Pertemuan 2 : Citra Digital, Sampling, dan Quantization - Part 4 : Model pembentukan citra digital

Summary

This script discusses the fundamentals of image formation in imaging systems. It explains how sensors capture light energy reflected from objects, converting it into digital signals through a digitizer. The importance of amplitude, representing light intensity, and the factors influencing it, such as illuminance and reflectance, are highlighted. Examples of different illuminance levels in various lighting conditions and the reflectance of materials like black velvet and stainless steel are provided. The script also touches on the digital representation of these values, with a scale from 0 (black) to 255 (white), illustrating the transition from dark to light.

Takeaways

• 🌞 The imaging system captures the energy reflected from an object illuminated by a light source, like the sun.
• 📸 The sensor plays a crucial role in detecting light intensity reflected by the object and converting it into signal values.
• 🔢 The digitizer converts continuous signals from the sensor into digital format, resulting in a digital image.
• 📈 The captured light intensity must be positive and its amplitude represents the physical properties of the object being imaged.
• ⚡ The two main factors affecting light reflection are illuminance (the light hitting the object) and reflectance (the light reflected by the object).
• 💡 The function f(x, y) represents the product of illuminance (I) and reflectance (R), where I varies from 0 to infinity and R ranges from 0 to 1.
• 🔄 Reflectance can range from 0 (no reflection) to 1 (perfect reflection), though real-world objects rarely achieve these extremes.
• 🌑 Illumination and reflection can also be replaced by transmission in scenarios like X-ray imaging, where light passes through objects.
• 🌍 Various objects in nature have different levels of reflectance, such as black velvet with 0.01 reflectance or snow with 0.93 reflectance.
• 🎨 The intensity values in a monochrome image are represented by a grayscale range, usually from 0 (black) to a maximum value, such as 255 (white).

Q & A

What is the main source of energy or illumination in the example provided?

The main source of energy or illumination in the example is the sun, which reflects light off objects to create an image that can be captured by an imaging system.

What is the role of the sensor in the imaging process described?

The sensor's role is to capture the energy reflected from an object, specifically the light intensity, and convert it into a signal that can be digitized to form a digital image.

How does a digitizer contribute to the imaging system?

The digitizer converts the continuous signal captured by the sensor into a discrete digital signal, which results in a digital image that can be further processed or analyzed.

What is meant by 'amplitude' in this context?

Amplitude refers to the intensity of the reflected light that is captured by the sensor. It is a scalar value that represents the brightness of the object being imaged.

How is the intensity of light related to the object's physical properties?

The intensity of light reflected from an object is determined by two factors: the amount of illumination the object receives and the object's reflectance, or how much light it reflects back.

What is the relationship between illuminance and reflectance in the formula f(x, y)?

In the formula f(x, y), the intensity function is the product of illuminance (the amount of light hitting the object) and reflectance (the proportion of light reflected by the object).

What is the range of illuminance values for sunlight on Earth, and how does it vary under different conditions?

On a clear day, sunlight provides around 90,000 lumens per square meter at the Earth's surface. On a cloudy day, this drops to around 10,000 lumens per square meter, and under moonlight, it is as low as 0.1 lumens per square meter.

What is the reflectance range for natural objects, and what do the extremes represent?

Reflectance values range from 0 (total absorption, no reflection) to 1 (perfect reflection). However, most natural objects fall within this range, with black velvet having a reflectance of 0.01 and snow having a reflectance of 0.93.

How do transmitted and reflected light differ in certain imaging systems, like X-rays?

In systems like X-rays, the focus is on transmitted light rather than reflected light. The object's ability to transmit light (transmittance) replaces reflectance in the formula for calculating intensity.

How is the grayscale range represented in digital imaging systems?

In digital imaging, grayscale intensity ranges from a minimum (black, with no light) to a maximum (white, full light). This is typically represented in a range from 0 to 255, with 0 being black and 255 being white, allowing for 256 levels of gray.

Outlines

00:00

📸 Introduction to Basic Image Formation

This paragraph introduces the concept of image formation in a digital system. It explains the interaction between an object and illumination from a natural source like the sun. The object reflects the energy, which is captured by a sensor sensitive to light intensity. The sensor converts the reflected light into signals, which are processed by a digitizer. The final output is a digital image that represents the intensity of the reflected light. This paragraph emphasizes the importance of ensuring the sensor captures accurate light intensity and signals.

