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diff --git a/gaussian.py b/gaussian.py
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+# Copyright 2016 (c) Egor Tensin <Egor.Tensin@gmail.com>
+# This file is part of the "Simple image filters" project.
+# For details, see https://github.com/egor-tensin/filters.
+# Distributed under the MIT License.
+
+import argparse
+import sys
+
+import cv2
+import numpy as np
+
+def gen_kernel(radius, sigma):
+    kernel = np.array([[i ** 2 + j ** 2
+        for i in range(-radius, radius + 1)]
+        for j in range(-radius, radius + 1)])
+    kernel = -kernel / (2 * sigma ** 2)
+    kernel = np.exp(kernel)
+    kernel = kernel / np.sum(kernel)
+    return kernel
+
+def convolve(img, kernel):
+    #print(kernel)
+    radius = kernel.shape[0] // 2
+    output = np.zeros(img.shape, dtype=img.dtype)
+    for i in range(radius, img.shape[0] - radius):
+        for j in range(radius, img.shape[1] - radius):
+            neighborhood = img[i - radius:i + radius + 1, j - radius:j + radius + 1]
+            output[i, j] = np.sum(neighborhood * kernel)
+    return output
+
+DEFAULT_SIGMA = 1.
+DEFAULT_RADIUS = 1
+
+def do(img_path, radius=DEFAULT_RADIUS, sigma=DEFAULT_SIGMA,
+       output_path=None):
+
+    img = cv2.imread(img_path, cv2.IMREAD_GRAYSCALE)
+    kernel = gen_kernel(radius, sigma)
+    output = convolve(img, kernel)
+    if output_path is None:
+        cv2.imshow("Output", output)
+        cv2.waitKey()
+    else:
+        cv2.imwrite(output_path, output)
+
+def _parse_non_negative_integer(s):
+    try:
+        x = int(s)
+    except ValueError:
+        raise argparse.ArgumentTypeError('must be a non-negative integer: ' + s)
+    if x < 0:
+        raise argparse.ArgumentTypeError('must be a non-negative integer: ' + s)
+    return x
+
+def _parse_args(args=sys.argv):
+    parser = argparse.ArgumentParser()
+    parser.add_argument('img_path')
+    parser.add_argument('--output', '-o',
+                        dest='output_path', default=None)
+    parser.add_argument('-s', '--sigma',
+                        type=float, default=DEFAULT_SIGMA)
+    parser.add_argument('--radius', '-r',
+                        type=_parse_non_negative_integer,
+                        default=DEFAULT_RADIUS)
+    return parser.parse_args(args[1:])
+
+def main(args=sys.argv):
+    do(**vars(_parse_args(args)))
+
+if __name__ == '__main__':
+    main()