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PERTEMUAN KE 2 – CITRA DIGITAL

PENGOLAHAN CITRA

PROGRAM STUDI INFORMATIKA

UNIVERSITAS GUNADARMA

PROGRAM STUDI INFORMATIKA

UNIVERSITAS GUNADARMA

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DEFINISI CITRA DIGITAL

UKURAN CITRA

SAMPLING

KUANTISASI

PROSES DIGITALISASI CITRA

REPRESENTASI CITRA

PROGRAM STUDI INFORMATIKA

UNIVERSITAS GUNADARMA

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DEFINISI CITRA DIGITAL

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DEFINISI CITRA DIGITAL

Citra Digital�adalah citra yang dihasilkan melalui proses digitalisasi, dari citra kontinu menjadi citra digital ataupun dari citra digital menjadi citra digital lainnya.

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DEFINISI CITRA DIGITAL

Pada umumnya,

citra digital berukuran persegi panjang dengan dimensi :�tinggi/panjang x lebar

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DEFINISI CITRA DIGITAL

Citra digital yang

tingginya N, lebarnya M, dan memiliki L derajat keabuan

dapat dianggap sebagai fungsi matematika berikut :

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DEFINISI CITRA DIGITAL

Sehingga,

citra digital yang berukuran

N x M

lazim dinyatakan dengan matriks yang

berukuran N baris dan M kolom

f(x,y) menyatakan intensitas cahaya/warna pada titik (x,y)

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DEFINISI CITRA DIGITAL

Nilai dari f(x,y) tersebut menandakan kedalaman citra/bit depth, yang nilainya tergantung dari jenis dan ukuran bit depthnya

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DEFINISI CITRA DIGITAL

Nilai dari f(x,y) tersebut menandakan kedalaman citra/bit depth, yang nilainya tergantung dari jenis dan ukuran bit depthnya

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DEFINISI CITRA DIGITAL

Berikut ini adalah contoh

Citra grayscale berukuran Panjang x tinggi 256 x 256.�

Jika diperhatikan, nilai-nilai tersebut seperti sebuah matriks, yang terdiri dari :

256 baris (0 - 255), �256 kolom (0 - 255),

dan 256 derajat keabuan (0-255)

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DEFINISI CITRA

Bagaiaman mendapatkan nilai-nilai tersebut ?

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PROSES DIGITALISASI CITRA

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PROSES DIGITALISASI CITRA

Digitalisasi citra adalah

proses mengubah

citra kontinu menjadi citra digital (diskrit)

Terdapat dua Langkah yaitu :

1. Digitalisasi spasial (x, y),

sering disebut sebagai penerokan (sampling).

2. Digitalisasi intensitas f(x, y),

sering disebut sebagai kuantisasi.

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20NN

PROSES DIGITALISASI CITRA

Sampling (penerokan) adalah proses mengkonversi gambar analog ke dalam kotak-kotak kecil (biasa disebut grid).

Ukuran grid selalu sama dalam satu citra digital

SAMPLING

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PROSES DIGITALISASI CITRA

Grid ini secara teknis disebut sebagai pixel yang merupakan unit terkecil dalam citra digital.

Suatu citra digital memiliki jumlah grid /pixel yang berbeda-beda, tergantung spesifikasi perangkat yang digunakan

SAMPLING

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PROSES DIGITALISASI CITRA

Citra berukuran 10 x 10 inchi

dinyatakan dalam matriks yang berukuran 5 pixel x 4 pixel.

Sehingga, tiap pixel lebarnya 2.5 inchi dan tingginya 2 inchi.

SAMPLING

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PROSES DIGITALISASI CITRA

Pembagian citra menjadi ukuran tertentu menentukan

Resolusi

sebuah citra.

Semakin tinggi resolusi,

maka,

Semakin kecil grid/pixel

Semakin banyak jumlah grid/pixel

Semakin rapat/halus gambar yang ditampilkan

SAMPLING

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PROSES DIGITALISASI CITRA

SAMPLING

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20NN

PROSES DIGITALISASI CITRA

Kuantisasi adalah proses mengisi tiap grid/pixel dengan nilai tertentu.

Nilai ini adalah representasi dari warna yang akan diberikan terhadap grid tersebut.

Pada gambar hitam-putih, pilihan nilainya adalah 0 dan 1. �Nilai 0 mempresentasikan warna hitam dan �Nilai 1 mempresentasikan warna putih.

