Hi and welcome to your first code along lesson!

Reading, writing and displaying images with OpenCV

Let's start by importing the OpenCV libary



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# Press CTRL + ENTER to run this line
# You should see an * between the [ ] on the left
# OpenCV takes a couple seconds to import the first time
import cv2



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import cv2



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# Now let's import numpy
# We use as np, so that everything we call on numpy, we can type np instead
# It's short and looks neater

import numpy as np

Let's now load our first image



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# We don't need to do this again, but it's a good habit
import cv2 

# Load an image using 'imread' specifying the path to image
input = cv2.imread('./images/input.jpg')

# Our file 'input.jpg' is now loaded and stored in python 
# as a varaible we named 'image'

# To display our image variable, we use 'imshow'
# The first parameter will be title shown on image window
# The second parameter is the image varialbe
cv2.imshow('Hello World', input)

# 'waitKey' allows us to input information when a image window is open
# By leaving it blank it just waits for anykey to be pressed before 
# continuing. By placing numbers (except 0), we can specify a delay for
# how long you keep the window open (time is in milliseconds here)
cv2.waitKey()

# This closes all open windows 
# Failure to place this will cause your program to hang
cv2.destroyAllWindows()



In [5]:

    
# Same as above without the extraneous comments

import cv2 

input = cv2.imread('./images/input.jpg')

cv2.imshow('Hello World', input)
cv2.waitKey(0)
cv2.destroyAllWindows()



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import cv2

image = cv2.imread('./images/20170407-IMG_5559.dng')

# OpenCV's 'split' function splites the image into each color index
B, G, R = cv2.split(image)

print B.shape
cv2.imshow("Red", R)
cv2.imshow("Green", G)
cv2.imshow("Blue", B)
cv2.waitKey(0)
cv2.destroyAllWindows()

# Let's re-make the original image, 
merged = cv2.merge([B, G, R]) 
cv2.imshow("Merged", merged) 

# Let's amplify the blue color
merged = cv2.merge([B+100, G, R])
cv2.imshow("Merged with Blue Amplified", merged) 

cv2.waitKey(0)
cv2.destroyAllWindows()


cv2.waitKey(0)
cv2.destroyAllWindows()









    



(171L, 256L)

Let's take a closer look at how images are stored



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# Import numpy
import numpy as np



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print input.shape









    



(830L, 1245L, 3L)

Shape gives the dimensions of the image array

The 2D dimensions are 830 pixels in high bv 1245 pixels wide. The '3L' means that there are 3 other components (RGB) that make up this image.



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# Let's print each dimension of the image

print 'Height of Image:', int(input.shape[0]), 'pixels'
print 'Width of Image: ', int(input.shape[1]), 'pixels'









    



Height of Image: 830 pixels
Width of Image:  1245 pixels

How do we save images we edit in OpenCV?



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# Simply use 'imwrite' specificing the file name and the image to be saved
cv2.imwrite('output.jpg', input)
cv2.imwrite('output.png', input)









    Out[11]:





True



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