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Digital photography, as opposed to film photography, uses an electronic sensor to record the image as a piece of electronic data rather than as chemical changes on film. Digital cameras now outsell film cameras, and include features not found in film cameras such as the ability to shoot video and record audio. Some other devices, such as cell phones, now include digital photography features.
Sensors
There are two main types of sensors:
There are also two main types of sensor mechanisms:
- Area array
- Linear array (very rare, only limited to the highest-end)
An area array sensor reads the entire image plane at once, whereas a linear array sensor works more like a flatbed scanner. Since this technology predates area arrays, it was available earlier, in professionally-priced cameras. With the advent of area array sensors, consumer digital cameras became available for considerably lower prices. (The Ritz Dakota Digital is an extreme example.)
Multifunctionality and connectivity
Except for some linear array type at the highest-end and simple web cams at the lowest-end, 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.
Digital cameras can usually take pictures and additionally sound and video. Some can be used like webcams, some can use the PictBridge standard to connect to a printer without using a computer, and some can display pictures directly on a television set.
Most digital cameras can connect directly to a computer in order to store pictures or to be used as a webcam. Digital cameras generally includes a USB or Firewire port, and a memory card slot.
Digital cameras can record movies but may be limited by storage capacity. A 1GB memory card will store approximately 1 hour's worth of video in an MP4 format. Newer digital cameras, such as the Canon PowerShot S1 IS, Canon PowerShot SD200/300 and the Pentax Optio MX/MX4 will capture continuous footage at a rate of 30 frames per second at a display resolution of 640x480 pixles (similar to a television screen). Some digital cameras can connect directly to a computer and store video on the computer's hard disk or DVD recorder.
Comparison with film cameras
Advantages of digital
The advantages of digital photography over traditional film include:
- Instant review of pictures, with no wait for the film to be developed: if there's a problem with a picture, you find out immediately and can correct the problem and take another picture.
- You only pay for the printing of successful pictures.
- Permanent storage on digital media is considerably cheaper than film.
- There's no need to scan the picture before using it in a computer.
- Digital cameras can be much smaller than film cameras of equivalent quality.
- Infrared photography is easier to perform with a digital camera since the CCD is sensitive to infrared light. A film camera requires special infrared film, while a digital camera can take infrared shots by simply using an infrared filter or light source.
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 35 mm images. [1] (http://www.luminous-landscape.com/reviews/shootout.shtml)
Some professional models can capture more than 20 megapixel images. These ultra high resolution cameras may not be very available to the ordinary consumer, or even so-called prosumers, but they are useful to artists, scientists and commercial uses.
Advantages of film
- Batteries last longer in film cameras and are usually of a standard type that is inexpensive and widely available.
- Manual film cameras require no batteries and being mechanically simple are able to operate in extreme environments.
- A digital camera's LCD may become unusable in very bright light.
- Some types of film, especially positive film, offer better colour resolution than most digital cameras.
- When taking shots of extremely long exposure (eg. 60 seconds) in very low light conditions (eg. night shots) photographs taken on a digital camera are normally more noisy than those taken on film.
- Film performs better for black and white photography with contrast enhancing monochrome filters (eg. green filter for portraits or red filter for sea and sky shots). Black and white digital photographs taken in this manner, or by modifiying the amplitude of each colour channel, can be very noisy.
- Digital SLR cameras (preferred by more advanced photographers) are currently many times more expensive than film SLR cameras.
- It is unclear how digital media will perform over long periods of time as a storage system.
Equivalent features
- Image noise / grain: film grain is equivalent to image noise, at high ISO levels (film speed) the grain / noise becomes more apparent in the final image. Although film ISO levels can be lower than digital ISO levels (25 and 50 respectively), digital settings can be changed quickly according to requirements whilst film must be physically replaced. Additionally image noise reduction techniques can be used to remove noise from digital images whilst film grain is fixed. From an artistic point of view, film grain and image noise may be desirable when creating a specific mood for an image. Modern digital cameras have very low noise on high ISO, at ISO 400-3200 they have much lower noise than any film.