05:03

💡 Capturing Amplitude and Light Intensity

This section focuses on the amplitude function, which captures light intensity as a scalar value. The reflected energy from an object is represented by the amplitude of the electromagnetic waves. The paragraph explains that physical properties such as illumination and reflection determine the values of the amplitude. The intensity of light captured is related to the illumination source (e.g., sunlight) and the reflection properties of the object. This forms the basis of image representation, where both the amount of illumination and the reflective qualities of the object define the final image.

10:03

🔄 Illuminance and Reflectance in Image Formation

The paragraph explains two important components of image formation: illuminance (the light illuminating the object) and reflectance (the light reflected by the object). It describes how the final image function, f(x,y), is the product of illuminance and reflectance. The values of these two components range from zero (no light/reflection) to maximum levels. Reflectance, for example, ranges between 0 and 1, where 0 represents total absorption and 1 represents perfect reflection. However, perfect reflection or absorption is rare. These factors define the overall light intensity captured in the image.

🔬 Transmission in Imaging Systems (e.g., X-Rays)

This paragraph expands on how the image formation model applies to different imaging scenarios, such as X-ray imaging, where light is transmitted rather than reflected. Instead of reflectance, the system measures transmission, determining how much light passes through an object. This model is adaptable to different types of waves (e.g., electromagnetic waves in X-rays) and various imaging technologies, allowing a broader understanding of how different materials and objects interact with light in medical or scientific imaging systems.

🌞 Real-World Examples of Illuminance and Reflectance

Here, real-world examples are provided to give a clearer idea of illuminance and reflectance values. For instance, on a sunny day, sunlight can provide up to 90,000 lumens per square meter, while on a cloudy day, it drops to 10,000 lumens. The paragraph also compares reflectance values for various objects: black velvet has very low reflectance (0.01), while stainless steel and snow have much higher reflectance (up to 0.93). This contrast in reflectance helps explain how different surfaces reflect light differently, influencing the final image brightness.

📊 Digital Image Intensity and Grey Levels

This final paragraph explains how captured intensities in a digital image are mapped onto a grey scale. It covers the transformation of real-world light intensity into a digital format, where the minimum intensity is mapped to 0 (black) and the maximum to 255 (white). In between, the grey levels represent varying degrees of brightness. The range and resolution of the grey levels depend on the digital system's capabilities, typically covering a range of 256 shades from black to white. This process allows for the accurate representation of light intensity in monochrome images.

Keywords

💡Image formation

Image formation refers to the process of capturing visual information, such as light or reflected energy, from an object and translating it into a digital image. In the video, it is described as the process that begins with the object receiving energy from a source like the sun, reflecting that energy, and then being captured by an imaging system.

💡Sensor

A sensor in the context of the video is a device that detects and captures energy (such as light) reflected from an object. The sensor is essential for translating the reflected energy into data, which is then processed to create a digital image. The video emphasizes the role of sensors in capturing the light intensity from objects illuminated by a source like the sun.

💡Illuminance

Illuminance refers to the amount of light that falls onto a surface, often measured in lumens per square meter. In the video, it is explained as a crucial factor in image formation, with examples like sunlight providing high illuminance during the day. The level of illuminance influences how much light is reflected from an object and subsequently captured by the imaging system.

💡Reflectance

Reflectance is the measure of how much light or energy is reflected by an object. In the video, it is described as the second key component in image formation, alongside illuminance. Objects with high reflectance, like snow, reflect a large portion of the light, while others, like black velvet, absorb most of the light and reflect very little.

💡Electromagnetic waves

Electromagnetic waves are the form of energy, such as light, that travels through space and can be absorbed, transmitted, or reflected by objects. The video explains that the imaging process depends on capturing the electromagnetic waves reflected by objects, which are then converted into digital signals by the sensor.

💡Digitizer

A digitizer is a component that converts the continuous signals captured by the sensor into discrete digital signals, creating a digital image. The video explains that after the sensor captures the light or energy, the digitizer transforms these continuous signals into a form that can be processed digitally, enabling the creation of digital images.

💡Amplitude

Amplitude, in the context of image formation, refers to the intensity of the reflected light or energy from an object. The video explains that the amplitude of the captured signal represents the brightness or intensity of the image, which is influenced by factors like the object's reflectance and the source of illumination.

💡Monochrome image

A monochrome image is an image composed of varying intensities of a single color, typically grayscale. In the video, it is discussed as an initial step in image processing, where the captured data is represented as variations in brightness, before moving into more complex color channels.

