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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.

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Computer Systems

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Computer Systems

Nat 4.5 Computing Science

Data Representation

Lesson 4:

Storing Graphics EXTENSION

Data RepresentationComputing Science

Bitmap and Vector Graphics

National 5Colour 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 5Colour 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 5True Colour
• True Colour is defined as an image with 24bit bit depth.
• This means that 16,777,216 colourscan 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, 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) * 24bits = 17,280,000 bits
• Step 2: Convert into appropriate units
• 17,280,000/8 = 2,160,000 bytes
• 2,160,000 bytes /1024 = 2,109.375 Kb
• 2,109.375 Kb/1024 = 2.06 Mb
National 5Alternate 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 = 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