Media Types

• Information Systems can contain the following types of media:

• Sound, graphics, video & text

Sound

• Sound files can be very useful when developing an information system.

• Sound files can hold e.g. :• recordings of – Facts / information e.g. click here– Explanations of complex ideas– Music click here– Sound effects : click here

Graphics

• Graphics are very useful for • Illustrating facts / information / explanations• Making the information system more

attractive

Video

• Video clips are very useful • They combine moving images and sound and

can illustrate very complex ideas• They can make the information in a system

readily accessible to everyone e.g.– Here is a video clip of Asimo the robot

• You can even link to a video clip on the internet – http://asimo.honda.com/asimotv/

Text

• Information systems can • Display text on a screen• Hold text files which you can choose to open.

Text files• Text files can be saved in many formats• You need to know about these: txt , rtf• A .txt filehas none of the information about the

formatting of the document such – text style, alignment, fonts, sizes

• Because it lacks formatting information– a .txt file will be smaller than a Rich Text file– will need less storage space and – be quicker to transmit across a network.

• You can open a .txt file using any text editing or word processing program.

Rich Text Format (RTF)

• Rich Text Format (RTF)• A file saved in .rtf has all the formatting

information which a .txt file lacks as well as the actual text.

• It includes all the information about styles, fonts, sizes, paragraphing and indentation

• It will be larger than an equivalent .txt file

The need for compression• Graphic, Sound and Video files can be very

large indeed. Video files can be Gigabytes in size.

• They take up lots of storage space.• They can take a long time to transmit across a

network.• So they need to be compressed:

Factors affecting the file size and quality of graphics files

• Resolution

• Colour depth

Resolution

• The resolution is the number of pixels that make up an image e.g

• 1280 x 1024• 1600 x 1200• 1920 x 1200

The higher the resolution the better quality of the graphic + the greater the file size.

Resolution

Colour Depth

• The colour depth is the number of bits used to represent each pixel

• The greater the bit depth, – the more colours +– The greater the file size

Bit depth Number of possible colours.

1 2 ( black or white)

8 256

16 65,536

24 16,777,216

Colour Depth

Calculating the size of a graphic

• Use this formula to calculate the size of a graphic:– File size = colour bit depth x resolution x dimensions of graphic

File size =

Colour bit depth Resolution Dimensions

24 1920 x 1200 6” x 6“

= 237.3 Megabytes= without compression graphic files can be very large

Graphic Files

• You need to know about the following graphic files:

.BMP, .GIF, .JPEG, .PNG

BitMap (BMP)

• The .bmp format stores color data for each pixel in the image without any compression. and so .bmp files can be very large indeed.

Graphics Interchange Format (GIF)• GIF is based on an 8-bit colour code giving a

maximum of 28, 256, colours. • A maximum of 256 colours means that GIFs are

unsuitable for storing photographic images and is used to represent charts, cartoons, or drawings.

• The GIF file format uses lossless compression to reduce the file size without losing any of the data about the image.

JPEG• is a bit map graphics file format which uses lossy

compression. • This makes the graphic file smaller by cutting out

parts of the graphic, usually colour tones, that won’t be noticed by the human eye.

• is often used in digital cameras when storing digital photographs.

• is not used for storing cartoons or drawings because some of the data is lost and this reduces the quality of the image

Portable Network Graphics {PNG}

• PNG compresses files• Like GIF format it uses lossless compression• It can compress graphics even more than the

GIF format { a PNG file can be up to 25% smaller than the equivalent GIF file}

• Because they are lossless and smaller = very useful for sending across a network.

• it can have a bit depth of up to 48 bits = range of 248 colours.

Factors affecting the file size and quality of sound files

• Sampling rate:– E.g. 44.1 kHz

• Bit depth– E.g. 8 bits, 16 bits

• Time ( seconds)

Sampling Rate

• The sampling rate is the number of samples of a sound wave taken each second.

• This is measured in kHz ( thousands per second)

• E.g. 44.1 kHz = 44,100 samples per second

Sampling rateThe higher the sampling rate the better the quality of the sound + the bigger the file size

Audio sample Bit depth

• The bit depth is the number of bits used to represent each sample of the sound wave.

• The more bits used = the higher the quality = the larger the file size.

Calculating the size of an audio file

• Use this formula to calculate the size of an audio file:

• File size = sampling frequency x bit depth x time x number of channels

• File size =sampling frequency

bit depth per sample

Time ( seconds) number of channels (mono, stereo, quad)

44.1 16 60 2

= 10.1 megabytes

= without compression audio files can be very large.

Audio Files

• You need to know about these audio file formats:

WAV , MP3

WAV

• WAV is the standard for storing sound files on windows systems and

• can be sampled at a bit depth of either 8 bits or 16 bits

• uses one of the following sampling rates: 11.025KHz, 22.05 KHz, or 44.1KHz.

• Wav files can be very large. One minute of sound can take up as much as 27Mbytes of storage.

MP3

MP3 is a file format for for compressing sound files.It cuts out parts of the sound that human ears cannot hear.

It reduces the file size without a noticeable loss of quality

WAV and MP3 ComparisonNote the difference in file size between the .mp3 version and the WAV version

Factors affecting the file size and quality of video files

• Resolution of each image(frame)• Frame rate: the number of frames per second• Time: in seconds

• Use this formula to calculate the size of a video file

File size = resolution x frame rate x bit depth X time

• File size = Resolution Frame rate per

secondBit depth Time in seconds

720 x576 X 25 X 24 X 5400

= 1291 Gigabytes = 1.26 terabytes= without compression video files can be very large indeed

Video File Formats

• You need to know about the following Video File Formats:

AVI , MP4

Audio Video Interleave format (.AVI)

• AVIThe Audio Video Interleave format was developed by Microsoft and is commonly used in Windows applications like Media Player. This format does not have built-in compression.

Avi

• AVI files contain the audio and video data in one file. This allows synchronous audio/video playback of a file.

• AVI is a container format, meaning it can contain video audio compressed using many different combinations of codecs.

MPEG4

• MPEG-4 is an(audio and video) compression method designed specially for low-bandwidth (less than 1.5MBit/sec bitrate) video/audio encoding purposes.

• MPEG-4 can deliver high-quality audio and video over the Internet to desktops, laptops, tablets &smartphones

Comparison of AVI & Mpeg4

• Both AVI and MPEG are lossy formats which sacrifices quality for file size.2.

• Both AVI and MPEG can contain both audio and video data in a file container

• The quality of a video file is not dependent on the type of container file format as it is dependent on the type of codec contained within the container file format.

• H.264 video codec frequently used with the MP4 container is thought to be one of the highest-quality video standards available.

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