mengubah media menjadi bit digital
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DIGITALISASI MEDIA. Mengubah Media Menjadi Bit Digital. Representasi Digi tal. - PowerPoint PPT PresentationTRANSCRIPT
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Mengubah Media Menjadi Bit Digital
DIGITALISASI MEDIA
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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
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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
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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]
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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
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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
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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…
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Digitisasi Teks
Scanner + OCR
Digital TextHandwriting recognizer
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Digitisasi Image, Video & Audio
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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
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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
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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
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Digital Advantages
• Digital data not affected by processing
• Compression => more data /channel
• Processing costs: analog but digital
• Complexity costs: analog but digital
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PROSES KONVERSI ANALOG KE DIGITAL
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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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• 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
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• 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
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Konsep Sinyal Analog
ttAtxa ;cos
tFtAtxa ;2cos
t
xa(t) FTp
1
A
Acos
A: Amplituda: Frekuensi RadianF: Frekuensi Hertz: Fasa
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Konsep Sinyal Digital
nnAnx ;cos
nfnAnx ;2cos
n
x(n) N
A
Acos
A: Amplituda: Frekuensi Radianf: Frekuensi: Fasa
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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
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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
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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)
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• 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)
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• 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)
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Nonlinear encoding
0123456789101112131415
Strong signal
Weak signal
0
1
2
3
456789
101112
13
14
15Quantizing levelQuantizing level
Without nonlinear encoding With nonlinear encoding
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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
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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
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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
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RAW DIGITAL DATA
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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?
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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
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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!
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Jika sebuah lagu pada CD Audio ≈ 50 MB,
sementara lagu yang sama dengan format MP3 ≈ 5 MB
TANYAKENAPA?
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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
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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
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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)
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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
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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.
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Sinyal Video DigitalTimeIndex
1
TimeIndexL
N x M pixel /frame
N x M x L x B bits video file
B bit/pixel
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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
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LEVEL OF ABSTRACTION
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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
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Levels of abstraction
Meanings… ScenesActions Movements People / ObjectsRegions (colour, shape, texture, motion) PixelsElectronic bits
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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)
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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…
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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
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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
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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
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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