Digital photography

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The Nikon Coolpix 950
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Casio Exilim

Digital photography, as opposed to film photography, uses an electronic sensor to record the image as a piece of electronic data rather than as chemical changes on film. Digital cameras now (2005) outsell film cameras, and include features not found in film cameras such as the ability to shoot video and record audio. Some other devices, such as mobile phones, now include digital photography features.

Contents
1 Sensors
2 Multifunctionality and connectivity
3 Comparison with film cameras

3.1 Advantages of digital: Consumer Cameras
3.2 Advantages of digital: Professional Cameras
3.3 Advantages of film
3.4 Equivalent features
3.5 A comparison of frame aspect ratios

4 Performance metrics

4.1 Pixel counts

5 Applications and considerations
6 Market impact
7 File types and data storage formats
8 Digital camera backs
9 Sensor size and angle of view
10 See also
11 External links

Sensors

There are two main types of sensors:

There are also two main types of sensor mechanisms:

An area array sensor reads the entire image plane at once, whereas a linear array sensor works more like a flatbed scanner. Since this technology predates area arrays, it was available earlier, in professionally-priced cameras. With the advent of area array sensors, consumer digital cameras became available for considerably lower prices. (The Ritz Dakota Digital is an extreme example.)

Multifunctionality and connectivity

Except for some linear array type at the highest-end and simple web cams at the lowest-end, a digital memory device (usually flash memory; floppy disks and CD-RWs are less common) is usually used for storing images, which may then be transferred to a computer later.

Digital cameras can usually take pictures and additionally sound and video. Some can be used like webcams, some can use the PictBridge standard to connect to a printer without using a computer, and some can display pictures directly on a television set. Similarly, many camcorders can take still photographs, and store them on videotape or on flash memory cards.

Most digital cameras can connect directly to a computer in order to store pictures or to be used as a webcam. Digital cameras generally include a USB or Firewire port, and a memory card slot.

Digital cameras can record movies but may be limited by storage capacity. A 1GB memory card will store approximately 1 hour's worth of video in an MP4 format. Newer digital cameras, such as the Canon PowerShot S1 IS, Canon PowerShot SD200/300 and the Pentax Optio MX/MX4 will capture continuous footage at a rate of 30 frames per second at a display resolution of 640x480 pixels (similar to a television screen). Some digital cameras can connect directly to a computer and store video on the computer's hard disk or DVD recorder.

Comparison with film cameras

Advantages of digital: Consumer Cameras

The advantages of digital photography over traditional film include:

Advantages of digital: Professional Cameras


Recent digital cameras from leading manufacturers such as Nikon and Canon have promoted the adoption of digital Single-lens reflex cameras (SLRs) by photojournalists. Images captured at 2+ megapixels are deemed to be of sufficient quality for small images in newspaper or magazine reproduction. 6 to 12 megapixel images, found in modern digital SLRs, when combined with high-end lenses can match or even exceed the detail of film prints taken with 35 mm film based SLRs, and the latest 16 megapixel models can produce astoundingly detailed images better than a 35mm film images and the majority of medium format cameras. [1]

Some medium format digital backs can capture a 22+ megapixel image. These ultra high resolution cameras may not be usually available to the ordinary consumer, or even so-called prosumers, but they are useful to artists, scientists and commercial uses.

Advantages of film

Equivalent features

A comparison of frame aspect ratios

A typical digital camera's aspect ratio is 1.33 (4:3), the same as today's NTSC or PAL/SECAM TVs or earliest movies. However, a 35 mm picture's aspect ratio is 1.5 (3:2). Several new digital cameras will take photos in either ratio and nearly all digital SLRs take pictures in a 3:2 ratio as they usually use lenses designed for 35mm film (Olympus digital SLRs are a notable exception). Photo labs also offer the option of printing photos on 4:3 ratio paper, as well as the existing 3:2.

Essentially it depends on how much you want to spend, if you have enough money then digital is an option, and so is a good film camera. Another factor is the photographer; a camera is a tool for the photographer to use. Any picture can be taken by both types of camera, but the quality of the picture depends largely on the photographer.

