Digitization of Multimedia Elements

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1 MULTI-MEDIA PRODUCTION Basic Multimedia Elements i. Text ii. Graphics iii. Sound iv. Video v. Animations Digitization of Multimedia Elements Analogue and digital signals Analogue signal: a continuous signal which varies over time. Digital signal: a signal represented by discrete symbols such as digits. E.g. an traditional analogue clock vs. a digital clock Digitization Analogue signals Digital signals Sample Digitization analogue signals digitizing device digital signals video in video tape video capture card digital video files (.mpg,.avi) sound captured by microphone sound card digital audio files (.wav,.mp3) image from books scanner digital images (.jpg,.gif,.bmp) real life image digital camera digital images (.jpg,.gif,.bmp) In general, the higher the quality of the digitized information, the larger the size of the digital file Text Merits of Text: Text is used in conveying messages in an accurate and unambiguous way. Compared to other multimedia elements, text is much smaller in size (1 byte for 1 English character, 2 bytes for 1 Chinese character) takes up smaller amount of store and is transmitted quickly. Codes for Characters ASCII (American Standard Codes for Information Interchange). i. Text in English are stored in ASCII codes. ii. ASCII codes can encode a total of 256 (2 8 ) characters, including English alphabets (both upper and lower cases), Arabic digits and some common symbols. Big-5, GB (GuoBiao), HZ (Hanzi). MULTIMEDIA PRODUCTION Page 1

2 i. Text in Chinese are not stored in one single standard codes. ii. They can code at most (2 16 ) characters. iii. For a web page that consists of Chinese characters, the web page constructors must specify the character set used in order to ensure that the users browsers can display the text properly. Formatting Features Character Formatting. It determines the appearance of characters, like colour, typeface, font size and font style. Paragraph Formatting. New paragraphs are created by pressing the Enter key. It includes line spacing, paragraph width and text alignment. Page Formatting. It specifies the size of paper used, orientation (landscape/portrait), margins, header and footer. Text Document Formats Text file (.txt). The files contain text codes only, without any formatting code. Thus it can be edited in all kinds of editors. Rich Text Format (.rtf). It is developed for cross-platform document interchange RTF files are actually ASCII files with special encoding codes to indicate formatting information such as fonts and margins. Word Processing Document (.doc). The files can be edited easily. The formatting codes are softwarespecific. Portable Document Format (.pdf). The files cannot be edited. The plug-in player to view the documents can be downloaded freely. The original format of the source document is preserved. Hypertext Document (.html). An HTML document is also a plain text document containing special codes (HTML tags) which tells Web browsers how to display the document. Creating Text Methods Typing through keyboard. For Chinese, special input methods like (Changjei, Quick, Phonetic, etc) are used. Scanning and then using OCR. Image of text is first captured by a text by an OCR (Optical Character Recognition) software. scanner and then changed to Handwriting ( 手寫板 ). A handwriting recognition device is used. It consists of a touch sensitive plate and a handwriting recognition software. Speech. Voice is captured by a microphone and a sound card. The text is then produced by a voice recognition software. Note that the correctness of spelling can be checked by most word processors. They checks your document for spelling errors by using their main dictionaries, i.e. a file containing most common words. (Refer to notes of Microsoft word. MULTIMEDIA PRODUCTION Page 2

3 Bits and Bytes A bit is the smallest unit of computer data. (0 or 1) 1 byte (B) = 8 bits (b) 1 kilobyte (KB) = 1024 B = 2 10 B 10 3 B 1 megabyte (MB) = 1024 KB = 2 20 B 10 6 B 1 gigabyte (GB) = 1024 MB = 2 30 B 10 9 B 1 terabyte (TB) = 1024 GB = 2 40 B B Graphics Computer graphic images are usually captured i. using digital devices, e.g. stills from digital camera or individual frames of a video from digital video recorder. ii. using scanners. iii. from screen images by pressing the Print Screen key and then pasted on documents of various applications. iv. from clipart and stock photographs from CD-ROMs or web pages. v. from computer drawing using various graphics programs, e.g. Paintbrush ( 小畫家 ), Flash, etc. Bitmap graphics vs. vector graphics (p ) Bitmap graphics. i. Under this system, images are represented as an array of pixels of various colours, e.g. images obtained from digital camera. ii. Advantage: Producing high-quality and photo-realistic images. iii. Common file formats: jpg, gif, png and bmp. Vector graphics. i. Under this system, images are geometric objects such as straight lines, ovals and arcs, e.g. graphs drawn with drawing tools of Word. ii. Advantage: a. The vector graphics can be magnified without the loss of image quality. (no zig-zag along edges) b. In general, for the same graphical image, the vector graphics version occupies less storage space. iii. Common file formats: fh (Freehand), swf (Flash) and wmf (Windows Metafile). MULTIMEDIA PRODUCTION Page 3

