Definitely Not Photoshop

Announcements

• Problem Sets 5 and Midterm #2 grading were posted last week

• Although the majority did well, I’m considering curving the grades across by 10%

• Grading of project 1 to be published soon on canvas

  • It appears you’ve got some feedback already.

• My version of solution to Midterm #1 exam is posted in this week module

• Feeling that things are not going as expected and need to discuss?

  • Please come and see me to discuss.
  • From my assessment, almost everyone turning in assignments are doing okay

• Project #3 ImageShop is posted and is due next week Monday 8th Apr at 10pm

• Polling: https://www.polleverywhere.com/agbofred203

Review Question

class Pet:
    def __init__(self, name, color, age):
        self.name = name
        self.color="black"
        self.age = age

    def bmi(self, weight, height):
        if weight/height > 2:
            self.age = self.age*2
        else:
            self.age += 1
dog = Pet("Loly", "brown", 2)
dog.bmi(180,45)
print(f'{dog.name}, {dog.color}, {dog.age}')

Introducing ImageShop

• While you are refreshed from spring break, the next project is starting today and will be due next week Monday
• Taking a moment today to introduce Imageshop, and the guide is already posted

Starting

• ImageShop initially has only two buttons
  • “Load” will bring up a file selection box where you can chose what image to display
    • Internally, this is handled by a function that returns the chosen file path
  • “Flip Vertical” is the example feature button that flips an image vertically

Big Picture

• Each milestone in ImageShop boils down to:
  • Adding a button to the window to handle a new feature
  • Writing a simple callback function that sets the new image to be equal to the output of a new function you’ll write
  • Writing that function, which will return a GImage type object
• You are always free to write whatever other helper functions you might like!
• ImageShop is the first project to start leveraging multi-file layouts:
  • Some functions will already be provided in GrayscaleImage.py that you can import into your main program
  • You are encouraged to write the necessary functions for Milestone 5 in their own file and import them in accordingly
  • To avoid scrolling madly around trying to find the code you want, this helps with that!

GButtons

• To help facilitate working with buttons, ImageShop introduces a new type called GButton
• Each GButton gets a label and a callback function name that determines what function is called when that button is clicked
• ImageShop will come with a pre-defined add_button function which will take care of adding a new button to the correct part of the screen.
  • You’ll just need to provide it a label and function name to callback to

The Current Image

• ImageShop holds the GImage currently displayed on the window in a variable called gw.current_image
• The variable is specifically added as an attribute to gw so that you will have access to it in any callback function you write
• This will generally be the input to your manipulation functions, since most work with whatever image was currently displayed on the screen
• Your callback function will run set_image on the output of your manipulation function, which will take care of updating the value of gw.current_image

Milestone 1

• Milestone 1 has you adding a “Flip Horizontal” button
  • Add the button
  • Add the action callback function
  • Write a function to manipulate the pixels to flip the image horizontally
• Slightly more complicated than the example function, but not much

Milestone 2

Milestone 3

• Here you’ll add a button to convert an image to grayscale
• If you understand the other library files that have been given to you as part of the project, this project should be the simplest!

Milestone 4

• Here you get to enable a green screen effect!
• Unlike other buttons, when this one is clicked, you should use the file chooser library to prompt the user to select another image
  • This is the image that will be overlaid on whatever image is currently shown on the screen
• You will want to start with an “empty” pixel array with the same dimensions as the background
• Depending on how “green” a pixel is, you will choose between different choices:
  • If green enough, you will copy the pixel from the background image to your pixel array
  • If not green enough, you will copy the pixel from the foreground image to your pixel array

Milestone 5

• Here you’ll implement one algorithm for increasing dynamic contrast across an image!
• Doing so requires several steps and different functions. It can be convenient to place these in their own file and import them into ImageShop.py as needed.
  • Compute all the pixel luminosities
  • Construct a histogram of these luminosity counts
    • Your histogram should have 256 elements, one for each possible luminosity
  • Construct a cumulative histogram using your histogram
  • Use the cumulative histogram to adjust the luminosity of each pixel in the pixel array
• You don’t need to display the visual histograms! But they can be a great way to check that you are doing the other parts correctly.
  • Related to Problem 2 on this week’s PS

Extensions

• Give yourself time for extensions on this project!
• They are easy! Just come up with interesting or cool graphical effects and add a button for them!
• You’ll look at several this week in your section meetings
  • Adding these in your project is encouraged and will be regarded as “sub-extensions”, but come up with your own as well!

Maps and Dictionaries

• A common form of information associates pairs of data values
  • Commonly called a map in computer science
  • Python calls such a structure a dictionary
• A dictionary associates two different values:
  • A simple value called the key, which is often a string but doesn’t need to be
  • A larger and more complex object called the value
• This idea of associating pairs of values is exhibited all over in the real world
  • Actual dictionaries! The words are the keys, the definitions the values.
  • Web addresses! Keys are the urls, the values are the webpage contents.

Creating Dictionaries

• Python dictionaries use squiggly brackets {} to enclose their contents

• Can create an empty dictionary by providing no key-value pairs:

  empty_dict = {}

• If creating a dictionary with key-value pairs

  • Keys are separated from values with a colon :
  • Pairs are separated by a comma ,

  generic_dict = {'Bob': 21, 0: False, 13: 'Thirteen'}