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NG.py
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# Image compression by Neural Gas
import numpy as np
from scipy import misc, spatial
from math import log, exp, pow
from sklearn.metrics import mean_squared_error
import cv2
from math import sqrt
from scipy.cluster.vq import vq
import scipy.misc
import sys
def mse(image_a, image_b):
# calculate mean square error between two images
err = np.sum((image_a.astype(float) - image_b.astype(float)) ** 2)
err /= float(image_a.shape[0] * image_a.shape[1])
return err
def psnr(a):
tmp = (255*255)/float(a)
return 10*log(tmp, 10)
class NG(object):
def __init__(self, cb_size, dimensions, iterations, number_of_input_vectors, alp_i, alp_f,
lam_i, lam_f):
self.number_of_clusters = int(cb_size)
self.dimensions = dimensions
self.number_of_iterations = int(iterations)
self.alpha_i = alp_i
self.alpha_f = alp_f
self.lambda_i = lam_i
self.lambda_f = lam_f
self.number_of_input_vectors = number_of_input_vectors
self.weight_vectors = np.random.uniform(0, 255, (self.number_of_clusters, self.dimensions))
def get_k(self, input_vector, weights):
distance_from_input = [np.linalg.norm(input_vector - weight_vector) for weight_vector in weights]
sorted_indices = sorted(range(len(distance_from_input)), key=lambda j: distance_from_input[j])
k = [sorted_indices.index(ind) for ind in range(0, self.number_of_clusters)]
return np.array(k)
def update_weights(self, iter_no, k, input_data):
alpha_op = self.alpha_i * pow(self.alpha_f/float(self.alpha_i), iter_no/float(self.number_of_iterations))
lambda_op = self.lambda_i * pow(self.lambda_f/float(self.lambda_i), iter_no/float(self.number_of_iterations))
neighbourhood_function = [exp(-val / float(lambda_op)) for val in k]
final_learning_rate = [alpha_op * val for val in neighbourhood_function]
for l in range(self.number_of_clusters):
weight_delta = [val*final_learning_rate[l] for val in (input_data - self.weight_vectors[l])]
updated_weight = self.weight_vectors[l] + np.array(weight_delta)
self.weight_vectors[l] = updated_weight
def get_distortion(self, input_data, reconstruction_values):
global image_width, image_height, block_height, block_height, image, codebook_size
image_vector_indices, distance = vq(input_data, reconstruction_values)
image_after_compression = np.zeros([image_width, image_height], dtype="uint8")
for index, image_vector in enumerate(input_data):
start_row = int(index / (image_width / block_width)) * block_height
end_row = start_row + block_height
start_column = (index * block_width) % image_width
end_column = start_column + block_width
image_after_compression[start_row:end_row, start_column:end_column] = \
np.reshape(reconstruction_values[image_vector_indices[index]],
(block_width, block_height))
output_image_name = "CB_size=" + str(codebook_size) + ".png"
scipy.misc.imsave(output_image_name, image_after_compression)
return psnr(mse(image, image_after_compression))
def train(self, input_data):
epoch = 1
for iteration_no in range(1, self.number_of_iterations+1):
input_vector_index = (iteration_no-1) % self.number_of_input_vectors
k = self.get_k(input_data[input_vector_index], self.weight_vectors)
self.update_weights(iteration_no, k, input_data[input_vector_index])
if (iteration_no % self.number_of_input_vectors) == 0:
epoch += 1
return self.weight_vectors
# source image
image_location = sys.argv[1]
image = cv2.imread(image_location, cv2.IMREAD_GRAYSCALE)
image_height = len(image)
image_width = len(image[0])
# dimension of the vector
block_width = int(sys.argv[3])
block_height = int(sys.argv[4])
vector_dimension = block_width*block_height
# dividing the image into 4*4 blocks of pixels
image_vectors = []
for i in range(0, image_height, block_height):
for j in range(0, image_width, block_width):
image_vectors.append(np.reshape(image[i:i+block_width, j:j+block_height], vector_dimension))
image_vectors = np.asarray(image_vectors).astype(float)
number_of_image_vectors = image_vectors.shape[0]
bits_per_codevector = int(sys.argv[2])
codebook_size = pow(2, bits_per_codevector)
epochs = int(sys.argv[5])
number_of_iterations = epochs * number_of_image_vectors
epsilon_i = float(sys.argv[6])
epsilon_f = float(sys.argv[7])
tau_i = float(sys.argv[8])
tau_f = float(sys.argv[9])
ng = NG(codebook_size, vector_dimension, number_of_iterations, number_of_image_vectors, epsilon_i, epsilon_f,
tau_i, tau_f)
reconstruction_values = ng.train(image_vectors)
image_vector_indices, distance = vq(image_vectors, reconstruction_values)
image_after_compression = np.zeros([image_width, image_height], dtype="uint8")
image_vectors_after_compression = np.zeros([number_of_image_vectors, vector_dimension], dtype="uint8")
for index, image_vector in enumerate(image_vectors):
image_vectors_after_compression[index] = reconstruction_values[image_vector_indices[index]]
start_row = int(index / (image_width / block_width)) * block_height
end_row = start_row + block_height
start_column = (index * block_width) % image_width
end_column = start_column + block_width
image_after_compression[start_row:end_row, start_column:end_column] = \
np.reshape(reconstruction_values[image_vector_indices[index]],
(block_width, block_height))
output_image_name = "CB_size=" + str(codebook_size) + ".png"
scipy.misc.imsave(output_image_name, image_after_compression)
print "Mean squared error = ", mean_squared_error(image_vectors, image_vectors_after_compression)