4 ** Conversion between vector graphics and bitmap graphics vector graphics outline tracing bitmap graphics rasterisation Bitmap graphics attributes (p ) Pixel. A pixel is the name given to a PICture Element, and refers to the smallest element used for building up a picture in a particular graphics mode. Graphical resolution (Image size). i. The dimension of a bitmap graph, i.e. the number of pixels in length times the number of pixels in width, e.g. 300 x 200. ii. Graphical resolution Output quantity and storage space. Aspect ratio. i. The ratio of the width to the height of an image. ii. If a image has a resolution of 2272 x 1704, its aspect ratio is found as follows: Colour depth. AspectRati o = 2272 :1704= = = 4 : i. The number of bits used to represent the colour of each pixel. ii. It can also be regarded as the maximum number of unique colours. iii. The number of different colours can be assigned to each pixel depends on the number of bits used to represent it. (8 bits 2 8 = 256 colours, 24 bits 2 24 = 16,777,216 colours) Colour models - the coding methods for representing colours i. RGB. ( red green blue ) (24-bit) a. For example, a light blue is represented by #9ACCFF or (154, 204, 255). b. It is commonly used to reproduce colours for screen display or projectors. ii. CMYK ( cyan magenta yellow black ) (32-bit) a. For example, a dark green (100, 50, 100, 0). b. It is commonly used in printers. iii. Grey scale (8-bit) a. From black (0) to white (255) iv. Indexed colour (8-bit, 256 colours) a. Only 256 colours selected from RGB. b. Stored in a colour table. MULTIMEDIA PRODUCTION Page 4

5 Printing Resolution. i. It is measured in dpi (dot per inch), i.e. density of dots. ii. It is usually smaller than that appears on the screen. (Minimum printing resolution may be 150 dpi while that of screen may be around 72 dpi.) Graphics file size The amount of memory to store an uncompressed bitmap image is found as follows: image width x image height x colour depth For example, the uncompressed file size of a 24-bit bitmap image with 800 x 600 pixels is, 800 x 600 pixels x 24 bits/pixel = b = B = KB Short Exercise: find the uncompressed file size of a bitmap image with the following attributes i. 256 colours with a resolution of 300 x 200 pixels 300 x 200 pixels x 8 bits/pixel = x 8 / 8 B = B 58.6 KB (cor. to 1 d.p.) ii. 32-bit colour depth with a resolution of 1600 x 1200 pixels 1600 x 1200 pixels x 32 bits/pixel = x 32 / 8 B = B = 7500 KB 7.32MB (cor. to 2 d.p.) Figure 1: Open a jpeg file using Microsoft Image Editor, then choose properties ( 屬性 ) under the file ( 檔案 ) menu, the following dialog box will be displayed, Colour depth: 2 24 = Image size: 1024 x 768 pixels Different file format for bitmap graphics, Bitmap( BMP ). Uncompressed format. Joint Photographic Experts Group ( JPG ). Lossy compressed format, i.e. not capable to get back the original uncompressed format. Suitable for compressing photos. Graphics Interchange Format ( GIF ). Lossless compressed format. Suitable for drawings. Supporting animation, transparent background and interlaced image. Portable Network Graphics ( PNG ). Similar to GIF. Lossless compressed format with smaller file size than GIF. Not supporting animation. Supporting different degrees of colour transparency. Tag Image File format ( TIF ). Common format for exchanging bitmaps between application programs. Original image format from scanner and fax. Capable of storing multiple images. MULTIMEDIA PRODUCTION Page 5

Figure: If you save a bitmap graphic file as a different file format using Photoshop Elements, one of the following

For lossy compression using JPEG, compression ratio = uncompressed file size : compressed file size ii.

If an image needs to be edited repeatedly, use uncompressed or lossless compression format.

95 99) Adjusting brightness and contrast. Resizing, trimming and rotating graphics. Adjusting sharpness and blur.

6 Figure: If you save a bitmap graphic file as a different file format using Photoshop Elements, one of the following dialog boxes with different options would be displayed as follows, For.gif files Note that: i. For lossy compression using JPEG, compression ratio = uncompressed file size : compressed file size ii. compression ratio image quantity iii. If an image needs to be edited repeatedly, use uncompressed or lossless compression format. The JPEG conversion should be reserved for final publishing. Graphics Editing and Processing (p ) Adjusting brightness and contrast. Resizing, trimming and rotating graphics. Adjusting sharpness and blur. Applying graphics filters. **Note that text on some web pages were saved in graphic format. Why? The text format can be shown exactly even the file is opened by different browsers. Moreover, more special effects can be added to the text to make it more attractive. MULTIMEDIA PRODUCTION Page 6

