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 |
