- Explain the representation of an image as a series of pixels represented in binary
- Explain the need for metadata to be included in the file such as height, width and colour depth
- Discuss the effect of colour depth and resolution on the size of an image file
Suggested time: 50 mins
I started by displaying a photograph of my Christmas jumper on the board and asking students what an image is made up of. I then explained that Pixel is short for Picture Element and showed the students a close up of my jumper showing each of the individual pixels:
I began by displaying a simple 1-bit image on the board and asked students to suggest how it could be converted to binary:
Next, I asked students how we could represent 4 colours in binary. Once they got the correct answer, I showed them the following example:
Next, I gave each students a pre-printed computer science cracker joke, each with a different challenge attached – tasks based on level of ability. (See below). I then instructed the students to complete the challenge attached to their cracker joke.
I asked some students to share the hexadecimal / binary code of their favourite bitmap image with a classmate to see if they could convert it back to the original image.
Next I wrote an example binary code on the board and asked the students how the computer would interpret the numbers (the idea being for the students to ask questions such as how many colours etc.)
I followed this by asking students what does a computer need to know to be able to convert the image. I then explained that, in order for the computer to interpret the file, the computer needs to know:
- Colour depth – how many bits represent each pixel
- Resolution - Width & Height (in pixels)
I then explained that we call this “metadata”
I finished by recapping the learning objectives using the Pose, Pause, Pounce and Bounce method.
Pose a question to the whole class e.g. Explain how a 16 colour image can be represented in binary
Pause to give students time to digest the question and think of their answer. If the students are engaged, try holding the pause for a little while longer to build up the tension.
Pounce: Quickly, select a student to answer the question. i.e. Insist the answer to the question comes from student A and possibly student B, directly and fast! Obviously, plan in your mind who you are going to direct the questions to before hand.
Bounce the question or student's response on to another student (immediately after the pounce). e.g. Ask them if they agree with the students previous answer and to explain why.
For more information about the Pose, Pause, Pounce and Bounce technique, visit: @teachertoolkit - http://teachertoolkit.me/2013/01/04/pppb-version2/
Suggested time: 50 mins
Keeping the theme of pixels, students were shown an 8-bit image created using touchdevelop. Click here to see example.
Students were then directed to the TouchDevelop Challenge Hour of Code tutorials (touchdevelop.weebly.com/hoc) and asked to create a festive 8-bit image of their very own.
Once completed, students where asked to submit their apps to the TouchDevelop Challenge website: http://touchdevelop.weebly.com/student-blog.html
Below is a sample of some of the artwork created by the students during the lesson: