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Introduction. What are we going to learn? Course outline. Some details. Assessment. Introduction to media technology and revision. Course outline. Introduction and revision. Text and e-mail. Audio. MIDI. Video. Graphics. Image manipulation. Compression techniques.

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Introduction
Introduction

  • What are we going to learn?

  • Course outline.

  • Some details.

  • Assessment.

  • Introduction to media technology and revision.


Course outline
Course outline

  • Introduction and revision.

  • Text and e-mail.

  • Audio.

  • MIDI.

  • Video.

  • Graphics.

  • Image manipulation.

  • Compression techniques.

  • Video compression 1

  • Video compression 2

  • Audio compression.

  • Revision.

  • Time constrained assignment.


Who where and when
Who, Where and When?

  • Who am I ? – Dr. Malcolm Wilson.

  • Where am I ? – Rm. MR15, but not all the time.

  • Email ? - [email protected]

  • Course notes – eng.nene.ac.uk/~malc.


Who where and when1
Who, Where and When?

  • New topic every week.

  • Assignment 1 – Issued week 9-10, hand in week 18 (After Easter).

  • Assignment 2 – Time constrained assignment in the final class.


Media technology
Media Technology

  • Primarily concerned with the following digital media:

    • Text

    • Graphics

    • Animation

    • Synthesised Sound (Headphones)

    • Digitised Sound (Headphones)

    • Digitised Images

    • Digitised Moving images.

  • Multimedia is the integration of the above.

  • This is NOT a multimedia course.


Media technology1
Media Technology

  • Some of the above are computer generated.

  • Others are digitised representation of real-world data.

  • The computer data which represents these categories may be also subdivided into:

    • Static (images)

    • Continuous (sound, movies)



Data files
Data Files

  • All of the media data have specific file types.

  • The extension identifies the file type.

  • Examples:

    • Mydrawing.gif, “.gif” identifies a graphics file. “gif” stands for “graphics interchange format”

    • Mynoise.wav, “.wav” identifies a sound. “wav” is short for (sound) wave.


Data files1
Data Files

  • Most media data files contain and start with “headers”.

  • “Headers” contain information about the file such as:

    • How long it is.

    • How it should be played back.

    • How it is coded.

  • Media files are often specially coded forms of the original data.


Text

  • Plain text and formatted text.

  • Plain text is usually coded in “ASCII” (American Standard Code for Information Interchange).

  • A 7 bit code which allows 128 characters.

  • Computers usually deal with 8 bits so ASCII appears to “waste” one bit.


Text

  • “ASCII” coded text was originally designed to connect terminals (keyboard and text monitors) to remote computers.

  • Errors could occur in the connection.

  • Bit 8 used for parity checks.


Ascii
ASCII

  • Full list of ASCII codes will appear on my website and will be given as a handout.

  • But common letters and numbers are easy to remember.

  • Upper case letters

    • Add 64 (decimal) (40 (hex)) to position in alphabet.

      • Eg Code for B is 64 + 2 = 66

      • Or 40 + 2 = 42 in hexadecimal.


Ascii1
ASCII

  • Lower case letters

    • Add 96 (decimal) (60 (hex)) to position in alphabet.

      • Eg Code for a is 96 + 1 = 97

      • Or 60 + 1 = 61 in hexadecimal.

  • Numbers

    • Add 48 (decimal) (30 (hex)) to number.

      • Eg Code for 5 is 48 + 5 = 53

      • Or 30 + 5 = 35 in hexadecimal.

  • Working in hex may be easier.


Parity
Parity

  • Since we mentioned it.

  • Error checking mechanism.

  • Odd or even, (but we decide first).

  • In 7 bit code (like ASCII) we use the 8th (MSB) for parity.

  • We set the bit to one or zero to make the total number of 1’s odd (for odd parity) or even (for even parity).


Odd parity
Odd Parity

  • Example 1

    • Say our seven bit number is 011101. There are 4 ones.

    • We add an 8th bit of value 1 to make the total number of ones odd, giving (1)011101.

  • Example 2

    • Say our seven bit number is 010101. There are 3 ones.

    • We add an 8th bit of value 0 to keep the total number of ones odd, giving (0)010101.


Even parity
Even Parity

  • Example 1

    • Say our seven bit number is 001101. There are 3 ones.

    • We add an 8th bit of value 1 to make the total number of ones even, giving (1)001101.

  • Example 2

    • Say our seven bit number is 110101. There are 4 ones.

    • We add an 8th bit of value 0 to keep the total number of ones even, giving (0)110101.


Parity1
Parity

  • Checked by receiving computer to see if there is an error.

  • Can you see a problem with this?

  • Clue - 2 errors.

  • Midi code (for sound synthesiser communication) very similar to ASCII, but no parity.


