Mengubah Media Menjadi Bit Digital

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1 Mengubah Media Menjadi Bit Digital
DIGITALISASI MEDIA Mengubah Media Menjadi Bit Digital

2 Representasi Digital “The power of multimedia systems originates in their ability to represent disparate information as a bit stream … every form of representation, from video to text, can be stored, processed and communicated using the same device: a computer.” Jain (1994), IEEE Multimedia vol. 1(2), p.3

3 Representasi Digital Kekuatan dari sistem multimedia adalah pada kemampuan multimedia untuk merepresentasikan berbagai informasi yang berbeda dalam bentuk bit stream … semua bentuk representasi, dari video sampai teks, dapat disimpan, diproses dan dipertukarkan menggunakan divais yang sama yaitu komputer Jain (1994), IEEE Multimedia vol. 1(2), p.3

4 Multimedia: ART Joins BRAIN
Merging of advanced digital and analog technology Digital Domain Analog Domain Digital or Computer-World Signals Analog or Real-World Signals Analog Signal Processing Digital Signal Processing A/D D/A Converter Technology Provides the Bridge [ICE 1997]

5 Digital Media System Diagram
A/D converter mengubah sinyal multimedia menjadi bit digital Bit digital adalah representasi digital dari sinyal media Enkoder kompresi mengurangi jumlah bit representasi tanpa menghilangkan konten media Bitstream adalah bit digital kompak hasil kompresi Dekoder kompresi merekonstruksi bit digital kembali dari bitstream D/A converter mengubah bit digital menjadi sinyal multimedia

6 Digitisation Dunia nyata (real world) adalah sistem analog kontinyu, sementara dunia digital (komputer) adalah digital diskrit. Media analog perlu dirubah menjadi digital dengan perangkat untuk digitalisasi: scanner, digital-camera, dll Media digital juga dapat dibuat langsung dengan komputer. Perangkat display data digital : Komputer; Digital TV; DVD / MP3 players; 3G / WAP phones, dll

7 Perangkat untuk Digitisasi
Teks: scanners & OCR  .txt, .html… Citra (Images): scanners; cameras; Photoshop  .gif, .jpg… Audio: microphones; MIDI devices  .wav, .midi, .mp3… Video: video cameras; capture cards; Premiere  .mpg, .avi…

8 Digitisasi Teks Scanner + OCR Handwriting recognizer Digital Text

9 Digitisasi Image, Video & Audio

10 Karakteristik Media Digital
All data is now numeric: Images, video and sound is digitized into numbers. Digital data can be processed in a computer into compressed formats. Data is stored on disk (rather than VHS tapes or audio cassette Data is transmitted digitally with additional information to help correct errors

11 Digital Disadvantages
Much more complex than analog systems Much more raw data Requires very high speed processing More processing steps Transmission data errors => serious damage

12 Overcome the problems System complexity => most functions in software Compress raw data => maths + software High speed processing => digital technology More processing steps => software + memory data errors => corrected by maths + software software => algoritma

13 Digital Advantages Digital data not affected by processing
Compression => more data /channel Processing costs: analog but digital Complexity costs: analog but digital

14 PROSES KONVERSI ANALOG KE DIGITAL

15 Digitisation “rich variety of sensory inputs that make up images, text, moving pictures and sounds must be reduced to patterns of binary digits inside a computer” Chapman and Chapman (2000:34)

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17 “rich variety of sensory inputs that make up images, text, moving pictures and sounds must be reduced to patterns of binary digits inside a computer” Chapman and Chapman (2000:34) Good if you want to interact by selecting and editing regions of pixels, or query by patterns of pixels

18 Data Analog -> Sinyal Digital
Dua teknik dasar yang digunakan PCM (Pulse Code Modulation) DM (Delta Modulation) Sampling clock PAM signal PCM signal Digitization is a process of convering analog data into digital data. The digital signal is converted back into analog signal at the receiver. The device used for converting analog data into digital form, and recovering the original analog data is known as CODEC (Coder-Decoder). Sampling Circuit Quantizer and compander Analog voice signal Digitized voice signal

19 Pulse Code Modulation Blok diagram proses konversi bentuk gelombang analog ke data digital Fs sampel/detik N level/sampel B bits/sampel xa(t) Sampling Kuantisasi Encoding c[n] x[n] Continuous time Continuous amplitude xq[n] Discrete time Discrete (integer) amplitude Discrete time Continuous amplitude Discrete time Discrete (real) amplitude N = 2B Bit Rate = Fs . B bits/detik

20 Konsep Sinyal Analog xa(t) A Acos t A: Amplituda : Frekuensi Radian
F: Frekuensi Hertz : Fasa

21 Konsep Sinyal Digital x(n) A Acos n A: Amplituda : Frekuensi Radian
f: Frekuensi : Fasa

22 Konversi Analog-Digital
Sinyal analog Sampling, dengan Fs = 1/T Kuantisasi Koding Filter Waktu Diskrit Sampling Nilai Diskrit Kuantisasi Koding Digital