💡Grey levels

Grey levels refer to the range of intensity values in a grayscale image, typically from black to white. The video explains that the range of grey levels represents different levels of light intensity, with the lowest value being black (no light) and the highest value being white (maximum light reflection). This range is used to encode the brightness of each pixel in a digital image.

💡Transmission

Transmission refers to the passage of light or energy through an object, rather than being reflected. In the video, transmission is discussed in the context of imaging techniques like X-rays, where the goal is to capture light that passes through an object rather than light that is reflected. This contrasts with reflectance-based imaging methods.

Highlights

Introduction to a simple image formation model using an object illuminated by a light source like the sun.

The sensor is the primary component in the imaging system, capturing energy reflected from objects to produce signals representing light intensity.

The captured continuous signals from the sensor are digitized to produce discrete digital signals, forming a digital image.

The main parameters of image formation are illuminance (amount of light falling on the object) and reflectance (amount of light reflected from the object).

Illuminance depends on the intensity of light sources, while reflectance is determined by the surface properties of the object.

Mathematically, the intensity of light captured (f) is a product of the illuminance (I) and reflectance (R) values.

Typical illuminance values: direct sunlight on a clear day (~90,000 lumens/m2), overcast conditions (~10,000 lumens/m2), and full moonlight (~0.1 lumens/m2).

Reflectance values range from 0 to 1, where 0 means complete absorption and 1 means perfect reflection. For example, black velvet has a reflectance of 0.01, while polished metal can reach 0.93.

Reflectance and illuminance values vary widely across different materials and surfaces, influencing the final image intensity.

The imaging model also applies to other forms of imaging, like X-rays, where transmitted energy is used instead of reflected light.

In digital imaging, the intensity values of captured images are mapped to a defined range, typically 0 (black) to 255 (white), creating a grayscale image.

The image's minimum and maximum intensity values depend on the lowest and highest levels of illumination and reflectance in the scene.

In digital imaging, intensity values are often scaled to standard ranges to ensure consistency and ease of interpretation.

Grayscale images are represented by a range of gray levels, where each pixel's value corresponds to a specific intensity of light in the image.

Digital images with a range of 256 gray levels (0-255) allow for smooth transitions from black to white, representing variations in surface reflectance and illuminance.

Transcripts

Hai

[Musik]

