What is a digital camera?

What is a digital camera? The first step is to understand what a digital camera is. With a film camera, an image is formed by collecting light from a particular scene or subject and focusing on film, which reacts chemically when struck by light and is said to "capture" the image. What makes a camera "digital" is that, instead of film, it has an image sensor that reacts to light by sending out electrical signals. Digital and film 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 the correct amount of light to the imager, 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 video with sound. Some digital cameras can crop and stitch pictures and performs other elementary image editing. The camera takes the information from the image sensor and processes and stores it as a collection of pixels in a digital file, usually on a memory card inside the camera. Although the actual process is more complex than that, in essence it is how a digital photo image is made. It's essentially made up of thousands and thousands of tiny dots, or pixels.
Categorizing Types of Digital Cameras
Digital cameras fall into several overlapping categories, which are usually defined by a number of features. Specifications that define a category change over time. However, the categories themselves have remained fairly constant in terms of who uses them and how: ·         Web cams/phone cams: Most Web and phone cams (like the one shown in this figure) can’t do serious digital photography. ·         Point-and-shoot models: Point-and-shoot digital cameras can do anything a simple film camera can do. This figure shows a typical point-and-shoot model. ·         Intermediate models: Intermediate digital cameras (see this figure) are the most widely used. They have the best compromise of features to suit most consumer needs. ·         Advanced consumer models: These cameras (like the one in this figure) are aimed at those who want some special features. ·         Advanced consumer cameras usually require a session or two with the instruction manual to master all their capabilities. ·         Prosumer: dSLR models: Prosumer digital SLR cameras (see this figure) are the models that photo buffs and even a few professional photographers favor. ·         The key differences between high-priced prosumer digital SLR cameras and professional digital SLR cameras are resolution, speed, and ruggedness. ·         Professional models: These high-end models (like the one in this figure) are the equal of their film camera counterparts in every way. ·         Our Ratings are divided into two main categories: Basic cameras, are simple point-and-shoots with just the features needed for routine shots, and advanced cameras, which are feature-laden cameras that include sophisticated point-and-shoot and models that let you change lenses. Note that all point-and-shoots, whether basic or advanced, include cameras with lenses built into the camera (that is, non-removable). ·         Our basic camera category is divided into three subcategories: subcompacts, compacts and super zooms. ·         Subcompacts fit in a pocket, are lightweight but generally have few manual controls. A few include non telescoping zoom lenses, and others have zooms as high as 14x. Compacts are a bit larger, and often have more manual controls than subcompacts. They can also be among the most inexpensive cameras available. ·         Super zooms offer 15x or greater zoom, with some recent models including optical zooms as great as 35x. Like compacts, super zooms often, though not always, include manual controls. They're also among the more expensive basic cameras. ·         Our advanced camera category is also divided into three subcategories: advanced point-and-shoots, SLR-like and SLRs. ·         Advanced point-and-shoots have a non detachable lens but differ from basic models because they have lots of manual controls, a hot shoe for an external flash, and support for RAW files. It's the lightest advanced type. SLR-like models have interchangeable lenses, but they lack a through-the-lens viewfinder. They're smaller and lighter than an SLR but usually larger than a point-and-shoot. SLRs have the most features, with interchangeable lenses and the largest sensors for the best image quality in low light, and a through-the lens viewfinder. Controls are extensive. They're also the heaviest, most expensive cameras.
What are megapixels?
