Mengubah Media Menjadi Bit Digital

DIGITALISASI MEDIA

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

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

Multimedia: ART Joins BRAIN

Merging of advanced digital and analog technology

DigitalSignal

Processing

AnalogSignal

Processing

A/DD/A

Analog orReal-World

Signals

Digital orComputer-WorldSignals

Analog Domain Digital Domain

ConverterTechnology

Provides the

Bridge[ICE 1997]

Digital Media System Diagram

A/DConverter

CompressionEncoder

Media:SpeechAudio

ImagesVideo

MediaDigital Bit

CompressionDecoder

MediaBitstream

Storage:CD, VCD, DVD, HD, Tape

Channel:Internet, Broadcast, Point-to-Point,

Telephone, Satellite, Cable, Wireless

D/AConverter

Media:SpeechAudio

ImagesVideo

MediaDigital Bit

Receiver /Decoder /

Player

Transmitter /Encoder /Recorder

• 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

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

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…

Digitisasi Teks

Scanner + OCR

Digital TextHandwriting recognizer

Digitisasi Image, Video & Audio

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

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

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

Digital Advantages

• Digital data not affected by processing

• Compression => more data /channel

• Processing costs: analog but digital

• Complexity costs: analog but digital

PROSES KONVERSI ANALOG KE DIGITAL

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)

111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100101110101100001010100101000010100001000010010000010100010101000010000001110010100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100101110101100001010100101000010100001000010010000010100010101000010000001110010100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100101110101100001010100101000010100001000010010000010100010101000010000001110010100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100101110101100001010100101000010100001000010010000010100010101000010000001110010100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100101110101100001010100101000010100001000010010000010100010101000010000001110010100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100100111010110000101010010100001010000100001001000001010001010100001000000111001010010011101011000010101001010000101000010000100100000101000101010000100000011100101001001110101100001010100101000010100001000010010000010100010101000010000001110010100101110101100001010100101000010100001000010010000010100010101000010000001110010100

• Dua teknik dasar yang digunakan– PCM (Pulse Code Modulation)– DM (Delta Modulation)

AnalogAnalogvoicevoice signalsignal

Sampling Sampling clockclock

PAMPAM signalsignal PCMPCM signalsignal

SamplingCircuit

SamplingCircuit

Quantizerand compander

Quantizerand compander

DigitizedDigitizedvoicevoice signalsignal

Data Analog -> Sinyal Digital

• Blok diagram proses konversi bentuk gelombang analog ke data digital

xa(t)x[n]

xq[n]Continuous timeContinuous amplitude Discrete time

Continuous amplitudeDiscrete timeDiscrete (real) amplitude

Sampling

Fs sampel/detik

Kuantisasi

N level/sampel

Encoding c[n]

B bits/sampel

][ˆ nxDiscrete timeDiscrete (integer) amplitude

N = 2B

Bit Rate = Fs . B bits/detik

Pulse Code Modulation

Konsep Sinyal Analog

ttAtxa ;cos

tFtAtxa ;2cos

t

xa(t) FTp

1

A

Acos

A: Amplituda: Frekuensi RadianF: Frekuensi Hertz: Fasa

Konsep Sinyal Digital

nnAnx ;cos

nfnAnx ;2cos

n

x(n) N

A

Acos

A: Amplituda: Frekuensi Radianf: Frekuensi: Fasa

Konversi Analog-Digital

• Sampling, dengan Fs = 1/T

• Kuantisasi

• Koding

nTxtxnx anTta |

nTxtxnx anTta |

Lb 2

Sampling

Kuantisasi

Koding

Sinyal analog

Waktu Diskrit

Nilai Diskrit

Digital

Filter

Sampling Sinyal Suara (Speech)

• Teorema Sampling Nyquist– Fs 2. Fmax

• Untuk kualitas suara pada telepon – Fs = 8 KHz

1000 2000 3000 40000

dB

0

+10

-10

Hz

A typical telephone transmission path

3.23.9

2.8 3.41.2

4.2

3 4 3 3

1

4

011 100 011 011 001 100

Original signal

PAM pulse

PCM pulse with quantized error

011100011011001100 PCM output

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.

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).

