Image representation - 87 - 91

Question 1

how can images in computers be stored

Answer 1

as bitmaps or vectors

Question 2

difference between bitmaps and vectors

Answer 2

• bitmaps use single discrete, individual pixels of colour, which make up image
• whereas a vector uses lists of information and mathematical equations to draw an image based on the data

Question 3

how to calculate size of image in pixels

Answer 3

width in pixels x height in pixels

Question 4

what is a pixel

Answer 4

every dot of colour in the image

Question 5

what is resolution

Answer 5

• number of pixels per inch (ppi or dpi)
• measured in pixels per inch

Question 6

what is colour depth

Answer 6

number of bits stored for each
pixel.
- n bits gives 2^n combinations

Question 7

How many bits are usually in modern images?

Answer 7

24

Question 8

how to calculate storage requirement for bitmaps

Answer 8

height in pixels x width in pixels x colour depth

Question 9

relationship between the quality, colour depth, and file size

Answer 9

as the quality and colour depth of an image increases, its file size increases

Question 10

what is metadata

Answer 10

data about data
- is stored along with the actual bits which make up the image and increase the overall file size

Question 11

examples of metadata

Answer 11

• dimensions
• colour depth
• width and height in pixels
• location
• creation date
• file name

Question 12

examples of information needed to draw a vector image

Answer 12

• fill colour
• radius
• outline colour and width
• coordinates

Question 13

advantages of vector graphics

Answer 13

• individual parts of the image can be manipulated independently
• the image can be scaled without loss of quality
• if an object id deleted, the software knows what is behind it
• Vector graphics are resolution independent;
• Images saved as vector graphics (typically) take up less storage space // can be
  transmitted more quickly than an (equivalent) bitmap

Question 14

disadvantages of vector graphics

Answer 14

• cannot easily replicate an image with continuous areas of changing colours
• basically cant do the advantages of bitmap

Question 15

advantages of bitmapped graphics

Answer 15

Can represent images with complex textures // lots of variation in colour

• Can represent images that are not composed of regular shapes;
• used in photographs, scanned images

Question 16

disadvantages of bitmapped graphics

Answer 16

• generally take up more memory and file storage
• images don’t scale very well, they become pixelated the larger they get

Question 17

describe how a vector graphic is represented

Answer 17

• image is represented as object
• properties of objects are stored
• a property is given, eg fill colour

Question 18

explain why compression is considered necessary for images on the web

Answer 18

transmission of data is faster, and used less data allowance with smaller image files

Question 19

advantages of vectors over bitmaps

Answer 19

• individual parts of the image can be manipulated
• the parts of the image can be scaled without loss of quality
• if an object is deleted, the software knows what is behind it

Question 20

explain why the amount of storage space taken up by vector graphics is significantly less than the space taken up by bitmaps

Answer 20

• bitmap images store the colour of each pixel, whilst vector graphics do not need to store the colour of each pixel
• images can contain lots of pixels
• vector graphics store properties of the object that an image is composed of, and it takes a small amount of memory to store properties

Question 21

Explain what is meant by “dot” in “dots per inch” when referring to resolution.

Answer 21

Each dot is a pixel; “dots per inch” refers to how many of these pixels are printed or displayed per inch.

Question 22

Describe how a bitmap image is represented and stored on a computer

Answer 22

A bitmap image is represented as a grid/array of pixels, where each pixel is a tiny square of color.
Each pixel’s color is stored as a binary number, and the number of bits used for each pixel determines the color depth and thus the number of colors the image can display.