Storing Grpahics - Shawlands Academy
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Transcript Storing Grpahics - Shawlands Academy
Computer
Systems
Nat 4.5 Computing Science
Data Representation
Lesson 4:
Storing Graphics EXTENSION
Data Representation
Computing Science
Bitmap and Vector Graphics
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.
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!
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
National 5
Increasing Bit Depth
Higher colour
Depth = More
Colours
File Size
Increases
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
Step
* 900) * 24bits = 17,280,000 bits
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 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
((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
1: ((Length x dpi) x (Breadth x dpi)) * bit depth
2: Convert into appropriate units
34,560,000 /8 = 34,560,000 bytes
34,560,000 bytes /1024/1024 = 4.119 Mb
National 5
Bitmap Graphics – Pros and Cons
Advantages
Can be manipulated
at pixel level
Can create a wide
array of graphic effects
Can represent photorealistic images
Disadvantages
Requires large storage
space
Image becomes
jagged when scaled
National 5
Vector Graphics – Pros and Cons
Advantages
Do not lose quality
when scaled
Require less storage
space
Objects are easily
moved/manipulated
Resolution
independent
Disadvantages
Cannot be edited at
pixel level
Cannot show photo
realistic scenes
Will usually require
particular applications
to open