4.1 Digital Multimedia Elements Graphics Audio Video

4.1 Digital Multimedia Elements Graphics Bitmaps A bitmap image is a collection of colour dots called pixels arranged in rows and columns. A pixel is the smallest picture element that can be shown on a computer screen. The number of colours can be displayed in a pixel is determined by the number of bits used to represent the pixel (known as colour depth). The larger the colour depth, the larger the number of colours can be displayed in the image. 2

4.1 Digital Multimedia Elements Graphics Bitmaps Colour depth (bits per pixel) = 1 Number of colours that can be displayed = 21 = 2 File size = 1.3 MB Comparison of images in different colour depths 3

4.1 Digital Multimedia Elements Graphics Bitmaps Colour depth (bits per pixel) = 8 Number of colours that can be displayed = 28 = 256 File size = 10.3 MB Comparison of images in different colour depths 4

4.1 Digital Multimedia Elements Graphics Bitmaps Colour depth (bits per pixel) = 24 Number of colours that can be displayed = 224 = 16,777,216 File size = 30.8 MB Comparison of images in different colour depths 5

4.1 Digital Multimedia Elements Graphics Bitmaps Resolution Is the measurement of the number of pixels per unit length in a bitmap image. Is measured by pixels per inch (ppi). The higher the resolution, the more details of the image can be shown. But the file size of an image will increase dramatically. 6

4.1 Digital Multimedia Elements Graphics Bitmaps Resolution 72 ppi, 99 KB 150 ppi, 351 KB 300 ppi, 1,333 KB Comparison of images with different resolutions 7

4.1 Digital Multimedia Elements Graphics Bitmaps Digital images for screen display are usually stored at a resolution ranging from 72 to 95 ppi. For photograph printing, the images can be stored at a resolution ranging from 200 ppi to 400 ppi. Common file formats of bitmap BMP JPEG GIF 8

4.1 Digital Multimedia Elements Graphics Vector graphics They are composed of a number of objects. A vector object can be a shape, a line or a string of text. The shape and location of vector objects are defined by mathematical formulae. Can rescale and modify every detail of each vector object easily without affecting the quality of vector graphics. 9

4.1 Digital Multimedia Elements Graphics Vector graphics Bitmap Vector graphics Magnification of an image in vector graphic and bitmap format 10

4.1 Digital Multimedia Elements Graphics Vector graphics The file size of vector graphics does not grow rapidly even when more and more vector objects are drawn in the image. The file size of vector graphics is usually much smaller than that of a bitmap image. They suit for representing simple charts, line arts and illustrations. They are not suitable for representing images with complicated colour patterns. Examples of popular vector graphic formats Windows Metafile (WMF) Shockwave Flash (SWF) Postscript (EPS) 11

4.1 Digital Multimedia Elements Graphics Vector graphics Details of the original bitmap image (left) are lost when it is represented in vector graphic format (right). 12

4.1 Digital Multimedia Elements Audio Audio files in a computer are the digitized data of music, speech and any kind of audio signals. The quality of a digital audio file is determined by its bit resolution and sampling rate. Bit resolution Is the number of bits used to represent the amplitude of an audio signal. The higher the number of bits used, the more precise the amplitude of the audio signal will be. 13

4.1 Digital Multimedia Elements Audio Sampling rate Is the number of samples taken each second during the conversion process Is measured in Hz. The higher the sampling rate, the better the quality of the digital audio will be. Audio type Bit resolution Sampling rate (Hz) Voice over telephone 8-bit 11,025 FM broadcast 16-bit 22,050 Compact disc 44,100 DVD 24-bit 96,000 Characteristics of different types of audio 14

4.1 Digital Multimedia Elements Audio Audio file with 16-bit resolution and 44 kHz sampling rate Audio file with 8-bit resolution and 44 kHz sampling rate The smooth 16-bit waveform indicates that it has a better quality than the jagged 8-bit waveform. 15

4.1 Digital Multimedia Elements Audio Audio file with 8-bit resolution and 44 kHz sampling rate Audio file with 8-bit resolution and 11 kHz sampling rate The 44 kHz audio file contains more samples to represent the original audio signal and therefore it is more precise than the 11 kHz audio file. 16

4.1 Digital Multimedia Elements Audio Stereo audio contains two streams of audio signals, known as left sound track and right sound track. Mono audio contains only one sound track. Audio data can be stored either in uncompressed or compressed format. WAV is the most popular type of uncompressed audio file format. WMA and MP3 are examples of compressed audio widely used in portable music players and web pages. 17