7 Sound (Ch. 4) Nature of sound When we make a sound, vibrations, called sound waves, are created as follows, wavelength amplitude time A sound is characterized by loudness and pitch. The Loudness, or volume, is related to the height of the wave, i.e. amplitude. The higher the wave peaks, the louder the sound is. The pitch is related to the frequency. The higher the frequency, the higher the pitch is. It is measured in hertz (Hz), i.e. number of vibrations in 1 second. Sampling and audio attributes (p ) Digitisation of sound, i.e. the process of selecting digital audio samples. Sampling rate: the number of times a sample is taken for one-second audio signal (e.g khz, 96 khz). Sample size: the amount of information stored for each sample of a time interval. (e.g. 8 bits, 16 bits) The higher the sampling rate and the larger sampling size, the higher the sampling quality will be. The rule of sampling: Sample Rate > 2 x Maximum Sound Frequency. MULTIMEDIA PRODUCTION Page 7

8 E.g. Audio channels Sample size (bit) Sampling rate (khz) Audio CD FM broadcast AM broadcast i. A recording may include one waveform ( mono ) or two waveforms ( stereo ), which simulates human hearing. ii. The amount of storage space for a stereo recording is twice that for a mono recording. Audio file size i. The amount of memory to store an uncompressed audio file is found as follows: sampling rate x sample size x no. of channels x time ii. For example, the uncompressed file size of a 3-minute stereo recording at a sampling rate of 44.1 khz and with 16-bit sample size is: 44.1 x 1000 Hz x 16 bits x 2 x 3 x 60 s= b = B 30.3 MB (cor. to 1 d. p.) Bit rate i. It is the amount of data passing through a particular point in an audio stream in one second. ii. The file size of an uncompressed audio file can be estimated Bit rate x time iii. For example, if the bit rate of a song is constant and the song lasts for 4 minutes is 128 kbps, the file size should be: 128 x 1000 kbps x 4 x 60s = b = B MB (cor. to 3 d. p.) Codec (p. 129) Audio codec is the hardware or software as a compressor and a decompressor (or a coder and a decoder) of audio files. Encoding bit rate. The bit rate used in compressing the audio file. Audio compression can be either lossy or lossless. MIDI (Musical Instrument Digital Interface) (p ) It stores the musical notes of a music played by an electronic musical instrument, such as an electronic piano or an electronic violin. A MIDI file can be view as a musical score storing digital musical instructions which represent the volume, pitch and duration of the sound from various specific musical instruments. MULTIMEDIA PRODUCTION Page 8

9 By using MIDI software, the musical notes from the score can be edited. MIDI stores codes of musical notes only. Small file size. Preparing Sound Methods Ready-made sound clips from CD-ROM or the web. Recording using a microphone in a computer or mobile phones. Recording MIDI files using MIDI keyboard and other digital musical instruments. Digitising analogue sound from various sources using a sound card. Audio File formats (p ) Wave Format (.wav ). Uncompressed audio format. It supports a variety of sampling rates ( / / 44.1 khz), sample size (8- or 16-bit) and audio channels (mono or stereo). Best audio quality but largest file size. MIDI format (.mid). MPEG-1 Audio Layer-3 (.mp3 ). It is a popular standard for lossy audio compression, which reduces the storage space required for recorded WAV audio. It removes part of the sound signals that our ears cannot detect. It supports streaming. RealAudio / RealMedia (.ra,.rm ). RealAudio is a streaming audio format developed by RealNetworks for delivering quality music efficiently on the Web. It supports lossy compression only. An audio decompression software, RealPlayer, is necessary to play RealAudio. Same audio source may be encoded in different bit-rates. Windows Media Audio (.wma,.asx ). WMA is a compressed streaming format developed by Microsoft and supports both lossless and lossy compression. Advanced Audio Coding (.aac,.m4a ). AAC is a lossy compressed streaming audio format developed by MPEG as successor of MP3. It is used as the default format in iphone and ipod. Audio Editing and Processing (p ) Adjusting volume. Applying fade in and fade out. Trimming audio file. Mixing audio files. Video (Ch. 5) A video is a full motion recording of an event. A frame is one of the still images displayed on the screen. Frames are shown successively to give an illusion of continuous motion. Unlike animation, video begins with continuous motion and breaks it up into frames. MULTIMEDIA PRODUCTION Page 9

