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

2. Data Representation Computing Science Bitmap and Vector Graphics

3. 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

4. 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

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.  Redgreenblue  Red, green and blue National 5 RGB Colour Codes

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

7. Storage Space Example .  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 5 A true colour image is 800 pixels by 900 pixels. Calculate the storage requirements and express the answer in appropriate units

8. 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 = 4.119 Mb National 5

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

10. 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 Vector Graphics – Pros and Cons National 5