4.1 Digital Multimedia Elements Video Is a sequence of full-motion images together with sound tracks. The file size of it can be very large. Videos can be played by using Windows Media Center. 18

4.1 Digital Multimedia Elements Video Factor Description Example Frame size Number of horizontal and vertical pixels on each video picture (frame) Frame size for VCD-PAL is 352 × 288 pixels. Frame size for DVD-PAL is 720 × 576 pixels. Frame rate Number of frames displayed per second Frame rate for both VCD-PAL and DVD-PAL is 25 fps. Frame rate of a MPEG-4 video played in PlayStation Portable is 30 fps. Duration Play time of a video clip - Compression Reduction of quantity of data of video clips by changing the content or the way of representation of video frames VCD: MPEG-1 DVD: MPEG-2 iPod and PlayStation Portable: MPEG-4 Streaming video on the Internet: WMV and RealMedia Colour depth Number of bits used to represent a pixel VCD: 24 or 32 bits DVD: 24 or 32 bits Factors affecting the size of a video file 19

4.1 Digital Multimedia Elements Video The higher the frame size and frame rate, the better the video quality and the larger the file size. A particular compression method has its own specification of compression ratios, frame sizes and frame rates. Different video file formats require different media players and plug-ins. AVI is the most popular standard of uncompressed video. MPEG-1, MPEG-2 and WMV are examples of compressed video file formats. 20

4.1 Digital Multimedia Elements Video WMV File size = 40 MB Frame size = 320 × 240 pixels Frame rate = 25 fps Uncompressed AVI video clip File size = 300 MB Frame size = 720 × 576 pixels Frame rate = 30 fps MPEG-1 (VCD) File size = 52 MB Frame size = 352 × 288 pixels Frame rate = 25 fps Video files can be compressed into different video file formats for different playback media. 21

4.1 Digital Multimedia Elements Video MPEG-2 (DVD) File size = 180 MB Frame size = 720 × 576 pixels Frame rate = 25 fps Uncompressed AVI video clip File size = 300 MB Frame size = 720 × 576 pixels Frame rate = 30 fps MPEG-4 video clip File size = 45 MB Frame size = 320 × 240 pixels Frame rate = 30 fps Video files can be compressed into different video file formats for different playback media. 22

4.1 Digital Multimedia Elements Video MPEG-2 (DVD) File size = 180 MB Frame size = 720 × 576 pixels Frame rate = 25 fps Uncompressed AVI video clip File size = 300 MB Frame size = 720 × 576 pixels Frame rate = 30 fps MPEG-4 video clip File size = 45 MB Frame size = 320 × 240 pixels Frame rate = 30 fps Video files can be compressed into different video file formats for different playback media. 23

4.2 Analogue Data and Digital Data Characteristics of analogue data and digital data Characteristic Analogue data Digital data Way of measurement Continuous signals of amplitude and frequency of the source are measured. Information is represented in discrete form. In other words, a set of finite numbers of symbols (usually ‘0’ and ‘1’) is used to represent a piece of information Efficiency on data storage Low: The physical size of storage media such as cassette tape and video tape are much larger than the corresponding digital storage media. Their life-time is much shorter. High: Data can be stored in compact media such as CD-ROM and flash memory for long term storage. Comparison of the characteristics of analogue data and digital data

4.2 Analogue Data and Digital Data Characteristics of analogue data and digital data Characteristic Analogue data Digital data Efficiency on transmission High rate of transmission error Low rate of transmission error Accuracy of information Accuracy depends on the sampling technique used. Lower accuracy: Not all information is converted and recorded in the process of converting analogue signals to digital signals. Replication Absolute replication is nearly impossible. Data is lost in the replication process. Absolute replication and error-free transmission of data are possible and easy. Comparison of the characteristics of analogue data and digital data

4.2 Analogue Data and Digital Data Characteristics of analogue data and digital data Characteristic Analogue data Digital data Mode of data access Mostly sequential access Direct access is possible, depending on the media used for storage. Efficiency on data analysis Low: Analogue content is difficult to search for, analyze and reconstruct to produce other information. High: Digital contents can be efficiently reused or processed by computers to generate information. Comparison of the characteristics of analogue data and digital data

4.2 Analogue Data and Digital Data Applications of digital data in IT All electronic devices including computers and modern data transmission channels handle data in binary forms. Digital data and computer programs can be represented in sequences of binary numbers. This makes operations of electronic devices on digital data such as storage, transmission, manipulation and duplication highly precise and efficient.

