A
digital camera (or
digicam) is a
camera that takes
video or still
photographs, or both,
digitally by recording
images via an
electronic image sensor. It is the main device used in the field of
digital photography. Most 21st century cameras are digital.
[1]
Digital cameras can do things film cameras cannot: displaying images on a screen immediately after they are recorded, storing thousands of images on a single small memory device, and deleting images to free storage space. The majority, including most compact cameras, can record moving
video with
sound as well as still
photographs. Some can
crop and
stitch pictures and perform other elementary
image editing. Some have a
GPS receiver built in, and can produce
Geotagged photographs.
The optical system works the same as in
film cameras, typically using a lens with a variable
diaphragm to focus light onto an image pickup device. The diaphragm and shutter admit the correct amount of light to the imager, just as with film but the image pickup device is electronic rather than chemical. Most digicams, apart from camera phones and a few specialized types, have a standard
tripod screw.
Digital cameras are incorporated into many devices ranging from
PDAs and
mobile phones (called
camera phones) to vehicles. The
Hubble Space Telescope and other
astronomical devices are essentially specialized digital cameras
Types of digital cameras
Digital cameras are made in a wide range of sizes, prices and capabilities. The majority are
camera phones, operated as a
mobile application through the cellphone menu. Professional
photographers and many amateurs use larger, more expensive
digital single-lens reflex cameras (DSLR) for their greater versatility. Between these extremes lie digital
compact cameras and
bridge digital cameras that "bridge" the gap between amateur and professional cameras. Specialized cameras including
multispectral imaging equipment and
astrographs continue to serve the scientific, military, medical and other special purposes for which
digital photography was invented.
Compact digital cameras
Subcompact with lens assembly retracted
Compact cameras are designed to be tiny and portable and are particularly suitable for casual and "
snapshot" use. Hence, they are also called
point-and-shoot cameras. The smallest, generally less than 20 mm thick, are described as
subcompacts or "ultra-compacts" and some are nearly
credit card size.
[2]
Most, apart from ruggedized or water-resistant models, incorporate a retractable lens assembly allowing a thin camera to have a moderately long
focal length and thus fully exploit an image sensor larger than that on a camera phone, and a mechanized
lens cap to cover the lens when retracted. The retracted and capped lens is protected from keys, coins and other hard objects, thus making it a thin, pocketable package. Subcompacts commonly have one lug and a short
wrist strap which aids extraction from a pocket, while thicker compacts may have two lugs for attaching a neck strap.
Compact cameras are usually designed to be
easy to use, sacrificing advanced features and picture quality for compactness and simplicity; images can usually only be stored using
lossy compression (
JPEG). Most have a built-in
flash usually of low power, sufficient for nearby subjects.
Live preview is almost always used to frame the photo. Most have limited
motion picture capability. Compacts often have
macro capability and
zoom lenses but the zoom range is usually less than for
bridge and
DSLR cameras. Generally a contrast-detect
autofocus system, using the image data from the live preview feed of the main imager, focuses the lens.
Typically, these cameras incorporate a nearly-silent
leaf shutter into their lenses.
For lower cost and smaller size, these cameras typically use
image sensors with a diagonal of approximately 6 mm, corresponding to a
crop factor around 6. This gives them weaker low-light performance, greater
depth of field, generally closer focusing ability, and smaller components than cameras using larger sensors.
Starting in 2011, some compact digital cameras can take 3D still photos. These 3D compact
stereo cameras can capture 3D panoramic photos for play back on a
3D TV.
[3] Some of these are rugged and waterproof, and some have
GPS, compass,
barometer and
altimeter.
[4]
Bridge cameras
Main article:
Bridge camera are higher-end digital cameras that physically and
ergonomically resemble
DSLRs and share with them some advanced features, but share with compacts the use of a fixed lens and a small sensor. Like compacts, most use
live preview to frame the image. Their
autofocus uses the same contrast-detect mechanism, but many bridge cameras have a
manual focus mode, in some cases using a separate focus ring, for greater control. They originally "bridged" the gap between affordable point-and-shoot cameras and the then unaffordable earlier digital SLRs.
