > 0:
box_widths.append(np.sqrt(self.min_size * self.max_size))
box_heights.append(np.sqrt(self.min_size * self.max_size))
elif ar != 1:
box_widths.append(self.min_size * np.sqrt(ar))
box_heights.append(self.min_size / np.sqrt(ar))
box_widths = 0.5 * np.array(box_widths)
box_heights = 0.5 * np.array(box_heights)
# define centers of prior boxes
step_x = img_width / layer_width
step_y = img_height / layer_height
linx = np.linspace(0.5 * step_x, img_width - 0.5 * step_x,
layer_width)
liny = np.linspace(0.5 * step_y, img_height - 0.5 * step_y,
layer_height)
centers_x, centers_y = np.meshgrid(linx, liny)
centers_x = centers_x.reshape(-1, 1)
centers_y = centers_y.reshape(-1, 1)
# define xmin, ymin, xmax, ymax of prior boxes
num_priors_ = len(self.aspect_ratios)
prior_boxes = np.concatenate((centers_x, centers_y), axis=1)
prior_boxes = np.tile(prior_boxes, (1, 2 * num_priors_))
prior_boxes[:, ::4] -= box_widths
prior_boxes[:, 1::4] -= box_heights
prior_boxes[:, 2::4] += box_widths
prior_boxes[:, 3::4] += box_heights
prior_boxes[:, ::2] /= img_width
prior_boxes[:, 1::2] /= img_height
prior_boxes = prior_boxes.reshape(-1, 4)
if self.clip:
prior_boxes = np.minimum(np.maximum(prior_boxes, 0.0), 1.0)
# define variances
num_boxes = len(prior_boxes)
if len(self.variances) == 1:
variances = np.ones((num_boxes, 4)) * self.variances[0]
elif len(self.variances) == 4:
variances = np.tile(self.variances, (num_boxes, 1))
else:
raise Exception('Must provide one or four variances.')
prior_boxes = np.concatenate((prior_boxes, variances), axis=1)
prior_boxes_tensor = K.expand_dims(K.variable(prior_boxes), 0)
if K.backend() == 'tensorflow':
pattern = [tf.shape(x)[0], 1, 1]
prior_boxes_tensor = tf.tile(prior_boxes_tensor, pattern)
elif K.backend() == 'theano':
#TODO
pass
return prior_boxes_tensor