Add Java and Python code for the following tutorials:

- Changing the contrast and brightness of an image!
      - Operations with images

samples/python/tutorial_code/core/mat_operations/mat_operations.py

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+from __future__ import division
+import cv2 as cv
+import numpy as np
+
+# Snippet code for Operations with images tutorial (not intended to be run)
+
+def load():
+    # Input/Output
+    filename = 'img.jpg'
+    ## [Load an image from a file]
+    img = cv.imread(filename)
+    ## [Load an image from a file]
+
+    ## [Load an image from a file in grayscale]
+    img = cv.imread(filename, cv.IMREAD_GRAYSCALE)
+    ## [Load an image from a file in grayscale]
+
+    ## [Save image]
+    cv.imwrite(filename, img)
+    ## [Save image]
+
+def access_pixel():
+    # Accessing pixel intensity values
+    img = np.empty((4,4,3), np.uint8)
+    y = 0
+    x = 0
+    ## [Pixel access 1]
+    intensity = img[y,x]
+    ## [Pixel access 1]
+
+    ## [Pixel access 3]
+    blue = img[y,x,0]
+    green = img[y,x,1]
+    red = img[y,x,2]
+    ## [Pixel access 3]
+
+    ## [Pixel access 5]
+    img[y,x] = 128
+    ## [Pixel access 5]
+
+def reference_counting():
+    # Memory management and reference counting
+    ## [Reference counting 2]
+    img = cv.imread('image.jpg')
+    img1 = np.copy(img)
+    ## [Reference counting 2]
+
+    ## [Reference counting 3]
+    img = cv.imread('image.jpg')
+    sobelx = cv.Sobel(img, cv.CV_32F, 1, 0);
+    ## [Reference counting 3]
+
+def primitive_operations():
+    img = np.empty((4,4,3), np.uint8)
+    ## [Set image to black]
+    img[:] = 0
+    ## [Set image to black]
+
+    ## [Select ROI]
+    smallImg = img[10:110,10:110]
+    ## [Select ROI]
+
+    ## [BGR to Gray]
+    img = cv.imread('image.jpg')
+    grey = cv.cvtColor(img, cv.COLOR_BGR2GRAY)
+    ## [BGR to Gray]
+
+    src = np.ones((4,4), np.uint8)
+    ## [Convert to CV_32F]
+    dst = src.astype(np.float32)
+    ## [Convert to CV_32F]
+
+def visualize_images():
+    ## [imshow 1]
+    img = cv.imread('image.jpg')
+    cv.namedWindow('image', cv.WINDOW_AUTOSIZE)
+    cv.imshow('image', img)
+    cv.waitKey()
+    ## [imshow 1]
+
+    ## [imshow 2]
+    img = cv.imread('image.jpg')
+    grey = cv.cvtColor(img, cv.COLOR_BGR2GRAY)
+    sobelx = cv.Sobel(grey, cv.CV_32F, 1, 0)
+    # find minimum and maximum intensities
+    minVal = np.amin(sobelx)
+    maxVal = np.amax(sobelx)
+    draw = cv.convertScaleAbs(sobelx, alpha=255.0/(maxVal - minVal), beta=-minVal * 255.0/(maxVal - minVal))
+    cv.namedWindow('image', cv.WINDOW_AUTOSIZE)
+    cv.imshow('image', draw)
+    cv.waitKey()
+    ## [imshow 2]