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Chapter 04

Chapter 4 Multimedia Elements and Digitization
Complete Practical 1 and Practical 2

4.1 Digital Multimedia Elements

Two main types of graphics: vector graphics and bitmaps (Raster) graphics

Bitmap graphics
A bitmap image is a collection of pixels 像素 arranged in row and columns.
Characteristics of a bitmap image:
- resolution
- Number of pixels
- color depths
- compression ratio
Common File format of bitmap graphics: bmp, jpg, gif, png

Resolution: 1024 x 768
Aspect Ratio: 4: 3

Resolution: 1400 x 900
Aspect: 14:9

ppi: pixel per inch (for display)

dpi: dot per inch (for hard copy)

Practical 1 (sub-page)
Common file type: jpg , bmp, gif

For .bmp
Resolution: 1024 x 768 =  ______________ pixels
Color Depth: 24 bits = 3 Bytes (True color)

for jpg
Compression ratio = original file size / compressed file size  > 1

Vector Graphics
composed of different objects, objects can be a shape, a line or a formula.
we can rescale and modify every details of each object without affecting the quality of vector graphics.

4.1.2 Audio

Recorded sound: wav , mp3 (compressed)

For audio file, wav  (not compressed)
Sampling rate: 44100 Hz
Bit resolution: 16 bits = 2 Bytes
mono / Stereo

for mp3, rma: 
Compression ratio

midi file: store musical note

Demonstration: Try using Audacity to record some sound wave.

File size depends on 
- Sampling rate 
- bit resolution (bit rate)
- duration 
- compression ratio

4.1.3 Video 
Graphics properties
- resolution 
- color depth

Size of one picture = resolution x color depth

- Frame rate( fps : frame per second)
- duration

Number of image = frame rate x duration

- compression ratio

resolution : 1024 x 768
color = 3 bytes

duration: 10 s
frame rate = 24 fps
240 frame

Calculation of multimedia file size
uncompressed file
 Multimedia type Formula file extension Compression 
 Bitmap file Resolution x  color depth
(No of pixel) x (Color Depth in byte)
 bmp  jpg
 Sound file Sampling rate x bit resolution x No of channel x duration wav  mp3 
 Video file Resolution x  color depth x frame per second x duration avi  mpg 

4.2 Analogue data and digital data

Analogue data; Continuous signal. e.g. photograph taken with a file. (P.119)
Digital data: discrete form.

analogue: Data is loss in replication. degrade, aging problem in storage.
digital: data is approximation of analogue data.

Advantage of digital format.
storage, transmission, manipulation, duplication highly precise and efficient.

4.2.3 Conversion between analogue data and digital data (Digitization)

Sampling and quantization

 audio graphics 
sampling sampling rate resolution 
 quantizationbit rate  color depth

Refer to table in P.124 (image) and P.129 (audio)

Scanning - convert analogue to digital
Printing - convert digital to analogue

compressed: JPG
uncompressed:  bmp

Compression, 2 kinds of compression
- Lossy compression (jpg) 
       Some details will be lost.
       It can not be decompressed to original file.
- Lossless compression (zip, rar, RAW)
       It can be decompressed to the original  files, folders. 
       No information is loss.

Practical 3: GIMP

1.         Open GIMP

2.         Create a new image with resolution 1600 x 1200

3.         Add Background color

4.         Open As Layer Files (Path T: \Computer \ S4_ICT)

5.         Layer – Transform – Arbitrary rotation

6.         Layer – Scale

7.         Move the layer

8.         Set Transparency

9.         Save As xcf – It can further edit

10.    Export a jpg file

11.    Submit your jpg and xcf file in eclass

Workbook Chapter 4
Short Question
Q1:   P.119-120

Mistral                     Open (vector)                        188KB
Modern                   Raster (bitmap) - Pixel             9KB
Modern No.20         Open (vector)                          62KB



compression / save to jpg   - some details of the image may be lost
reduce the color depth - some colors will be lost.

mpeg version 1  *.mpg   - VCD
mpeg version 2    DVD 
      mp3 - sound track
mpeg 4 - mp4 : high compression rate

*.dat   rename it to *.mpg

T. Chan,
Dec 16, 2013, 10:11 PM
T. Chan,
Dec 16, 2013, 10:10 PM