- Speed of use: Current digital and film cameras can be switched on and take images instantly. Saving images to disk takes no longer than winding on the film (see Frames per second).
- Frames per second: The maximum number of frames per second (frame/s) achievable on digital and film cameras is 8 frame/s (Nikon D2H digital SLR, Nikon F5 35 mm film SLR). Canon 1D Mark II can achieve 8.5 frame/s which makes it fastest SLR camera in the world. The F5 is limited to 36 continuous frames (the length of the film) whilst the D2H is able to take 40 images before its buffer must be cleared and the remaining space on the storage media can be used.
- Image longevity: Although digital image data does not degrade (whilst film stock can fade), the media on which the digital images are stored can decay or become corrupt, leading to a loss of image integrity. Both formats should be stored under archival conditions for maxium longevity.
- Colour reproduction: Colour reproduction (gamut) is dependent on the type of film / sensor used and the quality of the capture media, lens group and processing. Different films and sensors are sensitive to differing subsets of colour whilst the photographer needs to have an understanding of the light conditions and the media used to ensure accurate colour reproduction. Many digital cameras offer RAW format (sensor data) which makes it possible to choose color space on developement stage regardless of camera settings.
A comparison of frame aspect ratios
A typical digital camera's aspect ratio is 1.33 (4:3), the same as today's NTSC or PAL/SECAM TVs or earliest movies. However, a 35 mm picture's aspect ratio is 1.5 (3:2). Several new digital cameras will take photos in either ratio and nearly all digital SLRs take pictures in a 3:2 ratio as they usually use lenses designed for 35mm film (Olympus digital SLRs are a notable exception). Photo labs also offer the option of printing photos on 4:3 ratio paper, as well as the existing 3:2.
Performance metrics
The quality of a digital image is the sum of various factors many of which are similar to film cameras. Pixel count (typically listed in megapixels) is only one of the major factors, though it is the most heavily marketed.
- Lens quality: resolution, distortion, dispersion (see Lens (optics))
- Capture medium: CMOS, CCD, Negative film, Reversal Film etc.
- Capture format: pixel count, digital file type (RAW, TIFF, JPEG), film format (135 film, 120 film, 5x4, 10x8).
- Processing: digital and / or chemical processing of 'negative' and 'print'.
Pixel counts
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 (= 1,920,000 pixels) for an image of 1600 x 1200. 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 6 MP Bayer filter sensor is roughly equivalent to a 10.2 MP Foveon X3 (3.4 MP*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.
Applications and considerations
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.
Digital photography has also been adopted by many amateur snapshot photographers, who take advantage of the convenience of the form when sending images by email or placing them on the World Wide Web. Digital cameras have also been integrated into many cell phones.
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.
Market impact
In late 2002, 2 megapixel cameras were available in the United States for less than $100, with some 1 megapixel cameras for 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.
In July 2003, digital cameras entered the "single-use" market with the release of the Ritz Dakota Digital, a 1.2 megapixel (1280 x 960) CMOS-based digital camera costing only $11 (USD). Following the familiar single-use concept long in use with film cameras, the Dakota Digital was intended to be used by a consumer one time only, be returned to the store, and the consumer would receive back prints and a CD with the digital photos, but not the camera (The camera gets refurbished and resold). Since the introduction of the Dakota Digital, a handful of similar single-use digital cameras have appeared, most of which are functionally identical to the original Dakota Digital, and others that have superior specifications, such as higher resolutions and LCD displays that show the previous picture taken. Most, if not all, of these single-use digital cameras cost less than $20 (USD), not including processing.
