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Photography is the process of making pictures by means of the action of light. Light patterns reflected or emitted from objects are recorded onto a sensitive medium or storage chip through a timed exposure. The process is done through mechanical, chemical or digital devices known as cameras.

The word comes from the Greek words phos ("light"), and graphis ("stylus", "paintbrush") or graphê, together meaning "drawing with light" or "representation by means of lines" or "drawing." Traditionally the product of photography has been called a photograph. The term photo is an abbreviation, many people also call them pictures. In digital photography, the term image has begun to replace photograph. (The term image is traditional in geometric optics.)

Most commonly a camera or camera obscura is the image forming device and photographic film or a digital storage card is the recording medium, although other methods are available. For instance, the photocopy or xerography machine forms permanent images but uses the transfer of static electrical charges rather than photographic film, hence the term electrophotography. The rayographs published by Man Ray in 1922 are images produced by the shadows of objects cast on the photographic paper, without the use of a camera. Objects can be placed directly on the glass of a scanner to produce pictures digitally.

Photographers control the camera to expose the light recording material (usually film or a charge-coupled device) to the required amount of light. After processing, this produces an image whose contents are acceptably sharp, bright and composed to achieve the objective of taking the photograph.

* Focus
* Aperture of the lens
* Duration of exposure (or shutter speed)
* Focal length and type of lens (telephoto, macro, wide angle, or zoom)
* Sensitivity of the medium to light intensity and color/wavelength
* Filters, scrims, or other special effects that may be placed between the subject and the light recording material, either in front of or behind the lens
* The nature of the light recording material itself, for example its resolution as measured in pixels or "grains" of silver halide

The controls are inter-related, as the total amount of light reaching the film plane (the "exposure") changes proportionately with the duration of exposure, aperture of the lens, and focal length of the lens (which changes as the lens is focused, or if it is "zoomed"). Changing any of these will, therefore, alter the exposure. Many cameras will automatically adjust the aperture of the lens to account for changes in focus, and some will do so for changes in zoom as well.

The duration of an exposure is referred to as the "shutter speed," often even in cameras that don't have a physical shutter, and is typically measured in fractions of a second. The aperture is expressed by an f-number or f-stop, which is proportional to the ratio of the focal length to the diameter of the aperture. If the f-number is decreased by a factor of \sqrt 2, the aperture diameter is increased by the same factor, and its area is increased by a factor of 2. The f-stops that might be found on a typical lens include 2.8, 4, 5.6, 8, 11, 16, 22, 32, where going up "one stop" doubles the amount of light reaching the film, and "stopping down" one stop halves the amount of light.

To achieve a given exposure, various combinations of shutter speed and aperture could be used. For example, f/8 at 1/125th of a second and f/4 at 1/500th of a second yield the same amount of light. However, the combination chosen impacts the final result. In addition to the subject or camera movement that might vary depending on the shutter speed, the aperture (and focal length of the lens) determine the "depth of field," which refers to the range of distances from the lens that will be considered in acceptable focus. For example, using a long lens and a large aperture, such as might be used with a large format camera, a subject's eyes might be in sharp focus while the tip of the nose is noticeably blurred. If the aperture is made smaller, or a shorter lens is used, then both the subject's eyes and nose can be brought into focus at the same time. If a very small aperture is used, such as a pinhole, then a very wide range of distance can be brought into focus at once.

Image capture is only part of the image forming process. Regardless of the light recording material used, some sort of process or processes must be employed to render the "latent image" captured by the camera into the final photographic work. This process consists of two steps, development, and printing. For people who do not do their own printing, these two steps are often considered the same step, "getting the pictures developed" is thought of as analgous to "getting the pictures printed", but they are separate steps.

During the printing process, additional modifications can be made to the print via several controls. Many of these controls are analogous to controls during the time of capturing the image, and some of them are exclusive to the printing process. Most of these controls have equivalent concepts in the digital world, but in some cases the effect is not exactly the same. This difference between digital and film is especially pronounced for the dodging and burning controls.

* Chemicals and Process used during film development
* Duration of exposure (equivalent to shutter speed)
* Printing Aperture (equivalent to aperture, but has no effect on depth of field)
* Contrast
* Dodging (Localized reduction in duration of exposure, resulting in a lighter areas)
* Burning (Localized increase in duration of exposure, resulting in darker areas)
* Paper Quality (Gloss, Matte, Etc)

Photography can be classified under imaging technology and has gained the interest of scientists and artists from its inception. Scientists have used its capacity to make accurate recordings, such as Eadweard Muybridge in his study of human and animal locomotion (1887). Artists have been equally interested by this aspect but have also tried to explore other avenues than the photo-mechanical representation of reality, such as the pictorialist movement. Military, police and security forces use photography for surveillance, recognition and data storage. Photography is used to preserve memories of favourites and as a source of entertainment.