When you collect a million pixels, you have a megapixel. The number of megapixels tells you how many pixels the image file has. A camera that captures 8 million pixels, for example, is called an 8-megapixel camera. The number of megapixels a camera features can also help to determine the size photos you can print or the amount of cropping you can do. For example, a 6-megapixel camera may be enough for snapshots, but if you want to print poster-size images or crop heavily, 8 megapixels (or greater) is more suitable. A 6-megapixel camera might be all you'll need because higher resolution doesn't necessarily produce better prints. Lenses and other factors affect quality too. But most cameras today have at least 10-megapixel sensors. The size of the sensor, and the size of each individual image sensor element, which corresponds to pixels, can affect photo quality. But remember, the number of megapixels alone doesn't determine the quality of a digital camera's images. Megapixels are NOT everything One of the features that you’ll see used to sell digital cameras is how many megapixels a digital camera has. When I first got into digital photography, a few years back, the megapixel rating of cameras was actually quite important as most cameras were at the lower end of today’s modern day range and even a 1 megapixel increase was significant. These days, with most new cameras coming out with at least 5 megapixels, it isn’t so crucial. In fact at the upper end of the range it can actually be a disadvantage to have images that are so large that they take up enormous amounts of space on memory cards and computers. One of the main questions to ask when it comes to megapixels is ‘Will you be printing shots’? If so – how large will you be going with them? If you’re only printing images at a normal size then anything over 4 or so megapixels will be fine. If you’re going to start blowing your images up you might want to pay the extra money for something at the upper end of what’s on offer today.	Types of digital cameras Digital cameras are made in a wide range of sizes, prices and capabilities. The majority are camera phones, operated as a mobile application through the cell phone menu. Professional photographers and many amateurs use larger, more expensive digital single-lens reflex cameras (DSLR) for their greater versatility. Compact digital cameras Compact cameras are designed to be tiny and portable and are particularly suitable for casual and "snapshot" uses. Hence, they are also called point-and-shoot cameras. The smallest, generally less than 20 mm thick, are described as subcompacts or "ultra-compacts" and some are nearly credit card size. Bridge cameras Bridge are higher-end digital cameras that physically and ergonomically resemble DSLRs and share with them some advanced features, but share with compacts the use of a fixed lens and a small sensor. Like compacts, most use live preview to frame the image. Their autofocus uses the same contrast-detect mechanism, but many bridge cameras have a manual focus mode, in some cases using a separate focus ring, for greater control. They originally "bridged" the gap between affordable point-and-shoot cameras and the then unaffordable earlier digital SLRs. In bright sun, the quality difference between a good compact camera and a digital SLR is minimal but bridge cams are more portable, cost less and have similar zoom ability to dSLR. Thus a Bridge camera may better suit outdoor daytime activities, except when seeking professional-quality photos. In low light conditions and/or at ISO equivalents above 800, most bridge cameras (or mega zooms) lack in image quality when compared to even entry level DSLRs. However, they do have one major advantage: their much larger depth of field due to the small sensor as compared to a DSLR, allowing larger apertures with shorter exposure times. A 3D Photo Mode was introduced in 2011, whereby the camera automatically takes a second image from a slightly different perspective and provides a standard .MPO file for stereo display
Mirror less interchangeable-lens camera In late 2008, a new type of camera emerged, combining the larger sensors and interchangeable lenses of DSLRs with the live-preview viewing system of compact cameras, either through an electronic viewfinder or on the rear LCD. These are simpler and more compact than DSLRs due to the removal of the mirror box, and typically emulate the handling and ergonomics of either DSLRs or compacts. The system is used by Micro Four Thirds, borrowing components from the Four Thirds DSLR system. Some MILCs use a larger APS-C sensor, such as the Sony NEX series and the Pentax K-01 Digital single lens reflex cameras Digital single-lens reflex cameras (DSLRs) are digital cameras based on film single-lens reflex cameras (SLRs). They take their name from their unique viewing system, in which a mirror reflects light from the lens through a separate optical viewfinder. At the moment of exposure the mirror flips out of the way, making a distinctive "clack" sound and allowing light to fall on the imager. While digital SLRs are getting more affordable they are not for everyone. Keep in mind that they are usually bigger, heavier, harder to keep clean (if you’re changing lenses) and can be more complicated to operate than point and shoot. Of course there are some upsides also. If you’re trying to make a decision between a point and shoot and DSLR you might want to read my previous posts titled Should you buy a DSLR or a Point and Shoot Digital Camera? and it’s companion piece How to Choose a DSLR. Digital rangefinders A rangefinder is a user-operated optical mechanism to measure subject distance once widely used on film cameras. Most digital cameras measure subject distance automatically using electro-optical techniques, but it is not customary to say that they have a rangefinder. Line-scan camera systems A line-scan camera is an industrial instrument having a single row of pixel sensors, instead of a matrix of them. The camera captures a data stream by imaging a constant stream of moving material. The data stream is commonly processed by a computer to create two-dimensional image data for industrial purposes. Integration Many devices include digital cameras built into or integrated into them. For example, mobile phones often include digital cameras; those that do are known as camera phones. Other small electronic devices (especially those used for communication) such as PDAs, laptops and BlackBerry devices often contain an integral digital camera, and most 21st-century camcorders can also make still pictures. Due to the limited storage capacity and general emphasis on convenience rather than image quality, almost all these integrated or converged devices store images in the lossy but compact JPEG file format.	Methods of image capture ·         There have been three main methods of capturing the image, each based on the hardware configuration of the sensor and color filters. In the industrial and high-end professional photography market, some camera systems use modular (removable) image sensors. For example, some medium format SLR cameras, such as the Mamiya 645D series, allow installation of either a digital camera back or a traditional photographic film back. Area array CCD CMOS Linear array CCD (monochrome) 3-strip CCD with color filters Linear array cameras are also called scan backs. Single-shot Multi-shot (three-shot, usually) ·         single-shot ·         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, 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. Multi-shot ·         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 is called Micros canning. This technique utilizes 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. ·         scanning ·         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 photo sensors, or three lines for the three colors. In some cases, scanning is accomplished by moving the sensor e.g. when using Color co-site sampling or rotate the whole camera; a digital rotating line camera offers images of very high total resolution. ·         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 available with multi-shot and scanning backs make them attractive for commercial photographers working with stationary subjects and large-format photographs.
