ICT ch.4 mind map
4.1 Digital Multimedia Elements
graphics
video
bitmap
A bitmap image is a collection of color dots called pixels arranged in
A pixel is the smallest picture element that can be shown on a computer screen.
he number of colors can be displayed in a pixel is determined by the number of color depth
bits used to represent the pixel (known as color depth). color depth
The larger the color depth, the larger the number of colors can be displayed in the image.
image
Is the measurement of the number of pixels per unit length in a bitmap image.
Is measured by 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.
Digital images for screen display are usually stored at a resolution ranging from 72 to 95 ppi.
For photograph , the images can be stored at a resolution ranging from 200 ppi to 400 ppi.
Common file formats of bitmap: bmp, ipeg and gif.
vector graphics
They are composed of a number of object
A vector object can be a shape, a line or a a string of text
a string pf 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.
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 chart , line arts and illustrations. - They are not suitable for representing images with complicated color patterns.
Examples of popular vector graphic formats: Window Metafile, Shockwave Flash and postscript (EPS).
Details of the original bitmap image are blurred when it is represented in vector graphic format.
Is a sequence of full-motion images together with sound tracks.
The file size of it can be very large.
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
Video files can be compressed into different video file formats for different playback media
4.2 Analogue Data and Digital Data
Application of digital data in IT
All electronic devices including computers and modern data transmission channels handle data in binary forms
Digital graphics and computer programs can be represented in sequences of binary numbers.
This makes operations of electronic devices on digital data such as text , graphics, audio and video highly precise and efficient.
Conversion between analogue data and digital data
Digitization is the process of converting analogue data into digital data.
Digitization involves two procedures: sampling and quantization
Sampling:
Quantization : The process of converting the attribute of each sample data into a digital code using a predefined scale
Conversion of analogue multimedia elements
Audio
Sound is inherently analogue.
A soundcard 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 channels
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 audio
reproduce audio output audio to the original one.
Image
Analogue images such as photographs or printed materials can be converted into scanner
digital images using a scanner.
The scanned images are stored as bitmap graphics.
The quality of a bitmap graphic is determined by
resolution
color depth
compression ratio
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. Printing a digital image on paper and projecting it on a screen are examples of conversion of digital images into analogue images.
The color ranges of different presentation media are different, deviate
so the output analogue images deviate from the digital images. manufacturing quality
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 image 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 recorder
Digital video camera
Wed cam
Digital camera
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, R
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) port