Digital Cameras
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Wikipedia-Article "Digital Cameras"
A digital camera, is an electronic device to transform images into electronic data. Modern digital cameras are typically multifunctional and the same device can take photographs, video, and/or sound.
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History
Steven Sasson, an engineer working for Eastman Kodak, is credited with developing the first digital camera, an 8-pound toaster sized box that captured a black-and-white image on a digital cassette tape at a resolution of .01 megapixels. Sasson's masters supervisor, Gareth Lloyd, set him an open ended assignment. The question was simply 'Could we build a camera using solid-state imagers?' At that time (1970s) the CCD had just come out, and people were curious about its applications. Before that time television cameras had converted images into analog electrical signals, cameras aboard robot space probes had digitized photographs using vacuum tube components and relayed them back to Earth, and Texas Instruments had designed a filmless but analog-based electronic camera in 1972. No one, however, had attempted a completely solid-state digital-video device.
For his device, Sasson used an analog-to-digital converter adapted from Motorola Inc. components, a Kodak movie-camera lens and the tiny CCD chips introduced by Fairchild Semiconductor in 1973.
Sony marketed Mavica, the first filmless camera in 1981. Mavica worked off magnetic disks and was based on television technology that inherently limited image quality.
Classification
Digital cameras can be classified into several groups:
Video cameras
- 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.
- 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.
Still cameras
Digital still cameras are cameras whose primary purpose is to capture photography in a digital format. Initially, a digital camera was characterized by the use of flash memory and USB or FireWire for storage and transfer of still photographs, and this is still the common meaning of the unadorned term. However, modern digital photography cameras have a video function, and a growing number of camcorders have a still photography function. In addition, some newer camcorders record video directly to flash memory and transfer over USB and FireWire. Among digital still cameras, most have a rear LCD for reviewing photographs. They are rated in megapixels; that is, the product of their maximum resolution dimensions in millions. 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 either a CCD (Charge-Coupled Device) or a CMOS sensor, i.e. chips comprised of a grid of phototransistors to sense the light intensities across the plane of focus of the camera lens. CMOS (Complementary Metal-Oxide Semiconductor) sensors are differentiated from CCDs 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 (also called compact digital cameras or digicams): 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 (DSLR) typically have a sensor many 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, most 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 systems
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.
Interpolation
Image color or resolution interpolation is used unless the camera uses a beam splitter single-shot approach, three-filter multi-shot approach, or Foveon X3 sensor currently used in Sigma SD10 DSLR and Polaroid x530 point and shoot. 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. A normal sensor element cannot simultaneously record these three values.
The Bayer filter pattern is typically used. A Bayer filter pattern is a 2x2 pattern of light filters, with green ones at opposite corners and red and blue elsewhere. The high proportion of green takes advantage of properties of the human visual system, which determines brightness mostly from green and is far more sensitive to brightness than to hue or saturation. Sometimes a 4-color filter pattern is used, often involving 2 different hues of green. This provides a wider color gamut, but requires a slightly more complicated interpolation process.
The luminous intensity color values not captured for each pixel can be 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.
Connectivity
Many digital cameras can connect directly to a computer to transfer data. Early cameras used the PC serial port. USB is the most widely used method, though some have a FireWire port or use Bluetooth. Some cameras such as the Kodak EasyShare One are able to connect to computer networks wirelessly via 802.11 Wi-Fi.
Integration
Some devices, like mobile phones and PDAs, contain integrated digital cameras. Mobile phone cameras are even more common than standalone digital cameras.
Storage
Digital cameras need memory to store data. Cheap cameras and cameras secondary to the devices main use (such as a camera phone) use onboard memory, such as flash memory. Most dedicated cameras, however, use a removable memory card to store data. In common use are Compact Flash (CF) (which includes microdrives, as they use the same format), Secure Digital (SD) cards and xD cards.
Autonomous devices
An autonomous device, such as a PictBridge printer, operates without need of a computer . The camera connects to the printer, which then downloads and prints its images. Some DVD recorders and television sets can read memory cards too.
Formats
Common formats in digital camera images are DCF, DPOF, EXIF, JPEG, RAW, TIFF; formats for movies are AVI, DV, MPEG, MOV, WMV etc.
See also
- Bluetooth
- Camera phone
- Computer printer
- Digital camera memory media
- Digital image editing
- Digital photography
- List of digital camera brands
- Mobile Imaging and Printing Consortium
- Still video camera
- Personal storage device
External links
- The first digital camera involving Kodak engineer Steven Sasson.
- Digital camera related freeware archive (Windows/MAC/Linux)
- HD/DV Cameras at FilmDailies.com - a filmmaker's blog
- Article on Steven Sasson
- Digital cameras on About.com
- DPreview a popular guide to digital cameras.