CS 101 - Introduction to Computing, Spring 2007

Lab 6

This lab assignment will have you write at least two functions in jython that will create a new image that will show a portion from another image. This technique is called cropping.

Reminder

In the ACCC Labs that have JES, it can be found by:

1. Clicking on Start
2. Then click on All Programs
3. Then click on Class Applications
4. Then click on Engineering
5. Finally click on Jython Environment for Students

Cropping an image

Cropping of an image is to take a certain part of image and discard the rest of the image. Once the user has picked an image, we shall create an empty image which will store the resulting cropped image. Then we shall copy the pixels from the part of the original to the new image. "Copying the pixels" is nothing but copying the colors of pixels from original image to the new image. Here is a program to do this:

def cropImage():
  
  #Allow the user to pick up an image file
  file = pickAFile()

  #print the file name user chose
  print file

  #now convert the image in JES format
  pic = makePicture(file)

  # decide the size of new image
  newWidth = 100
  newHeight = 150

  #now create a new image in JES format
  new_pic = makeEmptyPicture(newWidth, newHeight)

  # now decide starting with which part of image
  # we should crop the image
  start_x = 50
  start_y = 100

  # so we will crop the image starting from pixel
  # at row 100 column 50 and size of the image would be
  # 100 columns and 150 rows.

  for x in range(1, newWidth+1):
    for y in range(1, newHeight+1):

      # get pixel from original image
      orig_pixel = getPixel(pic, x+start_x, y+start_y);

      # get pixel from new image
      new_pixel = getPixel(new_pic, x, y);

      # get the color from original pixel
      c = getColor(orig_pixel)

      # set the color of new pixel to c
      setColor(new_pixel, c)

  # Now display the new image
  show(new_pic)

  # save the new image
  writePictureTo(new_pic, pickAFile())

Lab Assignment 6

Create a file using JES that will:

1. Contain a comment indicating
   • your Name,
   • Net-ID,
   • Course Name,
   • Assignment Name and
   • a short description of the assignment

2. Contain a JES function that will
   • allow the user to pick an image using pickAFile().
   • call the function cropImage () twice.

     Each call will send the image selected by the user but must crop a different section of the image and crop a different sized section image. You are to crop an interesting item from the original image and not just some random location. You will also be required to submit your image with your JES program file. The BlendIn.jpg image offers a few interesting spots that could be cropped. You may use this image or any other image of your choosing. You may wish to use the JES pictureTool to help find the x and y coordinates of different interesting sections of an image.

3. Contain a JES function called cropImage () that will:
   • take 5 parameters:
     1. the image to be cropped
     2. the x position were the cropping is to start
     3. the y position were the cropping is to start
     4. the x position were the cropping is to end
     5. the y position were the cropping is to end
   • verify that the starting x position is less than the ending x position
   • verify that the starting y position is less than the ending y position
   • verify that the x and y positions are within the boundaries of the original image
   • create a new empty image just large enough to hold the cropped image. You are expected to use makeEmptyPicture () for this.
   • copy the pixels from the original images passed in as the parameter to the new image
   • display the new cropped image
   • allow the user to save the new cropped image where the name of the file is determined by using pickAFile().
   This function may call other functions that are built-in to JES or that you have written. Note that the code give above is close to what is needed here but it is not exact. If any of the verify checks fail, print out a good error message and return from the function.

Submittal of the Lab Assignment

• You are submit your program electronically by placing it in the digital drop box in blackboard.
• You are also required to submit the image that you selected the x-start, y-start, x-end and y-end values.
• Programs that are correct and submitted by noon on the Wednesday the lab assignment is discussed will receive an extra 10% on the score of the lab.
• When saving your program, use a meaningful name like lab6.py.
• When submitting your lab assignment, place all of the needed files it in a zippped folder (even if you are only submitting one file) with the name of yournetid_lab# and submit that zipped folder to the digital drop box. For instance, if your net id is abc32 then the folder name should be abc32_lab#6.

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