Nikon D700 — a 12.1 megapixel full-frame DSLR |
The Canon EOS 350D |
The Canon PowerShot A95 |
Until the advent of such technology, photographs were made by exposing light sensitive photographic film, and used chemical photographic processing to develop and stabilize the image. By contrast, digital photographs can be displayed, printed, stored, manipulated, transmitted, and archived using digital and computer techniques, without chemical processing.
Digital photography is one of several forms of digital imaging. Digital images are also created by non-photographic equipment such as computer tomography scanners and radio telescopes. Digital images can also be made by scanning other photographic images.
The digital camera
History
The first recorded attempt at building a digital camera was in 1975 by Steven Sasson, an engineer at Eastman Kodak. It used the then-new solid-state CCD image sensor chips developed by Fairchild Semiconductor in 1973. The camera weighed 8 pounds (3.6 kg), recorded black and white images to a cassette tape, had a resolution of 0.01 megapixels (10,000 pixels), and took 23 seconds to capture its first image in December 1975. The prototype camera was a technical exercise, not intended for production. The first true digital camera that recorded images as a computerized file was likely the Fuji DS-1P of 1988, which recorded to a 16 MB internal memory card that used a battery to keep the data in memory. This camera was never marketed in the United States, and has not been confirmed to have shipped even in Japan.The first commercially available digital camera was the 1990 Dycam Model 1; it also sold as the Logitech Fotoman. It used a CCD image sensor, stored pictures digitally, and connected directly to a computer for download.
The first flyby spacecraft image of Mars was taken from Mariner 4 on July 15, 1965 with a camera system designed by NASA/JPL. It used a video camera followed by a digitizer, rather than a mosaic of sensor elements, so it was not what we usually define as a digital camera, but it produced a digital image that was stored on tape for later slow transmission back to earth.
Sensors and storage
Image sensors read the intensity of light, and digital memory devices store the digital image information as RGB color space or as raw data.The two main types of sensors are charge-coupled devices, in which the photocharge is shifted to a central charge-to-voltage converter, and CMOS or active pixel sensors.
Nearly all digital cameras use built-in and/or removable solid state flash memory. Digital tapeless camcorders that double as a digital still cameras use flash memory, discs and internal hard drives. Certain 20th century digital cameras such as the Sony Mavica range used floppy disks and mini-CDs.
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 a memory card; floppy disks and CD-RWs are less common) is used for storing images, which may be transferred to a computer later.Digital cameras can take pictures, and may also 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 with the same functionality as digital cameras.
Performance metrics
The quality of a digital image is a composite of various factors, many of which are similar to those of 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 figure of merit. Digital camera manufacturers advertise this figure because consumers can use it to easily compare camera capabilities. It is not, however, the major factor in evaluating a digital camera for most applications. The processing system inside the camera that turns the raw data into a color-balanced and pleasing photograph is usually more critical, which is why some 4+ megapixel cameras perform better than higher-end cameras.Resolution in pixels is not the only measure of image quality. A larger sensor with the same number of pixels generally produces a better image than a smaller one. One of the most important differences is an improvement in image noise. This is one of the advantages of digital SLR cameras, which have larger sensors than simpler cameras of the same resolution.
- 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) is the product n = w × h. This yields e. g. 1.92 megapixels (1,920,000 pixels) for an image of 1600 × 1200. The majority of compact as well as some DSLR digital cameras have a 4:3 aspect ratio, i.e. w/h = 4/3. According to Digital Photography Review, the 4:3 ratio is because "computer monitors are 4:3 ratio, old CCD's always had a 4:3 ratio, and thus digital cameras inherited this aspect ratio."The pixel count quoted by manufacturers can be misleading as it may not be the number of full-color pixels. For cameras using single-chip image sensors the number claimed is the total number of single-color-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 images have different numbers of RGB pixels: Bayer-sensor cameras produce as many RGB pixels as photosensors via demosaicing (interpolation), while Foveon sensors produce uninterpolated image files with one-third as many RGB pixels as photosensors. It is difficult to compare the resolutions based on the megapixel ratings of these two types of sensors, and therefore sometimes a subject of dispute.
The relative increase in detail resulting from an increase in resolution is better compared by looking at the number of pixels across (or down) the picture, rather than the total number of pixels in the picture area. For example, a sensor of 2560 × 1600 sensor elements is described as "4 megapixels" (2560 × 1600 = 4,096,000). Increasing to 3200 × 2048 increases the pixels in the picture to 6,553,600 (6.5 megapixels), a factor of 1.6, but the pixels per cm in the picture (at the same image size) increases by only 1.25 times. A measure of the comparative increase in linear resolution is the square root of the increase in area resolution, i.e., megapixels in the entire image.
