Like the standard film camera, the digital camera uses a lens to focus an image on a focal plane. While the film camera captures the image on the film, the digital camera relies on an image sensor. As light strikes the array of photosites which make up the sensor, it is converted to a current that is then passed to the Analogue to Digital Converter (A-D converter). Algorithms are then applied to convert the data in the sensor to pixels in a digital image. The size of the captured image is proportional to the size of the sensor.

Types of digital cameras

Entry-level fixed-focus cameras. These cameras, designed for point-and-shoot applications, have long battery life and are generally highly portable. While image quality is not the highest, these cameras are extremely convenient. Because of these cameras' low resolution, generally less than a megapixel (images made up of 1 million pixels), printed output is limited to about 4" x 6" or so. Despite this small size, the images are ideal for Web pages and e-mail attachments.

Mid-level cameras. (also referred to as prosumer). These cameras, based on the 35mm model but designed exclusively for digital photography, add new capabilities to a fixed-focus. Generally, the larger image size (approximately 2 megapixels) is combined with more advanced features such as through-the-lens (TTL) focusing, overrides of manual controls, and a choice of exposure modes such as aperture-priority or shutter-priority. These cameras appeal to photographers who like to have creative control of their camera settings; they produce prints up to about 8" x 10" in size.

High-end cameras. These cameras are used to capture images at very high quality, with resolution of 3 or 4 megapixels or more. In addition to higher resolution, they feature zoom lenses, exchangeable lenses and other features designed to push the quality of digital imaging to its highest. They're intended for professional applications, and can be used to capture images for archival purposes.