Performance metrics

The quality of a digital image is the sum of various factors many of which are similar to film cameras. Pixel count (typically listed in megapixels) is only one of the major factors, though it is the most heavily marketed. Pixel count metrics were created by the marketing organizations of digital camera manufacturers because consumers can use it to easily compare camera capabilities. It is not, however, the major factor in evaluating a digital camera. The processing system inside the camera that turns the raw data into a color-balanced and pleasing photograph is the most critical, which is why some 4+ megapixel cameras perform better than higher-end cameras in a few cases.

Pixel counts

The number of pixels n for a given maximum resolution (w horizontal pixels by h vertical pixels) can be found using the formula: n = wh. This yields e. g. 1.92 megapixels (= 1,920,000 pixels) for an image of 1600 x 1200. The majority of digital cameras have a 4:3 aspect ratio, i.e. w/h = 4/3.

The megapixel or pixel count quoted by the manufacturers is misleading because it is not truly representative of the number of full colour pixels. For cameras using a Bayer sensor it is the number of single coloured photosites (light sensitive areas) on the sensor. For the Foveon X3 sensor the number currently (Feb 2004 - Sigma SD-10) presented by Sigma is the number of photosites times three (multiplied because each photosite records three colours), however the images that result will have a number of pixels equivalent to the number of photosites - not the tripled number quoted. It is not possible to directly compare the megapixel ratings of these two sensors but in many people's opinions a 6 MP Bayer filter sensor is roughly equivalent to a 10.2 MP Foveon X3 (3.4 MP*3). Some hold the opinion that the Foveon is worse than this and the ratio is more like one Bayer to two Foveon. It is largely a matter of personal opinion so prints from the two sensors should be inspected by interested parties.

Applications and considerations

With the acceptable image quality and the other advantages of digital photography (particularly the time pressures, of vital importance to daily newspapers) an increasing number of professional news photographers use these devices.

Digital photography has also been adopted by many amateur snapshot photographers, who take advantage of the convenience of the form when sending images by email or placing them on the World Wide Web. Digital cameras have also been integrated into many cell phones.

Some commercial photographers, and some amateurs interested in artistic photography, tend to avoid digital photography at this stage, as they believe that the image quality available from a digital camera of a given price is still inferior to that available from a film camera, and the quality of images taken on medium format film is near-impossible to match at any price with a digital camera. Some have expressed a concern that changing computer technology may make digital photographs inaccessible in the future while printed images have a very long lifespan. A related concern in a specialised application is the use of digital photographs in court proceedings, with the perceived difficulty of demonstrating an image's authenticity.

Other commercial photographers, and many amateurs, have enthusiastically embraced digital photography, as they believe that its flexibility and lower long-term costs outweigh its initial price disadvantages. Almost all of the cost of digital photography is capital cost, meaning that the cost is for the equipment needed to store and copy the images, and once purchased requires virtually no further expense outlay. Film photography requires continuous expenditure of (much higher amounts of) funds for supplies and developing. Commercial photographers are also moving to digital technology because of the tremendous editing capabilities now offered on computers. The photographer is able to color-balance and manipulate the image in ways that traditional darkroom science cannot offer. With fully color-balanced systems from the camera to the monitor to the printer, the photographer can now print what they actually see on the screen.

Digital photography was used in astronomy long before its use by the general public and had almost completely displaced photographic plates by the early 1980s. Not only are CCDs more sensitive to light than plates, but have much more uniform and predictable response, and the information can be downloaded onto a computer for data analysis. The CCDs used in astronomy are similar to those used by the general public, but are generally monochrome and cooled to liquid nitrogen temperatures so as to reduce the noise which is caused by heat. Many astronomical instruments have arrays of many CCDs, sometimes totalling almost a billion pixels. Nowadays amateur astronomers also commonly use digital cameras, including the use of webcams for speckle imaging or "video astronomy".

Market impact

In late 2002, 2 megapixel cameras were available in the United States for less than $100, with some 1 megapixel cameras for under $60. At the same time, many discount stores with photo labs introduced a "digital front end," allowing consumers to obtain true chemical prints (as opposed to ink-jet prints) in an hour. These prices competed with prints from negatives.

In July 2003, digital cameras entered the single-use market with the release of the Ritz Dakota Digital, a 1.2 megapixel (1280 x 960) CMOS-based digital camera costing only $11 (USD). Following the familiar single-use concept long in use with film cameras, the Dakota Digital was intended to be used by a consumer one time only. 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.