10 Video attributes (p ) Frame size. Graphic resolution of an individual frame. Frame size video quantity. E.g. 240 x 180 pixels, 1920 x 1080 pixels. (Beware of the aspect ratio.) Colour depth. Most video have 24-bit colour depth. Frame rate. The number of frames displayed per second. E.g. 12 fps( frames per second ), 30 fps. Audio sampling size and rate. Video frames can be accompanied by audio tracks. Video standards. Different countries use different video standards for broadcasting. E.g. PAL, NTSC. Bit rate. Similar to compressed audio, it is the amount of data passing through a particular point in a video stream in one second. Video file size The amount of memory to store an uncompressed silent video image is found as follows: frame size x colour depth x frame rate x duration For example, the uncompressed silent video file size of a two-minute video with frame size 800 x 600, colour depth 24 bits and frame rate 30 fps is, 800 x 600 pixel/frame x 24 bits/pixel x 30 fps x 2 x 60s = b = B = GB(cor. to 3 d. p.) Short Exercise: find the uncompressed silent video file size of a video with the following attributes: i. 30-second video with frame size 320 x 240, colour depth 24 bits and frame rate 25 fps 320 x 240 pixel/frame x 24 bits/pixel x 25 fps x 30s = b = B = MB(cor. to 1 d. p.) ii. four-minute video with frame size 1024 x 576, colour depth 32 bits and frame rate 24 fps 1024 x 576 pixel/frame x 32 bits/pixel x 24 fps x 4 x 60s = b = B = GB(cor. to 2 d. p.) Video capture card Analogue and digital. i. Digital video source: Digital video camera and video clips from CD-ROM or the web. ii. Analogue video source: Television broadcasting and video cassette recorder. Analogue video signals are sent to the computer through a video capture card, which converts the analogue signals into digital signals, and thus can be processed by the computer. MULTIMEDIA PRODUCTION Page 10

11 Compression of video Compression of video is necessary for reducing file size and enabling live broadcast on the Internet. The standardized compression technique is Moving Picture Expert Groups (MPEG). It may still take too long time to download a entire compressed video file on the Internet. Video streaming allow the client browser start displaying the video before entire file has been transmitted. (Sample file type: ASF, WMV, RM) Sources of Video Digital video clips from CD-ROM or the web. Recording video using digital devices like digital video recorder or digital camera.. Capturing video from various analogue video source (e.g. TV signals) using video capture cards. Video File Formats (p. 111) Audio Video Interleave (.avi ). Video data and audio data are stored in an interleaved manner, so as to improve synchronization of audio playing and video playing. The file size is large and it supports many codecs. Motion Picture Experts Group (.mpg ). The group develops standards for digital video and digital audio. It is a lossy compression file format. It stores only the changes between successive frames. RealVideo (.rv,.rm ). It is a compressed streaming video format developed by RealNetwork and can be played by RealPlayer. Window Media Video (.wmv,.asf ). It is a streaming compressed video format developed by Microsoft and can be played by Microsoft Windows Media Player. QuickTime (.mov ). It is a compressed streaming video format developed by Apple and can be played by QuickTime player. It can also store other multimedia elements including text, still images and animation. Flash video (.flv ). It is used to deliver videos over the Internet with Adobe Flash Player. Highly compressed. Popular in YouTube and Google Video. Video Editing and Processing (p ) Applying video filters. Adding transition effects. Adding titles and subtitles. MULTIMEDIA PRODUCTION Page 11

12 Animation (Ch. 6) An animation is the simulation of the movement of figure objects, which is created by displaying a series of pictorial frames sequentially. Animation attributes Animation file formats. GIF animation and Flash animation. Type of Images. Vector graphic or bitmap graphic Frame Rate. A higher frame rate makes the animation smoother. E.g. 12 fps. Frame size. For bitmap graphics animation it is the graphic resolution. For vector graphics, it is resolution independent. Colour depth. GIF animation 8-bit. Flash animation 24-bit. Sound Effects Looping and autoplay. An animation starts over again and starts automatically. Two output format on the web: Animated GIF. i. Independent bitmap images are stitched together by a software. No tweening. ii. Used for only small images. iii. Shown in any browser without any plug-ins Animations of special format like Flash. i. The animated objects are vector-based. ii. Keyframes with objects are created and tweening between them is defined. iii. Plug-in must be installed in the user s computer to play the animation. Flash animation editing and processing Tween animation. In tweened animation, the user only needs to create the staring and ending frames (i.e. keyframes). Flash will create the frames in between. There are two types of tweened animation. i. Motion Tween. The postion and rotation of an object can be changed. ii. Shape Tween. The shape and colour of an object can be changed gradually (morphing). Creating Buttons. A user can interact with an animation by clicking the appropriate button, which in turn controls the flow of the animation. Using ActionScripts. The set of commands used in flash movies is called ActionScript. Adding Sound. MULTIMEDIA PRODUCTION Page 12

3.01C Multimedia Elements and Guidelines Explore multimedia systems, elements and presentations.

3.01C Multimedia Elements and Guidelines 3.01 Explore multimedia systems, elements and presentations. Multimedia Fair Use Guidelines Guidelines for using copyrighted multimedia elements include: Text Motion