Why infrared signal can be detected by ccd camera?

Question

Why it looks white?

Answer 1

CCDs are naturally sensitive out to about 1000 nm (nanometers), while the human eye can't see much past 760 nm. CCD cameras have infrared blocking filters, but some of them still let a fair amount of infrared in. A quick test of whether your camera is infrared sensitive is to point your TV remote at it and push a button. If it's sensitive, you'll see the IR LED light up in the LCD viewer.

A CCD camera uses red, green, and blue filtered pixels to form a color image. Infrared looks white because apparently all of these pixel filters let IR through.

Answer 2

CCDs or charge-coupled device uses a silicon to receive light - it is a group of photosites or light-sensitive cells. A photosite corresponds to a single pixel. So a CCD cam with resolution of 320X240 has 76.8K photosites.

Everything around us emit IR or heat. Those sensors in CCD cams are nothing more than microbolometer (thermometers). So the hotter the object, the brighter it represents.

As photons from heat bounces of the objective lens (most likely germanium), an electron is released from certain materials - photoelectric effect. This creates something called "light frame". There is also something called a "dark frame" - which is nothing more than an exposure taken when the camera is off or not recieving any signals.

To create the IR image you are wondering about , the "dark frame" is subtracted from the "light frame" - this is called "dark subtraction". What you get is a "White Hot" image.

Answer 3

The CCD sensor is sensitive to light. Its range happens to include infrared. Since you can't see infrared, the only way for you to see it is to transform the infrared portion of the spectrum into the human-visible portion of the spectrum. One could write software to transform the sensor data so far-IR displays red and near-IR displays green or blue. Or just add it all together into a gray scale. That's basically what infrared photographic film does.

Answer 4

You're "seeing" near infrared. It appears white because it is not actually visible reflected light, but a heat signature.