1. Computer Systems Nat 4.5 Computing Science Data Representation
Storing Graphics
Computer Systems
Nat 4.5 Computing Science
Data Representation
Lesson 4:
Storing Graphics EXTENSION

2. Data Representation Computing Science
Bitmap and Vector Graphics

3. National 5
Colour Bitmaps
The colour bitmap method is exactly the same as for black and white with one difference.
Each pixel is not black and white but can represent a variety if colours.

4. National 5
Colour Bitmaps
Each pixel has a binary value representing the colour. The amount of colours is known as the bit depth.
So an image with 8 bit colour depth could have 256 Colours
True Colour is defined as an image with 24bit colour depth. 16,777,216 colours!

5. True Colour True Colour is defined as an image with 24bit bit depth.
National 5
True Colour
True Colour is defined as an image with 24bit bit depth.
This means that 16,777,216 colours can be represented.
The colour code for each pixel is constructed of a single 8 bit number for each of the main 3 additive colours.
Red, green and blue
RGB Colour Codes

6. File Size Increases Increasing Bit Depth
National 5
Increasing Bit Depth
Higher colour Depth = More Colours
File Size Increases

7. Storage Space Example . Step 1: (Length x Breadth) * bit depth
National 5
Storage Space Example
A true colour image is 800 pixels by 900 pixels.
Calculate the storage requirements and express the answer in appropriate units .
Step 1: (Length x Breadth) * bit depth
(800 * 900) * 24bits = 17,280,000 bits
Step 2: Convert into appropriate units
17,280,000/8 = 2,160,000 bytes
2,160,000 bytes /1024 = 2, Kb
2, Kb/1024 = 2.06 Mb

8. Alternate Storage Space Example
National 5
Alternate Storage Space Example
Sometimes you will be given the size and the resolution of the image.
One way in which this can be measured is dpi
Dots per inch is the amount of pixels in an inch.
A 16bit colour image is 4 inches by 6 inches with a resolution of 300dpi.
Step 1: ((Length x dpi) x (Breadth x dpi)) * bit depth
((4*300) * (6*300))* 16 = 2,160,000 pixels
Step 2: number of pixels * bit depth
2,160,000 * 16 = 34,560,000 bits
Step 2: Convert into appropriate units
34,560,000 /8 = 34,560,000 bytes
34,560,000 bytes /1024/1024 = Mb

9. Bitmap Graphics – Pros and Cons
National 5
Bitmap Graphics – Pros and Cons
Advantages
Disadvantages
Can be manipulated at pixel level
Can create a wide array of graphic effects
Can represent photo-realistic images
Requires large storage space
Image becomes jagged when scaled

10. Vector Graphics – Pros and Cons
National 5
Vector Graphics – Pros and Cons
Advantages
Disadvantages
Do not lose quality when scaled
Require less storage space
Objects are easily moved/manipulated
Resolution independent
Cannot be edited at pixel level
Cannot show photo realistic scenes
Will usually require particular applications to open