Filter mosaics, interpolation, and aliasing ·         Most current consumer digital cameras use a Bayer filter mosaic 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, Color co-site sampling or Foveon X 3 sensor do not use anti-aliasing filters, or demosaicing. Sensor size and angle of view Cameras with digital image sensors that are smaller than the typical 35mm 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. If a sensor smaller than the full-frame 35mm film format is used, as in most digicams, then the field of view is cropped by the sensor to smaller than the 35mm full-frame format's field of view. This narrowing of the field of view is often described in terms of a focal length multiplier or crop factor, a factor by which a longer focal length lens would be needed to get the same field of view on a full-frame camera. The result is geometrically similar to taking the image from the film camera and cutting it down (cropping) to the size of the sensor, ignoring various questions such as resolution. For moderately large DSLRs the crop factor may be in the range of 1.3-2 while smaller cameras use smaller sensors with a larger crop factor.	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 differs 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 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 that 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 produces 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.
Finding the Best Digital Camera · What are you looking to accomplish? What are your goals? Do you want to simply document the life and times of your family, for example, or do you fancy yourself become a digital artist? · Do you want to print your images? In large sizes? Look for high resolution   If you are going to print, what kind of output device (i.e. printer) will you be using and what are its resolution requirements? Again, look for resolution The resolution of a digital camera is often limited by the image sensor (typically a CCD or CMOS sensor chip) that turns light into discrete signals. The sensor is made up of millions of "buckets" that essentially count the number of photons that strike the sensor. 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 a demosaicing/interpolation algorithm. The number of resulting pixels in the image determines its "pixel count". For example, a 640x480 image would have 307,200 pixels, or approximately 307 kilopixels; a 3872x2592 image would have 10,036,224 pixels, or approximately 10 megapixels. · Do you only see yourself publishing your images on the Web or emailing them to friends? You don't need much resolution - don't worry about it · Will you be taking this digital camera to Europe or around the world? Look for lots of storage	Many camera phones and most separate digital cameras use memory cards having flash memory to store image data. The majority of cards for separate cameras are SD format; many are Compact Flash and the other formats are rare. In January 2012, a faster XQD card format was announced.[15] Digital cameras have computers inside, hence have internal memory, and many cameras can use some of this internal memory for a limited capacity for pictures that can be transferred to or from the card or through the camera's connections. A few cameras use some other form of removable storage such as Microdrives (very small hard disk drives), CD single (185 MB), and 3.5" floppy disks. Other unusual formats include: Onboard flash memory — Cheap cameras and cameras secondary to the device's main use (such as a camera phone) PC Card hard drives — early professional cameras (discontinued) Thermal printer — known only in one model of camera that printed images immediately rather than storing · Do you own a laptop? (Look for a Compact Flash or other PCMCIA storage device · Will you be taking pictures of small items like stamps, coins, bugs, flowers, etc? Look for a digital camera with a macro feature · Do you already own Photoshop or Photoshop Elements? Then you might want to just get a camera with a Photoshop plug-in
File formats The Joint Photography Experts Group standard (JPEG) is the most common file format for storing image data. Other file types include Tagged Image File Format (TIFF) and various Raw image formats. Many cameras, especially high-end ones, support a raw image format. A raw image is the unprocessed set of pixel data directly from the camera's sensor, often saved in a proprietary format. Adobe Systems has released the DNG format, a royalty-free raw image format used by at least 10 camera manufacturers. Raw files initially had to be processed in specialized image editing programs, but over time many mainstream editing programs, such as Google's Picasa, have added support for raw images. Rendering to standard images from raw sensor data allows more flexibility in making major adjustments without losing image quality or retaking the picture. Formats for movies are AVI, DV, MPEG, MOV (often containing motion JPEG), WMV, and ASF (basically the same as WMV). Recent formats include MP4, which is based on the QuickTime format and uses newer