Formats

Common formats for digital camera images are the Joint Photography Experts Group standard (JPEG) and Tagged Image File Format (TIFF).

Many cameras, especially professional or DSLR cameras, support a Raw format. A raw image is the unprocessed set of pixel data directly from the camera's sensor. They are often saved in formats proprietary to each manufacturer, such as NEF for Nikon, CRW for Canon, and MRW for Minolta. Adobe Systems has released the DNG format, a royalty free raw image format which has been adopted by a few camera manufacturers.

Raw files initially had to be processed in specialized image editing programs, but over time many mainstream editing programs have added support for them, such as Google's Picasa. Editing raw format images allows much more flexibility in settings such as white balance, exposure compensation, color temperature, and so on. In essence raw format allows the photographer make major adjustments without losing image quality that would otherwise require retaking the picture.

Formats for movies are AVI, DV, MPEG, MOV, WMV, and ASF (basically the same as WMV). Recent formats include MP4, which is also a MOV file but uses newer compression algorithms to allow longer recording times in the same space.

Other formats that are used in cameras but not for pictures are the Design Rule for Camera Format (DCF), an ISO specification for the camera's internal file structure and naming, Digital Print Order Format (DPOF), which dictates what order images are to be printed in and how many copies, and the Exchangeable Image File Format (EXIF), which uses metadata tags to document the camera settings and date and time for image files.

Batteries

Digital cameras have high power requirements, and over time have become increasingly smaller in size, which has resulted in an ongoing need to develop a battery small enough to fit in the camera and yet able to power it for a reasonable length of time.

Essentially two broad divisions exist in the types of batteries digital cameras use.

Off-the-shelf

The first is batteries that are an established off-the-shelf form factor, most commonly AA or CR2 batteries, with AAA batteries in a handful of cameras. The CR2 batteries are lithium based, and intended for single use. They are also commonly seen in camcorders. The AA batteries are far more common, however the non-rechargeable alkaline batteries are capable of providing enough power for only a very short time in most cameras. Most consumers use AA Nickel metal hydride batteries (NiMH) (see also chargers and batteries) instead, which provide an adequate amount of power and are rechargeable. NIMH batteries do not provide as much power as lithium ion batteries, and they also tend to discharge when not used. They are available in various ampere-hour (Ah) or milli-ampere-hour (mAh) ratings, which affects how long they last in use. Typically mid-range consumer models and some low end cameras use off-the-shelf batteries, only a very few DSLR cameras accept them.

Proprietary

The second division is proprietary battery formats. These are built to a manufacturer's custom specifications, and can be either aftermarket replacement parts or OEM. Almost all proprietary batteries are lithium ion. While they only accept a certain number of recharges before the battery life begins degrading (typically up to 500 cycles), they provide considerable performance for their size. A result is that at the two ends of the spectrum both high end professional cameras and low end consumer models tend to use lithium ion batteries.

Autonomous devices

An autonomous device, such as a PictBridge printer, operates without need of a computer. The camera connects to the printer, which then downloads and prints its images. Some DVD recorders and television sets can read memory cards too. Several types of flash card readers also have a TV output capability.

Storage

Digital cameras need memory to store data. A wide variety of storage media has been used. These include:

Onboard flash memory

Cheap cameras and cameras secondary to the device's main use (such as a camera phone).

3.5" floppy disks

Mainly the Sony Mavica line of the late 1990s.

Video Floppy

A 2x2 inch (50 mm × 50 mm)floppy disk used for early analog cameras.

PCMCIA hard drives

Early professional cameras, discontinued.

CD single or DVD

a 185 MB small form factor CD, most commonly seen in the Sony CD-1000.

Thermal printer

Known only in one model of camera that printed images immediately rather than storing.

Memory cards

CompactFlash cards/Microdrives

Typically higher end professional cameras. The microdrives are actual hard drives in the CompactFlash form factor. Adapters exist to allow using SD cards in a CompactFlash device.

Memory Stick

A proprietary flash memory type manufactured by Sony.

