Binary Image Representation

Binary Image Representation
Year 8

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Slide 1: Diapositive
ComputingLower Secondary (Key Stage 3)

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Binary Image Representation
Year 8

Slide 1 - Diapositive

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.


Slide 2 - Diapositive

Starter

Slide 3 - Diapositive

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

Slide 4 - Question ouverte

Main Activity

Slide 5 - Diapositive

What are the different types of images?

Slide 6 - Diapositive

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.

Slide 7 - Diapositive

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.

Slide 8 - Diapositive

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”.

Slide 9 - Diapositive

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.

Slide 10 - Diapositive

Let's try and make our own Bitmap.

Slide 11 - Diapositive

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

Slide 12 - Diapositive

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.

Slide 13 - Diapositive

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.

Slide 14 - Diapositive

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?

Slide 15 - Diapositive

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.

Slide 16 - Diapositive

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 1280 by 800 pixels which works out as (1280 x 800) 1,024,000 pixels to cover the whole screen.

Slide 17 - Diapositive

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.

Slide 18 - Diapositive

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

Slide 19 - Diapositive

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.

Slide 20 - Diapositive

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.

Slide 21 - Diapositive

Research Task
Click on this link

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

Slide 22 - Diapositive

What is your fact?

Slide 23 - Question ouverte