4.2 Analogue Data and Digital Data Applications of digital data in IT Workstation A Workstation B Hard copy Computer network Transfer data Output copy Transfer data Duplicate Store data Transfer processed data Digital camera Hard disk CD-R Printer Daily-life applications of digital data

4.2 Analogue Data and Digital Data Conversion between analogue data and digital data Digitization is the process of converting analogue data into digital data. Digitization involves two procedures Sampling Quantization

4.2 Analogue Data and Digital Data Sampling The process of obtaining discrete sample data from the continuous analogue signal for every fixed time interval Sampling an analogue signal

4.2 Analogue Data and Digital Data Quantization The process of converting the attribute of each sample data into a digital code using a predefined scale The digital code is usually represented by a binary number. Quantizing an analogue signal

4.2 Analogue Data and Digital Data Conversion between analogue data and digital data Original analogue photograph Sample data obtained from the analogue photograph Digital code representation of sample data Digitizing an analogue photograph

4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Audio Sound is inherently analogue. A sound card is an electronic circuit board that is responsible for conversion. Digital audio files can be stored in a large variety of file formats, for example, WAV, MP3, WMA and RA. The quality of digital audio is determined by Sampling rate Bit resolution (number of bits per sample) Number of channels

4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Audio Speakers Monitor Microphone System unit Keyboard Mouse Standard configuration of a computer system for audio recording and playback

4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Audio Since the digital audio is an approximation of the analogue source, the audio playback cannot be the same as the original one. However, higher sampling rate and bit resolution can record and reproduce audio output closer to the original one.

4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Image Analogue images such as photographs or printed materials can be converted into digital images using a scanner. The scanned images are stored as bitmap graphics. The quality of a bitmap graphic is determined by Resolution Colour depth Compression ratio

4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Image Image type Setting Plain text and art line Black & white photo (for screen display) Colour photo (for screen display) Colour photo (for high quality printing) Resolution 300 ppi 72 ppi Colour depth 1 bit / pixel (21 = 2 levels: black and white) 8 bits / pixel (28 = 256 levels of grey-scale). 24 bits / pixel (8 bits for Red, Green and Blue Respectively) (224 ≈ 16.8 million colours) 24 bits / pixel (8 bits for Red, Green and Blue respectively) (224 ≈ 16.8 million colours) Colour mode Halftone Grey-scale RGB File format recommended BMP JPEG Compression No Yes Typical settings for image scanning

4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Image No matter what the scanning settings are, the scanned digital image cannot be the same as the original analogue source. There is always a loss in information during the digitization process. Conversion of an image from an analogue to a digital format

4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Image Printing a digital image on paper and projecting it on a screen are examples of conversion of digital images into analogue images. The colour ranges of different presentation media are different, so the output analogue images deviate from the digital images. The manufacturing quality of the output devices is another factor affecting the appearance of the output images. 39

4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Video To capture television programmes into a computer, we need a TV tuner card to receive TV signals from the antenna. A TV tuner card converts analogue TV signals into a sequence of digital images and digital audio. A video capture card works in a similar fashion except that it receives video sources instead of radio frequencies. Example of video sources Video cassette recorders (VCR) Digital video camera Web cam Digital camera 40

4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Video TV tuner card TV tuner box A TV tuner box (left) and a TV tuner card (right) 41

4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Video The quality of a digital video is determined by the frame size, frame rate and the video compression algorithm. Example of digital video file formats AVI MPEG-1 MPEG-2 WMV MOV RM 42

4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Video Typical video setting for a web cam File format: compressed AVI Frame size: 320 × 240 pixels Frame rate: 12 fps Typical video setting for a digital video camera File format: MPEG-1 Frame size: 352 × 288 pixels Frame rate: 25 fps Examples of different digital video file formats 43

4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Video Modern digital video cameras and web cams contain charge-coupled devices (CCD) used to convert analogue video signals into digital video data in real time. The captured digital video data can be transferred directly to computers through USB or FireWire (IEEE 1394) ports. 44

Charge-coupled device (CCD) 4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Video Digital video camera Charge-coupled device (CCD) A digital video camera (left) and a charge-coupled device (CCD) (right) 45

Charge-coupled device (CCD) 4.2 Analogue Data and Digital Data Conversion of analogue multimedia elements Video Digital video camera Charge-coupled device (CCD) A digital video camera (left) and a charge-coupled device (CCD) (right) 46