Digital camera
From Wikipedia, the free encyclopedia
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 35mm film counterparts. [1]
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Classification
Digital cameras can be classified into several groups:
Video cameras
- Professional video cameras such as those used in television and movie production. These typically have multiple image sensors (one per color) to enhance resolution and color gamut. Professional video cameras usually do not have a built-in VCR or microphone.
- Camcorders used by amateurs. They generally include a microphone to record sound, and feature a small LCD to watch the video during taping and playback.
- Webcams are digital cameras attached to computers, used for video conferencing or other purposes. Webcams can capture full-motion video as well, and some models include microphones or zoom ability.
In addition, many still digital cameras have a "movie" mode, in which images are continuously acquired at a frame rate sufficient for video.
Still cameras
Digital still cameras are cameras whose primary purpose is to capture photography in a digital format. Initially, a digital camera was characterized by the use of flash memory and USB or FireWire for storage and transfer of still photographs (though some early cameras used a serial port connection), and this is still the common meaning of the unadorned term. However, modern digital photography cameras have a video function, and a growing number of camcorders have a still photography function. In addition, some newer camcorders record video directly to flash memory and transfer over USB and FireWire. Among digital still cameras, most have a rear LCD 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 or a CMOS (Complementary Metal-Oxide Semiconductor) 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.
Standard Digital Cameras
- Main article: Compact digital camera
(also called digicams): This encompasses most digital cameras. They are characterized by great ease in operation and easy focusing; this design allows for limited motion picture capability. They have an extended depth of field. This allows objects at multiple depths to be in focus simultaneously, which accounts for much of their ease of focusing. It is also part of the reason professional photographers find their images flat or artificial-looking. They excel in landscape photography and casual use. The typical file format they save pictures in is JPEG.
Prosumer Cameras
- Main article: Bridge digital camera
Prosumer cameras or Extended Zoom cameras form a general group of higher end cameras that physically resemble SLR "professional" cameras and share some features, but are still geared towards consumers. Thus, the name Prosumer from Professional and Consumer. These cameras tend to have a large optical zoom lens, which compromises 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 they do not have a removable lens (though additional lenses can be attached in some models), can take movies, record audio and the scene composition is done with either the LCD display or the EVF (Electronic Viewfinder). 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. Many of the these cameras can save in JPEG or raw format.
Digital single-lens reflex camera
- Main article: Digital single-lens reflex camera
DSLRs are conceived for professional photographers and are well adapted for action photography or specialized uses. They are based on film single-lens reflex cameras and retain their main features : image composing done through the optical viewfinder using a mirror reflected image and exchangeable lenses, albeit a few early SLR cameras like the Olympus E-10 have a fixed lens.
The ability to change lenses gives the same benefits as in film cameras, allowing tailoring a lens to an intended use instead of a compromise. They can use the same lenses as their film counterparts, but the smaller sensor than 135 film, generally around 1.5 to 1.6 times, imply a same order lens field of view reduction.
DSLR cameras have larger image sensors than compacts or prosumers, and thus higher sensitivity in dim lighting and less noise overall in the pictures they take. They usually are instantly on and the autofocus and operation is faster. Most of them can save in JPEG and raw formats even simultaneously.
They are bulkier, heavier and frequently much more expensive. Two characteristics many consumers are surprised to find due to the reflex viewfinder is they can't record movies and the screen is only for reviewing pictures. All composing is done through the optical viewfinder, which is more precise than an electronic viewfinder and does not produce any delay. In 2006 the Olympus E-330 is the only DSLR that can use the LCD for a live preview, and will be joined by the Panasonic Lumix DMC-L1.
Professional modular digital camera systems
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 35mm 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 an LCD screen to preview, would require removing the back of the camera and replacing it with a custom built digital unit.
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 1.3MP resolution and a capacity of 24 shots. Units were demonstrated, and in 2002 the company was developing the EFS-10, a 10MP device that was more a true digital back.
A few 35mm 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 35mm), 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 Hasselblad H2D, which makes images 39MP in size from a 36.7mm X 49mm sensor. Medium format digitals are geared more towards studio and portrait photography than their smaller DSLR counterparts, the ISO sensivity in particular tends to have a maximum of 400, versus 3200 for some DSLR cameras.
Since the first backs were introduced there have been three main methods of "capturing" the image, each based on the hardware configuration of the particular back.
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 stamped onto it or three separate CCDs (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 CCD 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 stamping a Bayer filter onto the chip.
