1. Learning Intention
I will learn how a computer stores graphics

2. Computer Graphics Computers store graphics in 2 different ways
vector graphics
bitmap graphics

3. Storing Bitmap Graphics
Bitmap graphics are made up of lots of individual pixels (Picture element).

4. Storing Bitmap Graphics
E.g. 8 pixel x 8 pixel black and white image:
64 bits to store the bitmap.

5. Storing Bitmap Graphics
Good for storing photograph quality images
Can edit a single pixel
For black and white bitmaps:
0 stored for white pixel
1 stored for black pixel

6. Storing Bitmap Graphics
colour bitmaps
the colour depth (bit depth) of a bitmap graphic is the number of bits needed to store the colour of each pixel
more colours = higher colour depth = more bits per pixel = larger file size

7. Storing Bitmap Graphics
Colours
Colour Depth
2 (black+white)
1 bit per pixel (21 = 2) 4
2 bits per pixel (22 = 4) 8
(23 = 8)
1024
(210 = 1024)
16,777,216
24 (True colour)

8. Storing Bitmap Graphics
the resolution is the name given to the number of pixels that the image is made of
Higher resolution = clearer and more detailed picture = larger file size
8 x 8 = 64 bits x 16 = 256 bits

10. Which of these two bitmap pictures will take up the most space on disk
Which of these two bitmap pictures will take up the most space on disk? (assume same colour depth – same number of bits for each pixel)
The colour of each pixel does not affect the file size. A white pixel takes up as much space as a colour pixel. These two pictures are the same size on disk
ipad1 ipad2

11. Bitmap graphics task
Complete #1, #2 and #3 on Task 4 – Computer Graphics
#1 – black and white
#2 – 4 colours
#3 – you create the file

12. Bitmap Questions
What are the two factors that affect the storage size of a bitmap graphic file?
Resolution Bit/Colour Depth
Which file would be larger on disk? A or B and why?
a 10 pixel x 10 pixel black and white only image
a 10 pixel x 10 pixel 4 colour image
B because each of the 100 pixels needs 2
bits, not 1 bit to store it

14. Storing Vector Graphics
Vector graphics are made up of lots of overlapping shapes.
Each shape can be edited independently from the other shapes.

15. Storing Vector Graphics
When you save a vector graphic
file, only instructions to draw the
objects are saved, not the whole
page.
More objects = larger file size
Vector graphic files are small in
size compared to bitmap

16. Storing Vector Graphics
Vector graphic files are stored by storing attributes about each of the objects in the picture.
E.g. for a rectangle
start co-ordinates
fill colour
line colour
length
breadth

17. Vector graphics task
Complete #4 on Task 4 – Computer Graphics

18. Bitmap Graphics – Pros and Cons
Advantages
Disadvantages
Can edit pixel by pixel
Can represent photo-realistic scenes
Range of graphic effects can be applied
Image becomes jagged when scaled
Large file size
Bottom shape “rubbed out” when shapes overlap

19. Vector Graphics – Pros and Cons
Advantages
Disadvantages
Do not lose quality when scaled
Require less storage space
Objects are easily changed
Cannot show photo realistic scenes
Usually require specialist programs to open the files

20. Success Criteria
I can describe how vector and bitmap graphics are stored.