Information Representation and Multimedia PDF

UNIT 1: Information Representation and Multimedia **Data Representation** **Binary** -- base two number system based on the values 0 and 1 only. **Bit** -- abbreviation for binary digit. **One's complement** -- each binary digit in a number is reversed to allow both negative and positive numbers...

UNIT 1: Information Representation and Multimedia **Data Representation** **Binary** -- base two number system based on the values 0 and 1 only. **Bit** -- abbreviation for binary digit. **One's complement** -- each binary digit in a number is reversed to allow both negative and positive numbers to be represented. **Two's complement** -- each binary digit is reversed and 1 is added in the right-most position to produce another method of representing positive and negative numbers. **Sign and magnitude** -- binary number system where the left-most bit is used to represent the sign (0 = + and 1 = --); the remaining bits represent the binary value. **Hexadecimal** -- a number system based on the value 16 (uses the denary digits 0 to 9 and the letters A to F). **Memory dump** -- contents of a computer memory output to screen or printer. **Binary-coded decimal (BCD)** -- a number system that uses 4bits to represent each denary digit. **ASCII code** -- coding system for all the characters on a keyboard and control codes. **Character set** -- a list of characters that have been defined by computer hardware and software. A coding method is necessary so that the computer can understand human characters. **Unicode** -- a coding system that represents all the languages of the world (the first 128 characters are the same as the ASCII code). **[Binary Number system]** - **[Hexadecimal Number system]** - **[ASCII & Unicode]** - Pros Cons ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ---------------------------------------------------------------------------- Very easy to read, write and understand ASCII code, simple for a human being to memorise each character. Small storage and transmission size ( 7 bits for standard ASCII 8bits for extended ASCII) Only works for the English language, limited number of special characters. - +-----------------------------------------------------------------------+ | Pros | +=======================================================================+ | Allowed the use of more European language characters and accents | +-----------------------------------------------------------------------+ | Cons | +-----------------------------------------------------------------------+ | 1 bit longer than ASCII so requires more storage space | | | | Still couldn't support Eastern alphabets/characters | +-----------------------------------------------------------------------+ - Pros ---------------------------------------------------------------------------------------------------------------- Millions of different characters are available due to the larger number of bits per character ( 16 or 32 bits) Cons 2 or 4 times more storage space is taken up per letter **Multimedia.** **Bit-map image** -- a system that uses pixels to make up an image. **Pixel** -- smallest picture element that makes up an image. **Colour depth** -- number of bits used to represent the colours in a pixel, e.g. 8-bit colour depth can represent 2^8^ = 256 colours. **Bit depth** -- the number of bits used to represent the smallest unit in, for example, a sound or image file -- the larger the bit depth, the better the quality of the sound or colour image. **Image resolution** -- number of pixels that make up an image, for example, an image could contain 4096 × 3192 pixels (12738656 pixels in total). **Screen resolution** -- number of horizontal and vertical pixels that make up a screen display. If the screen resolution is smaller than the image resolution, the whole image cannot be shown on the screen, or the original image will become lower quality. **Resolution** -- number of pixels per column and per row on a monitor or television screen. **Pixel density** -- number of pixels per square centimetre. **Vector graphics** -- images that use 2D points to describe lines and curves and their properties that are grouped to form geometric shapes. **Sampling resolution** -- number of bits used to represent sound amplitude (also known as bit depth). **Sampling rate** -- number of sound samples taken per second. **Frame rate** -- number of video frames that make up a video per second. **[Bitmap images]** - - 1. 2. 3. - **[Vector images]** - It is now worth considering whether a vector graphic or a bit-map image would be the best choice for a given application. When deciding which is the better method, we should consider the following: - - - - **[Sound files]** Sound is vibrations that travel through a medium (usually air) from one point to another, caused by rapid changes in pressure within that medium. All sound waves have 2 components -- volume and pitch. - - If the sound is to be used as a music file, it is often filtered first to remove higher frequencies and lower frequencies which are outside the range of human hearing. To convert the analogue data to digital, the sound waves are sampled at a given time rate. The amplitude of the sound cannot be measured precisely, so approximate values are stored. The sampling rate is the number of sound samples taken per second. The higher the sampling rate and/or sampling resolution, the greater the file size. For example, a 16-bit sampling resolution is used when recording CDs to give better sound quality. So, how is sampling used to record a sound clip? - - - Using a higher sampling rate or larger resolution will result in a more faithful representation of the original sound source.  **[Video files]** - - **File Compression.** **Lossless file compression** -- file compression method where the original file can be restored following decompression. **Lossy file compression** -- file compression method where parts of the original file cannot be recovered during decompression, so some of the original detail is lost. **JPEG -- Joint Photographic Expert Group** -- a form of lossy file compression based on the inability of the eye to spot certain colour changes and hues. **MP3/MP4 files** -- file compression method used for music and multimedia files. **Audio compression** -- method used to reduce the size of a sound file using perceptual music shaping. **Perceptual music shaping** -- a method where sounds outside the normal range of hearing of humans, for example, are eliminated from the music file during compression. **Bit rate** -- number of bits per second that can be transmitted over a network. It is a measure of the data transfer rate over a digital telecoms network. **Run length encoding (RLE)** -- a lossless file compression technique used to reduce text and photo files in particular. - **[File compression applications]** *MPEG-3 (MP3) and MPEG-4 (MP4)* - - - - *Photographic (bit-map) images* - *Run-length encoding (RLE)* - **[General methods of compressing files]** All the above file compression techniques are excellent for particular types of files. However, it is also worth considering some general methods to reduce the size of a file without the need to use a lossy or lossless file compression: