add gaussian filter algorithm and lena.jpg (#955)

digital_image_processing/filters/gaussian_filter.py

@@ -0,0 +1,53 @@
+"""
+Implementation of gaussian filter algorithm
+"""
+from cv2 import imread, cvtColor, COLOR_BGR2GRAY, imshow, waitKey
+from numpy import pi, mgrid, exp, square, zeros, ravel, dot, uint8
+
+
+def gen_gaussian_kernel(k_size, sigma):
+    center = k_size // 2
+    x, y = mgrid[0-center:k_size-center, 0-center:k_size-center]
+    g = 1/(2*pi*sigma) * exp(-(square(x) + square(y))/(2*square(sigma)))
+    return g
+
+
+def gaussian_filter(image, k_size, sigma):
+    height, width = image.shape[0], image.shape[1]
+    # dst image height and width
+    dst_height = height-k_size+1
+    dst_width = width-k_size+1
+
+    # im2col, turn the k_size*k_size pixels into a row and np.vstack all rows
+    image_array = zeros((dst_height*dst_width, k_size*k_size))
+    row = 0
+    for i in range(0, dst_height):
+        for j in range(0, dst_width):
+            window = ravel(image[i:i + k_size, j:j + k_size])
+            image_array[row, :] = window
+            row += 1
+
+    #  turn the kernel into shape(k*k, 1)
+    gaussian_kernel = gen_gaussian_kernel(k_size, sigma)
+    filter_array = ravel(gaussian_kernel)
+
+    # reshape and get the dst image
+    dst = dot(image_array, filter_array).reshape(dst_height, dst_width).astype(uint8)
+
+    return dst
+
+
+if __name__ == '__main__':
+    # read original image
+    img = imread(r'../image_data/lena.jpg')
+    # turn image in gray scale value
+    gray = cvtColor(img, COLOR_BGR2GRAY)
+
+    # get values with two different mask size
+    gaussian3x3 = gaussian_filter(gray, 3, sigma=1)
+    gaussian5x5 = gaussian_filter(gray, 5, sigma=0.8)
+
+    # show result images
+    imshow('gaussian filter with 3x3 mask', gaussian3x3)
+    imshow('gaussian filter with 5x5 mask', gaussian5x5)
+    waitKey()

digital_image_processing/filters/median_filter.py

@@ -28,7 +28,7 @@ def median_filter(gray_img, mask=3):
 
 if __name__ == '__main__':
     # read original image
-    img = imread('lena.jpg')
+    img = imread('../image_data/lena.jpg')
     # turn image in gray scale value
     gray = cvtColor(img, COLOR_BGR2GRAY)