Computer Systems

1 / 13

Computer Systems - PowerPoint PPT Presentation

Computer Systems. Nat 5 Computing Science Data Representation Lesson 4b: Storing Graphics EXTENSION. Lesson Aims. Pupils at National 5 level will be able to: Describe how a vector image is stored Calculate the storage requirements of a bitmap image with colours

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

PowerPoint Slideshow about 'Computer Systems' - latika

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Computer Systems

Nat 5 Computing Science

Data Representation

Lesson 4b:

Storing Graphics EXTENSION

Lesson Aims
• Pupils at National 5 levelwill be able to:
• Describe how a vector image is stored
• Calculate the storage requirements of a bitmap image with colours
• Explain the difference between a vector and bitmap image
• Explain the advantages and disadvantages of bitmap images compared to vector images
Nat 5Vector Graphics
• This image is an example of a vector image.
• A vector image is made up of lots of overlapping shapes
• Each of the shapes can be edited separately from the other shapes.
Nat 5Vector Graphics
• A vector image is stored using

a different method than bitmapped images

• The attributes (or qualities) of each shape are stored.
• EG, the eyes(ellipses) may be stored as:
• Centre X/Y-co-ordinates
• Fill Colour
• Border Style
• Border Colour etc…
National 5Storing Colour Bitmaps
• Storing a colour bitmap is exactly the same as for black and white with one difference - Each pixel is not just black and white but can represent a variety of colours.
• This is done by allocating more than one bit for each pixel:
• 2 bits/pixel = 4 colours
• 4 bits/pixel = 16 colours
• 6 bits/pixel = 64 colours
National 5Colour Bitmaps
• The amount of bits allocated to each pixel is known as the bit depth.
• So an image with 8 bit colour depth could have 256 colours [28 = 256]
• True Colour is defined as an image with 24 bit colour depth. It has 16,777,216 colours! [224 = 16,777,216]
National 5True Colour
• True Colour is defined as an image with 24 bit bit depth.
• The colour code for each pixel is constructed of a single 8 bit number for each of the main 3 additive colours.
• Red, GreenandBlue

RGB Colour Codes

National 5Storage 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) * 24 bits = 17,280,000 bits
• Step 2: Convert into appropriate units
• 17,280,000/8 = 2,160,000 bytes
• 2,160,000 bytes /1024 = 2,109.375 KB
• 2,109.375 Kb/1024 = 2.06 MB
National 5Storage Space: Example 2
• A 16 bit colour image is 4 inches by 6 inches with a resolution of 300dpi.
• Step 1: (Length x dpi) x (Breadth x dpi)
• (4*300) * (6*300)= 2,160,000 pixels
• Step 2: number of pixels * bit depth
• 2,160,000 * 16 = 34,560,000 bits
• Step 3: Convert into appropriate units
• 34,560,000 /8 = 4,320,000 bytes
• 4,320,000 bytes /1024 = 4,218.75KB
• 4,218.75KB /1024 = 4.119 MB

National 5

Bitmap Graphics – Pros and Cons

Requires large storage space

Image becomes jagged when scaled

• Can be manipulated at pixel level
• Can create a wide array of graphic effects
• Can represent photo-realistic images

National 5

Vector Graphics – Pros and Cons

Cannot be edited at pixel level

Cannot show photo realistic scenes

Will usually require particular applications to open

• Do not lose quality when scaled
• Require less storage space
• Objects are easily moved/manipulated
• Resolution independent