For centuries images have been projected onto surfaces. The camera obscura and the camera lucida were used by artists to trace scenes as early as the 16th century. These early cameras did not fix an image in time; they only projected what passed through an opening in the wall of a darkened room onto a surface. In effect, the entire room was turned into a large pinhole camera. Indeed, the phrase camera obscura literally means "darkened room," and it is after these darkened rooms that all modern cameras have been named.

The first photograph is considered to be an image produced in 1826 by the French inventor Nicéphore Niépce on a polished pewter plate covered with a petroleum derivative called bitumen of Judea. It was produced with a camera, and required an eight hour exposure in bright sunshine. However this process turned out to be a dead end and Niépce began experimenting with silver compounds based on a Johann Heinrich Schultz discovery in 1724 that a silver and chalk mixture darkens when exposed to light.

Niépce, in Chalon-sur-Saône, and the artist Louis Daguerre, in Paris, refined the existing silver process in a partnership. In 1833 Niépce died of a stroke, leaving his notes to Daguerre. While he had no scientific background, Daguerre made two pivotal contributions to the process. He discovered that by exposing the silver firstly to iodine vapour, before exposure to light, and then to mercury fumes after the photograph was taken, a latent image could be formed and made visible. By then bathing the plate in a salt bath the image could be fixed. In 1839 Daguerre announced that he had invented a process using silver on a copper plate called the Daguerreotype. A similar process is still used today for Polaroids. The French government bought the patent and immediately made it public domain.

Across the English Channel, William Fox Talbot had earlier discovered another means to fix a silver process image but had kept it secret. After reading about Daguerre's invention Talbot refined his process, so that it might be fast enough to take photographs of people as Daguerre had done and by 1840 he had invented the calotype process. He coated paper sheets with silver chloride to create an intermediate negative image. Unlike a daguerreotype a calotype negative could be used to reproduce positive prints, like most chemical films do today. Talbot patented this process which greatly limited its adoption. He spent the rest of his life in lawsuits defending the patent until he gave up on photography altogether. But later this process was refined by George Eastman and is today the basic technology used by chemical film cameras. Hippolyte Bayard also developed a method of photography but delayed announcing it and so was not recognized as its inventor.

Slovene Janez Puhar invented the technical procedure for making photographs on glass in 1841. The invention was recognized on July 17th 1852 in Paris by the Académie Nationale Agricole, Manufacturière et Commerciale.

The Daguerreotype proved popular in responding to the demand for portraiture emerging from the middle classes during the Industrial Revolution. This demand, that could not be met in volume and in cost by oil painting, may well have been the push for the development of photography. However daguerreotypes, while beautiful, were fragile and difficult to copy. A single photograph taken in a portrait studio could cost US$1000 in 2006 dollars. Photographers also encouraged chemists to refine the process of making many copies cheaply, which eventually lead them back to Talbot's process. Ultimately, the modern photographic process came about from a series of refinements and improvements in the first 20 years. In 1884 George Eastman, of Rochester, New York, developed dry gel on paper, or film, to replace the photographic plate so that a photographer no longer needed to carry boxes of plates and toxic chemicals around. In July of 1888 Eastman's Kodak camera went on the market with the slogan "You press the button, we do the rest". Now anyone could take a photograph and leave the complex parts of the process to others. Photography became available for the mass-market in 1901 with the introduction of Kodak Brownie. Since then color film has become standard, as well as automatic focus and automatic exposure. Digital recording of images is becoming increasingly common, as digital cameras allow instant previews on LCD screens and the resolution of top of the range models has exceeded high quality 35mm film while lower resolution models have become affordable. For the enthusiast photographer processing black and white film, little has changed since the introduction of the 35mm film Leica camera in 1925.

In the nineteenth century, photography developed rapidly as a commercial service. End-user supplies of photographic equipment accounted for only about 20% of industry revenue.

Given the development of new digital technologies for creating and sharing images, and of new communications devices, e.g. camera phones, understanding the economics of image use are becoming increasingly important for understanding the evolution of the communications industry as a whole.

Color photography was explored throughout the 1800s. Initial experiments in color could not fix the photograph and prevent the color from fading. The first permanent color photo was taken in 1861 by the physicist James Clerk Maxwell.

