Pixels and binary digits

This task can be used for formative assessment purposes or as a summative assessment to assess what students have learned as a result of investigating bitmap images, in particular, the way in which binary digits are used to encode individual pixels of an image.

Provide students with the handout: Pixels and binary digits.

Formative assessment

Use the handout: Pixels and binary digits to find out what students now about pixels and the way an image is coded using binary. Ask them to explain the relationship between the image and the grid that contains the 3 digit binary numbers.

To what extent:

• Are students aware that if the grid was made up of only 1 binary digit (a 1 or a 0) then the image would be made up of black or white pixels?
• Do they know what the binary numbers represent ie 111 is white?
• Can they work out how to create their own image by encoding the grid using binary digits?

Summative assessment

To what extent:

• Do they correctly explain the relationship between the coloured pixels and the 3 digit binary numbers?
• Can they correctly match the coloured pixel to the correct 3-digit binary number?
• Can they work out the remaining three bit binary numbers that where not used in the bitmap image?
• Can they create their own image by encoding the grid using binary digits?
• Can they decode someone else’s encoded grid to produce the relevant image made up of?

Use the assessment checklist provided to record comments for each student.

The key active verbs used in the Australian Curriculum: Digital Technologies have been aligned to Bloom’s Revised Taxonomy.

In this task students explain and represent. The related Revised Blooms taxonomy are:

• (explain) Make (an idea or situation) clear to someone by describing it in more detail or revealing relevant facts (ACARA).

and

Applying

• (represent) Use words, images, symbols or signs to convey meaning (ACARA).

This assessment checklist provides a guide to record the student's demonstrated skills and knowledge.

Word and pdf versions of the checklist can be downloaded in the resources section.

Demonstrated knowledge/skills	Yes/No or progressing	Comments
The student explains the way an image is encoded using binary data. 1 bit per pixel produces either a black pixel or a white pixel 3 bits per pixel produces 8 colours The bitmap image provided is used to explain how binary digits are combined to create a coloured pixel. The student explains that an image is made up of individual pixels. The student connects the 3 bit binary digits with the colours represented in the bitmap image The student: can correctly represent the 5 colours. identifies the 3 remaining combinations of binary digits
The student can create their own bitmap image by encoding a grid using binary bit representation. The grid is encoded using binary digits for each grid square The encoded grid produces an image The student can decode someone else’s grid to produce an accurate image

• Assessment checklist (PDF version)
• Assessment checklist (Word version)
• Pixels handout (PDF version)
• Pixels handout (Word version)