KUANTISASI

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UNIVERSITAS GUNADARMA

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PROSES DIGITALISASI CITRA

Rentang nilai tiap pixel ditentukan oleh ukuran bit citra. Rentang ini disebut sebagai bit-depth. Semakin besar bit-depth, maka rentang nilai/pilihwan warnanya semakin banyak.

KUANTISASI

PROGRAM STUDI INFORMATIKA

UNIVERSITAS GUNADARMA

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20NN

Besarnya derajat keabuan yang digunakan

menentukan kecerahan citra.

Semakin banyak jumlah derajat keabuan,

semakin bagus kualitas citra

PROSES DIGITALISASI CITRA

KUANTISASI

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UNIVERSITAS GUNADARMA

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PROSES DIGITALISASI CITRA

KUANTISASI

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UKURAN CITRA

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UKURAN CITRA

Citra digital akan disimpan, ditampilkan, diolah, dan didistribusikan menggunakan perangkat digital.

Oleh karenanya, ukuran citra menjadi sangat penting.

Maka, pada citra dengan resolusi n x m dengan bit-depth m, size/ukuran citra digitalnya bisa dirumuskan sebagai berikut.

Size = n x m x m

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UKURAN CITRA

Contoh :�sebuah citra digital grayscale memiliki resolusi 512 x 512 pixel dengan bit-depth 8-bit

Berapa ukuran/size nya ?

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UKURAN CITRA

Tapi ingat !!�Ini adalah ukuran/size dari raw data/raw image.

Sedangkan format citra digital yang umum digunakan seperti .jpg/.png/.tiff adalah citra yang sudah dikompresi

Jika ingin membuktikan hasil perhitungan manual dengan ukuran file gambar di komputer, maka gunakan format gambar yang paling mendekati raw image, yaitu .BMP

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REPRESENTASI CITRA

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REPRESENTASI CITRA

Representasi citra adalah konsep bagaimana sebuah citra ditampilkan, disimpan, dan diolah.

Dalam konteks ini, citra digital direpresentasikan dalam sebuah matriks dua dimensi dengan dua atribut panjang (x) dan tinggi (y).

Sehingga secara matematis, citra digital bisa dianggap sebagai fungsi dua dimensi f(x,y).

Dimana :�(x,y) menunjukkan titik koordinat dan

f(x,y) menunjukkan nilai intensitas dalam koordinat (x,y).

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REPRESENTASI CITRA

Secara matematis, citra digital dengan panjang x dan tinggi y bisa direprensentasikan dalam sebuah matriks berukuran [x, y].

Dengan nilai f(x,y) dianggap sebagai nilai bit-depth ditempatkan pada setiap sel matriks

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REPRESENTASI CITRA

Di dalam komputer,

konsep matriks ini biasanya direpresentasikan dalam sebuah array.��Untuk citra grayscale, direpresenasikam dalam array dua dimensi sebagai berikut :

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REPRESENTASI CITRA

Sedangkan untuk citra berwarna (RGB),�direpresentasikan dalam bentuk array 3 dimensi

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REPRESENTASI CITRA

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REPRESENTASI CITRA

Pada pengolahan citra digital, pada dasarnya kita akan mengolah nilai-nilai pada tiap pixel tersebut.

Oleh karenanya penting untuk mengetahui cara mengakses nilai tersebut

Dikarenakan nilai-nilai tersebut direprensentasikan sebagai sebuah array, maka cara mengakses nilai tersebut adalah dengan cara mengakses nilai pada array.

Untuk mempermudah, citra digital tersebut bisa dibayangkan sebagai sebuah diagram kartesius.

Jika citra digitalnya adalah 2 dimensi, maka bisa digambarkan sebagai diagram kartesius (x,y).

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REPRESENTASI CITRA

Akan tetapi yang membedakannya adalah jika pada diagram kartesius, nilai koordinat diakses dari bawah, pada citra digital nilai koordinat diakses dari atas ke bawah

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REPRESENTASI CITRA

Contoh :�kita ingin mengakses nilai pada koordinat [3,2].

maka kita cari kolom dengan indeks 3 dan baris dengan indeks 2, sehingga nilainya adalah 1

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Tim Penyusun:

TERIMA

KASIH

PROGRAM STUDI INFORMATIKA

UNIVERSITAS GUNADARMA

PROGRAM STUDI INFORMATIKA

UNIVERSITAS GUNADARMA