One of the early methods of taking color photos was to use three cameras. Each camera would have a color filter in front of the lens. This technique provides the photographer with the three basic channels required to recreate a color image in a darkroom or processing plant. Russian photographer Sergei Mikhailovich Prokudin-Gorskii developed another technique, with three color plates taken in quick succession.

Practical application of the technique was held back by the very limited color response of early film; however, in the early 1900s, following the work of photo-chemists such as H. W. Vogel, emulsions with adequate sensitivity to green and red light at last became available.

The first color film, Autochrome, invented by the French Lumière brothers, reached the market in 1907. It was based on a 'screen-plate' filter made of dyed dots of potato starch, and was the only color film on the market until German Agfa introduced the similar Agfacolor in 1932. In 1935, American Kodak introduced the first modern ('integrated tri-pack') color film, Kodachrome, based on three colored emulsions. This was followed in 1936 by Agfa's Agfacolor Neue. Unlike the Kodachrome tri-pack process the colour couplers in Agfacolor Neue were integral with the emulsion layers, which greatly simplified the film processing. Most modern color films, except Kodachrome, are based on the Agfacolor Neue technology. Instant color film was introduced by Polaroid in 1963.

As an interesting side note, the inventors of Kodachrome, Leopold Mannes and Leopold Godowsky Jr. were both accomplished musicians. Godowsky was the brother-in-law of George Gershwin and his father was one of the world's greatest pianists.

Color photography may form images as a positive transparency, intended for use in a slide projector or as color negatives, intended for use in creating positive color enlargements on specially coated paper. The latter is now the most common form of film (non-digital) color photography owing to the introduction of automated photoprinting equipment.

Traditional photography was a considerable burden for photographers working at remote locations (such as press correspondents) without access to processing facilities. With increased competition from television there was pressure to deliver their images to newspapers with greater speed. Photo-journalists at remote locations would carry a miniature photo lab with them and some means of transmitting their images down the telephone line. In 1981 Sony unveiled the first consumer camera to use a CCD for imaging, and which required no film -- the Sony Mavica. While the Mavica did save images to disk, the images themselves were displayed on television, and therefore the camera could not be considered fully digital. In 1990, Kodak unveiled the DCS 100, the first commercially available digital camera. Its cost precluded any use other than photojournalism and professional applications, but commercial digital photography was born.

Digital photography uses an electronic sensor such as a charge-coupled device to record the image as a piece of electronic data rather than as chemical changes on film. Some other devices, such as cell phones, now include digital photography features.

Although not viewed by all photographers as true photography, digital photography in fact meets all requirements to be called such. Even though there are no chemical processes, a digital camera captures a frame of whatever it happens to be pointed at, which can be viewed later. In 10 years, digital point and shoot cameras have become widespread consumer products. These digital cameras now outsell film cameras, and many include features not found in film cameras such as the ability to shoot video and record audio.

Kodak announced in January 2004 that it would no longer produce reloadable 35mm cameras after the end of that year. This was interpreted as a sign of the end of film photography. However, Kodak was at that time a minor player on the reloadable film cameras market. In January 2006 Nikon followed suit and announced that they will stop the 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. 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.

There is debate over which of the two formats, digital or film, is superior. It cannot be said that either of the formats is superior to the other in every way. Rather, each of the formats has its own specific advantages. This section discusses the main points.

There are numerous measures which can be used to assess the quality of still photographs. The most discussed of these is spatial resolution, i.e. the number of separate points in the photograph. This is measured by how many millions of picture cells make up the photo.

The comparison of resolution between film and digital photography is complex. Measuring the resolution of both film and digital photographs depends on numerous issues. For film, this issue depends on the size of film used (35mm, Medium format or Large format), the speed of the film used and the quality of lenses in the camera. Additionally, since film is an analogue medium, it does not have pixels so its resolution measured in pixels can only be an estimate.

Similarly, digital cameras rarely perform to their stated megapixel count. Other factors are important in digital camera resolution such as the actual number of pixels used to store the image, the effect of the Bayer pattern of sensor filters on the digital sensor and the image processing algorithm used to interpolate sensor pixels to image pixels. In addition, digital sensors are generally arranged in a rectangular pattern, making images susceptible to moire pattern artifacts, whereas film is immune to such effects due to the random orientation of grains.

Estimates of the resolution of a photograph taken with a 35mm film camera vary. However, there exist many estimates around 12 Megapixels (4K). It is possible for more resolution to be recorded if, for example, a finer-grain film is used or less resolution to be recorded with poor quality optics or low light levels. This would place 35mm film cameras roughly equivalent with top-of-the-range digital cameras (as of 2006).