compression algorithms to allow longer recording times in the same space. ·  Do you prefer shooting digital photos over reworking them on the computer? Then you might want to go for a camera with a popular, easy-to-use software program ·  Do you foresee yourself shooting at night, at concerts, indoors, or in other low-light situations? Then get a camera with flexible over sensitivity or ISO equivalents ISO is a rough measure of low-light sensitivity. It only matters if you shoot in the dark, and then shoot without flash. As soon as your flash pops up, the higher ISOs aren't used anyway. Even if you learn how to use the higher ISO settings (few people do), there isn't much difference between cameras of the same type and era, regardless of cost! All the higher ISO settings do is make the picture look grainier, and the cameras that sport the highest ISO settings look horrible at those settings! Many cameras have built-in flashes, but this tiny external flash gives a lot more range, and most importantly, saves the camera's batteries and lets you shoot a lot faster because it recharges almost instantly after each shot. In-camera flashes drain the camera's battery and can take a long time to recycle after each shot. ·  Do you foresee yourself shooting sports, fashion, or anything else that moves quick? Then get a camera with a fast burst rate ·  Do you want to make sure that the money you save on film and developing doesn't just end up getting spent on batteries? Then you might want to get a camera with rechargeable Lithium-Ion batteries or some such similar set-up Batteries Digital cameras have high power requirements, and over time have become smaller, resulting 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. Two broad types of batteries are in use for digital cameras. Off-the-shelf Off-the-shelf batteries may be single-use disposable or reusable rechargeable batteries. In either case they conform to an established off-the-shelf form factor, most commonly AA, CR2, or CR-V3 batteries, with AAA batteries in a handful of cameras. The CR2 and CR-V3 batteries are lithium based, and intended for single use. They are also commonly seen in camcorders. AA batteries are the most common; however, the non-rechargeable alkaline batteries supplied with low-end cameras are capable of powering most cameras for only a very short time. They may serve satisfactorily in cameras that are only occasionally used. Consumers with more than an occasional need use AA Nickel metal hydride batteries (NiMH) instead, which provide adequate energy and are rechargeable. NIMH batteries do not provide as much energy per volume as lithium ion batteries, and they also tend to discharge when not used. For the same energy, a NiMH rechargeable battery takes up to twice the volume of a Li-on rechargeable battery, and is three to five times heavier, but only costs half as much. Rechargeable batteries are available in various ampere-hour (Ah) or milli-ampere-hour (mAh) ratings, which are approximately proportional to shots per charge. Proprietary The second type of battery for digital cameras 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. Keep in mind as you look at cameras that the price quoted may not be the final outlay that you need to make as there are a variety of other extras that you might want (or need) to fork out for including: •           Camera Case •           Memory Cards •           Spare Batteries/Recharger •           Lenses (if you are getting a DSLR) •           Filters (and other lens attachments) •           Tripods/Monopods •           External Flashes •           Reflectors ·  How much money do you have to spend? This is the final dictions. when you are buying the camera can support to find the suitable camera using above information of digital camera. Once you’ve narrowed down your search to a handful of cameras head into your local digital camera shop and ask to see and play with them. There’s nothing like having the camera in your hands to work out whether it suits your needs. When I shop for a camera I generally use the web to find reviews, then I head into a street in my city with 4 camera shops side by side and I go from shop to shop asking for recommendations and seeing the cameras live in the flash. In doing this I generally find the same camera or two are recommended in most shops and I get to see them demonstrated by different people (this gives a more well rounded demo). I also get to play with it and get a feel for which one I could see myself using. Even you can buy cheap but can shoot what do you want. That is the main idea of this information, for beginner or medium users. For professional users can follow advanced information by high-tech camera production guides. Thank you for reading this.
Collecting information by:  How to Buy a Digital Camera – A 9 Step Guide- http://digital-photography-school.com/cameras http://www.dummies.com/how-to.html http://www.consumerreports.org/cro/electronics-computers/index.htm http://en.wikipedia.org/wiki/Digital_camera http://www.kenrockwell.com/tech/reviews.htm http://www.betterphoto.com