# How are Images and their instructions stored in a computer system?

All the bits of each picture are called pixels. Each pixel is stored as percentage of three colours - Red, Green and Blue. These colours add up to 100% giving the final colour for that pixel. Note that the change in percentages of red, green and blue result in grey (red 34%, green 33%, blue 33%), black (red 43%, green 42%, blue 15%) and yellow (red 51%, green 48%, blue 0%). This is based on Additive Colour Theory, where coloured light adds up to white.

In this image you can see the yellow smiley is made up of many coloured pixels:

## Exercises

• Take some graph paper, pencils and reproduce this tree:

• What if you wanted to decorate this tree with red tinsel, what would you change?

• Try to draw this Smiley face:

• Try it with Hama beads!

# How are Images stored in a computer system?

Computers can store all of the pixel values and this format is call a BitMap - files ending in .bmp. These are very large files as they store every pixel.

Computers can calculate when large parts of the image are the same colour so they don't need to store the data for every pixel. This makes the size of the file smaller. There are many different algorithms for doing this resulting in many different file formats. For example .png, .jpg and .gif.

# How can Images be manipulated by a computer?

## Exercise 1

Your Smiley Face from above, redraw it 2 times bigger!

How did you make it bigger? Did you use more pixels?

## Exercise 3

What image did you learn most from?

What did you learn and what have you shared with others?

Where did the computer store the image, both temporarily and long term?