23 Sampling Sinyal Suara (Speech)
Teorema Sampling Nyquist Fs  2. Fmax Untuk kualitas suara pada telepon Fs = 8 KHz 1000 2000 3000 4000 dB +10 -10 Hz A typical telephone transmission path

24 Pulse Code Modulation (PCM)
Original signal 3.9 4.2 3.4 3.2 2.8 PAM pulse 1.2 PCM pulse with quantized error 3 4 3 3 4 PCM is based on the sampling theorem. The original signal is assumed to be bandlimited with a bandwidth of B. Signal is sampled at a rate 2B. Samples signal are represents as narrow pulse whose amplitude is proportional to the value of the original signal and is known as PAM (Pulse Amplitude Modulation). The amplitude of each PAM pulse is approximated by an n-bit interger,. In the sample above, n=3. Thus 8=23 levels are used for approximating the PAM pulses. 1 011 100 011 011 001 100 PCM output

25 Pulse Code Modulation (PCM)
Teorema sampling Nyquist menjamin sample data mengandung semua informasi dari sinyal orisinal Frekuensi voice (speech) berada dibawah 4000Hz Membutuhkan 8000 sample per detik Sistem telepon dapat mendigitalisasi voice dengan 128 level atau 256 level. Level-level tersebut disebut level kuantisasi Jika128 level, maka bit tiap sampel = 7 bits (27 = 128). Jika 256 level, maka bit tiap sampel = 8 bits (28 = 256). 8000 samples/sec x 7 bits/sample = 56Kbps for a single voice channel. 8000 samples/sec x 8 bits/sample = 64Kbps for a single voice channel.

26 Pulse Code Modulation (PCM)
PCM menggunakan pengkodean kuantisasi non-linear: spasi amplituda dari tiap level tidak linear Ada step kuantisasi yang lebih banyak pada amplituda rendah (low) Ini untuk mengurangi distorsi sinyal secara overall. Tetapi menghasilkan quantizing error (or noise).

27 Without nonlinear encoding With nonlinear encoding
Quantizing level 15 15 14 Strong signal 14 13 13 12 12 11 11 10 10 9 8 Weak signal 9 8 7 7 6 6 5 Quantization levels are not necessary equally spaced. The problem with equal spacing is that the mean absolute error for each sample is the same, regardless the signsl level. Lower amplitude values are relatively more distorted. [Stallings, p.118] 4 5 4 3 3 2 2 1 1 Without nonlinear encoding With nonlinear encoding

28 Delta Modulation (DM) Pada Delta Modulation, sinyal analog ditracking.
Analog input diaproksimasi dengan staircase function Apakah Move up (naik) atau down (turun) satu level () pada tiap interval sampel Bit 1 digunakan untuk merepresentasi kenaikan level tegangan pd sinyal, dan bit 0 untuk merepresentasi turunnya level tegangan. -> Output dari DM adalah bit tunggal Digunakan juga pada berbagai teknik Kompresi Data e.g. Interframe coding techniques for video

29 Aplikasi Pada Ucapan Digital
Sinyal suara manusia (speech) dari mikropon di filter (anti aliasing) 300Hz – 3300 Hz disampling 8000 sample per detik resolusi kuantisasi 8 bit per sample. Hasilnya sbb: Kebutuhan laju bit: 8000 x 8 = 64 kbps Kualitas: SNR sekitar 48 dB

30 Aplikasi Pada Audio / Musik
Sinyal audio dari sumber audio (microphone, audio out) di filter (anti aliasing) 0Hz – Hz disampling sample per detik resolusi kuantisasi 16 bit per sample Dilakukan pada dua kanal L-R stereo Hasilnya sbb: Kebutuhan laju bit: x 16 x 2 = 1,411,200 bps = sekitar 1.4 Mbps Kualitas: SNR sekitar 96 dB

31 RAW DIGITAL DATA

32 Raw Digital Audio AUDIO: a sequence of microphone readings on several channels. Readings (samples) are normally taken at 11000, 22K or 44K per second and may be 8, 12 or 16-bit values. Q: Berapa banyak memori dibutuhkan untuk menyimpan rekaman audio selama 5 menit dengan menggunakan 2 channel dan 16 bit per sample?

