Photography basics · Camera

Camera Sensor

A Guide for Photographers and Cinematographers

Written by Abin Alex and Anu Joseph.

Creative Hut Academy Library · Last updated 31 October 2026

Abstract

A camera sensor is a silicon chip covered in millions of light-sensitive spots called photosites, each of which turns light into an electrical charge that becomes one pixel. This guide explains how a pixel works, the difference between CCD and CMOS sensors, how a sensor sees colour, and whether bigger pixels and bigger sensors give better pictures. It also covers backside illumination, stacked sensors and rolling shutter, the processing of the signal after the sensor, and the sensor features that matter in each kind of photography. It is written for photographers and cinematographers.

Keywords: camera sensor; CMOS; CCD; pixel; sensor size

What is a camera sensor?
How does one pixel work?
What is the difference between a CCD and a CMOS sensor?
How does a sensor see colour?
Do bigger pixels and bigger sensors give better pictures?
What are backside illumination, stacked sensors and rolling shutter?
What happens to the signal after the sensor?
Which sensor features matter for each kind of photography?

What is a camera sensor?

Short answer. A camera sensor is a solid-state silicon chip made of an array of photosites. Each photosite absorbs photons and releases electrons, and each one represents one pixel of the final image.

The chip is thin silicon. It sits behind a transparent cover glass that protects it, in a package that protects the wiring and helps carry away heat. Fine wire bonds connect it to the rest of the camera.
Photosites are also called photodiodes or sensels. The sensor is a grid of them in rows and columns.
Makers quote effective pixels, the pixels used for the picture. Canon lists the PowerShot V10 with about 20.9 MP in total and about 15.2 MP for stills (Canon Europe, n.d.).
Every sensor is described by its structure (CCD or CMOS), colour or monochrome, shutter type (global or rolling), resolution, frame rate, pixel size and sensor format.
The signal travels as photon, electron, voltage and then binary number.

In photography

When you press the shutter, the sensor collects light for the exposure time. A brighter scene puts more charge into each photosite.

In cinematography

A cinema camera records on a sensor too. The sensor format and how fast it reads out are part of why a DOP chooses one camera over another.

[Lecture example slot: a camera with its lens removed showing the sensor]

Cham tipRemove the lens in a clean place, with the camera off, and look at your sensor. Never touch it.

Cham taskFind your camera’s sensor size, total pixels and effective pixels in its specifications and write them down.

Check yourself: What is the difference between a photosite and a pixel?

A photosite is the light-sensitive spot on the chip. Each one gives one pixel of the picture, although the totals can differ because of effective pixels.

Next question ↓Back to contents ↑

How does one pixel work?

Short answer. Each photosite is a small stack. A microlens focuses the light, a colour filter passes one colour, a photodiode turns photons into electrons, a potential well stores them and an amplifier boosts the signal.

Microlenses sit above each pixel. They widen the area that collects light and aim it at the photodiode, which helps in low light.
The photodiode is a semiconductor junction that turns light into electric current. The stronger the light, the more electrons it makes.
The electrons collect in a potential well, like water in a bucket. The full well capacity is how much charge the pixel can hold before it overflows. Larger pixels have deeper wells.
Quantum efficiency is the share of photons turned into electrons. If 10 photons arrive and 6 electrons are made, the efficiency is 60 per cent.
Transistors share the pixel area, so only part of it is light sensitive. Microlenses make up for this.

Figure 1. One pixel in cross-section. Light passes the microlens and the colour filter, reaches the photodiode and is stored as charge.

In photography

In a bright sky, the photosites fill their wells. When the well is full, the highlight is lost. This is why bright skies look pure white.

In cinematography

A DOP who reads a sensor’s dynamic range is really reading how deep its wells are and how quietly it reads them. The deeper the well, the more highlight detail survives.

[Lecture example slot: a diagram of a pixel stack from a camera maker]

Cham tipThink of a bucket in the rain. Light is rain, the pixel is the bucket. A bigger bucket overflows later.

Cham taskExplain to a friend, using the bucket idea, why a bright sky turns white.

Check yourself: If 20 photons hit a pixel and 9 electrons are produced, what is the quantum efficiency?

45 per cent, because 9 divided by 20 is 0.45.

