Representing Images

Question 1

What is a pixel?

Answer 1

The smallest unit of a bitmap image

Question 2

What is the maximum number of colours that that can be be represented given the colour depth?

Answer 2

2^{colour depth}

The greater the number of bits used to represent each pixel, the greater the number of unique colours that are available for each pixel.

Question 3

What is the colour depth of an image?

Answer 3

The number of bits that are used to encode each pixel

Question 4

What is the size of an image?

Answer 4

The width x the height of the image in pixels

Question 5

What is the resolution of an image?

Answer 5

The number of dots (pixels) in each square inch (PPI)

Question 6

What is a bitmap image?

Answer 6

An image file format made up of pixels which represent a small square of colour

file begins with header

remainder of files is the data for each pixel that makes up the image

Question 7

How do you calculate the file size of a bitmap image?

Answer 7

Image size x Colour depth

Question 8

What is a vector image?

Answer 8

Way of representing images using a series of geometric objects each of which have properties

vector image files stores data such as:
- position of shapes and paths within image
- size of the shapes and paths
- outline and fill colour and path width

Data is used to render vector image when displayed, resulting in small files sizes and images that can be infinitely scaled

vector images can be presented as lists, where the properties of each geometric object that make up the image are stored in the list’s elements as objects such as dictionaries.

Question 9

What are the advantages of bitmap images?

Answer 9

• Can represent photorealistic images
• Each individual pixel can be manipulated and edited

Question 10

What are the disadvantages of bitmap images?

Answer 10

• Often have a larger file size
• As images size is increased the resolution decreases leading to pixelation (not scalable)

Question 11

What are the advantages of vector images?

Answer 11

• Typically have smaller file sizes (typical 50-100KB)
• Image can be infinitely scaled
• Editable and can be easily manipulated as each shape or path that make up image can be individually altered

-Icons, logos, font type interfaces and other computer generated graphics

Question 12

What are the disadvantages of vector images?

Answer 12

• Require to be rendered which requires processing power and time especially for complex images
• cannot be used if colour is likely to vary from pixel to pixel therefore are not suitable for producing complex photo realistic images such as photographs

Question 13

What is in the header for bitmap files?

Answer 13

• metadata (info about image) : GPS, camera, time and date
• colour depth
• resolution
• THIS IS ESSENTIAL INFO NEEDED TO DECODE AND PRESENT IMAGE CORRECTLY