1. data representation

loss of data

• possible to reduce the resolution and colour depth of images

• any reduction in resolution, colour depth or sample resolution will result in a smaller file size

how can icons be represented?

compressed format where 1=white 0=black

rle frequency/data pairs

run length encoding

how does loseless work?

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

loseless compression

not lose any of the original data

blocks

often result from lossy compression

where can noise be seen

contrasting colours

lossy compression artefacts

results in small mistakes known as ‘digital artefacts’ appearing in images and video

lossy compression

permanently loses data

2 types of compression

- lossy compression - loseless compression

when is compression used?

sound, image, video files

compression

name given to algorithms which reduce file sizes

how are colour values represented?

expressed in the software as denary rgb values and in hexadecimal

colours in a pixel

each pixel has a proportion of red, green and blue

monochrome image representation

represented in binary in a bit pattern

what do portable bitmaps store?

- the image dimensions - black or white with a 0 or 1

pbm monochrome images

portable bitmap

effects of varying colour depth

changing the colour depth of an image will affect the number of colours it can display

16 bits per pixel

2^16 = 65,536 colours

8 bits per pixel

2^8 = 256 colours

higher colour depth =

greater range of colour and quality

how to dictate the bit depth

2^n

what can a pixel represent

an infinite number of colours

4 bit

8 colours

3 bit

6 colours

2 bit

4 colours

1 bit

2 colours

each value represents a ___

colour

image resolution

the number of pixels in the image

pixel

the smallest identifiable area of an image

bitmap is made up of

pixels or picture element

examples of bit-map image file formats

bmp, jpg, gif, png, tiff

lossy file formats are still very popular because

they reduce the file size well

uncompressed audio files examples

wav and aiff

lossless sound formats

flac (free lossless audio codec) alac (apple lossless audio codec) wma lossless (windows media audio)

lossless compression - mp3

lossless compression formats are able to reduce the file size when compressed but do not lose any information

lossy compression - mp3

lossy compression removes sounds that we can’t easily hear or that least affect the perceived playback quality

our hearing range

20-20,000 hz

increasing the sampling rate (frequency) means?

recording more data points

the more frequently we sample the sound ___

more accurately we record the wave height

calculating sound files

file size (bits) = sample rate × resolution × duration

greater the frequency =

greater accuracy, file size

sampling rate

frequency or sample rate per second affects the level of detail in the digital representation

cd sample rate

44,100 hz (44.1 khz)

hertz

- sample rate is usually measured in hertz (hz) - 1 hz = 1 sample per second

sound sampling

the number of samples taken per second

sample resolution

number of bits (audio bit depth) used to record each measurement is known as the resolution

what does the sound sample resolution determine?

how closely the wave is sampled on the y-axis

how is sound sampled?

using a bit depth and sample rate

sound sampling

a measurement of amplitude of a sound wave at a given time

dac

a digital to audio converter (dac) is used to convert digital signals to outputs

adc

an analog to digital converter (adc) is used to convert inputs to digital signals

digital =

not continuous

analog =

continuous

unicode use

for multilingual websites

first step

convert to an integer

always start counting at

1 ONE.

lowercase

97-122

uppercase in ascii

65-90

numeric characters 0 to 9

48 to 57

ascii

american standard code for information interchange has become the standard code used worldwide

two major character sets

ascii and unicode

uppercase and lowercase have ___ value?

different values

every character on the keyboard is represented by a ___

binary value

what system is used for negative numbers?

two's complement

effects of shifts

logical shifts can very quickly multiply or divide a binary number by a factor of two

a binary right shift of two places _

halves the number and rounds down each time

a binary left shift _

doubles the number