Representing Images
Overview
Hold a phone screen close enough and the photograph on it stops being a photograph. What you see instead is a grid of tiny coloured squares, laid out in rows and columns, each one a flat single colour. Step back and your eye blends them into a face or a landscape. That grid is the entire secret of how a machine that stores nothing but numbers manages to store a picture: the picture is chopped into squares and each square is written down as a number.
This lesson teaches you the two measurements that describe such an image, its size in pixels and its colour depth, and shows you how those two numbers alone determine the file size. You will calculate file sizes in bits and in bytes, turn a pattern of binary digits into a picture and a picture back into binary digits, and be able to say precisely what a photographer is trading away when they choose a smaller file.
Objectives
- Understand what a pixel is and be able to describe how pixels relate to an image and the way images are displayed.
- Describe the following for bitmaps:
- size in pixels
- colour depth.
- Describe how a bitmap represents an image using pixels and colour depth. Describe using examples how the number of pixels and colour depth can affect the file size of a bitmap image.
- Calculate bitmap image file sizes based on the number of pixels and colour depth.
- Convert binary data into an image.
- Convert an image into binary data.
Mind map
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Lesson Note
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Lesson Evaluation
Congratulations on completing the lesson on Representing Images. Now that youve explored the key concepts and ideas, its time to put your knowledge to the test. This section offers a variety of practice questions designed to reinforce your understanding and help you gauge your grasp of the material.
You will encounter a mix of question types, including multiple-choice questions, short answer questions, and essay questions. Each question is thoughtfully crafted to assess different aspects of your knowledge and critical thinking skills.
Use this evaluation section as an opportunity to reinforce your understanding of the topic and to identify any areas where you may need additional study. Don't be discouraged by any challenges you encounter; instead, view them as opportunities for growth and improvement.
- What does the term pixel stand for? A. Picture element B. Pixel encoding layer C. Point in colour D. Primary index Answer: A
- An image has a colour depth of 4 bits. How many different colours can each pixel be? A. 4 B. 8 C. 16 D. 32 Answer: C
- A bitmap is 10 pixels by 10 pixels with a colour depth of 8 bits. What is its file size in bytes? A. 80 B. 100 C. 800 D. 8,000 Answer: B
- An image is stored at 200 x 100 pixels. It is resaved at 400 x 200 pixels with the same colour depth. How does the file size change? A. It stays the same B. It doubles C. It quadruples D. It halves Answer: C
- An image uses exactly 5 different colours. What is the minimum colour depth needed? A. 2 bits B. 3 bits C. 5 bits D. 8 bits Answer: B
Work through these questions in the app
Work through these questions in the app
Recommended Books
Practice Mock Questions
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