1. Bitmap Basics Review
Refresher from Year 8

2. We’ll actually start this new unit by reviewing what we did last year.
Review of Year 8
We’ll actually start this new unit by reviewing what we did last year.
That will remind us about some basic ideas and some continuing themes…
Hello, I’m Herman
Did you
Forget me?!

3. bitmap images binary data
Review of Year 8
Last year’s focus was ‘theory’ with bitmap images and how they’re stored in files as binary data
bitmap images
binary data
So we’ll quickly review the key points because they’ll help our practical work making memes…

4. Review Page

5. Review – Range of Images
Our digital world is filled with all kinds of imagery, from photos & clip art through to animated films
Bitmap Image
Vector Image
3D Animation
e.g. photos
e.g. clip art
e.g. movies
We focused on photos because we all use them LOTS!

6. Review – Bitmaps & Pixels
Bitmaps are a grid of tiny squares or pixels

7. Review – Counting Pixels
How many pixels in this tiny sample?
15 pixels
10 pixels
15 x 10 = ? pixels
150

8. Review – Counting Pixels
How many pixels in the whole photo?
3,519 pixels
2,345 x 3,519 = ? pixels
8,252,055
Imagine you took this photo & clicked ‘share’. How big would the exported photo be?
million 8
megapixels 8
But many colours are there in our bitmap images?

9. Review – Counting Colours
For example, think about the colour ‘blue’
That’s 29 ‘colours’ – just for ‘blue’ !
Each needs a unique binary colour code
So the more binary bits you have…
…the more colour codes you can use!
Let’s recall why more bits is better…

10. bit
byte
8 bits = 1 byte
So how many colour codes can you have with one or more bytes…?

11. 128 64 32 16 8 4 2 1
8 bits = 1 byte = = 1 1 = 1 2 = 1 1 3
256
values
128 64 32 16 8 4 2 1 =
255 1 1 1 1 1 1 1 1

12. 8 bits
1 byte
9 bits
10 bits
11 bits
12 bits
13 bits
14 bits
15 bits
16 bits
2 bytes x2
256
values
65,536values x2
512 x2
32,768
1,024
16,384 x2 x2
2,048
8,196 x2
4,096 x2 x2

13. x2 x2 x2 x2 x2 x2 x2 x2 256 65,536values 16.7 million ? 131,072
1 byte
2 bytes
17 bits
18 bits
19 bits
20 bits
21 bits
22 bits
23 bits
3 bytes
256
values
65,536values
16.7 million
values ?
values x2 x2
131,072
8,388,608 x2 x2
262,144
4,194,304 x2 x2
524,288
2,097,152 x2
1,048,576 x2

14. Images, Pixels & Colours
GIF
JPEG
8 bits = 1 byte
24 bits = 3 bytes
256
16m
Colours
Colours

15. GIF JPEG GIFs & One Byte Sky & sea not ‘smooth’ More bits
8 bits = 1 byte
24 bits = 3 bytes
Sky & sea not ‘smooth’
More bits
GIF can’t do all colours
So more colours
‘Posterised’
‘True colour’
But can do animation!

16. Review Page

17. Review Page

18. JPEGs & Three Bytes
So each of the three primary colours can have a value from 0 to 255
You can write these colour codes in binary (eg )
Or you can use those hex codes like you can in Fireworks (eg FF0000)
But it’s easiest to use decimal RGB codes…
decimal RGB codes

19. Red
Green
Blue
RGB (255, 0, 0) = ?
Red R G B
255 1 1 1 1 1 1 1 1

20. RGB (255, 255, 0) = ? Yellow Red Green Blue R G B 255 255 1 1 1 1 1 1
RGB (255, 255, 0) = ?
Yellow R G B
255
255 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

21. RGB (0,255, 255) = ? Cyan Red Green Blue R G B 255 255 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1
RGB (0,255, 255) = ?
Cyan R G B
255
255 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

22. Your Book
255
255
255
Just so students know what’s coming up