How they Work

Digital Camera: Buyers Guide

How Digital Cameras Work

No two digital cameras are the same, and therefore this explanation of how a digital camera works is merely a generalization of the internal process of how a digital camera takes a picture. There are two versions of this description, an entry level description meant for the casual user who just wants to know how a digital camera works in general, and in relation to a 35mm camera. The other description is a little more technical, and for this review click here. As the internal workings on each camera works a little differently the following information may not be 100% correct as per your digital camera.

How the camera takes a picture

A digital camera is similar to a 35mm camera in the way that it takes pictures and stores them on some sort of memory card . The way a digital camera differs from a 35mm camera is what’s inside. When you prepare to take a picture on your digital camera, (by pressing the shutter release button half way down), the auto focus (if you are using it.), is applied, the CCD (charged-couple device) charges up and becomes prepared for the picture to be taken, and possibly the flash prepares to be used. Once the shutter button is fully depressed, the shutter will open, allowing light to enter the camera and strike the CCD. The light is then measured electronically on the CCD and is then sent off to the internal memory of the camera, called the buffer. Once the image information reaches the buffer, it is then compressed (if selected) into JPEG format. The completed image is then transferred to the memory card on the camera. Some cameras will need this process to finish before taking another picture, some cameras have an internal buffer that is large enough to hold a number of pictures, and can therefore take multiple pictures in a row, called burst shooting.

Before a picture is taken the camera must prepare for it. That is why there is sometimes a delay from when the shutter release button is pressed and when the picture is actually taken. Newer cameras have much faster response times, but some of the old cameras have quite a noticeable lag. To prepare for a picture to be taken, the shutter release button is pressed halfway and the camera performs a number of operations. If the camera has some of it’s automatic functions turned on, one or more of the following may need to be performed, the autofocus will need to focus in on the target, the white balance, exposure time and shutter speed need to be calculated, and the CCD (Charged-Couple Device) must be charged, as it can’t hold a charge very long. Once the shutter release button is pressed, the shutter is opened, and it allows light to pass though the lens and strike the CCD.

The CCD is made up of (usually) millions of tiny sensors that record the amount of light that hits them. The sensors only record the amount of light that hits them, not the color of the light. For the digital camera to detect what color is in each pixel, a special method is used. To capture color, the digital camera applies a color filter over the individual sensors, the filter is usually applied directly to the CCD using dye. The most common filter used is the Bayer filter, see the table at the bottom of this page for an example. This image would be 4 pixels square on the CCD, a 2×2 pixel pattern repeating thousands of times consisting of Red, Blue, and Green filters, and as you may have noticed there are twice as many green squares as red and blue. This is because human eyes have a sensitivity to the luminescence properties of green, because it is in the middle of the spectrum. So a 1 megapixel camera will have 540,000 green pixels, 270,000 red pixels, and 270,000 blue pixels. A few manufacturers use a different method involving 4 colors, (Cyan, Green, Magenta, and Yellow), see figure 2. Using this method there are an equal number of pixels for each color.