Media Types N4 & 5 Computing Science

Contents National 4 National 5 Sound, graphics, video, text 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

4/5 Media Types Information Systems can contain the following types of media: Sound, graphics, video & text

4/5 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

Graphics Graphics are very useful for 4/5 Graphics Graphics are very useful for Illustrating facts / information / explanations Making the information system more attractive

Video Video clips are very useful 4/5 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/

Text Information systems can - Display text on a screen 5 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 5 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

Rich Text Format (RTF) Rich Text Format (RTF) 5 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

Questions Describe an advantage of saving a document as an RTF file 4/5 Questions Describe an advantage of saving a document as an RTF file A document is saved as a txt file and as an RTF file:- Which is larger? Why is it larger? Which is quicker to transfer across a network?

The need for compression 5 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

Factors affecting the file size and quality of graphics files 5 Resolution Colour depth

5 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

5 Resolution example

5 Resolution

Number of possible colours. 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

How graphics are stored 4/5 How graphics are stored

5 Colour Depth

Questions How does the resolution affect the:- 4/5 Questions How does the resolution affect the:- the quality of a graphic? the file size of a graphic? How does the bit depth affect the:-

Calculating the size of a graphic - 1 5 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“

Calculating the size of a graphic - 2 5 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

Questions Calculate the file size of these graphics:- 5 Colour bit depth Resolution Dimensions a 24 1920 x 1200 b 8 72 dpi 4” x 3” c 16 3264 x 2448

5.a) File size = 1920 x 1200 x 24 bits = 55296000 bits = 6912000 bytes Colour bit depth Resolution Dimensions a 24 1920 x 1200 b 8 72 dpi 4” x 3” c 16 3264 x 2448 5 5.a) File size = 1920 x 1200 x 24 bits = 55296000 bits = 6912000 bytes = 6750 Kilobytes = 6.592 Megabytes

5.b) File size = 4 x 72 x 3 x 72 x 8 bits = 497664 bits = 62208 bytes Colour bit depth Resolution Dimensions a 24 1920 x 1200 b 8 72 dpi 4” x 3” c 16 3264 x 2448 5 5.b) File size = 4 x 72 x 3 x 72 x 8 bits = 497664 bits = 62208 bytes = 60.75 Kilobytes

5.c) File size = 3264 x 2448 x 16 bits = 127844352 bits Colour bit depth Resolution Dimensions a 24 1920 x 1200 b 8 72 dpi 4” x 3” c 16 3264 x 2448 5 5.c) File size = 3264 x 2448 x 16 bits = 127844352 bits = 15980544 bytes = 15606 Kilobytes = 15.3 Megabytes

Graphic Files You need to know about the following graphic files: 5 Graphic Files You need to know about the following graphic files: .BMP, .GIF, .JPEG, .PNG

5 BitMap (BMP) The .bmp format stores color data for each pixel in the image without any compression .bmp files can be very large

Graphics Interchange Format (GIF) 5 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

JPEG A bit map graphics file format which uses lossy compression 5 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

Portable Network Graphics {PNG} 5 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

Questions Name 2 graphic file formats that use lossless compression 5 Questions Name 2 graphic file formats that use lossless compression Name a graphic file format that uses lossy compression Name a graphic file format that does not use compression State 3 facts about the GIF format State the graphic file format that is most suitable for a photo that will be sent across a network

5 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 256 8 16 colour bitmap 16 4 2 colour bitmap 2 1

Factors affecting the file size and quality of sound files 5 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

Sampling Rate 5 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

Sampling rate 5 The higher the sampling rate the better the quality of the sound + the bigger the file size

Audio sample Bit depth (Sample depth) 5 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

Audio Files You need to know about these audio file formats: WAV , MP3 5 You need to know about these audio file formats: WAV , MP3

WAV WAV is the standard for storing sound files on windows systems 5 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

MP3 MP3 is a file format for compressing sound files 5 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

WAV and MP3 Comparison 5 Note the difference in file size between the .mp3 version and the WAV version

Factors affecting the file size and quality of video files 5 Resolution of each image(frame) Bit depth of each image Frame rate: the number of frames per second Time: in seconds

Video File Formats 5 You need to know about the following Video File Formats: AVI , MP4

Audio Video Interleave format (.AVI) 5 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

Avi AVI files contain the audio and video data in one file 5 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)

MPEG4 5 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 5 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.

PDF – Portable Document Format 5 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

Questions Describe the purpose of a of a codec? 5 Describe the purpose of a of a codec? Describe a container file Describe the AVI file format Describe the MPeg4 file format Do AVI and MPeg4 use lossy or lossless compression? Describe the PDF format and explain why it is useful

5 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

Revision 4/5 Create a mind map about Media Types