33 Raw Digital Audio .. KB = 1024 bytes MB = 1,048,576 bytes GB = 1,073,741,824 bytes Jika: Fs = Hz Nsampel = 5 (menit) x 60 (detik/menit) x (sampel/detik) = sampel Nbit = 16 (bit/sampel) x sampel = bit = byte = 6,295 MB Nbit Stereo (2 channel) = 6,295 MB x 2 ≈ 12,6 MB Jika: Fs = Hz Nsampel = 5 (menit) x 60 (detik/menit) x (sampel/detik) = sampel Nbit = 16 (bit/sampel) x sampel = bit = byte ≈ 25,234 MB Nbit Stereo = 25,234 MB x 2 ≈ 50,468 MB  satu lagu pada CD audio

34 Raw Digital Audio .. Makin besar FS, makin baik kualitas rekaman audio, makin banyak jumlah bit yang dibutuhkan! Makin besar jumlah bit / sampel, makin baik kualitas rekaman audio, makin banyak jumlah bit yang dibutuhkan!, demikian pula sebaliknya Kualitas Audio Digital adalah linear dengan kebutuhan memori!

35 TANYA KENAPA? Jika sebuah lagu pada CD Audio ≈ 50 MB,
sementara lagu yang sama dengan format MP3 ≈ 5 MB TANYA KENAPA?

36 Citra Digital Berbeda dengan ucapan dan musik, sinyal gambar dikenal sebagai sinyal intensitas dua dimensi. Size: 300x400, 24 bpp colour, BMP: byte; JPG: byte

37 Raw Digital Images A raw camera image is an array of colored dots (pixels). An RGB image has 3 color components: RED, GREEN, BLUE The image size is the total number of pixels. Q: what is the size of an image of 320 x 240 pixels? The pixel value is made from 3 numbers being the amount (intensity) of each RGB color component (normally 8 bits). The image file size is the total number of bytes of pixel data Q: what is the file size of an RGB image of 320x240 pixels? (assume RGB pixels are 3x8 = 24-bit color) We can alter the image by changing the pixel values

38 Sampling Citra Digital

39 Sinyal Video Digital 3 5 7 9 Time Index 1 Time Index 11 Sinyal video digital adalah kumpulan citra digital (disebut frame) yang di ‘tayangkan’ secara berurut menurut indeks waktu.

40 Raw Digital Video VIDEO: a timed sequence of images (eg 25 frames/sec) Raw video data consists of RGB images. Q: What is the data rate of RGB video at 25 frames/sec. Each frame being 320x240 pixels? (assume 24 bit color) Q: How much video time (secs) can be stored on a 4 gigabyte disk? It should be clear why we need compress video for transmission.

41 Sinyal Video Digital

42 Pengaruh Frame Per Detik
Semakin banyak fps, semakin mulus transisi gerak, sehingga gambar semakin ‘hidup’. Tetapi akibatnya semakin besar jumlah bit yang diperlukan. Tipikal jumlah frame per detik (fps) adalah 5 fps, 30 fps, dan 60 fps, untuk videophone, TV, dan HDTV fps Dim Mbps 5 256 x 256 24 bpp 7.8 25 39.3 30 47.2 60 94.4

43 LEVEL OF ABSTRACTION

44 Levels of Abstraction: a simple view
Multimedia information needs to be dealt with at different levels of abstraction, e.g.: In terms of bit-streams for digitisation, compression, transmission, display, etc. In terms of its content for intuitive retrieval and browsing

45 Levels of abstraction Meanings… Scenes Actions Movements
People / Objects Regions (colour, shape, texture, motion) Pixels Electronic bits

46 What is Content? “every symbolic object consists of two interacting components, one of which is situated on the plane of expression while the other is situated on the plane of content”  “difference between what constitutes the objects themselves (media objects) and what is actually being communicated” Smoliar and Wilcox (1997)

47 BUT… Multimedia Content
Digital multimedia means that multimedia information can be created, retrieved, presented and interacted with in new ways BUT… Computers don’t understand the content of multimedia items in the same way humans do…

48 Metadata Metadata = “data about data”
In this case, data about the bit-streams that are texts, images, video, audio,etc. By including metadata then multimedia applications can ‘know’ about media content, as well as about other things like who owns it, when it was made, who made it, etc. BUT – there is a cost associated with manually produced metadata; need to consider potential for automation

49 RANGKUMAN Media analog dirubah ke bentuk digital agar dapat disimpan,diproses dan dipertukarkan dengan bantuan komputer Raw data digital berukuran sangat besar sehingga perlu dilakukan kompresi Media (file) digital mempunyai meta-data agar komputer dapat mengenali konten-nya

50 TUGAS Cari sebuah format file multimedia (image, audio, video, dll) kemudian: Temukan berapa ukuran Header File Bagaimana Struktur Header Temukan informasi meta data apa saja yang ada pada header tersebut Bagaimana struktur penyimpanan konten media pada format file tersebut Jelaskan apa perbedaan tag header metadata IDv1 dan IDv2 dari format MP3

51 TUGAS Buat sebuah gambar dengan Windows Paint (BMP) dengan resolusi tertentu, hitung berapa kebutuhan jumlah bit-nya, buktikan dengan ukuran file yang terjadi Rekam suara/audio dengan Sound Recorder (WAV) selama beberapa detik (maks 10 detik), hitung kebutuhan jumlah bit-nya, buktikan dengan ukuran file yang terjadi