Introduction

• What are we going to learn?

• Course outline.

• Some details.

• Assessment.

• Introduction to media technology and revision.

Course outline

1. Introduction and revision.2. Text and e-mail.3. Audio.4. MIDI.5. Video.6. Graphics. 7. Image manipulation. 8. Compression techniques.9. Video compression 110. Video compression 211. Audio compression.12. Revision.13. Time constrained assignment.

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 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

• 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 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)

Media Technology

Continuous

Static

real-world synthesized

animation

graphics

sound moving images

still images text

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 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

• 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.

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

• 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

• 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

• 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.

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

• 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 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 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

• Does not use individual shapes.

• Whole image contains many pixel elements (pixels).

• Pixels are generally defined by colour alone.

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 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

• 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

• 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.

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

• 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.

• 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 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.

• 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 sizes.

• CD ROM holds about 700 MBytes.

• How much audio?

• How much video?

Data rates and file sizes.

• DVD holds about 15 GByte max.

• How much audio?

• How much video?

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

• 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.

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.

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.