DATA REPRESENTATION
IMAGES
COMPRESSION
SOUND
PBM monochrome images
Image resolution
Colour or bit depth
Metadata
LOSSY (JPG, GIF, MP3)
LOSSLESS (PNG, TIFF)
Some of the data is lost and cannot be recovered
Can be used on all types of data
BENEFITS
Greatly reduces file size
Reduces quality of images/sound
Suitable for images, sound and video
Cannot be used on text and executable files
Usually less effective than lossy compression at reducing file size
Can be turned back into original format. Uncompression also known as RLE (Run Length Encoding)
Mostly suitable for documents and executable files
None of the data is lost. It is encoded differently
Speeds up transmission of webpages that use images
Reduces space on disc/servers
Reduces downloads times of video, sound (including speech used for VOIP systems) and image files.
Enables better streaming of music and video
The number of combinations (2n) dictates the bit depth and therefore the number of colours that can be represented
A higher bit depth gives a greater range of colour and a better quality image
A pixel is attributed to a number of n bits
8 bits per pixel = 2 to the power of 8 = 256 colours
Each pixel can represent a finite number of colours
16 bits per pixel = 2 to the power of 16 = 65,536 colours
24 bits per pixel = 2 to the power of 24 = 16, 777, 216
The area is defined by the image width and height in pixels.
Eg... 3264 x 2448
72dpi = standard screen resolution
The more pixels, the clearer the image
300dpi = minimum resolution for quality printing (some glossy images / magazines may be at 1200dpi)
Resolution is the measure of the number of pixels within a specific area
dpi = Dots Per Inch ( modern technology uses PPI (Pixels Per Inch) )
Uses 1 bit per pixel
Store image dimensions
Lowest common denominator monochrome file format
Change 'colours' by changing binary values
PBM - Portable BitMap
Metadata is data about data and is stored in the file and gives the program information
Metadata can hold:
file size
date and time it was saved
type of file
who created it (author)
colour depth and resolution
Conversion
Sound sampling
Calculating sound file sizes
Digitized sound quality
Available file formats
.WAV - uncompressed files
.FLAC or .M4A - lossless compression, slightly smaller files
.MP3 - lossy compression, much smaller files
File size (bits) = sample rate x resolution x seconds
EG. 6 samples x 4 bit resolution x 3 seconds = 72 bits
72 / 8 = 9 bytes
Analogue sound signals are continuous
Digital sound signals are discreet
Sound is digitized by repeatedly measuring and recording the sound wave.
Sounds must be converted into digital form in order to be stored and processed by a computer
An ADC or DAC is used to process the input or output
Sound sampling is when sounds are repeatedly measured and recorded.
Sample resolution - number of bits per sample
The number of bits (audio bit depth) used to record each measurement is also known as the resolution.
More bits used per sample enables the height of the wave to be more accurately measured but increases file size