SD/MMC

A flash memory card in a small form factor that is gradually supplanting CompactFlash. The original storage limit was 2 GB, which is being supplanted by 4 GB cards. 4 GB cards are not recognized in all cameras as a revision was made to the SD standard as SDHC (SD High Capacity). The cards also have to be formatted in the FAT32 file format while many older cameras use FAT16 which has a 2 GB partition limit.

MiniSD Card

A smaller (slightly less than half-size) card used in devices such as camera phones.

MicroSD Card

A smaller yet (less than a quarter size) version of the SD card. Used in camera phones.

XD-Picture Card

Developed by Fuji and Olympus in 2002, a format smaller than an SD card.

SmartMedia

A now obsolete format that competed with CompactFlash, and was limited to 128 MB in capacity. One of the major differences was that SmartMedia had the memory controller built in the reading device, while in CompactFlash it was in the card. The xD picture card was developed as a replacement for SmartMedia.

FP Memory

A 2-4 MB serial flash memory, known from the Mustek/Relisys Dimera low end cameras.

Filter mosaics, interpolation, and aliasing

In most current consumer digital cameras, a Bayer filter mosaic is used, in combination with an optical anti-aliasing filter to reduce the aliasing due to the reduced sampling of the different primary-color images. A demosaicing algorithm is used to interpolate color information to create a full array of RGB image data.

Cameras that use a beam-splitter single-shot 3CCD approach, three-filter multi-shot approach, or Foveon X3 sensor do not use anti-aliasing filters, nor demosaicing.

Firmware in the camera, or a software in a raw converter program such as Adobe Camera Raw, interprets the raw data from the sensor to obtain a full color image, because the RGB color model requires three intensity values for each pixel: one each for the red, green, and blue (other color models, when used, also require three or more values per pixel). A single sensor element cannot simultaneously record these three intensities, and so a color filter array (CFA) must be used to selectively filter a particular color for each pixel.

The Bayer filter pattern is a repeating 2×2 mosaic pattern of light filters, with green ones at opposite corners and red and blue in the other two positions. The high proportion of green takes advantage of properties of the human visual system, which determines brightness mostly from green and is far more sensitive to brightness than to hue or saturation. Sometimes a 4-color filter pattern is used, often involving two different hues of green. This provides potentially more accurate color, but requires a slightly more complicated interpolation process.

The color intensity values not captured for each pixel can be interpolated (or guessed) from the values of adjacent pixels which represent the color being calculated.

Connectivity

Many digital cameras can connect directly to a computer to transfer data:

* Early cameras used the PC serial port. USB is now the most widely used method ( Most cameras are viewable as USB Mass Storage), though some have a FireWire port. Some cameras use USB PTP mode for connection instead of USB MSC; some offer both modes.

* Other cameras use wireless connections, via Bluetooth or IEEE 802.11 Wi-Fi, such as the Kodak EasyShare One.

A common alternative is the use of a card reader which may be capable of reading several types of storage media, as well as high speed transfer of data to the computer. Use of a card reader also avoids draining the camera battery during the download process, as the device takes power from the USB port. An external card reader allows convenient direct access to the images on a collection of storage media. But if only one storage card is in use, moving it back and forth between the camera and the reader can be inconvenient.

Many modern cameras offer the PictBridge standard, which allows sending data directly to printers without the need of a computer.

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.

The first method is often called single-shot, in reference to the number of times the camera's sensor is exposed to the light passing through the camera lens. Single-shot capture systems use either one CCD with a Bayer filter mosaic it, or three separate image sensors (one each for the primary additive colors red, green, and blue) which are exposed to the same image via a beam splitter.

The second method is referred to as multi-shot because the sensor is exposed to the image in a sequence of three or more openings of the lens aperture. There are several methods of application of the multi-shot technique. The most common originally was to use a single image sensor with three filters (once again red, green and blue) passed in front of the sensor in sequence to obtain the additive color information. Another multiple shot method utilized a single CCD with a Bayer filter but actually moved the physical location of the sensor chip on the focus plane of the lens to "stitch" together a higher resolution image than the CCD would allow otherwise. A third version combined the two methods without a Bayer filter on the chip.

