Overview

Learning Objectives

0 results forGuest

ID	Skill_name
4	I can explain what a pixel is and how pixels relate to an image and the way images are displayed.
4	I can describe for bitmaps the size in pixels.

🏁 Learning Objective Computer Graphics

Representing Images - Learning Activities

We can use a two-dimensional data array to define an image. Think about the pixels in a digital photograph. The greater the number of pixels, the larger the file size, but higher the image quality.

Create a bitmap image by clicking in the squares below

Binary grid

Characters used to be designed on an 8 x 8 grid, and created using eight numbers from 0-255. Each number was converted to binaryand the resulting pattern of 0s and 1s was used to make a pattern of black and white dots on a single row.

128

64

32

16

8

4

2

1

Design a character by entering numbers from 0-255 in the boxes to the left of the grid. Each number is converted to binary and used to create the pattern of dots.

Task: Spreadsheet Binary Grid

Can you see how the numbers are converted into the patterns of black and white blocks, using binary? If you can see the link between the number and the pattern, then think about how the web page works - maybe you could create something similar in a spreadsheet application?

Task: Adding colour

The system described so far is fine for black and white images, but most images need to use colours as well. Instead of using just 0 and 1, using four possible numbers will allow an image to use four colours. In binary this can be represented using two bits per pixel:

00 – white

01 – blue

10 – green

11 – red

Create a new grid that uses 2 bit values to give 4 colours like the one below

Extension Task: Adding more colour

While this is still not a very large range of colours, adding another binary digit will double the number of colours that are available:

1 bit per pixel (0 or 1): two possible colours

2 bits per pixel (00 to 11): four possible colours

3 bits per pixel (000 to 111): eight possible colours

4 bits per pixel (0000 – 1111): 16 possible colours

Can you make a grid that has more than 4 colours

Just think 16 bits per pixel (0000 0000 0000 0000 – 1111 1111 1111 1111): is over 65 000 possible colours

Computer Graphics