The third method is called "Scan" because the sensor moves across the focus plane much like the sensor of a desktop scanner. These CCDs are usually referred to as "sticks" rather than "chips" because they utilize only a single row of pixels (more properly "photosites") which are again "stamped" with the Bayer filter.
The fourth method is a rotational scan of a linear sensor. A digital rotating line camera offers images of very high 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 which moves (like people or objects in motion) with anything but a single shot system. However, the higher color fidelity and larger file sizes and resolutions available with multi-shot and scan-backs make them attractive for commercial photographers working with stationary subjects and large-format photographs.
Early History
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 that recorded to a 2x2 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 16MB 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 an LCD display on the back was the Casio QV-10 in 1995, and the first camera to used compact flash 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.
Interpolation
Image color or resolution interpolation is used unless the camera uses a beam splitter single-shot approach, three-filter multi-shot approach, or Foveon X3 sensor currently used in Sigma SD10 DSLR and Polaroid x530 point and shoot. The software specific to the camera interprets the information from the sensor to obtain a full color image. This is because in digital images, each pixel must have three values for luminous intensity, one each for the red, green, and blue channels. A normal sensor element cannot simultaneously record these three values.
The Bayer filter pattern is typically used. A Bayer filter pattern is a 2x2 pattern of light filters, with green ones at opposite corners and red and blue elsewhere. 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 2 different hues of green. This provides a wider color gamut, but requires a slightly more complicated interpolation process.
The luminous intensity color values not captured for each pixel can be interpolated (or guessed at) from the values of adjacent pixels which represent the color being calculated. In some cases, extra resolution is interpolated into the image by shifting photosites off of a standard grid pattern so that photosites are adjacent to each other at 45 degree angles, and all three values are interpolated for "virtual" photosites which fall into the spaces at 90 degree angles from the actual photosites.
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, though some have a FireWire port or use Bluetooth. Most cameras are viewable as USB Mass Storage but earlier ones used Picture Transfer Protocol or proprietary methods requiring software from the manufacturer. Some cameras such as the Kodak EasyShare One are able to connect to computer networks wirelessly via 802.11 Wi-Fi.
Increasingly popular is the use of a card reader which may be capable of reading several types of storage media, and transferring at high speed to the computer. This also avoids draining the camera battery during the download process as the device takes power from the USB port.
Integration
Some devices, like mobile phones and PDAs, contain integrated digital cameras. Mobile phone cameras are even more common than standalone digital cameras.
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).
- CompactFlash cards/Microdrives
- Typically higher end professional cameras. The microdrives are actual hard drives in the compact flash form factor. Adapters exist to allow using SD cards in a compact flash device.
- 3.5" floppy disks
- Mainly the Sony Mavica line of the late 1990s.
- Memory Stick
- A proprietary flash memory type manufactured by Sony.
- PCMCIA hard drives
- Early professional cameras, discontinued.
- CD single
- a 185MB small form factor CD, most commonly seen in the Sony CD-1000.
- SD/MMC
- A flash memory card in a small form factor that is gradually supplanting compact flash. The original storage limit was 2GB, which is being supplanted by 4GB cards. 4GB 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 2GB partition limit.
- MiniSD Card
- A smaller (slightly less than half-size) card used in devices such as camera phones.
- Thermal printer
- Known only in one model of camera that printed images immediately rather than storing.
- XD-Picture Card
- by Fuji and Olympus in 2002, a format smaller than an SD card.
- SmartMedia
- a now obsolete format that competed with Compact Flash, and was limited to 128MB in capacity. One of the major differences was that Smart Media had the memory controller built in the reading device, while in Compact Flash it was in the card. The developed replacement for Smart Media was the xD card.
- FP Memory
- A 2-4MB serial flash memory, known from the Mustek/Relisys Dimera low end cameras.
- Video Floppy
- A 2x2 inch floppy disk used for early analog cameras.
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.
Formats
- Main article: Image file formats
Common formats for digital camera images are the Joint Photography Experts Group standard (JPEG) and Tagged Image File Format (TIFF).
Some cameras support a Raw format. A raw image is an unprocessed set of pixel data directly from the camera's sensor. Raw files can be processed in specialized image editing programs and allow much more flexibility in settings such as white balance, exposure compensation, color temperature, and so on. In essence it lets 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.
See also
- Bluetooth
- Camera phone
- Computer printer
- Digital camera memory media
- Digital image editing
- Digital photography
- List of digital camera brands
- Mobile Imaging and Printing Consortium
- Still video camera
- Personal storage device
External links
- The first digital camera involving Kodak engineer Steven Sasson.
- Year-by-year developments up to 1998 and images of several types of cameras