Due to the combination of big physical size but a small sensor, many of these cameras have very highly specified lenses with large zoom range and fast
aperture, partially compensating for the inability to change lenses. On some, the lens qualifies as
superzoom. To compensate for the lesser sensitivity of their small sensors, these cameras almost always include an
image stabilization system to enable longer handheld exposures.
These cameras are sometimes marketed as and confused with digital SLR cameras since the appearance is similar. Bridge cameras lack the reflex viewing system of DSLRs, are usually fitted with fixed (non-interchangeable) lenses (although some have a lens thread to attach accessory wide-angle or
telephoto converters), and can usually take movies with sound. The scene is composed by viewing either the liquid crystal display or the
electronic viewfinder (EVF). Most have a longer
shutter lag than a true dSLR, but they are capable of good image quality (with sufficient light) while being more compact and lighter than DSLRs. High-end models of this type have comparable resolutions to low and mid-range DSLRs. Many of these cameras can store images in a
Raw image format, or processed and
JPEG compressed, or both. The majority have a built-in flash similar to those found in DSLRs.
In bright sun, the quality difference between a good compact camera and a digital SLR is minimal but bridgecams are more portable, cost less and have a similar zoom ability to dSLR. Thus a
Bridge camera may better suit outdoor daytime activities, except when seeking professional-quality photos.
[5]
In low light conditions and/or at
ISO equivalents above 800, most bridge cameras (or megazooms) lack in image quality when compared to even entry level DSLRs. However, they do have one major advantage, often not appreciated:- their much larger depth of field due to the small sensor as compared to a DSLR, allowing larger apertures with shorter exposure times.
A
3D Photo Mode was introduced in 2011, whereby the camera automatically takes a second image from a slightly different perspective and provides a standard .MPO file for stereo display.
[6]
Mirrorless interchangeable-lens camera
In late 2008, a new type of camera emerged, combining the larger sensors and interchangeable lenses of DSLRs with the
live-preview viewing system of compact cameras, either through an
electronic viewfinder or on the rear LCD. These are simpler and more compact than DSLRs due to the removal of the mirror box, and typically emulate the handling and ergonomics of either DSLRs or compacts. The system is used by
Micro Four Thirds, borrowing components from the
Four Thirds DSLR system. The
Ricoh GXR of 2009 puts the sensor and other electronic components in the interchangeable sensor–lens assembly or "camera unit," rather than in the camera body.
[7]
The Lumix G 12.5mm/F12 (H-FT012) is "3D" lens, using two lenses quite close together in one lens-module adaptor, compatible with the interchangeable-lens
Panasonic Lumix DMC-GH2.
[8]
Digital single lens reflex cameras
Digital single-lens reflex cameras (DSLRs) are digital cameras based on film
single-lens reflex cameras (SLRs). They take their name from their unique viewing system, in which a mirror reflects light from the lens through a separate optical viewfinder. In order to capture an image the mirror is flipped out of the way, allowing light to fall on the imager. Since no light reaches the imager during framing, autofocus is accomplished using specialized sensors in the mirror box itself. Most 21st century DSLRs also have a "live view" mode that emulates the live preview system of compact cameras, when selected.
These cameras have much larger sensors than the other types, typically 18 mm to 36 mm on the diagonal (
crop factor 2, 1.6, or 1). This gives them superior low-light performance, less
depth of field at a given aperture, and a larger size.
They make use of
interchangeable lenses; each major DSLR manufacturer also sells a line of lenses specifically intended to be used on their cameras. This allows the user to select a lens designed for the application at hand: wide-angle, telephoto, low-light, etc. So each lens does not require its own shutter, DSLRs use a
focal-plane shutter in front of the imager, behind the mirror.
The mirror flipping out of the way at the moment of exposure makes a distinctive "clack" sound.
Digital rangefinders
A rangefinder is a user-operated optical mechanism to measure subject distance once widely used on film cameras. Most digital cameras measure subject distance automatically using electro-optical techniques, but it is not customary to say that they have a rangefinder.
