CPSC120B
Fundamentals of Computer Science I

Lab 27

File I/O

Write a function called average_file(opened_file), which takes as a parameter an opened file. The opened file is a file that contains only numbers, each on their own line. Your function should return a floating point number, which is the average of all of the numbers from the file.

from io import StringIO #Do not remove. Needed for test cases def average_file(opened_file): 














  

      Write a function
      called non_blank_lines(opened_file), which
        takes an opened file as a parameter.  Your function should
      return a list of
        lines from the file, which contains only lines that are not
      blank.
  

  

from io import StringIO  #Do not remove.  Needed for test cases

def non_blank_lines(opened_file):
  

  

        
  

  





Lighten




  PPM image files are fairly easy to read and write.  Each file
  contains a header (which encodes information about the version of
  PPM, the size of the image, etc.), and then a series of integers
  representing color values on their own line.  Making modifications
  of an existing PPM image requires modifying these color values.
  Simple modifications only require working with an single color
  value, such as lightening an image.





Details



  Create a python program in a file
  called enlightening.py.  This program should read in
  some PPM image file, and write a different PPM image file
  which is the lightened version of the read file.




  In order to lighten an image, you need to take a color value, and
  multiply it by 1.5.  This is the color value that should be written
  to the new file.  Make sure it's an integer!






Example


Before




After




Hint




  
  

    
    
      
  • 
        
    
	  A PPM image has 3 lines at the beginning which encode meta
	  data for the image.  These 3 lines should be copied verbatim
	  into the next image.
        
    
      
    • 
      
  • 
        
    
	  Recall that you can use the int function to
	  convert a floating point value into an integer.
        
    
      
    • 
      
  • 
        
    
	  You will get errors in your image if you write a value
	  greater than 255 in the new image file.  If you need to
	  write a value greater than 255, simply write 255 into the
	  image file.
        
    
      
    • 
    

  





 



  
Challenge

  

    Another common filter people apply to images is a greyscale
    filter.  This filter goes through the images, and converts every
    pixel into a grey color.  A grey pixel is simply a pixel whose 3
    color values are exactly the same.  A simple way to accomplish this
    is to compute the average of the 3 color values for a pixel, and
    write this as the RGB value of each one.
  

  

    Create a program called greyscale.py, which converts
    images to greyscale.
  




Posterize




  While you might not recognize the name "posterize," I'm certain you
  have seen an example of it.  Posterization is a method by which the
  number of colors in the image is reduced.  In the case of the most
  famous example, it was reduced to a 3 color poster.  Here, we are
  going to only use 2 colors: black and white.





Details



  Create a python program in a file
  called posterize.py.  This program should read in
  some PPM image file, and write a different PPM image file
  which is the posterized version of the read file.




  To posterize a picture, you must read 3 color values at a time from
  the file.  Read these 3 colors values and compute the average of
  them.  If the value is less than 128, then you should write three
  0's to the file.  Otherwise, write 3 255's.






Example


Before




After




Hint




  
  

    
    
      
  • 
        
    
	  A PPM image has 3 lines at the beginning which encode meta
	  data for the image.  These 3 lines should be copied verbatim
	  into the next image.
        
    
      
    • 
      
  • 
        
    
	  Recall that you can use the int function to
	  convert a floating point value into an integer.
        
    
      
    • 
      
  • 
        
    
	  Be careful if you are mixing calls to readline
	  while you are also using the for line in
	  input_file type of loop!  The loop is already reading
	  one of the lines for you.
        
    
      
    • 
    

  





 



  
Challenge

  

    Modify your program so that it does some other number of colors.
    In the popular Obama example, they used 4 colors: red, light blue,
    dark blue, and beige.  For this, at least use 3 colors!
  




Submission


Please show your source code and run your programs for the instructor or lab assistant. Only a programs that have perfect style and flawless functionality will be accepted as complete.