nah ini adalah bentuk model image

formation yang paling sederhana jadi ada

di bisa lihat pada gambar ini misalkan

ada adek punya sebuah objek ya elemen

pada Shin seperti pada gambar kemudian

kebetulan ini di alam jadi dia menerima

sumber energi atau iluminasi nya dari

matahari nah pantulannya seperti yang

sudah dibahas sebelumnya Tentukan ada

panggilan energi dari objek tersebut nah

pantulan energi Inilah yang harus

ditangkap oleh imaging system dalam hal

ini yang pertama itu adalah sensornya

sensor yang peka untuk bisa menangkap

pancaran energi dari objek yang kita

ciptakan ya jadi sensor ini harus bisa

merepresentasikan

intensitas cahaya yang murni misalkan

dari pantulan objek dari matahari Hai

untuk bisa direpresentasikan pada

nilai-nilai sinyal yang ditangkap

melalui sensor tersebut Nah setelah itu

hasil penangkapan sinyal sinyal dari

sensor

gelombang ini akan mengirimkannya kepada

komponen berikutnya yaitu digitizer yang

berfungsi untuk melakukan output final

dari sinyal yang ditangkap tersebut

dalam versi digital atau sudah

terdigitalisasi ya sinyal yang awalnya

masuk dalam versi continue sudah menjadi

versi diskrit Nya sehingga dihasilkan

lah citra digital

hai hai

Hai nah hal-hal yang harus

diperhatikan disini adalah yang pertama

karena kita akan menangkap amplitudo

fungsi efeknya Kenapa itu dari sebuah

cita-cita ya yang awalnya itu continue

sekarang hal-hal yang harus dicatat ada

yang pertama dipastikan bahwa eh ketika

ditangkap nanti besarannya akan berupa

nilai skalar yang bernilai positif

Karena intensitas cahaya itu bernilai

positif kemudian secara fisik ya makna

yang ada pada amplitudo itu sangat

ditunjukkan oleh sumber gambar atau

sumber objek yang akan kita Citra akan

yang artinya kalau misalnya kita

menangkap objek itu dari pantulan

Indonesia cahaya matahari maka energi

yang ditangkap yang dipancarkan oleh

objek tersebut atau diserap dipantulkan

oleh objek-objek tersebut untuk kita

tangkap sebagai nilai amplitudo itu

sebenarnya adalah Eh nilai intensitas

cahaya dari gelombang elektromagnetik

jadi secara fisik nilai-nilai tersebut

Hai semuanya dari eh sumber objek yang

sedang kita Citra kan kalau memang

menggunakan

objek ya alam yang tidak benar matahari

maka sebenarnya amplitudo atau fungsi f

yang kita tangkap itu sebenarnya adalah

intensitas cahaya yang dipancarkan atau

dipantulkan sebagai bagian dari

gelombang elektromagnetik nah eh ada dua

komponen yang bisa mencirikan fungsi

enzim yang pertama itu adalah Jumlah

sumber energi atau cahaya yang menerangi

objek di tempat kita mencitrakan

eh Sin tersebut Yap jadi seberapa besar

tingkat iluminasi pada proses pencitraan

kita itu sangat ditentukan oleh seberapa

besar iluminasi yang dipantulkan oleh

objek dalam SIM tersebut Nah jadi dua

komponen ketika kita menangkap fungsi f

ini sebenarnya adalah yang pertama

seberapa tingkat ini nasi atau I yang

kedua adalah seberapa tingkat fans atau

tingkat pemantulan yang dilakukan oleh

objek tersebut jadi

berapa tingkat iluminasi dan berapa

tingkat refleksi reflectance atau Ida

terjadi fungsi f itu sebenarnya adalah

gabungan dari dua komponen ini seberapa

besar detail minasy seberapa besar nilai

reflectance dari permukaan objek yang

sedang kita ciptakan tersebut Nah ini

bisa dituliskan dalam formulasi

matematika bahwa fxc itu adalah blog

produk dari IC dan ereksi Jadi ia adalah

illuminance kemudian er itu adalah

reflectance dalam hal ini nilai

iluminasi itu tentu dari nol sampai

tidak hingga jadi seberapa kuat

pancaran iluminasi tingkat iluminasi

dari dari gelombang elektromagnetik dari

matahari yang menerpa objek tersebut itu

tentu bisa sangat tinggi sekali

sementara tingkat reflectance itu adalah

memiliki ring dari nol sampai 10 artinya

tentu tidak ada pemantulan sama sekali

sementara satu itu adalah pemantulan

yang sempurna Tapi tentu

saya jarang sekali ya ada objek yang

benar-benar bisa menyerap semuanya atau

ada objek yang benar-benar bisa

memantulkan secara penuh tingkat

iluminasi yang datang pada permukaan nya

Nah sehingga reflectance itu dibatasi

dengan Zero dan satu biru itu artinya

total absorption artinya iluminasi yang

datang energi yang datang itu

benar-benar diserap habis sementara satu

kalau total reflek terjadi benar-benar

dipantulkan secara sempurna ya jadi itu

ditunjukkan oleh sugar iluminasi

sementara er ditentukan oleh

karakteristik objek Ya seperti materi

sebelumnya setiap permukaan objek itu

memiliki karakteristik yang berbeda-beda

ketika jauh memantulkan gelombang yang

datang pada permukaan Nah untuk

