Digital photography
Digital photography is photography using a camera that uses an electronic sensor to record the image as a piece of electronic data rather than as chemical changes on a photographic film. The sensor is either a light sensitive charge-coupled device (CCD), or a CMOS semiconductor device. A digital memory device (usually flash memory; floppy disks and CD-RWs are less common) is usually used for storing images, which may then be transferred to a computer later.The advantages of this method over traditional film include:
- instant review of pictures, i.e. no wait for the film to be developed
- one only pays for any images one wants to print and one can delete the images one doesn't want to keep
- colour reproduction and gamut is not dependent on film quality
Recent digital cameras from leading manufacturers such as Nikon and Canon have promoted the adoption of digital Single-lens reflex cameras (SLRs) by photojournalists. Images captured at 2+ megapixels are deemed to be of sufficient quality for small images in newspaper or magazine reproduction. Six megapixel images, found in modern digital SLRs, when combined with high-end lenses can match or even exceed the detail of film prints taken with 35 mm film based SLRs, and the latest 12-megapixel models can produce astoundingly detailed images better than almost all 35mm images.
The number of pixels n for a given maximum resolution (w horizontal pixels by h vertical pixels) can be found using the formula: n = wh. This yields e. g. 1.92 megapixels for an image of 1600x1200. The majority of digital cameras have a 4:3 aspect ratio, i.e. w/h = 4/3.
The megapixel or pixel count quoted by the manufacturers is misleading because it is not truly representative of the number of full colour pixels. For cameras using a Bayer sensor it is the number of single coloured photosites (light sensitive areas) on the sensor. For the Foveon X3 sensor the number currently (Feb 2004 - Sigma SD-10) presented by Sigma is the number of photosites times three (multiplied because each photosite records three colours), however the images that result will have a number of pixels equivalent to the number of photosites - not the tripled number quoted. It is not possible to directly compare the megapixel ratings of these two sensors but in many people's opinions a 6MP Bayer filter sensor is roughly equivalent to a 10.2MP Foveon X3 (3.4MP*3). Some hold the opinion that the Foveon is worse than this and the ratio is more like one Bayer to two Foveon. It is largely a matter of personal opinion so prints from the two sensors should be inspected by interested parties.
With the acceptable image quality and the other advantages of digital photography (particularly the time pressures, of vital importance to daily newspapers) an increasing number of professional news photographers use these devices.
It has also been adopted by many amateur snapshot photographers, who take advantage of the convenience of the form when sending images by email and to place on the World Wide Web.
In late 2002, 2 megapixel cameras were available for less than $100 and some 1 megapixel cameras were under $60. At the same time, many discount stores with photo labs introduced a "digital front end," allowing consumers to obtain true chemical prints (as opposed to ink-jet prints) in an hour. These prices competed with prints from negatives. Kodak announced in January 2004 that they would no longer sell Kodak-branded film cameras in the developed world, an indication that the transition to digital photography for amateurs is well underway.
Some commercial photographers, and some amateurs interested in artistic photography, tend to avoid digital photography at this stage, as they believe that the image quality available from a digital camera of a given price is still inferior to that available from a film camera, and the quality of images taken on medium format film is near-impossible to match at any price with a digital camera. Some have expressed a concern that changing computer technology may make digital photographs inaccessible in the future while printed images have a very long lifespan. A related concern in a specialised application is the use of digital photographs in court proceedings, with the perceived difficulty of demonstrating an image's authenticity.
Other commercial photographers, and many amateurs, have enthusiastically embraced digital photography, as they believe that its flexibility and lower long-term costs outweigh its initial price disadvantages. Almost all of the cost of digital photography is capital cost, meaning that the cost is for the equipment needed to store and copy the images, and once purchased requires virtually no further expense outlay. Film photography requires continuous expenditure of (much higher amounts of) funds for supplies and developing.
Digital photography was used in astronomy long before its use by the general public and had almost completely displaced photographic plates by the early 1980s. Not only are CCDs more sensitive to light than plates, but the information can be downloaded onto a computer for data analysis. The CCDs used in astronomy are similar to those used by the general public, but are cooled to liquid nitrogen temperatures so as to reduce the noise which is caused by heat.
Exchangeable image file format (EXIF) is a set of file formats specified for use in digital cameras. This specifies the use of TIFF for the highest quality format and JPEG as a space-saving but lower quality format. Many low-end cameras can deliver only JPEG files. Another format that may be encountered is CCD-RAW, which is unstandardised.
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Data storage formats
A large variety of data storage device formats are used in consumer digital cameras:
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