Encoding images, video and sound

Question 1

File types which reduce in quality when compressed

Answer 1

Lossy Files:
jpg(JPEG)
MPEG(video)
H.264(video)
MP3 (music)

Question 2

File types which dont reduce in quality when compressed

Answer 2

Gifs
Tiff
PNG

Question 3

JPEG

Answer 3

lossy/raster
most common image format
you can select a compression level (0-12), this means you can keep the quality but this also keeps a large file size
good for online photos with lots of different colours
-works by averaging the chromincance values over 2x2 pixel squares, then divides into 8x8 pixel blocks and compresses the info in each block as a unit

Question 4

gif

Answer 4

lossless/raster
up to 256 colours ( not many colours, is a limitation)
good for animations, but this is used less so as the internet is a lot faster and can deal with video formats
allows transparancy (jpg does not)
each pixel represented by a byte.

Question 5

png

Answer 5

lossless/ raster
standard for web images (good for large areas of solid limited colours)
can allow a small file size with limited colours
allows transparency

Question 6

RAW files

Answer 6

original file
large file, with highest quality
not standardised, so some software cant read the file from certain cameras
raster files but not techincally images so need to be converted

Question 7

EPS

Answer 7

vector image
mostly used for logos
can contain a raster image but this does not turn it into a vector image

Question 8

SVG s

Answer 8

scalable vector graphics
defined by XML files
can be used with css for styling
popular for icons
specific uses

Question 9

PDF

Answer 9

portable document format
vector format but can contain raster images
common for sending to print and useful as is near universal
can contain many different file formats

Question 10

ADC

Answer 10

Analogue to digital converter - sound is a wave and is analogue so must be converted to a digital format

Question 11

sample rate

Answer 11

digital sound depends on the sample rate, quality is increased with a higher sample rate

Question 12

sampling sound examples

Answer 12

voice sampling (on a phone) is often 8000 samples per sec but cd is is 44100 samples per sec

Question 13

lossless data compression example

Answer 13

zipping or archiving a file

Question 14

how big are pixels

Answer 14

3 bytes, one for red, blue and green (RGB)

Question 15

RGBA

Answer 15

an extension of RGB to include the transparency

Question 16

how are red, green, blue, white and black represented in denary

Answer 16

Red - rgb(255,0,0)
Green - rgb(0,255,0)
Blue - rgb(0,0,255)
White - rgb(255,255,255)
black - rgb(0,0,0)

Question 17

How are red, green blue, white and black represented in hex

Answer 17

red - 0xFF0000
green - 0x00FF00
blue - 0x0000FF
Black - 0x000000
white - 0xFFFFFF

Question 18

What are videos compressed using

Answer 18

an MPEG, original film is digitised into a series of frames

Question 19

frames in an MPEG

Answer 19

I-frames - they are encoded in their entirety
P-frames and B-frames occur between the I-frames and encode changes using relative coding
- reduce redundancy, same white background in the video results in less i frames

Question 20

how frames in an mpeg work

Answer 20

I-frame - most data and act like a jpeg by averaging 8x8 pixel blocks
P-frames are compared with previous frames while b-frames are compared with previous and next frames (all areas that do not change are thrown away

Question 21

how many bytes in an rgb pixel

Answer 21

3

Question 22

how many bits in a pixel

Answer 22

24

Question 23

what is the maximum value of each colour in denary, hex and binary

Answer 23

denary - 255
binary - (11111111)
hex - 0xFF

Question 24

raster images

Answer 24

consists of a bitmap and its size is set by the resolution (number of pixels)
- allow for incredible detail if high res, but big file size
- includes jpeg, bmp, tiff and gif

Question 25

vector images

Answer 25

• described as an image with a collection of lines and curves
• represent images with geometric structurs using vectors that store shape and location (bolded)
• rendering is calculating the vectors
• rasterizing is converting the vectors to bits on display??
• slick design but not lifelike
• include SVG, EPS and PDF

Question 26

why do vector images need to be rastered

Answer 26

so they can be displayed on visual display units

Question 27

bitmap

Answer 27

a collection of encoded pixels

Question 28

text file

Answer 28

a file consisting of sequence of symbols encoded in ascii

Question 29

sampling

Answer 29

technique used to encode sound waves

Question 30

standard compression technique for raster images

Answer 30

GIF

Question 31

standard compression technique for audio

Answer 31

mp3

Question 32

standard compression technique for vector images

Answer 32

SVG

Question 33

standard compression technique for video

Answer 33

mp4

Question 34

how many bytes in RGBA encoding

Answer 34

4

Question 35

total combination of RGB colour codes

Answer 35

16,777,216 (256256256)

Question 36

what is pixellation

Answer 36

this happens when scaling raster images, making the picture bigger makes it appear grainy

Question 37

are vector image files smaller

Answer 37

yes

Question 38

frequency vs temporal masking

Answer 38

Temporal - for a short period of time, the human ear cannot detect softer sounds that would otherwie be audible
Frequency - a sound at one frequency tends to mask softer sounds at nearby frequencies`