Media Types

N4 & 5 Computing Science

Contents

National 4

• Sound, graphics, video, text

National 5

• Standard file formats:• text: txt, rtf• audio: wav, mp3• graphics: jpeg, bmp, gif, png• video: mp4, avi• pdf • Factors affecting file size and quality,

including resolution, colour depth, sampling rate.

• Calculation of file size for colour bitmap

• Need for compression

Media Types

• Information Systems can contain the following types of media:

• Sound, graphics, video & text

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Sound

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

• Sound files can hold e.g. :• recordings of – Facts / information e.g. Explanations of complex

ideas– Music– Sound effects

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Graphics

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

attractive

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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

• Asimo videos can be found here:-http://asimo.honda.com/asimotv/

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Text

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

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Text files• Text files can be saved in many formats• You need to know about txt and rtf• A .txt file has no information about the format of the

document e.g.– 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– be quicker to transmit across a network

• You can open a .txt file using any text editor or word processor

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Rich Text Format (RTF)

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

and the actual text

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

• It will be larger than an equivalent .txt file

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Questions

1. Describe an advantage of saving a document as an RTF file

2. A document is saved as a txt file and as an RTF file:-

a) Which is larger?b) Why is it larger?c) Which is quicker to transfer across a network?

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

large • 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

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Factors affecting the file size and quality of graphics files

• Resolution

• Colour depth

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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 the quality of the graphic & the greater the file size

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Resolution example 5

Resolution 5

Colour Depth

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

• The greater the colour depth:- – the more colours – the greater the file size

Colour depth Number of possible colours.

1 2 ( black or white)

8 256

16 65,536

24 16,777,216

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How graphics are stored 4/5

Colour Depth5

Questions

3. How does the resolution affect the:-a) the quality of a graphic?b) the file size of a graphic?

4. How does the bit depth affect the:-a) the quality of a graphic?b) the file size of a graphic?

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Calculating the size of a graphic - 1

• Use this formula to calculate the size of a graphic:

File size = number of pixels x bit depth

• File size = 6 x 150 x 4 x 150 x 24 • = 1.54 Megabytes

Colour depth Resolution Dimensions

24 150 dpi 6” x 4“

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Calculating the size of a graphic - 2

• Use this formula to calculate the size of a graphic:

File size = number of pixels x bit depth

• File size = 3664 x 2748 x 16 • = 19.2 Megabytes• Without compression graphic files can be very large

Colour depth Resolution

16 3664 x 2748

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Questions

5. Calculate the file size of these graphics:-

Colour bit depth Resolution Dimensions

a 24 1920 x 1200

b 8 72 dpi 4” x 3”

c 16 3264 x 2448

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5.a) File size = 1920 x 1200 x 24 bits = 55296000 bits = 6912000 bytes = 6750 Kilobytes = 6.592 Megabytes

Colour bit depth Resolution Dimensions

a 24 1920 x 1200

b 8 72 dpi 4” x 3”

c 16 3264 x 2448

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5.b) File size = 4 x 72 x 3 x 72 x 8 bits = 497664 bits = 62208 bytes = 60.75 Kilobytes

Colour bit depth Resolution Dimensions

a 24 1920 x 1200

b 8 72 dpi 4” x 3”

c 16 3264 x 2448

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5.c) File size = 3264 x 2448 x 16 bits = 127844352 bits = 15980544 bytes = 15606 Kilobytes = 15.3 Megabytes

Colour bit depth Resolution Dimensions

a 24 1920 x 1200

b 8 72 dpi 4” x 3”

c 16 3264 x 2448

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Graphic Files

• You need to know about the following graphic files:

.BMP, .GIF, .JPEG, .PNG

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BitMap (BMP)

• The .bmp format stores color data for each pixel in the image without any compression

• .bmp files can be very large

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Graphics Interchange Format (GIF)

• Each pixel is represented by an 8-bit colour code

• Number of possible colours is 28= 256 • Unsuitable for storing photographic images• Used to represent charts, cartoons, or

drawings • Uses lossless compression to reduce the file

size without losing any of the data about the image

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JPEG• A bit map graphics file format which uses lossy

compression

• Makes the graphic file smaller by changing the colour of some pixels (to match neighbouring pixels) that won’t be noticed by the human eye

• Often used in digital cameras when storing digital photographs

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

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Portable Network Graphics {PNG}

• PNG compresses files• Like GIF format it uses lossless compression• Compresses graphics more than the GIF format

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

• Used for graphics that will be sent across a network because they are lossless and small

• Bit depth of up to 48 bits = variety of 248 colours• Graphic can have a degree of transparency

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Questions6. Name 2 graphic file formats that use lossless

compression7. Name a graphic file format that uses lossy

compression8. Name a graphic file format that does not use

compression9. State 3 facts about the GIF format10.State the graphic file format that is most suitable

for a photo that will be sent across a network

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Practical Task Find a graphic that you like and save it in a folder called

Graphic files. Open the graphic with Paint then save it a number of times

using different file types to complete this table:-

File type Resolution File size Number of colours

Bit Depth Quality

JPEG 329 x 299 82.8 Kb 224 24 Excellent

GIF 329 x 299 256 8

16 colour bitmap

329 x 299 16 4

2 colour bitmap

329 x 299 2 1

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Factors affecting the file size and quality of sound files

• Sampling rate (frequency):– E.g. 44.1 kHz

• Bit depth– E.g. 8 bits, 16 bits

• Time ( seconds) affects the size – but not the quality

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Sampling Rate

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

• This is measured in kHz ( thousands per second) e.g. 44.1 kHz = 44,100 samples per second

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

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Audio sample Bit depth (Sample 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

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Audio Files

• You need to know about these audio file formats:

WAV , MP3

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WAV

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

• Bit depth: 8 bits or 16 bits• Sampling rates: 11.025KHz, 22.05 KHz, or

44.1KHz• Wav files can be very large• 1 minute of sound can take up as much as

27Mbytes of storage

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MP3

• MP3 is a file format for compressing sound files

• It cuts out parts of the sound that human ears cannot hear

• It cuts out quiet sounds when a loud sounds happens at the same time

• It reduces the file size without a noticeable loss of quality

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

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Factors affecting the file size and quality of video files

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

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Video File Formats

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

AVI , MP4

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Audio Video Interleave format (.AVI)

• The 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.

• Maximum resolution is 320 x 240• Maximum frame rate is 30 frames per second• File size limited to 2Gb

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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 and audio compressed using many different combinations of codecs

• (A codec is a program that compresses and decompresses files)

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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

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Comparison of AVI & Mpeg4

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

• 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 - it is dependent on the type of codec contained within the container file

• 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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PDF – Portable Document Format

• PDF was developed in the early 1990s as a way to share documents

• Adobe Acrobat or Foxit Reader are used to display the files

• Used for documents with text and images

• Allows documents to be viewed on different platforms that don’t have the same application software

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Questions

13. Describe the purpose of a of a codec?14. Describe a container file15. Describe the AVI file format16.Describe the MPeg4 file format17.Do AVI and MPeg4 use lossy or lossless

compression?18.Describe the PDF format and explain why it is useful

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File type Uses Type of compression Factors affecting file size

Text files

TXT

RTF

Graphics files

Bit map

Gif

JPEG

PNG

Audio files

WAV

MP3

Video files

AVI

MPEG-4

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Revision

• Create a mind map about Media Types

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