CMOS vs CCD Image Sensors Overview

Introduction

• The material covers digital image processing and related topics.

Electromagnetic Radiation

• Electromagnetic radiation (EMR) is composed of self-propagating electromagnetic waves.
• It does not require a medium for propagation.
• It travels at the speed of light (300,000 km/s).
• EMR can be analyzed as waves or particles (photons).

Sound Waves

• Sound waves are mechanical waves.
• They require a medium (e.g., air, water) for propagation.
• They do not propagate in a vacuum.
• Sound waves cause pressure and displacement changes in a medium.

Sources of EM Radiation

• EMR is generated by stars, atomic nucleus decay, and human activities.
• The Sun is a significant source of EMR, emitting a wide range.
• Common household devices, medical equipment, and telecommunications emit EMR.

Two natures of Light (The Wave Nature of Electromagnetic Radiation)

• EMR can be treated as perpendicular, time-varying electric (E) and magnetic (B) fields.
• The simplest EMR wave is a sinusoidal wave.
• The mathematical description of EMR treated as a wave: Ex = Ecos(wt – kz - φo).
• Wavelength (λ), angular frequency (ω), and phase (φo).
• Phase velocity (v) = ω/k = λf

Phase Velocity

• Phase velocity (v) is the rate at which a point of constant phase (e.g., maximum amplitude) travels along the z-axis in the optical medium.
• In a medium with a refractive index n, phase velocity is given by v = c/n, where c is the speed of light in a vacuum.

Wave Packets

• Two waves with slightly different wavelengths, travelling in the same direction, generate a wave packet.
• Wave packets have an amplitude that is modulated at a frequency.

Group Velocity and Group Index

• Group velocity (vg) in a medium is defined as vg = ω/k.
• Group index (Ng) is defined as Ng = c/v = n – λ (dn/dλ)
• Both group velocity and group index are functions of wavelength.

Plane Waves

• A monochromatic plane wave is described by Ex = Ecos(wt – kz - φ0), where the quantity is constant in any plane perpendicular to the z-axis.
• The plane of constant E and t is called the wavefront.

The Divergence of EMR

• Far from the EMR source, EMR waves can be approximated as plane waves.
• Real-world EMR sources often show divergence, requiring careful consideration of the diverging beam.
• An EMR point source produces a spherical wavefront.

Reflection of Light

• EMR/light is treated according to wave theory when analyzing phenomena like interference and diffraction.
• Snell's law relates the propagation angles to refractive indices of two different media.
• There are incident and transmitted wave angles (θ₁, θ₂).
• n₁ and n₂ are the refractive indices of the first and second media, with n₁≠ n₂.
• sin(θ₁)/n₁ = sin(θ₂)/n₂
• Total internal reflection (TIR) occurs when n₁ > n₂ and the incident angle θ₁ is large enough.

Total Internal Reflection (TIR)

• TIR occurs when θ₁ > θc, where θc is the critical incidence angle.
• Critical incidence angle for TIR is defined by sin θc = n₂ / n₁

Reflection of Light (Continued)

• The reflected wave in TIR has the same amplitude as the initial wave but with a phase shift.
• The formulas for phase changes in reflection are dependent on whether the incident wave is perpendicular or parallel to the boundary.

Reflection Coefficients and Reflectance

• Fresnel equations define the reflection and transmission coefficients in terms of the electric field components.
• When normal incidence (θ₁ = 90°) occurs, the reflection coefficients are equal.

Photons

• EMR/light energy is carried by quanta called photons.
• The energy of a photon is dependent on its frequency (υ) or wavelength (λ), and is computed from E = hv = hc/λ, where h is Planck's constant and c is the speed of light.

Photon Interaction with Matter

• In particle treatment, photons interact with semiconductors such as silicon photodiodes, which can be used for imaging sensors.

The Spectrum

• EMR is categorized by wavelength into distinct regions including radio, microwave, infrared, visible, ultraviolet, X-rays, and gamma rays.
• This course focuses on the visible spectrum relevant to imaging.

Spectrum of Visible Light

• The visible spectrum ranges from approximately 400 nm to 700 nm.
• Different wavelengths are sensed by human eyes as different colors, with 400 nm being blue and 700 nm being red.

Electromagnetic Radiation and the Atmosphere

• Earth's atmosphere blocks some ranges of EMR.
• Visible light and most radio waves pass through the atmosphere in both directions.

Solar Radiation Spectrum

• The Sun's emission spectrum at sea level appears almost uniform in the visible range.
• A significant portion of solar radiation is in the infrared region.
• Absorption of light by atmospheric molecules (O₂, O₃, H₂O) causes dips in the spectrum.

Traditional Light Sources

• Incandescent lamps emit a lot of infrared radiation.
• Halogen lamps are more efficient but still emit much infrared radiation.
• Fluorescent lamps are the most efficient of the three.

Light Emitting Diodes (LEDs)

• LEDs have higher efficiency than traditional lamps.
• LEDs typically emit one color, and white light is generated with a phosphor coating.

Bandwidth

• Bandwidth is the width of the optical spectrum of the output of a light source (e.g., a LED).
• It is often expressed as FWHM (full-width at half-maximum).

Luminous Intensity, Luminous Flux, and Illuminance

• Luminous intensity (cd): the power emitted by a light source in a given direction in a unit solid angle, weighted by human eye sensitivity.
• Luminous flux (lm): the total power of light emitted by a source to all directions, weighted by human eye sensitivity.
• Illuminance (lx): luminous flux per unit area (e.g., lm/m²).

Radiant Intensity and Irradiance

• Radiant intensity: total power emitted by a light source in a given direction with respect to a unit solid angle and is independent of wavelength.
• Irradiance: The total power of light arriving on a surface and is independent of wavelength.

Summary (Additional)

• Discussion of how the concepts of this lecture apply to real-world digital imaging systems, with a particular focus on image sensors such as CCD and CMOS, and the related techniques and procedures to analyze the properties of the image captured and the objects.

Further Topics

• The material includes discussion of image processing techniques (e.g., filtering), measurement uncertainties, additional techniques, and considerations for dealing with non-ideal characteristics. Other topics include how to segment, analyze objects based on edges, and apply these techniques to real-world scenarios. Methods, such as histogram equalization and other non-linear methods, along with important considerations to obtain good measurements.

Additional Note

• The study notes are derived from the provided materials and should therefore provide considerable insight into the subject material presented.

This quiz covers the key concepts related to CMOS and CCD image sensors, exploring their characteristics, applications, and underlying physics. Topics include pixel binning motivations, the properties of photodiodes, and the effects of light on sensor performance. Test your knowledge on the advanced imaging technology used in various devices.