Line-scan camera systems
A line-scan camera is a camera device containing a line-scan
image sensor chip, and a focusing mechanism. These cameras are almost solely used in industrial settings to capture an image of a constant stream of moving material. Unlike video cameras, line-scan cameras use a single array of
pixel sensors, instead of a matrix of them. Data coming from the line-scan camera has a frequency, where the camera scans a line, waits, and repeats. The data coming from the line-scan camera is commonly processed by a computer, to collect the one-dimensional line data and to create a two-dimensional image. The collected two-dimensional image data is then processed by image-processing methods for industrial purposes.
Line-scan technology is capable of capturing data extremely fast, and at very high image resolutions. Usually under these conditions, resulting collected image data can quickly exceed 100 MB in a fraction of a second. Line-scan-camera–based integrated systems, therefore are usually designed to streamline the camera's output in order to meet the system's objective, using computer technology which is also affordable.
Line-scan cameras intended for the parcel handling industry can integrate adaptive focusing mechanisms to scan six sides of any rectangular parcel in focus, regardless of angle, and size. The resulting 2-D captured images could contain, but are not limited to 1D and 2D barcodes, address information, and any pattern that can be processed via image processing methods. Since the images are 2-D, they are also
human-readable and can be viewable on a computer screen. Advanced integrated systems include
video coding,
optical character recognition (OCR) and finish-line cameras for high speed sports.
Integration
Many devices include digital cameras built into or integrated into them. For example, mobile phones often include digital cameras; those that do are known as
camera phones. Other small electronic devices (especially those used for communication) such as
PDAs, laptops and
BlackBerry devices often contain an integral digital camera, and most 21st century
camcorders can also make still pictures.
Due to the limited storage capacity and general emphasis on convenience rather than image quality, the vast majority of these integrated or converged devices store images in the lossy but compact
JPEG file format.
Mobile phones incorporating digital cameras were introduced in Japan in 2001 by J-Phone. In 2003 camera phones outsold stand-alone digital cameras, and in 2006 they outsold all film-based cameras and digital cameras combined. These camera phones reached a billion devices sold in only five years, and by 2007 more than half of the installed base of all mobile phones were camera phones. Sales of separate cameras peaked in 2008.
[9]
Integrated cameras tend to be at the very lowest end of the scale of digital cameras in technical specifications, such as resolution, optical quality, and ability to use accessories. With rapid development, however, the gap between mainstream compact digital cameras and camera phones is closing, and high-end camera phones are competitive with low-end stand-alone digital cameras of the same generation.
Conversion of film cameras to digital
When digital cameras became common, a question many
photographers asked was whether their
film cameras could be converted to digital. The answer was yes and no. For the majority of 35 mm film cameras the answer is no, the reworking and cost would be too great, especially as lenses have been evolving as well as cameras. For most a conversion to digital, to give enough space for the electronics and allow a liquid crystal display to preview, would require removing the back of the camera and replacing it with a custom built digital unit.
The major reason why affordable
Digital camera backs never became available was that the manufacturers of sensors were identical or associated with camera manufacturers that were interested in selling new, rather than extending the life of old equipment. In fact, the coming of digital cameras was a very beneficial to the Japanese camera industry, which showed signs of stagnation in the late 80s due to market saturation. The new digital SLRs were for the main part purposely made not to be downward-compatible in accepting the world's vast inventory of momentarily near-useless high-quality SLR lenses even if of the same bayonet. This in spite of the fact that one major high-end manufacturer used to advertise his pre-digital optics as being "like money in the bank". As of 2011, no DSLR has appeared to take the very common M42-Lenses. Russian and Chinese manufacturers have not been able to make a DSLR of any sort: it remains to be seen if they will, with the availability of the new 16MP APS-C size sensor MT9H004 from the US-manufacturer Aptina.
[citation needed]
Many early professional SLR cameras, such as the
Kodak DCS series, were developed from 35 mm film cameras. The technology of the time, however, meant that rather than being digital "backs" the bodies of these cameras were mounted on large, bulky digital units, often bigger than the camera portion itself. These were factory built cameras, however, not
aftermarket conversions.
