Digital Video Camera

 

A still video camera that records images in digital form. Unlike traditional analog cameras that record infinitely variable intensities of light, digital cameras record discrete numbers for storage on a flash memory card or optical disk. As with all digital devices, there is a fixed, maximum resolution and number of colors that can be represented. Images are transferred to the computer with a USB cable or via the memory card. Digital video cameras also use FireWire.

Digital Video Camera Advantages
There are two distinct advantages of digital cameras. The first is the capability to see the final image right away so you know you have the picture you wanted. Bad pictures can be instantly erased. The second is a very convenient feature. You can take one picture and print it without either waiting to develop the entire roll of film or wasting the whole roll for only one or two pictures. In addition, "digital film" is reusable, except for the write-once optical discs (CD-R) variety.

Chips and Flash

The film in a digital camera is made up of photosensor chips and flash memory. The camera records color images as intensities of red, green and blue, which are stored as variable charges on a CCD or CMOS image sensor chip. The charges, which are actually analog, are converted to digital and stored in one of several flash memory formats such as CompactFlash or Memory Stick. Instead of memory cards, some still cameras use optical disc for storage, and video cameras may use discs or tape (see DV).

The size of the chip determines the resolution, but the analog-to-digital converter (ADC), which converts the charges to digital data, determines the color depth. In 2002, Foveon introduced a breakthrough in color accuracy with its X3 CMOS chip (see Bayer pattern and X3).

Digital video cameras also use these same image sensing methods, but may also output traditional analog signals (NTSC) in addition to digital. See flash memory, photo editor, photo scanner, X3 and DSLR.

Major Features
Following are the major features and some caveats of digital cameras.

Resolution in Megapixels

The number of pixels determines the maximum size of a printed photo without sacrificing quality. For 3x5" and 4x6" prints, 2 megapixels is good. For 5x7" and 8x10" prints, 5 megapixels is preferred. For low-resolution images on the Web, almost any digital camera will suffice. However, you can easily reduce a high-quality image to the low resolution required online. The higher the resolution from the start, the better the results.

Optical Quality

Megapixel resolution is a quantitative measurement, but the lens itself is qualitative. The optical quality of the lens greatly contributes to the resulting picture quality as it has in analog cameras for more than a century. To make a decision on this one, the printed pictures have to be seen.

Optical vs. Digital (Interpolated) Zoom

The optical zoom is the real resolution of the lenses. The digital zoom is an interpolated resolution computed by software. The higher the optical number, the better. A 10x optical is far superior to a 10x digital. Some digital zoom numbers go into the stratosphere, especially for video, but optical is what counts.

Storage Media

There are several types of flash memory cards used for "digital film," but no matter which type the camera uses, the one that comes with the camera is typically undersized. Plan on purchasing a larger one when you buy the camera (see flash memory).

Data Transfer

Digital cameras come with a USB cable for transfer directly to the computer, and many computers come with one or more memory card slots. Printers may also come with card slots, allowing you to print your photos without using the computer at all.

Battery Duration

Digital cameras use either rechargeable or standard AA batteries. It can take an hour or more to recharge a battery, so an extra one, fully charged, is always a good idea to have along. AA batteries can be purchased almost anywhere, and rechargeable AA batteries can also be used.

Interchangeable Lenses

Digital single lens reflex (DSLR) cameras are the digital counterparts of their analog predecessors and may use the same removable lenses that you already own. However, the chip is often smaller in size than a 35mm frame, which means your 28mm wide angle lens may function like a 42mm lens. Increasingly larger chips and wider angle lenses are solving the problem.

Digital Video Camera

 

Digital Video Camera

Digital Camera

Behind the lens, a CCD or CMOS image sensor chip picks up the image as charges that are converted to digital data by an A/D converter chip (ADC). The DSP chip adjusts contrast and detail and compresses the digital data for storage.

 

Digital Video Camera

 

Digital still cameras are generally characterized by the use of flash memory and USB or FireWire for storage and transfer. Most have a rear LCD for reviewing photographs. They are rated in megapixels; that is, the product of their maximum resolution dimensions. The actual transfers to a host computer are commonly carried out using the USB mass storage device class (so that the camera appear as a drive) or using the Picture Transfer Protocol and its derivatives. All use a CCD (for Charged Coupled Device) which is a chip comprised of a grid of phototransistors to sense the light intensities across the plane of focus of the camera lens. There has recently been some application of a second kind of chip, called a CMOS (Complementary Metal-Oxide Semiconductor) sensor, and this chip is often differentiated from a CCD 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: 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.
  • Digital SLRs typically have a sensor nine times larger than that of a standard digital camera, and are targeted at professional photographers and enthusiasts. They resemble ordinary professional cameras in most ways, with replaceable flash and lens components, which give the user maximum control over light, focus and depth of field. They are also bulkier and more expensive than their casual-use oriented counterparts. They are superb for portraiture and artistic photography because they can be customized for various applications with a comprehensive range of exchangeable lenses.

 

Professional modular digital camera systems

High-end digital camera backs used by professionals are usually separate devices from the camera bodies which they are used with. (This is because most of the large- and medium-format camera systems in professional use at the time that digital capture overtook film as the professional's medium of choice were modular in nature, i.e. the camera body had multiple lenses, viewfinders, winders and backs available for use with it to fit different needs.) 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 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.

Digital Video Camera

 

Webcams

  • 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. These devices range in price from very inexpensive to expensive higher-end models; many complex webcams have a servo-controlled base capable of tracking facial motion with the help of software.

Practical resolution considerations

It is important to note that with any digital camera system not using the beam splitter single-shot approach or three-filter multi-shot approach, some image color or resolution "interpolation" is taking place. 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. However, a photosite on a regular (non-Foveon) sensor cannot simultaneously record these three values, which is why the Bayer filter is used. A Bayer filter is actually a pattern of red, green and blue light filters applied one color to each photosite on a chip or a stick (usually there are about twice as many green filters as there are either red or blue because the frequencies of light in the green spectrum tend to represent a more neutral intensity value for interpolation's sake, sitting as it does nearer the center of the visible light spectrum.) The two luminous intensity color values not captured for each pixel are then 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. USB is the most widely used method, though some have a Firewire port.

Storage

Digital cameras need memory to store data. The higher one goes in pixel size, the more memory will be needed. Cameras use a removable memory card to store data, but the cheapest and smallest cameras may simply use fixed internal memory instead. Some cameras come with inbuilt memory as well.

Autonomous devices

An autonomous device, such as a PictBridge-compatible printer, operates without need of computer control. The camera connects to the printer, which then downloads and prints its images. Some DVD recorders and television sets can read memory cards.

 

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