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What is the difference between a CCD and a CMOS sensor?

Short answer. Both turn light into charge. A CCD moves the charge across the chip to one corner to be read, which gives very uniform quality but uses more power. A CMOS sensor puts transistors at every photosite so it reads out faster, uses less power and costs less. CMOS is in almost every camera today (Canon Europe, n.d.).

The CCD was invented in 1969 by Willard Boyle and George Smith at Bell Laboratories (Boyle and Smith, 1970). They shared the 2009 Nobel Prize in Physics for it.
The CMOS active pixel sensor was developed by Eric Fossum at NASA’s Jet Propulsion Laboratory in 1993 (Fossum, 1993).
In a CCD, the charges queue up and move step by step to one amplifier. In a CMOS sensor each pixel has its own amplifier, so it is more like a self-checkout.
CMOS can also carry other circuits on the same chip, such as converters, which is why it spread into phones and mirrorless cameras.
CCDs are still used where uniform, precise images matter more than speed and power, such as science work.

Feature	CCD	CMOS
Readout	Serial, through shift registers	Parallel, from each pixel
Speed	Slower	Faster
Power use	Higher	Lower
Cost	More expensive	Cheaper
Extra circuits on chip	Limited	Many

Table 1. CCD and CMOS compared (Canon Europe, n.d.).

In photography

A phone shooting a burst of 4K video is only possible because a CMOS sensor can read out quickly and cheaply. An old CCD camera could not.

In cinematography

Early digital cinema cameras used CCDs. Modern cinema cameras use CMOS sensors because they give high frame rates and low power use at large sizes.

[Lecture example slot: a CCD and a CMOS chip side by side]

Cham tipWhen you read the word CMOS in a spec sheet, remember it means each pixel reads out by itself.

Cham taskFind out whether your camera has a CCD or CMOS sensor and write one benefit you gain from it.

Check yourself: Which type of sensor has an amplifier at every pixel?

CMOS. A CCD uses one amplifier for the whole sensor.

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How does a sensor see colour?

Short answer. A photosite measures only how much light reaches it. To record colour, most sensors place a red, green or blue filter over every photosite in a Bayer pattern, with half green, a quarter red and a quarter blue. The camera then works out the missing colours at each pixel. This is called demosaicing (Canon Europe, n.d.).

The Bayer colour filter array was invented by Bryce Bayer at Eastman Kodak and patented in 1976 (Bayer, 1976).
There are more green photosites because the eye is most sensitive to green (Canon Europe, n.d.).
Each photosite sees one colour only. The processor demosaics, or debayers, the data to give each pixel full red, green and blue values (Canon Europe, n.d.).
Foveon sensors stack three layers so every pixel records all three colours without demosaicing. They are found mainly in Sigma cameras.
Fujifilm’s X-Trans uses a 6 × 6 variation of the Bayer idea. A monochrome sensor has no colour filters, so every pixel records the full range of light.

Figure 2. The Bayer pattern. Half of the photosites are green, a quarter are red and a quarter are blue.

In photography

A red flower fills the red photosites with charge and the blue ones with very little. The processor combines the neighbours to give each pixel its colour.

In cinematography

Colourists see the result of demosaicing in RAW video. Cinema cameras record the raw Bayer data, and the colour is built later in post.

[Lecture example slot: a close-up crop showing the Bayer pattern]

Cham tipIf a sensor has no colour filters it can be sharper and more sensitive, but it only makes black and white pictures.

Cham taskDraw a 4 × 4 Bayer grid. Mark each square R, G or B and count how many of each there are.

Check yourself: In a Bayer sensor, what share of photosites are green?

Half. A quarter are red and a quarter are blue.

Next question ↓Back to contents ↑

Do bigger pixels and bigger sensors give better pictures?

Short answer. Usually yes in low light. Larger photosites collect more light, which gives less noise and a wider dynamic range. Pixel pitch is the distance between pixel centres. It equals the sensor width divided by the number of pixels across it. Full frame has about 1.6 times the area of APS-C (Canon Europe, n.d.).

