Binary Image Representation

• Computing
• Lower Secondary (Key Stage 3)

Binary Image Representation

Year 8

KO: Understand how images can be represented using the Binary number system.

All

• Explain how computers use pixels and binary to store images.

Most 

• Explain how files are saved in bitmaps and how size and colour depth can affect the file size of an image.

Some 

• Identify factors that will affect the quality and file size of an image.
• Describe the difference between bitmaps and vector.

Starter

Does the quality of an image matter? If yes, why?

Main Activity

What are the different types of images?

Vector Graphics 

Vector graphics are constructed using mathematical formulas describing shapes, colors, and placement. Rather than a grid of pixels, a vector graphic consists of shapes, curves, lines, and text which together make a picture.

How vector graphics work with Binary

The colour of each pixel is represented as a binary number so the whole image is therefore stored as a series of binary numbers.

Bitmap Graphics

Bitmaps or Raster graphics are the name given to one way of storing graphics on a computer system.

A bitmap is laid out in a grid format with each box on the grid containing one “Picture element” which is better known as a “Pixel”.

How bitmap graphics work with Binary

Bitmap images are organised as a grid of coloured squares called pixels. Each different colour in the image is stored as a binary number.

Let's try and make our own Bitmap.

Click here to open the file

Drawing an Image - 8 x 8

• Look at the image in the grid on the left. You are going to fill in the grid on the right with either a 1 or a 0 in each box.
  
• 1 = part of the image is showing in the box
  
• 0 = the box is empty
  

Drawing an Image - Continues

Once you have completed the grid then click on the next worksheet called “Final 8 x 8 image” and all the 1’s will be shown as black and the 0’s you entered will be shown as white.

Why isn't your image the same?

• It is not the same quality as the original image.

• This is known as “Pixelated” where the image is made up of large blocks rather than smooth lines.
  

• This can happen to small or poor quality images you copy from the internet when you try to make them larger.
  

Let's try again - 16 x 16 

• Move onto the next worksheet and repeat the process with a 16 x 16 grid.
  
• Have a look at the final 16 bit image on the next worksheet.

• What is the difference?

Adding Colour

• The image you have just created uses 16 x 16 pixels and we are only allowing 1 bit or each pixel to show either 1 for black or 0 for white.

• If we wanted to have colour in the image you would need more bits per pixel so that you can allocate a particular colour rather than just black and white.
  

Image Sizes

• We have only been working on small grids but usually bitmaps have many more pixels to make up the picture and typically have thousands of pixels for one image.

• A typical screen size is 1280by 800 pixels which works outas (1280 x 800) 1,024,000 pixels to cover the whole screen.
  

Colour Images

If we wanted to have colour in the image you would need more bits per pixel so that you can allocate a particular colour rather than just black and white.

What is Image Resolution?

• Resolution is measured in dpi – dots per inch or ppi – pixels per inch​.

A higher resolution means 

•     more pixels, means more.
•     information
• It also means bigger file ​
•    sizes
  

Colour Images

We are going to use a wider range of numbers to make a colour image. Use the numbers 0 to 3 inclusive. Make up your own image using these colours.

Bit's and Colour Depth

How many colours can be saved with 3 bits per pixel?

8

How many colours can be stored with 16 bits per pixel?

65,536

Most images have 24 bit colour which allows over 16 million colours.

Research Task

Click on this link

I want you to find one fact each about Vector and Bitmap graphics.

What is your fact?