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Jai Ganesh

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Digital Camera

Digital Camera

Gist

A digital camera is a hardware device that takes photographs and stores the image as data on a memory card. Unlike an analog camera, which exposes film chemicals to light, a digital camera uses digital optical components to register the intensity and color of light, and converts it into pixel data. Many digital cameras are capable of recording video in addition to taking photos.

Summary

A digital camera is a device for making digital recordings of images. Texas Instruments Incorporated patented the first filmless electronic camera in 1972. In 1981 Sony Corporation brought out a commercial electronic model, which used a “mini” computer disk drive to store information captured from a video camera. As the cost of electronic components declined and the resolution of the cameras improved, the Eastman Kodak Company began selling professional digital cameras in 1991. Kodak and Apple Computer, which supplied the software for transferring the digital images to a personal computer, introduced the first consumer model in 1994. Digital cameras soon gained market share, gradually relegating most film camera sales to cheap, disposable, single-use models. However, with the introduction of smartphones containing ever more-advanced cameras, digital camera sales fell by 90 percent in the 2010s.

Unlike film cameras, digital cameras do not have chemical agents (film) and sometimes lack a viewfinder, which is typically replaced by a liquid crystal display (LCD). At the core of a digital camera is a semiconductor device, such as a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS), which measures light intensity and colour (using different filters) transmitted through the camera’s lenses. When light strikes the individual light receptors, or pixels, on the semiconductor, an electric current is induced and is translated into binary digits for storage within another digital medium, such as flash memory (semiconductor devices that do not need power to retain memory).

Digital cameras are commonly marketed by their resolution in megapixels (millions of pixels)—for example, a 24.2-megapixel camera has a resolution of 6,016 by 4,016 pixels. Kodak developed the first megapixel camera in 1986; it could produce a film-quality 5 × 7-inch (12.5 × 17.5-cm) print.

Details

A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile devices like smartphones with the same or more capabilities and features of dedicated cameras (which are still available). High-end, high-definition dedicated cameras are still commonly used by professionals and those who desire to take higher-quality photographs.

Digital and digital movie cameras share an optical system, typically using a lens with a variable diaphragm to focus light onto an image pickup device. The diaphragm and shutter admit a controlled amount of light to the image, just as with film, but the image pickup device is electronic rather than chemical. However, unlike film cameras, digital cameras can display images on a screen immediately after being recorded, and store and delete images from memory. Many digital cameras can also record moving videos with sound. Some digital cameras can crop and stitch pictures and perform other elementary image editing.

History

The first semiconductor image sensor was the charge-coupled device (CCD), invented by Willard S. Boyle and George E. Smith at Bell Labs in 1969, based on MOS capacitor technology. The NMOS active-pixel sensor was later invented by Tsutomu Nakamura's team at Olympus in 1985, which led to the development of the CMOS active-pixel sensor (CMOS sensor) at the NASA Jet Propulsion Laboratory in 1993.

In the 1960s, Eugene F. Lally of the Jet Propulsion Laboratory was thinking about how to use a mosaic photosensor to capture digital images. His idea was to take pictures of the planets and stars while travelling through space to give information about the astronauts' position. As with Texas Instruments employee Willis Adcock's film-less camera (US patent 4,057,830) in 1972, the technology had yet to catch up with the concept.

In 1972, the Landsat 1 satellite's multispectral scanner (MSS) started taking digital images of Earth. The MSS, designed by Virginia Norwood at Hughes Aircraft Company starting in 1969, captured and transmitted image data from green, red, and two infrared bands with 6 bits per channel, using a mechanical rocking mirror and an array of 24 detectors. Operating for six years, it transmitted more than 300,000 digital photographs of Earth, while orbiting the planet about 14 times per day.

Also in 1972, Thomas McCord from MIT and James Westphal from Cal Tech together developed a digital camera for use with telescopes. Their 1972 "photometer-digitizer system" used an analog to digital converter and a digital frame memory to store 256 x 256-pixel images of planets and stars, which were then recorded on digital magnetic tape.  CCD sensors were not yet commercially available, and the camera used a silicon diode vidicon tube detector which was cooled using dry ice to reduce dark current, allowing exposure times of up to one hour.   

The Cromemco Cyclops was an all-digital camera introduced as a commercial product in 1975. Its design was published as a hobbyist construction project in the February 1975 issue of Popular Electronics magazine. It used a 32×32 metal–oxide–semiconductor (MOS) image sensor, which was a modified MOS dynamic RAM (DRAM) memory chip.

Steven Sasson, an engineer at Eastman Kodak, built a self-contained electronic camera that used a monochrome Fairchild CCD image sensor in 1975. Around the same time, Fujifilm began developing CCD technology in the 1970s. Early uses were mainly military and scientific; followed by medical and news applications.

The first filmless SLR (single lens reflex) camera was publicly demonstrated by Sony in August 1981. The Sony "Mavica" (magnetic still video camera) used a color striped 2/3" format CCD sensor with 280K pixels, along with analogue video signal processing and recording. The Mavica electronic still camera recorded FM modulated analog video signals on a newly developed 2" magnetic floppy disk, dubbed the "Mavipak". The disk format was later standardized as the "Still Video Floppy", or "SVF".

The Canon RC-701, introduced in May 1986, was the first SVF camera (and first electronic SLR camera) sold in the US. It employed an SLR viewfinder, included a 2/3" format color CCD sensor with 380K pixels, and was sold along with removable 11-66mm and 50-150mm zoom lens. 

Over the next few years, many other companies began selling SVF cameras. These analog electronic cameras included the Nikon QV-1000C, which had an SLR viewfinder and a 2/3" format monochrome CCD sensor with 380K pixels, and recorded analog black and white images on a Still Video Floppy.