Pixel size is measured in microns (µm). One micron is one millionth of a metre.
Canon gives about 4.22 µm for a 21 MP APS-C camera and about 6.45 µm for a 21 MP full frame camera (Canon Europe, n.d.).
Worked example. A 24 MP full frame sensor is 36 mm wide with 6,000 pixels across. 36 mm ÷ 6,000 = 6.0 µm. A 24 MP Canon APS-C sensor is 22.2 mm wide, so 22.2 ÷ 6,000 = 3.7 µm.
More megapixels on the same sensor means smaller pixels. See the Resolution and Image Size guide.
Bigger pixels hold more charge, so they usually give better signal to noise and dynamic range. A bigger sensor does not guarantee a better picture, but it gives the maker more room.

Sensor	Size	Typical use
Full frame	36 × 24 mm	Stills, many cinema and video cameras
APS-C	22.2 × 14.8 mm (Canon)	Compact stills and video bodies
Super 35	about 24.6 × 13.8 mm active area	Cinema and video

Table 2. Common sensor sizes (Canon Europe, n.d.).

In photography

A full frame camera at ISO 6400 in a dim hall often looks cleaner than a small sensor at the same ISO because its pixels gather more light.

In cinematography

Cinema cameras often use Super 35 or larger sensors. The size changes how much of the lens is used and how shallow the depth of field looks.

[Lecture example slot: two sensors of different sizes next to each other]

Cham tipWhen comparing cameras, look at sensor size and pixel pitch together, not megapixels alone.

Cham taskFind your camera’s width in millimetres and pixels across. Work out its pixel pitch.

Check yourself: A sensor is 36 mm wide and has 8,000 pixels across. What is its pixel pitch?

4.5 µm, because 36 ÷ 8,000 = 0.0045 mm.

Next question ↓Back to contents ↑

What are backside illumination, stacked sensors and rolling shutter?

Short answer. In a backside illuminated (BSI) sensor the light reaches the photodiode without passing through wiring, which helps in low light. A stacked sensor adds a layer of circuits behind it so it reads out faster. Faster readout reduces rolling shutter, the skew you see when a CMOS sensor reads a moving subject line by line (Canon Europe, n.d.).

In front-illuminated designs the light passes through metal wiring first. Some light is lost or leaks into neighbouring pixels, which is called crosstalk.
In BSI, the chip is reversed so light enters from the back and hits the photodiode directly. Canon says BSI improves low-light performance (Canon Europe, n.d.).
Stacked designs put the photodiodes above the transistor layer. Canon says this improves light collection and allows faster readout (Canon Europe, n.d.).
Most CMOS sensors read out line by line. A fast-moving subject or a quick pan then looks skewed. This is rolling shutter (Canon Europe, n.d.).
A global shutter reads the whole sensor at once and avoids skew. Canon notes it is complex, and adds cost and noise (Canon Europe, n.d.). A small number of recent cameras use it.

Feature	Front-illuminated	Backside-illuminated
Light path	Passes through wiring layers	Direct to the photodiode
Efficiency	Lower	Higher
Crosstalk	More likely	Less likely
Cost	Lower	Higher

Table 3. Front and backside illumination compared.

In photography

Photographing a spinning propeller with an electronic shutter can show bent blades. A faster stacked sensor bends them less.

In cinematography

A fast whip pan on a slow-reading sensor makes vertical lines lean. Cinema cameras with fast readout or global shutters avoid this.

[Lecture example slot: a frame showing rolling shutter skew on a fast pan]

Cham tipIf you see bent verticals when you pan or shoot fast action, rolling shutter is the cause. Slow down the pan or change the shutter mode.

Cham taskPan quickly past a vertical pole in video and watch for lean. Then pan slowly and compare.

Check yourself: What does a global shutter do that a rolling shutter does not?

It reads the whole sensor at once, so moving subjects are not skewed.

Next question ↓Back to contents ↑

What happens to the signal after the sensor?

Short answer. The sensor’s charge is amplified, turned into a binary number by an analogue to digital converter, processed by the camera’s image processor, held in buffer memory and then written to the memory card.

The converter splits the signal into steps. A 12-bit file has 4,096 tonal levels and a 14-bit file has 16,384.
The image processor handles autofocus, exposure, white balance, noise reduction and compression to JPEG, HEIF or RAW.
Makers have their own processors, for example Canon DIGIC, Nikon EXPEED and Sony BIONZ.
The buffer is fast temporary memory. It holds images during a burst until the card has written them. RAW files fill it faster than JPEG files.
The memory card keeps the files. Its write speed limits bursts and video, and its read speed limits transfers.