The third method is called scanning because the sensor moves across the focal plane much like the sensor of a desktop scanner. Their linear or tri-linear sensors utilize only a single line of photosensors, or three lines for the three colors. In some cases, scanning is accomplished by rotating the whole camera; a digital rotating line camera offers images of very high total resolution.

The choice of method for a given capture is of course determined largely by the subject matter. It is usually inappropriate to attempt to capture a subject that moves with anything but a single-shot system. However, the higher color fidelity and larger file sizes and resolutions available with multi-shot and scanning backs make them attractive for commercial photographers working with stationary subjects and large-format photographs.

Recently, dramatic improvements in single-shot cameras and RAW image file processing have made single shot, CCD-based cameras almost completely predominant in commercial photography, not to mention digital photography as a whole. CMOS-based single shot cameras are also somewhat common.

Image resolution

The resolution of a digital camera is often limited by the camera sensor (usually a charge-coupled device or CCD chip) that turns light into discrete signals, replacing the job of film in traditional photography. The sensor is made up of millions of "buckets" that collect charge in response to light. Generally, these buckets respond to only a narrow range of light wavelengths, due to a color filter over each. Each one of these buckets is called a pixel, and a demosaicing/interpolation algorithm is needed to turn the image with only one wavelength range per pixel into an RGB image where each pixel is three numbers to represent a complete color.

The one attribute most commonly compared on cameras is the pixel count. Due to the ever increasing sizes of sensors, the pixel count is into the millions, and using the SI prefix of mega- (which means 1 million) the pixel counts are given in megapixels. For example, an 8.0 megapixel camera has 8.0 million pixels.

The pixel count alone is commonly presumed to indicate the resolution of a camera, but this is a misconception. There are several other factors that impact a sensor's resolution. Some of these factors include sensor size, lens quality, and the organization of the pixels (for example, a monochrome camera without a Bayer filter mosaic has a higher resolution than a typical color camera). Many digital compact cameras are criticized for having too many pixels, in that the sensors can be so small that the resolution of the sensor is greater than the lens could possibly deliver.

Excessive pixels can even lead to a decrease in image quality. As each pixel sensor gets smaller it is catching fewer photons, and so the signal-to-noise ratio will decrease. This decrease leads to noisy pictures, poor shadow region quality and generally poorer-quality pictures.

As the technology has improved, costs have decreased dramatically. Measuring the "pixels per dollar" as a basic measure of value for a digital camera, there has been a continuous and steady increase in the number of pixels each dollar buys in a new camera consistent with the principles of Moore's Law. This predictability of camera prices was was first presented in 1998 at the Australian PMA DIMA conference by Barry Hendy and since referred to as "Hendy's Law".

History

Early development

The concept of digitizing images on scanners, and the concept of digitizing video signals, predate the concept of making still pictures by digitizing signals from an array of discrete sensor elements. Eugene F. Lally of the Jet Propulsion Laboratory published the first description of how to produce still photos in a digital domain using a mosaic photosensor.[1] The purpose was to provide onboard navigation information to astronauts during missions to planets. The mosaic array periodically recorded still photos of star and planet locations during transit and when approaching a planet provided additional stadiametric information for orbiting and landing guidance. The concept included camera design elements foreshadowing the first digital camera.

Texas Instruments designed a filmless analog camera in 1972, but it is not known if it was ever built. The first recorded attempt at building a digital camera was by Steve Sasson, an engineer at Eastman Kodak. It used the then-new solid state CCD 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 megapixel (10,000 pixels), and took 23 seconds to capture its first image in December of 1975. The prototype camera was a technical exercise, not intended for production, and it still existed as of 2005.

