Add bilateral filter (#1786)

* Added Bilateral filter

* Added Bilateral filter

* changed types of varS and varI

* formatted with black

* added type hints

* changed variable names

* Update bilateral_filter.py

* Drop transitory variables, add parse_args()

Co-authored-by: vinayak <itssvinayak@gmail.com>
Co-authored-by: Christian Clauss <cclauss@me.com>

digital_image_processing/filters/bilateral_filter.py

@@ -0,0 +1,88 @@
+"""
+Implementation of Bilateral filter
+
+Inputs:
+    img: A 2d image with values in between 0 and 1
+    varS: variance in space dimension.
+    varI: variance in Intensity.
+    N: Kernel size(Must be an odd number)
+Output:
+    img:A 2d zero padded image with values in between 0 and 1
+"""
+
+import cv2
+import numpy as np
+import math
+import sys
+
+
+def vec_gaussian(img: np.ndarray, variance: float) -> np.ndarray:
+    # For applying gaussian function for each element in matrix.
+    sigma = math.sqrt(variance)
+    cons = 1 / (sigma * math.sqrt(2 * math.pi))
+    return cons * np.exp(-((img / sigma) ** 2) * 0.5)
+
+
+def get_slice(img: np.ndarray, x: int, y: int, kernel_size: int) -> np.ndarray:
+    half = kernel_size // 2
+    return img[x - half : x + half + 1, y - half : y + half + 1]
+
+
+def get_gauss_kernel(kernel_size: int, spatial_variance: float) -> np.ndarray:
+    # Creates a gaussian kernel of given dimension.
+    arr = np.zeros((kernel_size, kernel_size))
+    for i in range(0, kernel_size):
+        for j in range(0, kernel_size):
+            arr[i, j] = math.sqrt(
+                abs(i - kernel_size // 2) ** 2 + abs(j - kernel_size // 2) ** 2
+            )
+    return vec_gaussian(arr, spatial_variance)
+
+
+def bilateral_filter(
+    img: np.ndarray,
+    spatial_variance: float,
+    intensity_variance: float,
+    kernel_size: int,
+) -> np.ndarray:
+    img2 = np.zeros(img.shape)
+    gaussKer = get_gauss_kernel(kernel_size, spatial_variance)
+    sizeX, sizeY = img.shape
+    for i in range(kernel_size // 2, sizeX - kernel_size // 2):
+        for j in range(kernel_size // 2, sizeY - kernel_size // 2):
+
+            imgS = get_slice(img, i, j, kernel_size)
+            imgI = imgS - imgS[kernel_size // 2, kernel_size // 2]
+            imgIG = vec_gaussian(imgI, intensity_variance)
+            weights = np.multiply(gaussKer, imgIG)
+            vals = np.multiply(imgS, weights)
+            val = np.sum(vals) / np.sum(weights)
+            img2[i, j] = val
+    return img2
+
+
+def parse_args(args: list) -> tuple:
+    filename = args[1] if args[1:] else "../image_data/lena.jpg"
+    spatial_variance = float(args[2]) if args[2:] else 1.0
+    intensity_variance = float(args[3]) if args[3:] else 1.0
+    if args[4:]:
+        kernel_size = int(args[4])
+        kernel_size = kernel_size + abs(kernel_size % 2 - 1)
+    else:
+        kernel_size = 5
+    return filename, spatial_variance, intensity_variance, kernel_size
+
+
+if __name__ == "__main__":
+    filename, spatial_variance, intensity_variance, kernel_size = parse_args(sys.argv)
+    img = cv2.imread(filename, 0)
+    cv2.imshow("input image", img)
+
+    out = img / 255
+    out = out.astype("float32")
+    out = bilateral_filter(out, spatial_variance, intensity_variance, kernel_size)
+    out = out * 255
+    out = np.uint8(out)
+    cv2.imshow("output image", out)
+    cv2.waitKey(0)
+    cv2.destroyAllWindows()