A notable exception is the
Nikon E2, followed by
Nikon E3, using additional optics to convert the 35mm format to a 2/3 CCD-sensor.
A few 35 mm cameras have had
digital camera backs made by their manufacturer, Leica being a notable example.
Medium format and
large format cameras (those using film stock greater than 35 mm), have a low unit production, and typical digital backs for them cost over $10,000. These cameras also tend to be highly modular, with handgrips, film backs, winders, and lenses available separately to fit various needs.
The very large sensor these backs use leads to enormous image sizes. For example Phase One's P45 39 MP image back creates a single TIFF image of size up to 224.6 MB, and even greater pixel counts are available. Medium format digitals such as this are geared more towards studio and portrait photography than their smaller DSLR counterparts; the
ISO speed in particular tends to have a maximum of 400, versus 6400 for some DSLR cameras. (Canon EOS-1D Mark IV and
Nikon D3S have ISO 12800 plus Hi-3 ISO 102400)
History
Steven Sasson as an engineer at
Eastman Kodak invented and built the first digital camera using a
charge-coupled device image sensor in 1975.
[10][11]
Image sensors
Image resolution
The
resolution of a digital camera is often limited by the
image sensor (typically a
CCD or
CMOS sensor chip) that turns light into discrete signals, replacing the job of film in traditional photography. The sensor is made up of millions of "buckets" that essentially count the number of
photons that strike the sensor. This means that the brighter the image at a given point on the sensor, the larger the value that is read for that
pixel. Depending on the physical structure of the sensor, a
color filter array may be used which requires a
demosaicing/interpolation algorithm. The number of resulting pixels in the image determines its "
pixel count". For example, a 640x480 image would have 307,200 pixels, or approximately 307 kilopixels; a 3872x2592 image would have 10,036,224 pixels, or approximately 10 megapixels.
The pixel count alone is commonly presumed to indicate the resolution of a camera, but this simple
figure of merit is a misconception. Other factors impact a sensor's resolution, including sensor size, lens quality, and the organization of the pixels (for example, a monochrome camera without a
Bayer filter mosaic has a higher resolution than a typical color camera).
Where such other factors limit the resolution, a greater pixel count does not improve it, but may rather make the digital images inconveniently large and/or exacerbate
image noise. Many digital compact cameras are criticized for having excessive pixels. Sensors can be so small that their 'buckets' can easily overfill; again, resolution of a sensor can become greater than the camera lens could possibly deliver.
Demanding high quality and resolution (e.g. for use in professional photography), this count is an object of manufacturer competion. As of August 2011, the highest resolution available on the market is 80.1 MP.
[12]
Australian recommended retail price of Kodak digital cameras.
As the technology has improved, costs have decreased dramatically. Counting the "pixels per dollar" as a basic measure of value for a digital camera, there has been a continuous and steady increase in the number of pixels each dollar buys in a new camera, in accord with the principles of
Moore's Law. This predictability of camera prices was first presented in 1998 at the Australian
PMA DIMA conference by Barry Hendy and since referred to as "Hendy's Law".
[13]
Since only a few
aspect ratios are commonly used (mainly 4:3 and 3:2), the number of sensor sizes that are useful is limited. Furthermore, sensor manufacturers do not produce every possible sensor size, but take incremental steps in sizes. For example, in 2007 the three largest sensors (in terms of pixel count) used by
Canon were the 21.1, 17.9, and 16.6 megapixel CMOS sensors.
Methods of image capture
This digital camera is partly disassembled. The lens assembly (bottom right) is partially removed, but the sensor (top right) still captures a usable image, as seen on the LCD screen (bottom left).
Since the first digital backs were introduced, there have been three main methods of capturing the image, each based on the hardware configuration of the sensor and color filters.
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 mosaic, or three separate
image sensors (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
image sensor 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 is called
Microscanning. This technique utilizes 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 a Bayer filter on the chip.