diperhatikan bahwa model illuminance dan

reflektansi ini untuk bisa menghitung

nilai intensitas cahaya untuk menjadi

nilai F ada cita-cita kita itu

sebenarnya juga berlaku tidak hanya pada

kita ambil jutaan yang bersifat

reflectance tapi juga bisa melalui

transmisi atau iluminasi yang

ditransmisikan bukan di

reflectance kan bukan dipantulkan ya

tapi diteruskan contohnya pada rontgen

atau pada penggunaan pencitraan sinar-x

dalam hal ini tinggal diganti bahwa

nilai reflectance diganti dengan nilai

trans trans misi PT jadi seberapa besar

Illuminati itu diteruskan Ya karena

memang karakteristik dari pencitraan

seperti misalkan pada menggunakan

gelombang sinar-x itu memang tujuannya

itu bukan dipantulkan tapi diteruskan

kedalam tubuh kita jadi tinggal diganti

model yang sama

Hai

nah ini sebagai gambaran supaya jadi

tahu sebenarnya seberapa sih nilai

tingkat luminous dan reflektor dari

benda-benda di alamnya contohnya

matahari tentu yang pertama kali ada

sumber iluminasi utama kita pada saat

hari cerah banget matahari itu bisa

memberikan nilai 90.000 lumens per m2 di

permukaan bumi jadi Tingkat iluminasi

atau hari pada saat cerah itu permukaan

bumi itu sekitar Rp90.000 lu handphone

M2 sementara saat Berawan itu hanya

sekitar 10.000 lengan per m2 nah

kemudian saat malam misalkan tapi ada

Bulan Purnama itu kita masih punya

tingkat iluminasi Tetapi kan rendah

dibanding dengan hari cerah itu hanya

sekitar 0,1 lumen per m2 nah sementara

untuk reflected by objek-objek di alam

ini semuanya punya tingkat leaflet

aktivitas yang berbeda contoh misalkan

blackvelvet jadi ini blackvelvet ini

sepertinya adalah objek yang cukup hitam

ya dia tingkat refleksinya tentu kecil

sekali jadi hanya 2001 Jadi kalau ada

illuminance yang dateng sebesar X maka

dia hanya memantulkannya sebesar 0,01 X

sementara stainless steel ada di tahu

stainless steel Ya yang seperti logam

itu punya tingkat reflectance yang jauh

lebih tinggi yaitu dorongan

untuk dinding yang putih Flag wild world

ya jadi dinding yang putih bersih itu

0,8 sementara kalau yang logam logam

yang dilapisi oleh perak itu

salju 0,93 kita melihat salju itu sangat

silau kena

itu memantulkan hampir sempurna

iluminasi dari matahari 0,93 tapi tetap

tidak bernilai 1 ya Bahkan salju tidak

bisa memantulkan semuanya pasti ada

sebagian yang diabsorpsi jadi ini adalah

sebagai gambaran contoh tingkat

iluminasi dan fetus dari situasi di alam

karena memang sebagian besar kita

mencipta sesuatu itu dari a di alam dulu

kep

hai oke nah ketika proses capturing dari

illuminance dan Reflection itu sudah

masuk kemudian membentuk nilai f atau

amplitudo dari intensitas Citra digital

kita itu maka masing-masing nilai

intensitas pada citra monokrom kita

monokrom karena sekarang kita baru

membahas 11 channel dulu ya belum

benar-benar Kaler truk kalian Ines

jadiin nilai identitasnya pada koordinat

x koma y itu

akan dinyatakan dalam range misalkan l

minimum sampai l maksimum artinya berapa

sih nilai intensitas minimum dan

maksimum untuk nilai Citra digital kita

nah tentu saja nilai l minimum ini harus

bersifat positif sementara l maksimum

itu harus fined artinya terbatas tidak

boleh lagi tidak terbatas seperti nilai

UN siapa sih Kenapa karena kita sudah

berbicara pada scoop data digital Citra

digital Nah itu artinya apa Elo minimum

akan tercapai saat nilai ini cacat dan

nilai minimum jadi illuminate minimum

reflektansi a minimum sementara nilai

maksimum er atau kiri level yang

maksimal akan tercapai saat illuminance

yang maksimum dan juga maksimum nah

nilai Amin sama elmas inilah yang akan

menjadi skala Grey atau skala intensitas

pada cita-cita yang kita hasilkan nah

dalam praktisnya dalam implementasinya

nanti nilai elemen sama Elma sini

biasanya distilir atau di

gips disamakan rangenya dalam versi 0

sampai ukuran

110 dimulai dari nol l minimnya selalu

dimulai dengan nol sementara l maksudnya

akan menjadi nilai ujungnya atau Alquran

10 itu akan merepresentasikan black atau

saat-saat luminan saat intensitasnya

menolaknya illuminate tidak ada atau

dapet kerja juga menyinggung 70

sementara elne satu jadi fileflyer

paling tinggi itu dinyatakan untuk nilai

putih sempurna atau kulit nah sementara

pergerakan grill efel dari nol menuju l

kurang satu ini yang disebut dengan

sense atau apa namanya peralihan warna

grey dari Tam menuju putih jadi gede

levelnya ada berapa di sana kalau Omnya

misalkan 256 maka nilainya

0-255 nolnya adalah hitam sementara 255

adalah putih dan darienol menuju 255 itu

ada 256 perubahan

Grey warna grey dari hitam menuju putih