Graphics vector images
Graphics - Vector Images

  • Image composed and stored as a sequence of preset shapes or objects.

  • Lines, rectangles, ellipses, text etc.

  • Described in terms of size, position, drawing colour, fill colour.

  • Each object’s characteristics can be edited independently while in this graphical form.


Graphics vector images1
Graphics – Vector Images

  • Differs from a bitmap image which we will see later.

  • Often called vector graphics.

  • Common drawing packages allow the creation of this form of image.

  • Once converted into bitmap or (raster form) we can no longer edit individual shapes.


Graphics vector images2
Graphics – Vector Images

  • Example of a graphic vector image created using “Autoshapes”.

My text in red

  • Other popular vector graphic tools are Paint shop pro and Photoshop.


Bitmaps raster images
Bitmaps - Raster Images

  • Does not use individual shapes.

  • Whole image contains many pixel elements (pixels).

  • Pixels are generally defined by colour alone.


Bitmaps raster images1
Bitmaps - Raster Images

  • We cannot edit or change any shape drawn without changing all of the pixels concerned.

  • Microsoft Paint produces Bitmap images.

  • Once a vector graphic image has been converted to a bitmap it cannot be converted back.


Bitmaps raster images2
Bitmaps - Raster Images

  • If we “paste” from a vector graphics image into Paint the pasting process converts the vector graphic to a bitmap.

  • We can no longer edit the pasted image.

  • Try it.

  • Digitisation of real-life images produces bitmap images.


Moving images and animations
Moving images and animations

  • Images may be given the illusion of motion.

  • We display a succession of changing “frames” to give this illusion.

  • Moving raster images are usually called “movies” in computer media jargon.

  • Moving graphics (vector images) are called animations.


Sound
Sound

  • Just like images we can have two forms in the computer.

  • One form remembers the pitch, duration and loudness and individual sound of the notes.

  • This is stored as MIDI (musical instrument digital interface) form.

  • Like vector graphics the sound can be edited by changing the individual characteristics of the notes.


Sound1
Sound

  • Other form relies on digitisation of real life sounds.

  • Sampled sound.

  • A common example of this are “wav” sound wave sounds.

  • Like bitmap images we cannot edit individual notes without changing all of the samples which the note is comprised of.


Digitisation
Digitisation

  • Real-life images and sounds need to be digitised for computer representation.

  • Turning an analogue or continuous signal into a digital signal.

  • There are 3 stages to digitisation.

    • Sampling

    • Quantisation.

    • Coding.


Sample rates and bandwidth
Sample rates and Bandwidth.

  • The bandwidth of audio and video signals can be considered to be the highest frequency carried by the signal.

  • In sound “crispness”.

  • In vision “sharpness”.


Sample rates and bandwidth1
Sample rates and Bandwidth.

  • Sample rates must be (at least) twice the bandwidth

  • High quality audio requires a bandwidth of 20 KHz.

  • A sample rate of 44.1 kHz or 48 kHz is chosen.


Data rates and file sizes
Data rates and file sizes.

  • So an 16 bit audio signal sampled at 44.1 kHz produces 16 x 44100 = 705600 bits per second.

  • Double this for stereo

    • 1411200 or 1.4112 Mbps.

  • High quality video uses a 270Mbps data stream to allow for a 10bit 625 line television picture.


Data rates and file sizes1
Data rates and file sizes.

  • CD ROM holds about 700 MBytes.

  • How much audio?

  • How much video?


Data rates and file sizes2
Data rates and file sizes.

  • DVD holds about 15 GByte max.

  • How much audio?

  • How much video?


Data rates and file sizes3
Data rates and file sizes.

  • Original CD ROM could only deliver data at 1.2 Mbps.

  • 40 x is therefore 48 Mbps.

  • DVD data rate (single speed) 11 Mbps.

  • 16 x now exist giving 176 Mbps.

  • Still can’t do telly?


Compression
Compression

  • Digitised sound and video produces a lot of data.

  • In particular digitised television quality pictures produce data at 270 Mbits/second which is faster than most hard disks, CD roms and networks devices can accommodate.

  • We need to compress data for use on computers.


Compression1
Compression

  • We have two types of compression.

  • Lossy compression and lossless compression.

  • As the names suggest lossy compression loses some of the original signal, while lossless does not.

  • Lossless techniques such as run-length encoding and Huffman coding achieve compression by creating shorter codes. This is not always possible.


Compression2
Compression

  • Lossy techniques rely on throwing away some information which the viewer or listener will not notice too much.

  • Involves changing the data to some other form. (Transform)

  • Most lossy techniques are noticeable.

  • The more lossy compression that is applied, the more the compression effect will be noticeable.


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