Digital photography, as opposed to
film photography, uses electronic devices to record and capture the image as
binary data. This facilitates storage and editing of the images on
personal computers, and also the ability to show and delete unsuccessful images immediately on the camera or software itself.
Digital cameras now outsell film cameras and include features that are not found in film cameras such as the ability to shoot
video and record
audio. Some other devices, such as
mobile phones, include digital photography features.
Contents[
hide]
1 Sensors and storage2 Multifunctionality and connectivity3 Performance metrics3.1 Pixel counts3.2 Resolution4 Possible problems5 Applications and considerations6 Sensor size and angle of view7 File types and data storage formats8 Digital camera backs9 Comparison with film cameras9.1 Advantages of consumer digital cameras9.2 Advantages of professional digital cameras9.3 Disadvantages of digital cameras9.4 Equivalent features9.5 A comparison of frame aspect ratios10 Market impact11 Social impact12 Common resolutions13 Recent research and innovation14 See also15 References16 External links//
[
edit] Sensors and storage
Sensors read the
intensity of light as filtered through different
color filters, and
digital memory devices store the digital image information, either as
RGB color space or as
raw data.
There are two main types of sensors:
charge-coupled device (CCD) – photocharge is shifted to a central charge-to-voltage converter
CMOS sensors ("
Active pixel sensor")
Nearly all digital cameras now use solid state
flash memory, but for a time floppy disks were used in early digital cameras such as the
Sony Mavica.
[
edit] Multifunctionality and connectivity
Except for some
linear array type of cameras 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 take pictures and sometimes additionally record sound and video. Some can be used as
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. Similarly, many
camcorders can take still photographs, and store them on
videotape or on
flash memorycards.
[
edit] 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, millions of pixels) is only one of the major factors, though it is the most heavily marketed. Pixel count metrics were created by the marketing organizations of digital camera manufacturers because consumers can use it to easily compare camera capabilities. It is not, however, the major factor in evaluating a digital camera. The processing system inside the camera that turns the raw data into a color-balanced and pleasing photograph is the most critical, which is why some 4+ megapixel cameras perform better than higher-end cameras.
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'.
[
edit] 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 compact (not SLR) digital cameras have a 4:3
aspect ratio, i.e. w/h = 4/3. [
citation needed]
The megapixel or pixel count quoted by manufacturers can be misleading because it may not be truly representative of the number of full colour-pixels. For cameras using single-chip
image sensors, the number presented is the total number of single-colour-sensitive photosensors, whether they have different locations in the plane, as with the
Bayer sensor, or in stacks of three co-located photosensors as in the
Foveon X3 sensor. However, the native-size images that result will have different numbers of RGB pixels; the Bayer-sensor cameras produce as many RGB pixels as photosensors via
demosaicing (interpolation), while the cameras with Foveon sensors produce uninterpolated image files with one-third as many RGB pixels as photosensors. It is not possible to directly compare the resolutions based on the megapixel ratings of these two types of sensors.
[
edit] Resolution
Resolution provides an indication of the amount of detail that is captured, but, like the other metrics, resolution is just another factor out of many in determining the quality of an image. Furthermore, different methods of creating an image make it impossible to compare the resolutions of cameras simply based on the number of pixels produced by the
image sensor.
As a case in point, the
Sigma SD14 camera uses
Foveon technology, which is quite different from almost all other digital cameras. The Sigma SD14 is billed as being a 14 megapixel camera, but is generally judged to have detail-capturing capabilities roughly equivalent to 9 megapixels in terms of
Bayer sensors.
[1]Another factor to be taken into consideration is that the relative increase in detail resulting from an increase in resolution has to be judged based on the square roots of the resolutions. For example, increasing resolution from 8 megapixels to 10 megapixels does not give an increase in perceived detail of 25% as one might expect. Instead, compare the square root of 10 (3.16) with the square root of 8 (2.83), and you can determine that the increase in perceived resolution is only 12%, which is fairly difficult to see.
[
edit] Possible problems
Example of highlight burn-out at A, and black shadows at B.
Since the light-sensitive component in a digital camera consists of discrete
pixels, problems of
Moiré, or interference patterns may occur when photographing fine patterns, such as textiles, geometric figures, and computer or TV screens. The example at left shows severe Moirés in a shot of a TV screen. However, this is not a problem for most real-life situations.
"Highlight burn-out" is also a potential problem. Depending on the
dynamic range of the subject, the lightest parts of the image may be so over-exposed that there is no image information, other than total white, in these highlights. Also, the reverse may occur. Shadowy parts of the image may become murky to totally black, because of the inability of the camera's sensor to cope with the large range of brightnesses. The image at right shows both these conditions simultaneously. Some digital cameras can show these blown highlights in the image review, allowing the photographer to re-shoot the picture with a modified exposure. Others compensate for the total amount of contrast in an image by selectively exposing darker pixels longer. A third scheme is one used by Fujifilm in its
FinePix S3 Pro digital SLR. The image sensor contains an additional photo diode at each photo site that is of lower sensitivity and extends the range of brightnesses that the sensor can "see" in the highlights without burning out.
High dynamic range imaging addresses this issue by increasing the dynamic range of images by either
increasing the dynamic range of the image sensor or
by using
exposure bracketing and post-processing the separate images to create a single image with a higher dynamic range.
HDR images curtail burn-outs and black-outs by increasing the bit storage per pixel.
[
edit] 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) the majority of professional news photographers have begun capturing their images with digital cameras.
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, placing them on the
World Wide Web, or displaying them in digital picture frames. Digital cameras have also been integrated into many
cell phones, although, because of the small, poor quality lenses and sensors in most of these phones, the quality of these pictures makes them unsuitable for making even moderate size prints.
Some commercial
photographers, and some amateurs interested in artistic photography, have been resistant to using digital rather than film cameras because they believe that the image quality available from a digital camera 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. A related concern in a specialized application is the use of digital photographs in court proceedings, with the added difficulty of demonstrating an image's authenticity. Some high-end film can also still be projected for viewing at a much higher optical resolution than even the best digital projectors.
Other commercial photographers, and many amateurs, have enthusiastically embraced digital photography because 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 funds for supplies and developing, although the equipment itself does not outdate so quickly and has a longer service life. Some commercial photographers have also begun moving to digital technology because of the tremendous editing capabilities now offered on computers. The photographer is able to color-balance and manipulate the image in ways that traditional darkroom science cannot offer, although film users can utilize the same technology with a film scanner. With fully color-balanced systems from the camera to the monitor to the printer, the photographer can now print what is actually seen on the screen.
However, digital cameras require batteries that need to be recharged or replaced frequently, and this means that a photographer needs access to electrical outlets. Digital cameras also tend to be much more sensitive to moisture and extreme cold. For this reason, photographers who work in remote areas may favour film SLR cameras, though many higher-end dSLRs are now equipped with 'weather-proof' bodies. Medium- and large-format film cameras are also still preferred by publications insisting on the very highest detail and resolution, such as
Arizona Highways.
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 they have a much more uniform and predictable response, and 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 generally monochrome and cooled with
liquid nitrogen so as to reduce the visual
noise caused by heat. Many astronomical instruments have arrays of many CCDs, sometimes totaling almost a billion pixels. Nowadays amateur astronomers also commonly use digital cameras, including the use of
webcams for
speckle imaging or "video astronomy".
