Interesting Stuff: How does a digital camera work

Traditional film captures an image utilizing an eye and shutter apparatus. Once you snap or press the appropriate button or lever on a film camera, the shutter opens, passes light from the image through the lens to the eye and then quickly closes. A chemical process is then used to imprint the image sent from the lens to film or photo paper in the bottom or rear of the camera body. Similarly, a digital camera also uses a shutter and eye to capture light from an image. However, instead of using a chemical process to imprint the image on a film negative, a digital camera captures the image digitally. The data representing the image is stored in bits and bytes, allowing other computers and digital devices to interpret it. In most cases, digital cameras store images on flash memory cards or USB sticks, but some models store image data on disk drives like those found in laptop computers.

To capture light from an image in digital format, a digital camera uses a special sensor, usually called a CCD (charge-coupled device) or CMOS (complementary metal-oxide semiconductor) sensor. Both types of sensors are common in thousands of digital camera models and both provide excellent mediums for capturing digital images. CCD and CMOS sensors are typically the size of a fingernail and fabricated out of silicon. The surface of the sensor contains millions of micro-sized diodes that capture a single pixel of the image captured by the lens eye when the shutter opens and closes. Generally, the more diodes on the surface of the sensor, the better quality picture a digital camera is able to take. When you see references to megapixels in camera specifications, they refer to the number of sensors on the surface of the CCD or CMOS sensor. Digital cameras with higher megapixel ratings generally take higher resolution, or clearer, pictures than models with lower megapixel specifications.

Early film cameras could only capture a photographic image in black and white. Producing a color photograph required hand coloring after the picture was taken and developed. In 1860, James Clerk discovered a way to convert black-and-white images to color ones using special red, blue and green filters. Simply put, a camera creates three different images using each colored filter and then aligns the three filtered images to create one full-color image. Modern cameras use a sophisticated process called “interpolation” to filter red, blue and green colors and then combine them once the shutter allows an image to pass to the eye of the camera. All colors in the viewable spectrum contain some mixture of red, blue and green – even black and white – and the CCD or CMOS sensor in the camera provides all of the RGB (red, green, blue) information needed for the processor in the camera to interpret colors from the image scene passed from the lens to the sensor.

Whenever you take a picture with a digital camera, millions of operations occur very quickly inside the camera. In order for a digital camera to capture, interpolate, compress, filter, store and preview images, it uses a tiny on-board computer. In some respects, the computer in a digital camera is similar to the one you are probably using to view this article. It has a processor, memory and a storage medium; but unlike a laptop or desktop computer, the computer inside a digital camera usually resides on a single chip. While capturing and interpolating images would require a considerable amount of processing power if used on a computer with many software programs installed, manufacturers are able to use lower-cost and smaller single-chip computers in digital cameras because they perform only a very limited number of functions and advanced math operations. Digital cameras with the simplest on-board computer chips perform basic picture-taking functions relatively well. More advanced models often have larger, higher-capacity chips that allow the user to perform basic editing functions such as red-eye removal, image enhancement and borders, and even blur removal directly on the camera before the images are transferred to a PC.

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