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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 ? - malcolm.wilson@northampton.ac.uk
  • 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.
slide10
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.
slide11
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.