Year 8 Unit 2 Bitmap Graphics

Today’s Aims 1 Start to understand the terms bitmap, pixel and resolution 2 Start to grasp how colour depth sets the number of colours in an image 3 See links between how we use binary to handle numbers and colours

Bitmaps You know computers handle different kinds of images – but here’s what makes bitmaps special… Vector 3D Bitmap Shapes & fills Wireframes Pixels e.g. Clip art e.g. Movies e.g. Photos

Pixels Are the tiny coloured squares that make-up bitmap images such as photos… Each pixel is a single colour So each colour needs its own binary code And there are a LOT of pixels in a photo…

Resolution So how many pixels in this tiny sample? 15 pixels 10 pixels 15 x 10 = ? pixels 150

Resolution 2,345 x 3,519 = ? pixels 8,252,055 million 8 megapixels 8 How many pixels in the whole photo? 2,345 pixels 2,345 x 3,519 = ? pixels 8,252,055 million 8 3,519 pixels megapixels 8

2. Bitmap Basics Images such as photos are called bitmaps. x/9/18 Images such as photos are called bitmaps. They are made from a grid of tiny squares called pixels. Each pixel’s colour is stored as a number in binary.

Colour Depth Imagine a computer that works with just 1 bit How many colours could it use? White 1 Black 1 1 bit has 2 values so can handle 2 colours

Each pixel’s colour is stored as a number in binary. 1 1 This example uses just one bit that’s either 0 or 1. So you can only have 2 colours eg black & white. To store more colours, you need more bits. This is called colour depth:

Colour Depth Now imagine the computer can use 2 bits How many colours could it now use? Black White 1 Red Blue 01 00 10 11 1 1 1 1 2 bits have 4 values so can handle 4 colours

Spot anything familiar? Colour Depth Now imagine the computer can use 2 bits How many colours could it now use? Black White 1 Red Blue 01 00 10 11 1 1 1 1 1 1 1 1 Spot anything familiar? 2 bits have 4 values

Spot anything familiar? 1 1 1 1 It’s that same binary number pattern! Spot anything familiar?

Colour Depth Next, what if the computer uses 3 bits How many colours could it cope with now? 4s 2s 1s =0 1 =1 1 =2 1 1 =3 1 =4 1 1 =5 1 1 =6 1 1 1 =7 3 bits have 8 values so can handle 8 colours

Colour Depth Next, what if the computer uses 3 bits How many colours could it cope with now? Black White Red Blue 1 Orange Green Grey Yellow 111 001 110 101 010 100 1 1 1 1 110 011 000 1 1 1 1 1 1 1 1 3 bits have 8 values so can handle 8 colours

Spot anything else familiar? Colour Depth Do you recognise a number pattern here? 1 bit = 2 colours x2 bits = 2 4 colours x2 = bits colours 3 8 x2 = colours 4 bits 16 x2 = colours x2 5 bits 32 = colours x2 6 bits 64 = Spot anything else familiar? 7 bits 128 colours x2 bits 8 = 1 byte 256 colours

Spot anything else familiar? Colour Depth Do you recognise a pattern here? 1 bit = 2 colours x2 2 bits = 4 colours x2 = colours 3 bits 8 x2 = colours 4 bits 16 x2 = colours x2 5 bits 32 = colours x2 6 bits 64 = colours Spot anything else familiar? 7 bits 128 x2 bits = colours 1 byte 8 256

Spot anything else familiar? x2 x2 x2 x2 x2 x2 128 64 32 16 8 4 2 128s 64s 32s 16s 8s 4s 2s 1s 1 1 1 = ? 42 It’s that pattern of place values we used with binary! Spot anything else familiar?

Colour Depth So this number pattern is all about doubling – again! 1 bit = 2 colours bits = 2 4 colours = bits colours 3 8 = 4 bits colours 16 = colours 5 bits 32 = colours 6 bits 64 = 7 bits 128 colours bits 1 byte 8 = 256 colours And here’s another way to show that same pattern…

Can you see the pattern here? 1 bit 2 bits 3 bits 4 bits 5 bits x2 x2 x2 x2 2 values 4 values 8 values 16 values 32 values Can you see the pattern here?

1 bit 2 bits 3 bits 4 bits 5 bits 6 bits 7bits 8 bits 8 bits = 1 byte x2 x2 x2 x2 x2 x2 x2 2 values 4 values 8 values 16 values 32 values 64 values ? values ? values 128 values ? values 256 values

To store more colours, you need more bits. This is called colour depth: 1 bit = 2 colours x2 2 bits = 4 colours x2 3 bits = 8 colours x2 4 bits = 16 colours 5 bits = 32 colours 6 bits = 64 colours 7 bits = 128 colours 8 bits = 256 colours

Today’s Aims 1 Start to understand the terms bitmap, pixel and resolution 2 Start to grasp how colour depth sets the number of colours in an image 3 See links between how we use binary to handle numbers and colours