Dynamic range
Practical imaging systems, digital and film, have a limited "dynamic range": the range of luminosity that can be reproduced accurately. Highlights of the subject that are too bright are rendered as white, with no detail; shadows that are too dark are rendered as black. The loss of detail is not abrupt with film, or in dark shadows with digital sensors: some detail is retained as brightness moves out of the dynamic range. "Highlight burn-out" of digital sensors, however, can be abrupt, and highlight detail may be lost. And as the sensor elements for different colors saturate in turn, there can be gross hue or saturation shift in burnt-out highlights.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 contrast of a scene by selectively exposing darker pixels longer. A third technique is used by Fujifilm in its FinePix S3 Pro digital SLR. The image sensor contains additional photodiodes of lower sensitivity than the main ones; these retain detail in parts of the image too bright for the main sensor.
High dynamic range imaging (HDR) addresses this problem 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.
Storage
Many camera phones and most 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 and the other formats are rare. XQD card format is the latest form of storage medium. Modern digital cameras internal memory for a limited capacity for pictures that can be transferred to or from the card or through the camera's connections; even without a memory card inserted into the camera.Memory cards allow for vast numbers of photos to be taken, requiring attention only when the memory card has exhausted its free space. For most users this translates into dozens to hundreds of quality photos to be stored on the same memory card. Transferring the images is also possible for archival or personal use to another medium as required by the photographer.
Applications and considerations
With the acceptable image quality and the other advantages of digital photography (particularly the time pressures of daily newspapers) the majority of professional news photographers capture their images with digital cameras.Digital photography has also been adopted by many amateur snapshot photographers, who take advantage of the convenience of sending images by email, placing them on the World Wide Web, or displaying them in digital picture frames. The majority of cameras are camera phones integrated into cell phones but their usual small, poor quality lenses and sensors render most of 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 was thought to be impossible to match 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. Some professional photographers resist the use of digital cameras because they are poor performers when it comes to speed for multiple shots. Storing an 8MP image takes a lot of time and therefore, in some applications digital cameras are not currently appropriate.
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 otherwise manipulate the image in ways that traditional darkroom techniques cannot offer, or are far more laborious in the darkroom. With fully color-balanced systems from the camera to the monitor to the printer, the photographer can now supply, either as a print or as a computer display, what is actually seen on the photographer's screen. Film users can use a film scanner, thus mixing the two technologies. Rapid advances in the technologies have resulted in many specialised abbreviations and initialisms being freely used in publications and internet discussions.
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-resistant bodies. Medium and large-format film cameras are also still preferred by publications insisting on the very highest detail and resolution.
Digital photography was used in astrophotography long before its use by the general public and had almost completely displaced photographic plates by the early 1980s. CCDs are more sensitive to light than plates, and have a much more uniform and predictable response. The CCDs used in astronomy are similar to those used by the general public, but are generally monochrome. Many of those used in infrared astronomy are cooled with liquid nitrogen so as to reduce the image noise caused by heat. Many astronomical instruments have arrays of many CCDs, sometimes totaling almost a billion pixels. Amateur astronomers also commonly use digital cameras, including the use of webcams for speckle imaging or "video astronomy".
Comparison with film photography
Advantages and disadvantages of consumer digital cameras
The primary advantage of consumer-level digital cameras versus film cameras is that digital cameras eliminate the need to purchase photographic film, hence potentially saving the digital camera owner money on film purchasing costs, processing costs, etc. Also, the consumer avoids the need to return to the site of a photograph to re-shoot a poor exposure, because the LED display panel on the back of most digital cameras immediately shows the image.Another advantage is almost every digital camera has a video mode, and the most recent digital still cameras offer video mode with HD capability.
Disadvantages of consumer-level digital cameras versus higher-level digital cameras include the fact that the sensor size (image sensor format) on most consumer-level digital cameras is significantly smaller than the sensor size on the more expensive, "prosumer" or professional-level digital cameras, which translates to lower image quality than is produced by a camera with a larger sensor size.
Another significant disadvantage of many consumer-level digital cameras as compared with prosumer and professional-level digital cameras (as well as the majority of film cameras) is the long delay time between when the shutter release button is pushed and when the photograph is actually taken. To many, this is a major frustration and limitation since this problem makes the capturing of moving subjects largely impractical.
A disadvantage is the video modes have very poor focus in low-light situations. Many digital cameras from 2007 to 2011 do not offer a low-light mode for their video function.
