unit 3 - data representation

exported from anki for the eoy grind

what are examples of bitmap image file formats?

bmp, jpg, gif, png, tiff

why do we have different image file formats?

for different amounts of storage and different uses

what are bitmap images made up of?

pixels

what is a pixel?

the smallest identifiable area of an image

what is stored in each pixel?

a single colour represented by a binary value

how can a pixel’s colour be changed?

by changing its binary value

what is image resolution?

the concentration of pixels within a specific area

how is image area defined?

by image width and height in pixels

give an example of image dimensions in pixels.

1920 x 1080

what does ppi stand for?

pixels per inch

what does dpi stand for?

dots per inch

what is a typical screen resolution?

72 ppi

what is print quality resolution?

300 dpi

how is a bitmap image created?

each pixel is given a binary value representing a colour

if one bit per pixel is used, how many values are possible?

2 values (0 and 1)

with 1 bit per pixel, what does 1 represent?

black

with 1 bit per pixel, what does 0 represent?

white

how many colours can 1 bpi represent?

2 colours

how many colours can 2 bpi represent?

4 colours

how many colours can 3 bpi represent?

8 colours

what is the formula to calculate number of colours from bits per pixel?

2^number of bits

what happens to file size if the number of colours increases?

file size increases

what happens to file size if the number of pixels increases?

file size increases

what happens to file size if the physical size increases but pixel count stays the same?

no change in file size

what is compression

name given to algorithms which reduce file size

what is decompression

the process where compressed data is restored to original format

what are the two compression types

• lossy
  - lossless

is lossy better than lossless + why

no as it permanently loses some data

what are lossy comrpession artefacts

small artefacts like pixellation

how does lossless image compression work

the algorithm finds groups of repeating data and records the data once along with the number of repetitions

lossless compression types

RLE and huffman trees

what does RLE stand for

run length encoding

to be deleted

okay

how does lossless text compression work

uses repeated patterns in the original text and encodes each pattern in a dictionary

dyk huffman trees

yes

why do we use compression

"

• download times are reduced

• data allowances go further

possible to transmit video and music data streams as fast as they are playing

"

when does buffering happen

video or music streaming causes buffering if the download speed is slower than the playback speed

compressed file formats

• jpg
  - png
  - gif
  - avi
  - zip
  - mp3

to be deleted

okay

nibble

4 bits

byte

8 bits

kilobyte

8000 bits or 1000 bytes

what type of compression is JPG

lossy

what type of compression is png

lossless

what type of compression is zip

lossless

what type of compression is gif

lossy

what type of compression is mp4

lossy

what type of compression is mp3

lossy

what type of compression is FLAC/ALAC

losslesswha

what is JPEG used for

photoswh

what is png used for

images that may include transparency

what is zip used for

document compression

what is gif used for

simple images that may include animation

what is mp4 used for

video file formatw

what is mp3 used for

music format

what is FLAC/ALAC used for

lossless music format