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.
Practical 2: http://comp.rhs.edu.hk/svg-edit/
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
Duration
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
and
- Frame rate( fps : frame per second)
- duration
Number of image = frame rate x duration
- compression ratio
e.g.
resolution : 1024 x 768
color = 3 bytes
duration: 10 s
frame rate = 24 fps
240 frame
Calculation of multimedia file size
uncompressed file
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
Refer to table in P.124 (image) and P.129 (audio)
Scanning - convert analogue to digital
Printing - convert digital to analogue
Graphics
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
Q2:
Mistral Open (vector) 188KB
Modern Raster (bitmap) - Pixel 9KB
Modern No.20 Open (vector) 62KB
Cropped,
xcf
jpg
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
VCD
*.dat rename it to *.mpg