Another disadvantage of the video modes of digital cameras, is the image-stability function does not operate while the subject is being filmed. Many digital still cameras have offered the image stability function solely as an editing tool during post-production (after the video has been made.) Whereas image stability is intended to compensate for camera shake, in an editing function, it distorts the image by cropping the image to counter-act the camera shake. Conversely, the image stabilization offered on video cameras in 2012 functions while the video is being created, eliminating the need for post-production edits, which harshly crop the image.
Advantages of professional digital cameras
The Golden Gate Bridge retouched for painterly light effects |
- Immediate image review and deletion is possible; lighting and composition can be assessed immediately, which ultimately conserves storage space.
- High volume of images to medium ratio; allowing for extensive photography sessions without changing film rolls. To most users a single memory card is sufficient for the lifetime of the camera whereas film rolls are a re-incurring cost of film cameras.
- Faster workflow: Management (colour and file), manipulation and printing tools are more versatile than conventional film processes. However, batch processing of RAW files can be time consuming, even on a fast computer.
- Digital manipulation: A digital image can be modified and manipulated much easier and faster than with traditional negative and print methods. The digital image to the right was captured in RAW format, processed and output in 3 different ways from the source RAW file, then merged and further processed for color saturation and other special effects to produce a more dramatic result than was originally captured with the RAW image.
Disadvantages of digital cameras
- Whereas film cameras can have manual backups for electronic and electrical features, digital cameras are entirely dependent on an electrical supply (usually batteries but sometimes power cord when in 'tethered' mode).
- Many digital sensors have less dynamic range than color print film. However, some newer CCDs such as Fuji's Super CCD, which combines diodes of different sensitivity, have improved upon this issue.
- When highlights burn out, they burn to white without details, while film cameras retain a reduced level of detail, as discussed above.
- High ISO image noise may manifest as multicolored speckles in digital images, rather than the less-objectionable "grain" of high-ISO film. While this speckling can be removed by noise-reduction software, either in-camera or on a computer, this can have a detrimental effect on image quality as fine detail may be lost in the process.
- Aliasing may add patterns to images that do not exist and would not appear in film.
In some cases where very high-resolution digital images of good quality are needed it may be advantageous to take large-format film photographs and digitise them. This allows the creation of very large computer files without speed or capacity disadvantages at picture-taking time.
Equivalent features
- Image noise / grain
- Speed of use
- Frame rate
- Image longevity
- Colour reproduction
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 take photos in either ratio, and nearly all digital SLRs take pictures in a 3:2 ratio as they usually use lenses designed for 35 mm film (Olympus and Panasonic digital SLRs are notable exceptions). Some photo labs print photos on 4:3 ratio paper, as well as the existing 3:2. In 2005 Panasonic launched the first consumer camera with a native aspect ratio of 16:9, matching HDTV. This is similar to a 7:4 aspect ratio, which was a common size for APS film. Different aspect ratios is one of the reasons consumers have cropping issues when printing digital photos, or film photos. Moreover, the majority of digital cameras take an aspect ratio of 4:3, which translates to a size of 4.5" x 6.0". This translates into losing a half an inch when printing on the "standard" size of 4" x 6", an aspect ratio of 3:2. Similar cropping occurs when printing on other sizes, i.e., 5"x7", 8"x10", or 11"x14".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 were similar to those of prints made from film negatives. However, because digital images have a different aspect ratio than 35 mm film images, people have started to realize that 4x6 inch prints crop some of the image off the print. Some photofinishers have started offering prints with the same aspect ratio as the digital cameras record.In July 2003, digital cameras entered the disposable camera 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. When the pre-programmed 25 picture limit is reached, the camera is returned to the store, and the consumer receives back prints and a CD-ROM with their photos. The camera is then refurbished and resold. Since the introduction of the Dakota Digital, a number of similar single-use digital cameras have appeared. Most of the various single-use digital cameras are nearly identical to the original Dakota Digital regarding specifications and functionality, although a few include superior specifications and more advanced functions (such as higher image resolutions and LCD screens). Most, if not all, of these single-use digital cameras cost less than $20 (USD), not including processing fees. However, the huge demand for complex digital cameras at competitive prices has often resulted in manufacturing shortcuts, evidenced by a large increase in customer complaints over camera malfunctions, high parts prices, and short service life. Some digital cameras offer only a 90-day warranty.
