Graphics And Compression

Question 1

What is bit-mapped graphics

Answer 1

Where the image is divided into a grid, each cell is called a pixel and has its own colour

Question 2

What is colour depth in an image

Answer 2

The number of bits used to represent a colour of a single pixel using RGB

Question 3

How do you calculate image file size

Answer 3

Image size(in bits) = bits per colour x number of pixels

Question 4

What is metadata and an example of what is usually stored in it

Answer 4

Data about data and is stored in the same file as the image data

E.g.
-Date created, Width and height, Colour depth and GPS coordinates where taken

Question 5

What is vector graphics

Answer 5

Co-ordinates of objects making up pictures stored as mathematical data. Points are described by a relative distance from the origin. Objects are comprised of paths, which can be scaled and grouped together

Each Paths Features
- Start and end point in coords, Length, Thickness, Colour depth

Question 6

What is Data Compression

Answer 6

The process of reducing the number if bits required to represent data

Question 7

What are the two types of data compression

Answer 7

Lossy - Some of the original image quality is lost forever when decompressed cannot be retrieved

Lossless - The file can be uncompressed, and the original quality of the image can be restored

Question 8

What is run length encoding (RLE)

Answer 8

When there are more than 3 pixels in a row which are the same colour RLE is used, the first byte is the number of pixels in the run and the second is the colour of them

Lossless

Question 9

Name an advantage and a disadvantage of Run length encoding (RLE)

Answer 9

Adv
- Algorithm is very easy to implement and does not require much cpu power
- Computer-generated colour images can also give good compression ratios

Dis
- RLE is only efficient in files which contain lots of repeating data e.g. Spaces in text files or image files that contain lots of black and white

Question 10

Dictionary based method

Answer 10

Lots of common beginnings and ends to words are stored in a dictionary with their own unique number, then these can be put together to form strings using just their unique numbers
Lossless

Question 11

What is JPEG compression

Answer 11

Storing scenery at a reduced resolution versus the main part of the image
E.g. lots of blue sky in an image so reduce colours of blue in it to 1 instead of 16 different shades
Lossy