Digital cameras, in the sense of a device meant to be carried and used like a handheld film camera, appeared in 1981 with the demonstration of the Sony Mavica (Magnetic Video Camera). This is not to be confused with the later cameras by Sony that also bore the Mavica name. This was an analog camera based on television technology that recorded to a 2 × 2 inch "video floppy". In essence it was a video movie camera that recorded single frames, 50 per disk in field mode and 25 per disk in frame mode. The image quality was considered equal to that of then-current televisions.

Analog cameras do not appear to have reached the market until 1986 with the Canon RC-701. Canon demonstrated this model at the 1984 Olympics, printing the images in newspapers. Several factors held back the widespread adoption of analog cameras; the cost (upwards of $20,000), poor image quality compared to film, and the lack of quality affordable printers. Capturing and printing an image originally required access to equipment such as a frame grabber, which was beyond the reach of the average consumer. The "video floppy" disks later had several reader devices available for viewing on a screen, but were never standardized as a computer drive.

The early adopters tended to be in the news media, where the cost was negated by the utility and the ability to transmit images by telephone lines. The poor image quality was offset by the low resolution of newspaper graphics. This capability to transmit images without a satellite link was useful during the Tiananmen Square protests of 1989 and the first Gulf War in 1991.

The first analog camera marketed to consumers may have been the Canon RC-250 Xapshot in 1988. A notable analog camera produced the same year was the Nikon QV-1000C, which sold approximately 100 units.[citation needed] It recorded images in greyscale, and the quality in newspaper print was equal to film cameras. In appearance it closely resembled a modern digital single-lens reflex camera.

The arrival of true digital cameras

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. The first commercially available digital camera was the 1991 Kodak DCS-100, the beginning of a long line of professional SLR cameras by Kodak that were based in part on film bodies, often Nikons. It used a 1.3 megapixel sensor and was priced at $13,000.

The move to digital formats was helped by the formation of the first JPEG and MPEG standards in 1988, which allowed image and video files to be compressed for storage. The first consumer camera with a liquid crystal display on the back was the Casio QV-10 in 1995, and the first camera to use CompactFlash was the Kodak DC-25 in 1996.

The marketplace for consumer digital cameras was originally low resolution (either analog or digital) cameras built for utility. In 1997 the first megapixel cameras for consumers were marketed. The first camera that offered the ability to record video clips may have been the Ricoh RDC-1 in 1995.

1999 saw the introduction of the Nikon D1, a 2.74 megapixel camera that was the first digital SLR developed entirely by a major manufacturer, and at a cost of under $6,000 at introduction was affordable by professional photographers and high end consumers. This camera also used Nikon F-mount lenses, which meant film photographers could use many of the same lenses they already owned.

2003 saw the introduction of the Canon Digital Rebel, also known as the 300D, a 6 megapixel camera and the first DSLR priced under $1,000, and marketed to consumers.

Conversion of film cameras to digital

When digital cameras became common, a question many photographers asked was if their film cameras could be converted to digital. The answer was yes and no. For the majority of 35 mm film cameras the answer is no, the reworking and cost would be too great, especially as lenses have been evolving as well as cameras. For the most part a conversion to digital, to give enough space for the electronics and allow a liquid crystal display to preview, would require removing the back of the camera and replacing it with a custom built digital unit.

Many early professional SLR cameras, such as the NC2000 and the Kodak DCS series, were developed from 35 mm film cameras. The technology of the time, however, meant that rather than being a digital "back" the body was mounted on a large and blocky digital unit, often bigger than the camera portion itself. These were factory built cameras, however, not aftermarket conversions.

A notable exception was a device called the EFS-1, which was developed by Silicon Film from ca. 1998–2001. It was intended to insert into a film camera in the place of film, giving the camera a 1.3 MP resolution and a capacity of 24 shots. Units were demonstrated, and in 2002 the company was developing the EFS-10, a 10 MP device that was more a true digital back.

A few 35 mm cameras have had digital backs made by their manufacturer, Leica being a notable example. Medium format and large format cameras (those using film stock greater than 35 mm), have users who are capable of and willing to pay the price a low unit production digital back requires, typically over $10,000. These cameras also tend to be highly modular, with handgrips, film backs, winders, and lenses available separately to fit various needs.