Prices of 35mm compact cameras have dropped with manufacturers further outsourcing to countries such as China. Kodak announced in January 2004 that they would no longer sell Kodak-branded film cameras in the developed world. In January 2006, Nikon followed suit and announced they would stop production of all but two models of their film cameras. They will continue to produce the low-end Nikon FM10, and the high-end Nikon F6. In the same month, Konica Minolta announced it was pulling out of the camera business altogether. The price of 35mm and APS compact cameras have dropped, probably due to direct competition from digital and the resulting growth of the offer of second-hand film cameras. Pentax have reduced production of film cameras but not halted it. The technology has improved so rapidly that one of Kodak's film cameras was discontinued before it was awarded a "camera of the year" award later in the year.
Since 2002, digital cameras have outsold film cameras. However, the use of 35mm cameras is greater in developing countries. In Guatemala, for example, extremely high import duties on all digital products serves to encourage sales and use of film cameras.
The decline in film camera sales has also led to a decline in purchases of film for such cameras. In November 2004, a German division of Agfa-Gevaert, AgfaPhoto, split off. Within six months it filed for bankruptcy . Konica Minolta Photo Imaging, Inc. ended production of Color film and paper worldwide by March 31, 2007. In addition, by 2005, Kodak employed less than a third of the employees it had twenty years earlier. It is not known if these job losses in the film industry have been offset in the digital image industry.
In addition, digital photography has resulted in some positive market impacts as well. The increasing popularity of products such as digital photo frames and canvas prints is a direct result of the increasing popularity of digital photography.
An example of digital photography. This photo was taken and made into a digital print in less than 5 minutes. |
Social impact
Digital cameras have decimated the film photography industry through declining use of film rolls and development chemicals previously required to develop the photos. This led to a decrease in film and film camera sales and film processing, and has had a dramatic effect on companies such as Fuji, Kodak, and Agfa. In addition, many stores that used to offer photofinishing services or sell film no longer do, and those that do have seen a tremendous decline. In 2012, Kodak filed for bankruptcy after struggling to adapt to the changing industry.Up until the advent of the digital camera, amateur photographers could either buy print film for their camera, or slide film. If they purchased slide film, the resulting slides could be viewed using a slide projector. Digital photography revolutionized the industry by allowing for photographs to be viewed without conventional development processes and the significant time and costs associated with it. The ease of viewing, transferring and editing allowed consumers to manage their digital photos without use of specialized equipment.
Digital Cameras in cell phones however has arguably the largest impact on society. Smart phones have the ability to take and upload the taken images instantly to the Interet in minutes allowing the photographer in certain situations; even if the photographer is discovered and the images or recording are deleted pictures are not necessarily lost.
Simon Glik was arrested in 2007 for recording a police arrest on his cell phone, but after filing a federal lawsuit he won the case and even prompted the Obama administration to comment on the matter. Carlos Miller, a Miami journalist, recovered video of police officers arresting him after it was deleted from his camera. Throughout 2011 and 2012, images of Syrian protests were recorded and transmitted through the use of cell phones equipped with digital cameras.
Of growing concern for both archivists and historians is the relative non-permanence or transitory nature of digital media. Unlike film and print, which are tangible and immediately accessible to a person, storage of digital images is ever-changing with old media and decoding software becoming obsoleted or inaccessible by new technologies. Historians are concerned that we are creating a historical void where information and details about an era will have been lost within either failed or inaccessible digital media. It is recommended that both professional and amateur users develop strategies for migrating stored digital images from old technologies to new. Scrapbookers who may have used film for creating artistic and personal memoirs may need to modify their approach to digital photo books to personalize them and retain the special qualities of traditional photo albums.
The web has been a popular medium for storing and sharing photos ever since the first photograph was published on the web by Tim Berners-Lee in 1992 (an image of the CERN house band Les Horribles Cernettes). Today popular sites such as Flickr, Picasa and PhotoBucket are used by millions of people to share their pictures.
Recent research and innovation
Research and development continues to refine the lighting, optics, sensors, processing, storage, display, and software used in digital photography. Here are a few examples.- 3D models can be created from collections of normal images. The resulting scene can be viewed from novel viewpoints, but creating the model is very computationally intensive. An example is Microsoft's Photosynth, which provides some models of famous places as examples.
- High dynamic range cameras and displays are commercially available. Sensors with dynamic range in excess of 1,000,000:1 are in development, and software is also available to combine multiple non-HDR images (shot with different exposures) into an HDR image.
- Motion blur can be dramatically removed by a flutter shutter (a flickering shutter that adds a signature to the blur, which postprocessing recognizes). It is not yet commercially available.
- An object's specular reflection can be captured using computer controlled lights and sensors. This is needed to create attractive images of oil paintings, for instance. It is not yet commercially available, but is starting to be used by museums.
- Dust reduction systems to help keep dust off of image sensors, originally introduced only by a few cameras like Olympus DSLRs, have now become standard in most models and brands.
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