The third method is called
scanning because the sensor moves across the focal plane much like the sensor of a desktop scanner. Their
linear or
tri-linear sensors utilize only a single line of photosensors, or three lines for the three colors. In some cases, scanning is accomplished by moving the sensor e.g. when using
Color co-site sampling or rotate the whole camera; a digital
rotating line camera offers images of very high total resolution.
The choice of method for a given capture is determined largely by the subject matter. It is usually inappropriate to attempt to capture a subject that moves with anything but a single-shot system. However, the higher color fidelity and larger file sizes and resolutions available with multi-shot and scanning backs make them attractive for commercial photographers working with stationary subjects and large-format photographs.
Dramatic improvements in single-shot cameras and
raw image file processing at the beginning of the 21st century made single shot, CCD-based cameras almost completely dominant, even in high-end commercial photography. CMOS-based single shot cameras remained somewhat common.
Filter mosaics, interpolation, and aliasing
The Bayer arrangement of color filters on the pixel array of an image sensor.
Most current consumer digital cameras use a
Bayer filter mosaic in combination with an optical
anti-aliasing filter to reduce the aliasing due to the reduced sampling of the different primary-color images. A
demosaicing algorithm is used to
interpolate color information to create a full array of RGB image data.
Cameras that use a beam-splitter single-shot
3CCD approach, three-filter multi-shot approach,
Color co-site sampling or
Foveon X3 sensor do not use
anti-aliasing filters, nor demosaicing.
Firmware in the camera, or a software in a raw converter program such as
Adobe Camera Raw, interprets the raw data from the sensor to obtain a full color image, because the
RGB color model requires three intensity values for each pixel: one each for the red, green, and blue (other color models, when used, also require three or more values per pixel). A single sensor element cannot simultaneously record these three intensities, and so a
color filter array (CFA) must be used to selectively filter a particular color for each pixel.
The Bayer filter pattern is a repeating 2×2 mosaic pattern of light filters, with green ones at opposite corners and red and blue in the other two positions. 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 two different hues of green. This provides potentially more accurate color, but requires a slightly more complicated interpolation process.
The color intensity values not captured for each pixel can be interpolated (or guessed) from the values of adjacent pixels which represent the color being calculated.
Sensor size and angle of view
Cameras with digital
image sensors that are smaller than the typical 35mm film size has a smaller field or
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.
If a sensor smaller than the full-frame
35mm film format is used, such as the use of
APS-C-sized digital sensors in
DSLRs, then the field of view is cropped by the sensor to smaller than the 35mm full-frame format's field of view. This narrowing of the field of view is often described in terms of a
focal length multiplier or
crop factor, a factor by which a longer focal length lens would be needed to get the same field of view on a full-frame camera.
If the digital sensor has approximately the same resolution (effective pixels per unit area) as the 35mm film surface (24 x 36 mm), then the result is similar to taking the image from the film camera and cutting it down (cropping) to the size of the sensor. For an APS-C size sensor, this would be a reduction to the center 62.5% of the image. The cheaper, non-SLR models of digital cameras typically use much smaller sensor sizes and the reduction would be greater.
If the digital sensor has a higher or lower density of pixels per unit area than the film equivalent, then the amount of information captured differs correspondingly. While resolution can be estimated in pixels per unit area, the comparison is complex since most types of digital sensor record only a single colour at each pixel location, and different types of film have different effective resolutions. There are various trade-offs involved, since larger sensors are more expensive to manufacture and require larger lenses, while sensors with higher numbers of pixels per unit area are likely to suffer higher noise levels.
For these reasons, it is possible to obtain cheap digital cameras with sensor sizes much smaller than 35mm film, but with high pixel counts, that can still produce high-resolution images. Such cameras are usually supplied with lenses that would be classed as extremely wide angle on a 35mm camera, and that can also be smaller size and less expensive, since there is a smaller sensor to illuminate. For example, a camera with a 1/1.8" sensor has a 5.0x field of view crop, and so a hypothetical 5-50mm zoom lens produces images that look
similar (again the differences mentioned above are important) to those produced by a 35mm film camera with a 25–250mm lens, while being much more compact than such a lens for a 35mm camera since the imaging circle is much smaller.
