Image Sensor Chapter Overview

This chapter explains the optical structure of a modern CMOS image sensor (CIS) pixel and the chain of physical effects that turn incident photons into a measurable signal.

What an image sensor pixel is

A CIS pixel is a layered optical stack on top of a silicon photodiode. Light entering from the top passes through a microlens, planarization, color filter, anti-reflection layer (BARL), and finally into silicon, where it is absorbed and generates electron-hole pairs. The collected charge is read out as the pixel signal.

In COMPASS the layer order from bottom to top is:

silicon → BARL → color filter → planarization → microlens → air

Light propagates in the −z direction (air → silicon), and z = 0 is at the silicon bottom.

What this chapter covers

Page	Topic	Key takeaway
Image Sensor Optics	BSI architecture, microlens, CFA, BARL, DTI	Anatomy of the optical stack and what each layer does
Pixel Optical Effects	CRA, CFA spectral response, BARL, silicon absorption, DTI, angular and polarization response	Design trade-offs that shape QE and crosstalk
Quantum Efficiency	QE definition, computation methods, crosstalk	The headline metric and how COMPASS measures it
Signal Chain	Illuminant → scene → lens → sensor signal	How simulated QE turns into a radiometric pixel value
Color Reproduction	Camera RGB, CIE XYZ, Lab, sRGB, CCM, color error	How spectral sensor response becomes standard color metrics
Noise, SNR, and Dynamic Range	Shot/read/dark/FPN noise, FWC, DR, PTC, responsivity, linearity	Full noise model behind every signal-chain prediction
EMVA 1288 Characterization	EMVA 1288 parameter set, SNR curve, quality grades	Standard reporting format for sensor characterization
Resolution, MTF, and Pixel Scaling	Pixel aperture MTF, optical diffraction, Nyquist, pitch scaling	Spatial frequency response and pitch trade-offs

Boundary with nearby pages

Nearby page	Difference
Pixel Anatomy	A guided beginner tour of the same stack; this chapter is the compact technical model.
Optics	Defines the wave-optics laws; this chapter maps them onto sensor components.
Simulation	Explains the numerical methods that compute the fields and absorbed power.

How to read this chapter

• If you only care about the optical design of the pixel, Image Sensor Optics is enough.
• If you are evaluating sensor performance, continue with Pixel Optical Effects and Quantum Efficiency.
• If you need end-to-end image quality predictions, read Signal Chain, Color Reproduction, and Noise, SNR, and Dynamic Range.
• If you are reporting against an external standard, see EMVA 1288 Characterization.
• If you are choosing a pixel pitch or evaluating sharpness, see Resolution, MTF, and Pixel Scaling.

Prerequisites

This chapter assumes you are comfortable with the Optics chapter — at minimum, refractive index, absorption, and polarization.