At Photokina 1988, Fujifilm introduced the FUJIX DS-1P, the first fully digital camera, which recorded digital images using a semiconductor memory card. The camera's memory card had a capacity of 2 MB of SRAM (static random-access memory), and could hold up to ten photographs. In 1989, Fujifilm released the FUJIX DS-X, the first fully digital camera to be commercially released. In 1996, Toshiba's 40 MB flash memory card was adopted for several digital cameras.

The first commercial camera phone was the Kyocera Visual Phone VP-210, released in Japan in May 1999. It was called a "mobile videophone" at the time, and had a 110,000-pixel front-facing camera. It stored up to 20 JPEG digital images, which could be sent over e-mail, or the phone could send up to two images per second over Japan's Personal Handy-phone System (PHS) cellular network. The Samsung SCH-V200, released in South Korea in June 2000, was also one of the first phones with a built-in camera. It had a TFT liquid-crystal display (LCD) and stored up to 20 digital photos at 350,000-pixel resolution. However, it could not send the resulting image over the telephone function, but required a computer connection to access photos. The first mass-market camera phone was the J-SH04, a Sharp J-Phone model sold in Japan in November 2000. It could instantly transmit pictures via cell phone telecommunication. By the mid-2000s, higher-end cell phones had an integrated digital camera and by the early 2010s, almost all smartphones had an integrated digital camera.

Image sensors

The two major types of digital image sensor are CCD and CMOS. A CCD sensor has one amplifier for all the pixels, while each pixel in a CMOS active-pixel sensor has its own amplifier. Compared to CCDs, CMOS sensors use less power. Cameras with a small sensor use a back-side-illuminated CMOS (BSI-CMOS) sensor. The image processing capabilities of the camera determine the outcome of the final image quality much more than the sensor type.

Sensor resolution

The resolution of a digital camera is often limited by the image sensor that turns light into discrete signals. 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 demosaicing to recreate a full-color image. The number of pixels in the sensor determines the camera's "pixel count". In a typical sensor, the pixel count is the product of the number of rows and the number of columns. For example, a 1,000 by 1,000 pixel sensor would have 1,000,000 pixels, or 1 megapixel.

Resolution options

Firmwares' resolution selector allows the user to optionally lower the resolution, to reduce the file size per picture and extend lossless digital zooming. The bottom resolution option is typically 640×480 pixels (0.3 megapixels).

A lower resolution extends the number of remaining photos in free space, postponing the exhaustion of space storage, which is of use where no further data storage device is available, and for captures of lower significance, where the benefit from less space storage consumption outweighs the disadvantage from reduced detail.

Image sharpness

An image sharpness is presented through the crisp detail, defined lines, and its depicted contrast. Sharpness is a factor of multiple systems throughout the DSLR camera by its ISO, resolution, lens and the lens settings, the environment of the image and its post processing. Images have a possibility of being too sharp but it can never be too in focus.

A digital camera resolution is determined by a digital sensor. The digital sensor indicates a high level of sharpness can be produced through the amount of noise and grain that is tolerated through the lens of the camera. Resolution within the field of digital still and digital movie is indicated through the camera's ability to determine detail based on the distance which is then measured by frame size, pixel type, number, and organization although some DSLR cameras have resolutions limited it almost impossible to not have the proper sharpness for an image. The ISO choice when taking a photo effects the quality of the image as high ISO settings equates to an image that is less sharp due to increased amount of noise allowed into the image along with too little noise can also produce an image that is not sharp.

Methods of image capture

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.

Single-shot capture systems use either one sensor chip 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 (see Three-CCD camera).

Multi-shot exposes the sensor 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 was originally to use a single image sensor with three filters passed in front of the sensor in sequence to obtain the additive color information. Another multiple shot method is called microscanning. This method uses a single sensor chip with a Bayer filter and physically moves the sensor on the focus plane of the lens to construct a higher resolution image than the native resolution of the chip. A third version combines these 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 an image scanner. The linear or tri-linear sensors in scanning cameras utilize only a single line of photosensors, or three lines for the three colors. Scanning may be accomplished by moving the sensor (for example, when using color co-site sampling) or by rotating the whole camera. A digital rotating line camera offers images consisting of a total resolution that is very high.

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 that are available with multi-shot and scanning backs make them more attractive for commercial photographers who are working with stationary subjects and large-format photographs.

Improvements in single-shot cameras and image file processing at the beginning of the 21st century made single shot cameras almost completely dominant, even in high-end commercial photography.

Filter mosaics, interpolation, and aliasing

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 2x2 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 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 35 mm film size 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.

The crop factor is relative to the 35mm film format. If a smaller sensor is used, as in most digicams, the field of view is cropped by the sensor to smaller than the 35 mm full-frame format's field of view. This narrowing of the field of view may be described as crop factor, a factor by which a longer focal length lens would be needed to get the same field of view on a 35 mm film camera. Full-frame digital SLRs utilize a sensor of the same size as a frame of 35 mm film.

Common values for field of view crop in DSLRs using active pixel sensors 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-inch sensors currently used by Olympus and Panasonic. Crop factors for non-SLR consumer compact and bridge cameras are larger, frequently 4x or more.

Sensor resolution

The resolution of a digital camera is often limited by the image sensor that turns light into discrete signals. 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 demosaicing to recreate a full-color image. The number of pixels in the sensor determines the camera's "pixel count". In a typical sensor, the pixel count is the product of the number of rows and the number of columns. Pixels are square and is often equal to 1, for example, a 1,000 by 1,000 pixel sensor would have 1,000,000 pixels, or 1 megapixel. On full-frame sensors (i.e., 24 mm 36 mm), some cameras propose images with 20–25 million pixels that were captured by 7.5–m photosites, or a surface that is 50 times larger. 

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