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.