Figure 3. From light to file.

In photography

In a burst of sports shots, the camera shoots quickly until the buffer fills. Then it waits while the card catches up.

In cinematography

High-bitrate video needs fast cards because the buffer and card must keep up with a constant stream of data.

[Lecture example slot: a camera menu showing the burst buffer count]

Cham tipUse a fast card that suits your camera, especially for RAW bursts and 4K video.

Cham taskShoot a burst in RAW and then in JPEG. Count how many frames you get before the camera slows.

Check yourself: How many tonal levels does a 14-bit file have?

16,384. That is 2 to the power of 14.

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Which sensor features matter for each kind of photography?

Short answer. Match the sensor to the job. Low-light work wants big pixels, action wants fast readout, landscape and product work want high resolution and wide dynamic range, and video wants low rolling shutter and a suitable sensor size.

Weddings and events: large pixels and BSI for clean high-ISO files in dim halls.
Sports and wildlife: a stacked sensor with fast readout, for quick bursts and less rolling shutter.
Landscape: high resolution and wide dynamic range, shot at base ISO.
Product and fashion: high resolution and good colour, shot in controlled light.
Insects, reptiles and macro: high resolution so you can crop, and good performance at the higher ISO that small apertures need.
Automotive: fast readout for rolling shots and clean files for reflections and dark paint.
Photojournalism: strong low-light performance and a fast, quiet readout.
Cinematography: a suitable sensor size, wide dynamic range, low rolling shutter and a RAW recording format.

In photography

For a wedding in a dim hall, a full frame BSI camera at ISO 3200 usually gives a cleaner result than a small sensor camera.

In cinematography

For a fast action scene, a camera with a fast readout avoids skewed vertical lines during whip pans.

[Lecture example slot: one camera body with notes for each kind of use]

Cham tipChoose the sensor for your most demanding job, not for the specifications that look best on paper.

Cham taskName your main kind of photography. Write the three sensor features that matter most for it.

Check yourself: Which sensor feature helps most to reduce skew in fast action?

Fast readout, as in a stacked sensor, or a global shutter.

Go to the FAQ ↓Back to contents ↑

Questions beginners ask

What is a camera sensor?

A silicon chip covered in light-sensitive photosites. Each one turns light into an electrical charge that becomes one pixel of the picture.

Is CMOS better than CCD?

For most cameras, yes. CMOS reads out faster, uses less power and costs less. CCDs are still used where uniform, precise images matter most.

Does a bigger sensor mean better pictures?

Bigger sensors usually have bigger pixels, which helps in low light and dynamic range. Lens, light and technique still matter more.

Why do phones struggle in low light?

Their sensors are small and their pixels are small, so each collects less light. Phones use software to compensate.

What is rolling shutter?

The skew you see when a CMOS sensor reads a scene line by line and the subject or camera moves quickly. Faster readout or a global shutter reduces it.

References

Bayer, B. E. (1976) Color imaging array. US Patent 3,971,065. Washington, DC: United States Patent Office.
Boyle, W. S. and Smith, G. E. (1970) ‘Charge coupled semiconductor devices’, Bell System Technical Journal, 49(4), pp. 587–593.
Canon Europe. (n.d.) Camera sensors explained. www.canon-europe.com/pro/infobank/image-sensors-explained/
Fossum, E. R. (1993) ‘Active pixel sensors: are CCDs dinosaurs?’, Proceedings of SPIE, 1900, pp. 2–14.

How to cite this guide. Alex, A., & Joseph, A. (2026). Camera sensor: A guide for photographers and cinematographers. Creative Hut Academy. https://creativehut.org/library/camera-sensor/

© 2026 Creative Hut Academy. Written by Abin Alex and Anu Joseph. Drafted with AI assistance. Last updated 31 October 2026. This guide is free to read. To copy, republish, translate or adapt any part of it, including the diagrams, you need written permission. Ask through the contact page. The books, standards and data sheets listed above are sources, not copies. Found a mistake? Write to director@creativehut.org.

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