The price 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 [2]. Nikon has pulled out of the 35mm compact camera market but not the 35mm SLR market, which has been less affected since high quality digital SLR cameras are still considerably more expensive than their 35mm counterparts. Pentax have reduced production of film cameras but not halted it. [3]. The technology is improving so rapidly that a particular Kodak film camera went out of production before it was awarded a "camera of the year" award. Also, use of 35mm cameras is greater in developing countries. [4] However, since 2002, digital cameras have been outselling film cameras.

File types and data storage formats

Exchangeable image file format (Exif) is a set of file formats specified for use in digital cameras. This specifies the use of TIFF for the highest quality format and JPEG as a space-saving but lower quality format. Many low-end cameras can deliver only JPEG files. Another format that may be encountered is CCD-RAW, which is not standardised.

A large variety of data storage device formats are used in consumer digital cameras:

Most manufacturers of digital cameras do not provide drivers and software to allow their cameras to work with GNU/Linux or other free software. Still, many cameras use the standard USB storage protocol, and are thus easily usable. Other cameras are supported by the gPhoto project.

Digital camera backs

main article Digital camera back

Most digital cameras are built to operate as a self-contained unit. This is especially so at the lower-end, for these cameras usually include zoom lens and flashes that cannot be changed. However, at the highest-end, some digital cameras are nothing but a sophisticated light-sensing unit. Experienced photographers attach these digital "camera backs" to their professional medium format SLR cameras, such as a Hasselblad.

Linear array cameras are also called scan backs.

These camera backs are originally used only in a studio to take pictures of still objects. Most earlier digital camera backs were using linear array sensors which could take seconds or even minutes for a complete high-resolution scan. The linear array sensor acts like its counterpart in a flatbed image scanner by moving vertically to digitize the image.

Many of these cameras could only capture grayscale images. To take a color picture, it requires three separate scans done with a rotating colored filter. These are called multi-shot backs. Some other camera backs are using CCD arrays similar to typical cameras. These are called single-shot backs.

Since it is much easier to manufacture a high-quality linear CCD array that has only thousands of pixels than a CCD matrix that has millions of them, very high resolution linear CCD camera backs were available much earlier than their CCD matrix counterparts. For example, you could buy an, 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.

Many modern digital camera backs are using very large CCD matrices. This eliminated the need of scanning. For example, Fujifilm produces a 20 million pixel digital camera back with a 52 x 37 mm (2.04 x 1.45 inch) CCD in 2003. This CCD array is a little smaller than a frame of 120 film and much larger than a 35 mm frame (36 x 24 mm). In comparison, a consumer digital camera usually uses a much smaller 1/2.5 inch or 7.176 x 5.329 mm (~ 1/1.8 inch) CCD sensor. Further, the 1/2.5 or 1/1.8 inch diagonal measurement is the size of the entire CCD chip- the actual photo-sensitive area is much smaller.

A digital camera back is a good idea to smooth the transition from film to digital. A photographer can reuse his existing SLR camera and lens without much trouble. To some medium format camera users, the convenience of a bellows has no substitute.

Sensor size and angle of view

Cameras with digital sensors that are smaller than the typical 35mm film size will have a smaller 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.


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If a sensor smaller than the camera's original film format is used, such as the use of APS-C-sized digital sensors in 35mm format digital SLRs, then the image's field of view is cropped by the sensor giving the impression that the focal length of the lens has changed.

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 approximately the center 50% 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 will differ 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 will 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 which 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 will produce 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 will produce an equivalent image 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 downside to 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.

As of 2005, only a few high-end DSLR camera models from Canon and Kodak have sensor sizes that match a 35mm film frame. This is the ideal size for maximising the use of lenses designed for a 35mm camera, since it can reproduce the effect smaller sizes by cropping the image (assuming equal pixel density). Common values for field of view crop in DSLRs include 1.3x for some Canon sensors, 1.5x for Sony APS-C sensors used by Nikon, Pentax and Konica Minolta, 1.6 (APS-C) for most Canon sensors and Fujifilm sensors, ~1.7x for Sigma's Foveon sensors and 2x for Kodak 4/3" sensors currently used by Olympus.

See also

External links

See also: Digital photography, 120 film, 135 film, 1980, 1990, 2003, 2004, 2005, 35 mm film, Advanced Photo System