This can be useful if extra telephoto reach is desired, as a certain lens on an APS sensor produces an image equivalent to a significantly longer lens on a 35mm film camera shot at the same distance from the subject, the equivalent length of which depends on the camera's field of view crop. This is sometimes referred to as the focal length multiplier, but the focal length is a physical attribute of the lens and not the camera system itself. The disadvantage of this is that wide angle photography is made somewhat more difficult, as the smaller sensor effectively and undesirably reduces the captured field of view. Some methods of compensating for this or otherwise producing much wider digital photographs involve using a
fisheye lens and "defishing" the image in post processing to simulate a
rectilinear wide angle lens.
Full-frame digital SLRs, that is, those with sensor size matching a frame of 35mm film, include Canon 1Ds and 5D series, Kodak Pro DCS-14n, Nikon D3 line and Contax N Digital. There are very few digital cameras with sensors that can approach the resolution of larger-format film cameras, with the possible exception of the
Mamiya ZD (22MP) and the
Hasselblad H3D series of
DSLRs (22 to 39 MP).
Common values for field of view crop in DSLRs include 1.3x for some
Canon (APS-H) sensors, 1.5x for
Sony APS-C sensors used by
Nikon,
Pentax and
Konica Minolta and for
Fujifilm sensors, 1.6 (APS-C) for most Canon sensors, ~1.7x for
Sigma's
Foveon sensors and 2x for
Kodak and
Panasonic 4/3" sensors currently used by
Olympus and
Panasonic. Crop factors for non-SLR consumer compact and
bridge cameras are larger, frequently 4x or more
Relative sizes of sensors used in most current digital cameras.
| Table of sensor sizes [14] |
| Type | Width (mm) | Height (mm) | Size (mm²) |
| 1/3.6" | 4.00 | 3.00 | 12.0 |
| 1/3.2" | 4.54 | 3.42 | 15.5 |
| 1/3" | 4.80 | 3.60 | 17.3 |
| 1/2.7" | 5.37 | 4.04 | 21.7 |
| 1/2.5" | 5.76 | 4.29 | 24.7 |
| 1/2.3" | 6.16 | 4.62 | 28.5 |
| 1/2" | 6.40 | 4.80 | 30.7 |
| 1/1.8" | 7.18 | 5.32 | 38.2 |
| 1/1.7" | 7.60 | 5.70 | 43.3 |
| 2/3" | 8.80 | 6.60 | 58.1 |
| 1" | 12.8 | 9.6 | 123 |
| 4/3" | 18.0 | 13.5 | 243 |
| APS-C | 25.1 | 16.7 | 419 |
| 35 mm | 36 | 24 | 864 |
| Back | 48 | 36 | 1728 |
Connectivity
Transferring photos
Many digital cameras can connect directly to a computer to transfer data:
A common alternative is the use of a
card reader which may be capable of reading several types of storage media, as well as high speed transfer of data to the computer. Use of a card reader also avoids draining the camera battery during the download process, as the device takes power from the
USB port. An external card reader allows convenient direct access to the images on a collection of storage media. But if only one storage card is in use, moving it back and forth between the camera and the reader can be inconvenient. Many computers have a card reader built in, at least for SD cards.
Printing photos
Many modern cameras support the
PictBridge standard, which allows them to send data directly to a PictBridge-capable
computer printer without the need for a computer.
Wireless connectivity can also provide for printing photos without a cable connection.
Polaroid has introduced a printer integrated into its digital camera which creates a small, printed copy of a photo. This is reminiscent of the original
instant camera, popularized by Polaroid in 1975.
[15]
Displaying photos
Many digital cameras include a video output port. Usually
sVideo, it sends a standard-definition video signal to a television, allowing the user to show one picture at a time. Buttons or menus on the camera allow the user to select the photo, advance from one to another, or automatically send a "slide show" to the TV.
HDMI has been adopted by many high-end digital camera makers, to show photos in their high-resolution quality on an
HDTV.
