Digital Cameras

Cross-section of a Canon S2-IS camera (produced 2005),
a camera model I used to use personally.

I sold a camera on eBay today for $800. It's a super awesome camera worth several thousand dollars that records video in double-HD (2k) resolution and is usually used in laboratory settings. One of the neat things about it is that, just like on a high-end consumer camera and all professional cameras, its digital sensor is plainly visible when the lens is detached. I started thinking about the sensor and how cool they are then realized many people might not know how these devices actually work. So, how does a digital camera work?


As you can see from the cross-section, there is a LOT going on inside a digital camera, even in a mid-range consumer-level camera like this one. Let's not worry about most of it for now. We're just worried about the image sensor itself. Lenses, flash, screen, processor, batteries, buttons, logic boards, memory, auto-focus, and everything else will have to wait for another day.

The first thing you should know is that there are several types for digital image sensors, but that the most common are the CCD (Charge-Coupled Device) and CMOS sensors (Complementary Metal-Oxide-Semiconductor, or "SEE-mahs" for short). Both sensors do the same job and have very similar results, but they work in different ways.

A CCD sensor is actually an analog sensor. That may seem strange because the sensor is what makes the camera a "digital" camera, but the data is only analog for a very short period of time before it is digitized. When light hits the camera's lens barrel, it's refracted, bent, and focused to the small postage-stamp area inside the camera where the sensor chip is. When it hits a CCD chip, the photons react with small pockets on the chip (each containing a single sensor) and a very small electrical charge is created. This charge is different for every color and every brightness.

One at a time these charges are read from the chip and converted to voltages. These voltages are sent to a small computer in the camera where they are converted to usable data, then constructed into the full image. (Photonics Spectra, 2001) This all happens incredibly fast. An average modern camera has about 10 million or more sensors, yet the entire process of snapping a photo and seeing the end result happens in less than a second.

CMOS chips are actually very similar and have almost an identical image quality. The difference is that they are usually fully integrated circuits and are known as Active-Pixel Image Sensors which basically means that, rather than create one entire analog image at a time like CCDs and THEN convert it to voltage then digitized, the entire process happens on the chip itself. Every single pixel has a microscopic device paired with it that converts the pixels individually before they're fed to the camera's processor. (Digital Photo Review)

Neither type of sensor is really the superior one. Both have their faults. Have you ever seen an amateur video in which a light was too bright, causing obviously discolored lines running vertically on the screen? That's because the camera had a CCD sensor. Have you ever seen solid objects in a video seem to wobble like Jell-O when the camera moved too much? That was probably a CMOS sensor.

Look at the light on the right of the ski slope. The line coming

out of it means the camera used to shoot the video had a CCD

sensor. (Keep watching to see me crash on my skis with sparks

flying out)

As far as the wobbly video, I can't find any videos of mine that exhibit it clearly but this YouTube video does. It's a little bit different than the wobbly image I described, but it is another related side-effect possible with CMOS cameras.. As far as the actual function of the sensors and how they differ, you're now probably the most well-informed person in your circle of friends - spread the knowledge! It makes GREAT ice-breaker talk, oh yeah.

Maybe someday it won't be so technical...maybe someday our cameras will just have lab-grown eyeballs. That would be cool, too...no more static! (Mads Peitersen)