What I Should Know
Unit 1 – Bitmap Graphics
Use this checklist to review our unit, ticking each box as you go
1. Binary Basics
I’ve reviewed Binary Basics and so I know: Chips are made from circuits that can be off or on Off and on is represented by 0 and 1 This is called binary A single 0 or 1 is called a bit and 8 bits make a byte In a byte, the place values are 128-64-32-16-8-4-2-1 How to use place values to convert binary to ‘normal’ decimal numbers
2. Bitmap Basics
I’ve reviewed Bitmap Basics and so I know: Images such as photos as called bitmaps Bitmaps are made from a grid of pixels Each pixel’s colour is stored as a binary number The number of bits used is called colour depth For example, with 8 bits you can have 256 colours
3. Types of Image Files
I’ve reviewed Types of Image Files so I know: The details about GIF images The details about JPG images The details about PNG images
4. Key Editing Tools
I’ve reviewed Key Editing Tools so I know: The purpose of these tools: Select, Marquee,
Lasso and Magic Wand
1. Binary Basics
Amazingly, all digital devices like PCs and phones handle data such as text and images using binary numbers.
Binary uses just two digits to represent computer chip circuits
where electric signals are either on or off:
0 = off 1 = on
Each single 1 or 0 is called a bit. But you can’t do much with
just one bit!
So we put eight bits together to make a byte.
Binary bytes look confusing but we use place values to convert
them to decimal numbers like this:
128 64 32 16 8 4 2 1
0 0 1 0 1 0 1 0
32 8 2 = 42
dd/mm/yy
+
+
X 2 X 2
2. Bitmap Basics
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.
0 0 0 0 0 0 0 0
0 1 1 0 0 1 1 0
0 1 1 0 0 1 1 0
0 0 0 0 0 0 0 0
0 1 0 0 0 0 1 0
0 0 1 0 0 1 0 0
0 0 0 1 1 0 0 0
0 0 0 0 0 0 0 0
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:
1 bit = 2 colours
2 bits = 4 colours
3 bits = 8 colours
4 bits = 16 colours
5 bits = 32 colours
6 bits = 64 colours
7 bits = 128 colours
8 bits = 256 colours
dd/mm/yy
x 2
x 2
3. Types of Image Files
There are big differences between these types of image files:
dd/mm/yy
PNG JPG GIF
Colour depth
8 bits 1 byte
Number colours
256 16.8 m 16.8 m
Layers
Trans- parency
Anim- ation
Not smooth
True colour
Editable
layers
24 bits 3 bytes
32 bits 4 bytes
4. Key Editing Tools
These special tools help us edit images in more creative ways.
dd/mm/yy
Select
Marquee
Magic wand
Lasso