Pulse Code Modulation (PCM)

Nonlinear encoding

0123456789101112131415

Strong signal

Weak signal

0

1

2

3

456789

101112

13

14

15Quantizing levelQuantizing level

Without nonlinear encoding With nonlinear encoding

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

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

Aplikasi Pada Audio / Musik

• Sinyal audio dari sumber audio (microphone, audio out)– di filter (anti aliasing) 0Hz – 20000 Hz– disampling 44100 sample per detik– resolusi kuantisasi 16 bit per sample– Dilakukan pada dua kanal L-R stereo

• Hasilnya sbb:– Kebutuhan laju bit: 44100 x 16 x 2 =

1,411,200 bps = sekitar 1.4 Mbps– Kualitas: SNR sekitar 96 dB

RAW DIGITAL DATA

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?

Raw Digital Audio ..KB = 1024 bytes MB = 1,048,576 bytes GB =

1,073,741,824 bytes

Jika: Fs = 11000 Hz• Nsampel = 5 (menit) x 60 (detik/menit) x 11000 (sampel/detik) =

3.300.000 sampel• Nbit = 16 (bit/sampel) x 3.300.000 sampel = 52.800.000 bit =

6.600.000 byte = 6,295 MB• Nbit Stereo (2 channel) = 6,295 MB x 2 ≈ 12,6 MB

Jika: Fs = 44100 Hz• Nsampel = 5 (menit) x 60 (detik/menit) x 44100 (sampel/detik)

= 13.230.000 sampel• Nbit = 16 (bit/sampel) x 13.230.000 sampel

= 211.680.000 bit = 26.460.000 byte ≈ 25,234 MB• Nbit Stereo = 25,234 MB x 2 ≈ 50,468 MB satu lagu pada CD

audio

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!

Jika sebuah lagu pada CD Audio ≈ 50 MB,

sementara lagu yang sama dengan format MP3 ≈ 5 MB

TANYAKENAPA?

Citra Digital

• Berbeda dengan ucapan dan musik, sinyal gambar dikenal sebagai sinyal intensitas dua dimensi.

Size: 300x400, 24 bpp colour,BMP: 360.000 byte; JPG:49.504 byte

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 dataQ: 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

Sampling Citra Digital

Lebar N Kolom

TinggiM

Baris

Gambar UkuranLebar x Tinggi

N x M sampel file

Batas Baris Baru

Gambar DigitalN x M pixels

A PictureElemen(pixel)

Resolusi DPI =(N x M) / (Lebar

x Tinggi)

Sinyal Video Digital

• Sinyal video digital adalah kumpulan citra digital (disebut frame) yang di ‘tayangkan’ secara berurut menurut indeks waktu.

Time Index 1

3 5 7 9

Time Index 11

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 RGBvideo at 25 frames/sec. Eachframe being 320x240 pixels?(assume 24 bit color)

• Q: How much video time (secs) canbe stored on a 4 gigabyte disk?

• It should be clear why we need compress video for transmission.

Sinyal Video DigitalTimeIndex

1

TimeIndexL

N x M pixel /frame

N x M x L x B bits video file

B bit/pixel

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 25624 bpp

7.8

25 256 x 25624 bpp

39.3

30 256 x 25624 bpp

47.2

60 256 x 25624 bpp

94.4

LEVEL OF ABSTRACTION

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

Levels of abstraction

Meanings… ScenesActions Movements People / ObjectsRegions (colour, shape, texture, motion) PixelsElectronic bits

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)

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…

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

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

TUGAS

1. Cari sebuah format file multimedia (image, audio, video, dll) kemudian:

a) Temukan berapa ukuran Header Fileb) Bagaimana Struktur Headerc) Temukan informasi meta data apa saja yang

ada pada header tersebutd) Bagaimana struktur penyimpanan konten

media pada format file tersebut

2. Jelaskan apa perbedaan tag header metadata IDv1 dan IDv2 dari format MP3

TUGAS

3. Buat sebuah gambar dengan Windows Paint (BMP) dengan resolusi tertentu, hitung berapa kebutuhan jumlah bit-nya, buktikan dengan ukuran file yang terjadi

4. Rekam suara/audio dengan Sound Recorder (WAV) selama beberapa detik (maks 10 detik), hitung kebutuhan jumlah bit-nya, buktikan dengan ukuran file yang terjadi