Added sepia tone (#1877)

* Add sepia tone

* Add unit test

* technic --> technique

* Update digital_image_processing/sepia.py

Co-Authored-By: Christian Clauss <cclauss@me.com>

* Update digital_image_processing/sepia.py

Co-Authored-By: Christian Clauss <cclauss@me.com>

* Fixed errors after commit changes

* Fixed errors

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

digital_image_processing/sepia.py

@@ -0,0 +1,48 @@
+"""
+    Implemented an algorithm using opencv to tone an image with sepia technique
+"""
+
+from cv2 import imread, imshow, waitKey, destroyAllWindows
+
+
+def make_sepia(img, factor: int):
+    """ Function create sepia tone. Source: https://en.wikipedia.org/wiki/Sepia_(color) """
+    pixel_h, pixel_v = img.shape[0], img.shape[1]
+
+    def to_grayscale(blue, green, red):
+        """
+        Helper function to create pixel's greyscale representation
+        Src: https://pl.wikipedia.org/wiki/YUV
+        """
+        return 0.2126 * red + 0.587 * green + 0.114 * blue
+
+    def normalize(value):
+        """ Helper function to normalize R/G/B value -> return 255 if value > 255"""
+        return min(value, 255)
+
+    for i in range(pixel_h):
+        for j in range(pixel_v):
+            greyscale = int(to_grayscale(*img[i][j]))
+            img[i][j] = [
+                normalize(greyscale),
+                normalize(greyscale + factor),
+                normalize(greyscale + 2 * factor),
+            ]
+
+    return img
+
+
+if __name__ == "__main__":
+    # read original image
+    images = {
+        percentage: imread("image_data/lena.jpg", 1) for percentage in (10, 20, 30, 40)
+    }
+
+    for percentage, img in images.items():
+        make_sepia(img, percentage)
+
+    for percentage, img in images.items():
+        imshow(f"Original image with sepia (factor: {percentage})", img)
+
+    waitKey(0)
+    destroyAllWindows()

digital_image_processing/test_digital_image_processing.py

@@ -9,6 +9,7 @@ import digital_image_processing.filters.sobel_filter as sob
 import digital_image_processing.filters.convolve as conv
 import digital_image_processing.change_contrast as cc
 import digital_image_processing.convert_to_negative as cn
+import digital_image_processing.sepia as sp
 from cv2 import imread, cvtColor, COLOR_BGR2GRAY
 from numpy import array, uint8
 from PIL import Image
@@ -68,3 +69,8 @@ def test_median_filter():
 def test_sobel_filter():
     grad, theta = sob.sobel_filter(gray)
     assert grad.any() and theta.any()
+
+
+def test_sepia():
+    sepia = sp.make_sepia(img, 20)
+    assert sepia.all()