Hour of Code: Image Magic with Python Lesson Plan

Overview

This code activity extends on a basic understanding of the programming language Python to explore the world of image manipulation and data representation using the Python Imaging Library. The activity uses conditions and looping to edit images, and explores how more complex coding constructs can be used to efficiently manipulate every pixel in an image.

It is recommended that students have an understanding of input, if statements and for loops in Python before starting this course. Students who have completed the Beginners stream of the NCSS Challenge, Python for Beginners, or Introduction to Programming (Python) should find this an interesting next course. For new programmers we recommend completing the first 6 modules of Python for Beginners before starting.

Learning Objectives

Students will:

• Use input to request string and numerical data from the user
• Learn about opening image files and saving new image files
• Learn about data representation for greyscale and colour images
• Use the Python Imaging library to get and set pixel colours in an image
• Use the Python Imaging library to analyse image size and type
• Use conditions to make decisions when editing images
• Use loops to edit multiple pixels at once in a row
• Use more complex nested looping structures to edit all the pixels of an image

Extended Activities

Mixing colours

When you were dealing with colour images (RGB images) did you notice that it uses red, green and blue as the primary colours? It doesn't use red, yellow and blue like we use for paint.

When mixing light (like the light coming out a computer screen) colours mix differently than when you mix physical things like paint.

Light mixes using an additive colour system - when you add more colour it gets closer to the colour white.
Paint mixes using a subtractive colour system - when you add more colours of paint it gets closer to black.

You can play with mixing different colours of light here.

Analysing photo filters

Take a look at the available filters on an app like Instagram. Compare a filtered image to the original.

• What would you describe the filter as? (bright, dark, red, grey, etc)
• What kinds of edits do you think have been made to create this filter?
• Have the red, green and blue colours been considered together (like we did in our greyscale filter) or does the filter amplify specific colours?

Creating your own filters

Now you know a bit about editing colours can you come up with your own filter? Think about how you want to edit the colours, then try it out in the playground question at the end of the course.

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