However, while 35mm is the standard format for consumer cameras, many professional film cameras use Medium format or Large format films which, due to the size of the film used, can boast resolution many times greater than the current top-of-the-range digital cameras. For example, it is estimated that a medium format film photograph can record around 50 Megapixels, while a Large format films can record around 200 Megapixels (4x5 inch) which would equate to around 800 Megapixels on the largest common film format, 8x10 inch.

The resolution of modern black and white slow speed film, exposed through a high quality prime lens working at its optimum aperture yields usable detail at a scanned file size of greater than 30 megapixels. With consumer 35mm color negative film an effective resolution of over 12 megapixels is achievable and in an inexpensive 35mm point and shoot camera a resolution of over 8 megapixels may be achieved.

When deciding between film and digital and between different types of camera, it is necessary to take into account the medium which will be used for display. For instance, if a photograph will only be viewed on a television or computer display (which can resolve only about 2 Megapixels and 1.3 Megapixels, respectively, as of 2006), then the resolution provided by a low-end digital cameras may be sufficient. For standard 4x6 inch prints, it is debatable whether there will be any perceived quality difference between digital and film. If the medium is a large billboard, then it is likely that the extra resolution of a medium or large format will be necessary. For larger prints, the extra resolution of a good 35mm film photograph may be desirable.

It should be noted that a special case exists for long exposure photography - Currently available technology contributes random noise to the images taken by digital cameras, produced by thermal noise and manufacturing defects. For very long exposures it is necessary to operate the detector at low temperatures to avoid noise impacting the final image. Film grain is not affected by exposure time, although the apparent speed of the film does change with longer exposures.

This has been one of the major drivers of the widespread adoption of digital cameras. Before the advent of digital cameras, once a photograph was taken, the roll of film would need to be finished and sent off to a lab to be developed. Only once the film was returned was it possible to see the photograph. However, most digital cameras incorporate an LCD screen which allow the photograph to be viewed immediately after it has been taken. This allows the photographer to delete unrequired photographs and offers an immediate opportunity to re-take. When a user desires prints, it is only necessary to print the good photographs.

Another major advantage of digital technology is that photographs can be instantly moved to a personal computer for modification. Many digital cameras are capable of storing pictures in a RAW format which stores the output from the sensor directly rather than processing it immediately to an image. When combined with suitable software, such as dcraw, this allows the user to configure certain parameters of the taken photograph (such as sharpness or colour) before it is "developed" into a final image. More sophisticated users may choose to manipulate or alter the actual content of the recorded image.

Film photographs may be digitised in a process known as scanning. They may then be manipulated as digital photographs.

The two formats (film and digital) have different emphases as regards pricing. With digital photography, cameras tend to be significantly more expensive than film ones, comparing like for like. This is offset by the fact that taking photographs is effectively cost-free. Photographs can be taken freely and copies distributed over the internet free of charge.

This should be contrasted with film photography where good quality cameras tend to be less complicated and, therefore, less expensive. But this is at the expense of ongoing costs both in terms of film and processing costs. In particular, film cameras offer no chance to review photographs immediately after they are shot, and all photos taken must be processed before knowing anything about the quality of the final photograph.

There are costs associated with digital photography. Digital cameras use batteries, some of which are proprietary and quite expensive. While they are rechargable, they do degrade over time and must be periodically replaced. Although there is no film in digital cameras, there is the requirement to store the images on memory cards or microdrives which also have limited life. Additionally, some provision for storage of the digital image must be made. In general this would be either an optical disc produced by a shop or photofinisher, or by the photographer on a computer system. If physical prints are to be made they can either be purchased from a photofinisher, or produced by the photograper.

Nonetheless film still has advantages over digital, at least with current technology. One of the main advantages is its latitude, that is, the ability to produce a good image from over- or underexposed negatives. Digital images which are slightly overexposed can lose all data in the highlights, and underexposed digital will lose significant shadow detail. Film, on the other hand, can be greatly over- or underexposed and still be able to produce a normal image. This is especially true with black and white film.

Dust on the image plane is a constant issue for photographers. Digital cameras are especially prone to dust problems because the sensor is static, whereas film is always being replaced. For digital SLRs the presence of dust is often difficult to rectify. With film cameras dust is easy to manage through the use of good technique and clean handling methods.

When choosing between film and digital formats, it is necessary to consider the suitability of each as an archival medium.

Films and prints processed and stored in ideal conditions have demonstrated an ability to remain substantially unchanged for more than 100 years. Gold or platinum toned prints probably have a lifespan limited only by the lifespan of the base material, probably many hundreds of years.