In January 2008,
Silicon Image announced a new technology for sending video from mobile devices to a television in digital form.
MHL sends pictures as a video stream, up to 1080p resolution, and is compatible with HDMI.
[16]
Some DVD recorders and television sets can read memory cards used in cameras; alternatively several types of flash card readers have TV output capability.
Modes
Many digital cameras have preset
modes for different applications. Within the constraints of correct exposure various parameters can be changed, including
exposure,
aperture,
focusing,
light metering,
white balance, and equivalent sensitivity. For example a
portrait might use a wider aperture to render the background out of focus, and would seek out and focus on a human face rather than other image content.
Image data storage
A
CompactFlash (CF) card, one of many media types used to store digital photographs
Many
camera phones and most separate digital cameras use
memory cards having
flash memory to store image data. The majority of cards for separate cameras are
SD format; many are
CompactFlash or other formats.
Digital cameras have computers inside, hence have
internal memory, and many cameras can use some of this internal memory for a limited capacity for pictures that can be transferred to or from the card or through the camera's connections.
A few cameras use some other form of removable
storage such as
Microdrives (very small
hard disk drives),
CD single (185
MB), and
3.5" floppy disks. Other unusual formats include:
- Onboard flash memory — Cheap cameras and cameras secondary to the device's main use (such as a camera phone)
- PC Card hard drives — early professional cameras (discontinued)
- Thermal printer — known only in one model of camera that printed images immediately rather than storing
Most manufacturers of digital cameras do not provide drivers and software to allow their cameras to work with
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.
File formats
The Joint Photography Experts Group standard (
JPEG) is the most common file format for storing image data. Other file types include Tagged Image File Format (
TIFF) and various
Raw image formats.
Many cameras, especially professional or DSLR cameras, support a
Raw image format. A raw image is the unprocessed set of pixel data directly from the camera's sensor. They are often saved in formats proprietary to each manufacturer, such as NEF for Nikon, CRW or CR2 for Canon, and MRW for Minolta.
Adobe Systems has released the
DNG format, a royalty free raw image format which has been adopted by at least 10 camera manufacturers.
Raw files initially had to be processed in specialized
image editing programs, but over time many mainstream editing programs, such as Google's
Picasa, have added support for raw images. Editing raw format images allows more flexibility in settings such as white balance, exposure compensation, color temperature, and so on. In essence raw format allows the photographer to make major adjustments without losing image quality that would otherwise require retaking the picture.
Formats for movies are
AVI,
DV,
MPEG,
MOV (often containing motion JPEG),
WMV, and ASF (basically the same as WMV). Recent formats include
MP4, which is based on the QuickTime format and uses newer compression algorithms to allow longer recording times in the same space.
Other formats that are used in cameras but not for pictures are the Design Rule for Camera Format (
DCF), an
ISO specification for the camera's internal file structure and naming, and Digital Print Order Format (
DPOF), which dictates what order images are to be printed in and how many copies.
Most cameras include
Exif data that provides
metadata about the picture. Exif data may include
aperture,
exposure time,
focal length, date and time taken, and
location.
Batteries
Digital cameras have high
power requirements, and over time have become smaller, resulting in an ongoing need to develop a
battery small enough to fit in the camera and yet able to power it for a reasonable length of time.
Two broad types of batteries are in use for digital cameras.
Off-the-shelf
The first type of battery for digital cameras conform to an established off-the-shelf form factor, most commonly
AA, CR2, or
CR-V3 batteries, with
AAA batteries in a handful of cameras. The CR2 and CR-V3 batteries are
lithium based, and intended for single use. They are also commonly seen in camcorders. AA batteries are the most common; however, the non-rechargeable
alkaline batteries supplied with low-end cameras are capable of providing enough power for only a very short time in most cameras. They may serve satisfactorily in cameras that are only occasionally used.