The very large sensor these backs use lead to enormous image sizes. The largest in early 2006 is the Phaseone's P45 39 MP imageback, creating a single TIFF image of size upto 224.6 MB. Medium format digitals are geared more towards studio and portrait photography than their smaller DSLR counterparts, the ISO sensitivity in particular tends to have a maximum of 400, versus 3200 for some DSLR cameras.

Bridge cameras

Prosumer or Bridge digital cameras form a general group of higher end LPDs that physically resemble dSLR cameras and share with these some advanced features but share with compacts the same basic LPD design. Traditionally dSLRs are considered much more professional than bridge cameras which have so far been prosumer or at best semi-professional. However since the introduction of the Canon EOS Digital Rebel (a small-sized, low-priced dSLR introduced in 2003) and what followed it of similar entry-level dSLRs from different manufacturers, a new class of dSLR has emerged and the distinction between bridge versus dSLR as prosumer versus professional cameras has become less black and white than it used to be. The new class of dSLRs can be described as consumer (compared to the higher classes of dSLRs), while the top bridge cameras remain prosumer (compared to compact LPDs). A Comparison between the bridge and entry-level dSLRs would reveal that they are on par. The name prosumer from professional (or producer) and consumer, means a professional-consumer or a producer-consumer (who is involved somehow in the production of the product that they consume).

Bridge cameras tend to have long- or ultrazoom lens, which compromises -in varying degrees, depending on the quality of the zoom lens- a "do it all" ability with barrel distortion and pincushioning. Prosumer cameras are sometimes marketed as and confused with digital SLR cameras since the bodies resemble each other. The distinguishing characteristics are that prosumer cameras lack the mirror and reflex system of dSLRs, have so far been always produced with only one single sealed (non-interchangeable) lens (but accessory wide angle or telephoto converters can be attached to the front of the sealed lens), can usually take movies, record audio and the scene composition is done with either the liquid crystal display or the electronic viewfinder (EVF). The overall performance tends to be slower than a true digital SLR, but they are capable of very good image quality while being more compact and lighter than DSLRs. The high-end models of this type have comparable resolutions to low and mid-range DSLRs. Many of the these cameras can save in JPEG or .RAW format.

Live-Preview Digital cameras

A Live-Preview Digital camera (LPD) is a camera that uses a conventionally generated digital image (live-preview) on an electronic screen as its principal means of framing and previewing before taking the photograph. With the exception of very few live-preview dSLRs, any digital camera that has live-preview falls into this category.

Many modern LPDs have a movie mode, and a growing number of camcorders can take still photographs. However, even a low-end LPD can take far better still pictures than a mid-range video camera, and mid-range LPDs have much lower video quality than low-end Video cameras. In addition, some newer camcorders record video directly to flash memory and transfer over USB and FireWire. Among digital LPDs, most have a rear liquid crystal display for reviewing photographs. They are rated in megapixels; that is, the product of their maximum resolution dimensions in millions. The actual transfers to a host computer are commonly carried out using the USB mass storage device class (so that the camera appears as a drive) or using the Picture Transfer Protocol and its derivatives, in addition firewire is becoming more popular and supported among more digital cameras. All use either a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS) sensor or novel sensors based upon either of those two principles, i.e. chips comprised of a grid of phototransistors to sense the light intensities across the plane of focus of the camera lens. CMOS sensors are differentiated from CCDs proper in that it uses less power and a different kind of light sensing material, however the differences are highly technical and many manufacturers still consider the CMOS chip a charged coupled device. For our purposes, a chip sensor is a CCD.

Digital camera

A digital camera is an electronic device used to capture and store photographs electronically instead of using photographic film like conventional cameras. Modern compact digital cameras are typically multifunctional, with some devices capable of recording sound and/or video as well as photographs. In the Western market, digital cameras now outsell their 35 mm film counterparts.