The price of 35mm compact cameras have dropped with manufacturers outsourcing to countries such as China even more. Kodak announced in January 2004 that they would no longer sell Kodak-branded film cameras in the developed world [2] (http://www.theregister.co.uk/2004/01/20/kodak_to_drop_35mm_cameras/). Nikon has pulled out of the 35mm compact camera market but not the 35mm SLR market, which has been less hit since high quality digital SLR cameras are still considerably more expensive than their 35mm counterparts. Pentax have reduced production of film cameras but not halted it. [3] (http://www.photographyblog.com/index.php/weblog/comments/pentax_to_reduce_film_compact_and_slr_production/). The technology is improving so rapidly that one Kodak film camera already went out of production before it was awarded "camera of the year" award. Also, use of 35mm cameras is greater in developing countries. [4] (http://cio.co.nz/cio.nsf/0/7FAAE94969D13C78CC256F18007D9C8F?OpenDocument) However, since 2002, digital cameras have been outselling film cameras
File types and data storage formats
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.
A large variety of data storage device formats are used in consumer digital cameras:
Most manufacturers of digital cameras don't provide drivers and software to allow their cameras to work with GNU/Linux or other free software. Still, many cameras use the standard USB storage protocol, and are thus easily usable. Other cameras are supported by the gPhoto project.
Digital camera backs
- main article Digital camera back
Most digital cameras are built to operate as a self-contained unit. This is especially so at the lower-end, for these cameras usually include zoom lens and flashes that cannot be changed. However, at the highest-end, some digital cameras are nothing but a sophisticated light-sensing unit. Experienced photographers attach these digital "camera backs" to their professional medium format SLR cameras, such as a Hasselblad.
- Area array
- Linear array
- CCD (monochrome)
- 3-strip CCD with color filters
Linear array cameras are also called scan backs.
- Single-shot
- Multi-shot (three-shot, usually)
These camera backs are originally used only in a studio to take pictures of still objects. Most earlier digital camera backs were using linear array sensors which could take seconds or even minutes for a complete high-resolution scan. The linear array sensor acts like its counterpart used in a flatbed image scanner by moving vertically to digitize the image.
Many of these cameras could only capture grayscale images. To take a color picture, it requires three separate scans done with a rotating colored filter. These are called multi-shot backs. Some other camera backs are using CCD arrays similar to typical cameras. These are called single-shot backs.
Since it is much easier to manufacture a high-quality linear CCD array that has only thousands pixels than a CCD matrix that has millions of them, very high resolution linear CCD camera backs were available much earlier than their CCD matrix counterparts. For example, you could buy an expensive camera back with an over 7,000 pixel horizontal resolution in the mid-1990s. However, as of 2004, you can still hardly buy a comparable CCD matrix camera of the same resolution.
Many modern digital camera backs are using very large CCD matrices. This eliminated the need of scanning. For example, Fujifilm produces a 20 million pixel digital camera back with a 52 x 37 mm (2.04 x 1.45 inch) CCD in 2003. This CCD array is a little smaller than a frame of 120 film and much larger than a 35 mm frame (36 x 24 mm). In comparison, a consumer digital camera usually uses an itsy-bitsy so-called 1/2.5 inch or 7.176 x 5.329 mm (so-called 1/1.8 inch) CCD sensor. Beware, the 1/2.5 or 1/1.8 inch diagonal measurement is the size of the entire CCD chip. The actual photo-sensitive area is much smaller.
A digital camera back is a good idea to smooth the transition from film to digital. A photographer can reuse his beloved SLR camera and lens without much trouble. To some medium format camera users, the convienence of a bellows has no substitute.
Sensor size and angle of view
Cameras with digital sensors that are smaller than the typical 35mm film size will have a smaller angle of view when used with a lens of the same focal length. This is because angle of view is a function of both focal length and the sensor or film size used.
This is very noticeable with digital SLRs and digital backs, since these cameras typically use the same lens as similar film cameras. Because digital sensors are generally smaller than film, the effect is to reduce the angle of view. This is approximately the same effect as if a lens with a longer focal length had been used. This can be confusing to photographers transitioning from 35mm cameras to digital cameras.
Some professional cameras have a sensor with the same dimensions as a 35mm film frame, but these cameras are expensive. Canon has introduced a new lens mount, EF-S, that works with both 35mm coverage EF mount lens and lower coverage EF-S lens.
See also
External links
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