- This article contains text copied from Wikipedia under the terms of the GFDL. It needs to be edited to have a Computer vision focus.
A digital camera, as opposed to a film or video camera, uses an electronic sensor to transform images (or video) into electronic data. Modern digital cameras are typically multifunctional and the same device can take photographs, video, and/or sound.
In 2005, digital cameras are starting to push traditional film cameras out of many markets. Shrinking device sizes have recently allowed miniaturized digital cameras to be included in multifunctional devices, such as cell phones and PDAs.
Digital cameras can be classified into several groups:
- Professional video cameras such as those used in television and movie production. These typically have multiple image sensors (one per color) to enhance resolution and color gamut. Professional video cameras usually do not have a built-in VCR or microphone.
- Camcorders used by amateurs. These are a combination of camera and VCR to create an all-in-one production unit. They generally include a microphone to record sound, and feature a small LCD to watch the video during filming and playback.
Digital still cameras are generally characterized by the use of flash memory and USB or FireWire for storage and transfer. Most have a rear LCD for reviewing photographs. They are rated in megapixels; that is, the product of their maximum resolution dimensions. The actual transfers to a host computer are commonly carried out using the USB mass storage device class (so that the camera appear as a drive) or using the Picture Transfer Protocol and its derivatives. All use a CCD (for Charged Coupled Device) which is a chip comprised of a grid of phototransistors to sense the light intensities across the plane of focus of the camera lens. There has recently been some application of a second kind of chip, called a CMOS (Cadmium Metal-Oxide Silicon) sensor, and this chip is often differentiated from a CCD proper in that it uses less power and a different kind of light sensing material, however the differences are highly technical and many manufacturers still consider the CMOS chip a charged coupled device. For our purposes, a chip sensor is a CCD.
- Standard Digital Cameras: This encompasses most digital cameras. They are characterized by great ease in operation and easy focusing; this design allows for limited motion picture capability. They have an extended depth of field. This allows objects at multiple depths to be in focus simultaneously, which accounts for much of their ease of focusing. It is also part of the reason professional photographers find their images flat or artificial-looking. They excel in landscape photography and casual use.
- Digital SLRs typically have a sensor nine times larger than that of a standard digital camera, and are targeted at professional photographers and enthusiasts. They resemble ordinary professional cameras in most ways, with replaceable flash and lens components, which give the user maximum control over light, focus and depth of field. They are also bulkier and more expensive than their casual-use oriented counterparts. They are superb for portraiture and artistic photography because they can be customized for various applications with a comprehensive range of exchangeable lenses.
Professional modular digital camera systemsEdit
High-end digital camera backs used by professionals are usually separate devices from the camera bodies which they are used with. (This is because most of the large- and medium-format camera systems in professional use at the time that digital capture overtook film as the professional's medium of choice were modular in nature, i.e. the camera body had multiple lenses, viewfinders, winders and backs available for use with it to fit different needs.) Since the first backs were introduced there have been three main methods of "capturing" the image, each based on the hardware configuration of the particular back.
The first method is often called "Single Shot," in reference to the number of times the camera's sensor is exposed to the light passing through the camera lens. Single Shot capture systems use either one CCD with a Bayer filter stamped onto it or three separate CCDs (one each for the primary additive colors Red, Green and Blue) which are exposed to the same image via a beam splitter.
The second method is referred to as "Multi-Shot" because the sensor is exposed to the image in a sequence of three or more openings of the lens aperture. There are several methods of application of the multi-shot technique. The most common originally was to use a single CCD with three filters (once again red, green and blue) passed in front of the sensor in sequence to obtain the additive color information. Another multiple shot method utilized a single CCD with a Bayer filter but actually moved the physical location of the sensor chip on the focus plane of the lens to "stitch" together a higher resolution image than the CCD would allow otherwise. A third version combined the two methods without stamping a Bayer filter onto the chip.
The third method is called "Scan" because the sensor moves across the focus plane much like the sensor of a desktop scanner. These CCDs are usually referred to as "sticks" rather than "chips" because they utilize only a single row of pixels (more properly "photosites") which are again "stamped" with the Bayer filter.
The choice of method for a given capture is of course determined largely by the subject matter. It is usually inappropriate to attempt to capture a subject which moves (like people or objects in motion) with anything but a single shot system. However, the higher color fidelity and larger file sizes and resolutions available with multi-shot and scan-backs make them attractive for commercial photographers working with stationary subjects and large-format photographs.
- Webcams are digital cameras attached to computers, used for video conferencing or other purposes. Webcams can capture full-motion video as well, and some models include microphones or zoom ability. These devices range in price from very inexpensive to expensive higher-end models; many complex webcams have a servo-controlled base capable of tracking facial motion with the help of software.
Practical resolution considerationsEdit
It is important to note that with any digital camera system not using the beam splitter single-shot approach or three-filter multi-shot approach, some image color or resolution "interpolation" is taking place. The software specific to the camera interprets the information from the sensor to obtain a full color image. This is because in digital images, each pixel must have three values for luminous intensity, one each for the red, green, and blue channels. However, a photosite on a regular (non-Foveon) sensor cannot simultaneously record these three values, which is why the Bayer filter is used. A Bayer filter is actually a pattern of red, green and blue light filters applied one color to each photosite on a chip or a stick (usually there are about twice as many green filters as there are either red or blue because the frequencies of light in the green spectrum tend to represent a more neutral intensity value for interpolation's sake, sitting as it does nearer the center of the visible light spectrum.) The two luminous intensity color values not captured for each pixel are then interpolated (or guessed at) from the values of adjacent pixels which represent the color being calculated. In some cases, extra resolution is interpolated into the image by shifting photosites off of a standard grid pattern so that photosites are adjacent to each other at 45 degree angles, and all three values are interpolated for "virtual" photosites which fall into the spaces at 90 degree angles from the actual photosites.
Digital cameras need memory to store data. Cameras use a removable memory card to store data, but the cheapest and smallest cameras may simply use fixed internal memory instead. Some cameras come with inbuilt memory as well.
An autonomous device, such as a PictBridge-compatible printer, operates without need of computer control. The camera connects to the printer, which then downloads and prints its images. Some DVD recorders and television sets can read memory cards.