The archival potential of digital photographs is less well understood since digital media have existed for only the last 50 years. There exist three problems which must be overcome for archival usage: physical stability of the recording medium, future readability of the storage medium and future readability of the file formats used for storage.

Many digital media are not capable of storing data for prolonged periods of time. For example, magnetic disks and tapes may lose their data after twenty years, flash memory cards even less. Good quality optical media may be the most durable storage media for digital data.

It is important to consider the future readability of storage media. Assuming the storage media can continue to hold data for prolonged periods of time, the short lifespan of digital technologies often causes the drives to read media to become unavailable. For example, the first 5¼-inch Floppy disks were first made available in 1976. However, the drives to read them are already extremely rare just 30 years later.

It must also be considered whether there still exists software which can decode the data. For example, many modern digital cameras save photographs in JPEG format. This format has existed for only around 15 years. Whether it will still be readable in a century is unknown.

Most professional cameras can save in a RAW image format, the future of which is much more uncertain. Some of these formats contain proprietary data which is encrypted or protected by patents, and could be abandoned by their makers at any time for simple economic reasons. This could make it difficult to read these 'raw' files in the future, unless the camera makers were to release information on the file formats.

However, digital archives have several methods of overcoming such obstacles. In order to counteract the file format problems, many organizations prefer to choose an open and popular file format. Doing so increases the chance that software will exist to decode the file in the future.

Additionally many organisations take an active approach to archiving rather than relying on formats being readable decades later. This takes advantage of the ability to make perfect copies of digital media. So, for example, rather than leaving data on a format which may potentially become unreadable or unsupported, the information can typically be copied to newer media without loss of quality. This is only possible with digital media.

* Advertising photography: photographs made to illustrate a service or product. These images are generally done with an advertising agency, design firm or with an in-house corporate design team.
* Editorial photography: photographs made to illustrate a story or idea within the context of a magazine. These are usually assigned by the magazine.
* Photojournalism: this can be considered a subset of editorial photography. Photographs made in this context are accepted as a truthful documentation of a news story.
* Portrait and wedding photography: photographs made and sold directly to the end user of the images.
* Fine art photography: photographs made to fulfill a vision, and reproduced to be sold directly to the customer.

The market for photographic services demonstrates the aphorism "one picture is worth a thousand words," which has an interesting basis in the history of photography. Magazines and newspapers, companies putting up Web sites, advertising agencies and other groups pay for photography.

Many people take photographs for self-fulfillment or for commercial purposes. Organizations with a budget and a need for photography have several options: they can assign a member of the organization, hire someone, run a public competition, or obtain rights to stock photographs.

During the twentieth century, both fine art photography and documentary photography became accepted by the English-speaking art world and the gallery system. In the United States, a small handful of curators spent their lives advocating to put photography in such a system, with Alfred Stieglitz, Edward Steichen, John Szarkowski, and Hugh Edwards the most prominent among them.

The aesthetics of photography is a matter that continues to be discussed regularly, especially in artistic circles. Many artists argued that photography was the mechanical reproduction of an image. If photography is authentically art, then photography in the context of art would need redefinition, such as determining what component of a photograph makes it beautiful to the viewer. The controversy began with the earliest images "written with light": Nicéphore Niépce, Louis Daguerre, and others among the very earliest photographers were met with acclaim, but some questioned if it met the definitions and purposes of art.

Clive Bell in his classic essay "Art" states that only one thing can distinguish art from what is not art: "significant form." Bell wrote: "There must be some one quality without which a work of art cannot exist; possessing which, in the least degree, no work is altogether worthless. What is this quality? What quality is shared by all objects that provoke our aesthetic emotions? What quality is common to Sta. Sophia and the windows at Chartres, Mexican sculpture, a Persian bowl, Chinese carpets, Giotto's frescoes at Padua, and the masterpieces of Poussin, Piero della Francesca, and Cezanne? Only one answer seems possible - significant form. In each, lines and colors combined in a particular way, certain forms and relations of forms, stir our aesthetic emotions."

Others have since examined if this criterion be applied to photography. This question has been examined by the aesthetic realism understanding of beauty.

A form of art in photography is that of portrait photography. A portrait is the rendering of someone’s likeness. A portrait photographer not only wants to capture the true likeness, but also the personality of the individual. The photographer needs to be proficient not only in the workings and setting of the camera, but also needs to understand form and lighting. Great lighting and positioning can make someone appear at their best form if used correctly. Lighting and camera placement can also aid in correcting defects such as shortening a nose, making someone appear slimmer and other visual enhancements.