Consumers with more than an occasional need use AA
Nickel metal hydride batteries (NiMH) instead, which provide an adequate amount of power and are rechargeable. NIMH batteries do not provide as much power per volume as
lithium ion batteries, and they also tend to discharge when not used. To get same power,
NiMH Rechargeable battery takes up to two times in volume compare to Li-on Rechargeable Battery, by weight NiMH Rechargeable Battery is three to five times heavier, but by price NiMH Rechargeable Battery is only a half compare to Li-on Rechargeable Battery. Please see Wikipedia: Table of rechargeable battery technologies in
Rechargeable battery. They are available in various
ampere-hour (Ah) or
milli-ampere-hour (mAh) ratings, which affects how long they last in use. Typically mid-range consumer models and some low end cameras use off-the-shelf batteries; only a very few
DSLR cameras accept them (for example,
Sigma SD10). Rechargeable
RCR-V3 lithium-ion batteries are also available as an alternative to non-rechargeable CR-V3 batteries. Cameras, especially earlier ones made for AA-size batteries assumed that these would be of the non-rechargeable, preferably alkaline manganese type delivering 1.5 volts per cell. Rechargeable NiCd or NiMH cells only deliver 1.2 volts, which means that many such cameras will only operate for a short time or not at all even with new and newly charged 1.2 volt units. A portable ultra-high-endurance external power-supply for the shoulder bag to operate older 6 volt cameras can be made up of five 1.2 volt C-size cells which can be either NiCd or NiMH, with a cable and 4mm DC-plug.
Proprietary
The second type of battery for digital cameras is proprietary battery formats. These are built to a manufacturer's custom specifications, and can be either aftermarket replacement parts or
OEM. Almost all proprietary batteries are
lithium ion. While they only accept a certain number of recharges before the battery life begins degrading (typically up to 500 cycles), they provide considerable performance for their size. A result is that at the two ends of the spectrum both high end professional cameras and low end consumer models tend to use lithium ion batteries.
Digital camera backs
In the industrial and high-end professional photography market, some camera systems utilize modular (removable) image sensors. For example, some
medium format SLR cameras, such as the
Mamiya 645D series, allow installation of either a digital camera back or a traditional photographic film back.
- 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)
Most earlier digital camera backs used linear array sensors. The linear array sensor acts like its counterpart in a flatbed
image scanner by moving vertically to
digitize the image. Many early such cameras only capture
grayscale images. Color photography requires three separate scans, and a mechanical assembly to cycle a primary color filter in front of the sensor. These are called multi-shot backs. The entire scanning process requires relatively long expsoure times, in the range of seconds or even minutes. Due to this relatively long exposure-time, scanning and mutli-shot backs are generally limited to studio applications, where all aspects of the photographic scene are under the photographer's control.
Some other camera backs use 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 with only thousands of pixels than a CCD matrix with millions, very high resolution linear CCD camera backs were available much earlier than their CCD matrix counterparts. For example, you could buy an (albeit expensive) camera back with over 7,000 pixel horizontal resolution in the mid-
1990s. However, as of 2004, it is still difficult to buy a comparable CCD matrix camera of the same resolution. Rotating line cameras, with about 10,000 color pixels in its sensor line, are able, as of 2005, to capture about 120,000 lines during one full 360 degree rotation, thereby creating a single digital image of 1,200 Megapixels.
Most modern digital camera backs use CCD or CMOS matrix sensors. The matrix sensor captures the entire image frame at once, instead of incrementing scanning the frame area through the prolonged exposure. For example,
Phase One produces a 39 million pixel digital camera back with a 49.1 x 36.8 mm CCD in 2008. 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, consumer digital cameras use arrays ranging from 36 x 24 mm (full frame on high end consumer DSLRs) to 7.2 x 5.3 mm (on point and shoot cameras) CMOS sensor.
At present, there are relatively few complete digital SLR cameras with sensors large enough to compete with the image detail offered by medium to large format film cameras.
Phase One,
Mamiya, and
Hasselblad in 2011 manufacture medium format digital devices that can capture 30MP up to 80MP. The units tend to be quite large and expensive. Additionally, because of their high build quality and lack of moving parts, they tend to be quite long lasting and are prominent on the used market.
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