Format Film Camera
How Digital Cameras Work: Vital Information You Must Know Before You Buy
Digital cameras are basically the same as film cameras in their handling. They both have a lens to focus the specific image, a shutter to let light inside the camera, and an aperture to control the amount of light which enters the camera.
The differences between digital and traditional photography happen to be after the light enters the camera. A traditional camera captures the images on film, while a digital camera captures the image on an image sensor.
Image sensors are electronic devices made up of an array of electrodes (or photosites) which calculate light intensity. The most universally recognized type of image sensor for digital cameras is the CCD (Charge-Coupled Device) although others such as CMOS and Foveon are sometimes used.
The number of photosites in the image sensor gives the digital camera its megapixel (millions of pixels) rating. Each photosite corresponds to a pixel in the final image, so a camera which is rated at six megapixels, for example, has an image sensor which is 3008 pixels wide by 2000 pixels high.
When light hits the image sensor it is converted into electrical signals which are built-up and fed to an analog-to-digital (A/D) converter. The A/D converter changes the electrical signal into binary numbers which are processed by a computer housed in the camera body. Once the numbers have been harvested the resulting image is stored on a memory card.
Photosites can only measure intensity of light—not color. In order to produce a colour image, each photosite must be covered with a colored filter which can be red, blue, or green. These are the three primary colors which can be combined to produce any other colour including white.
The colored filters are arranged in a grid so that there are twice as many green filters as there are red or blue. This is because the human eye is twice as sensitive to green light. Filters are arranged in a pattern called the Bayer pattern - one row of red, green, red, green (etc.), and the next row of blue, green, blue, green (etc).
Since each photosite can only be covered with one coloured filter, computer processing is necessary to produce a full colored image. This is done by analyzing a certain pixel and its immediate neighbors and producing a composite colour from these calculations. For example, if a bright red pixel is surrounded by bright green and bright blue pixels, the bright red pixel must undeniably be white, because white is the combination of red, blue, and green. This process is called demosaicing.
After demosaicing the image is adjusted according to the settings on your camera. Most cameras have settings for brightness, contrast, and colour saturation. After these adjustments are made some cameras may also apply a sharpening algorithm to make the image clearer.
The final step before saving the image on the memory card is to compress it. Most cameras use JPEG as a compression format. This reduces the size of the file by eliminating excess data. This information cannot be recovered, so JPEG is called a 'lossy' format.
Several cameras have the ability to save uncompressed images as TIFF files or raw data. Raw data is the original photosite data even before demosaicing. It can be transferred to a computer for processing with special software that will perform all of the processing functions of the camera but with much greater control.
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Consumer Reports - Digital Cameras
Digital cameras, which employ reusable memory cards instead of film, give you far more creative control than film cameras can. With a digital camera, you can transfer shots to your computer, then crop, adjust color and contrast, and add textures and other special effects. Final results can be made into cards or T-shirts, or sent via e-mail, all using the software that usually comes with the camera. You can make prints on a color inkjet printer, or by dropping off the memory card at one of a growing number of photofinishers. You can upload the file to a photo-sharing Web site for storage, viewing, and sharing with others.
Like camcorders, digital cameras have LCD viewers. Some camcorders can be used to take still pictures, but a typical camcorder's resolution is no match for a good still camera's.
WHAT'S AVAILABLE
The leading brands are Canon, Fujifilm, HP, Kodak, Olympus, and Sony; other brands come from consumer-electronics, computer, and traditional camera and film companies.
Digital cameras are categorized by how many pixels, or picture elements, the image sensor contains. One megapixel equals 1 million picture elements. A 3-megapixel camera can make excellent 8x10s and pleasing 11x14s. There are also 4- to 8-megapixel models, including point-and-shoot ones; these are well suited for making larger prints or for maintaining sharpness if you want to use only a portion of the original image. Professional Digital cameras use as many as 14 megapixels.
Price range: $200 to $400 for 3 megapixels; $250 to $400 for 4 and 5 megapixels; $300 to $1,000 for 6 to 8 megapixels.
IMPORTANT FEATURES
Most Digital cameras are highly automated, with features such as automatic exposure control (which manages the shutter speed, aperture, or both according to available light) and autofocus.
Instead of film, digital cameras typically record their shots onto flash-memory cards. CompactFlash and SecureDigital (SD) are the most widely used. Once quite expensive, such cards have tumbled in price--a 128-megabyte card can now cost less than $50. Other types of memory cards used by cameras include Memory Stick, Smart Media and xD-picture card. A few cameras, mainly some Sony models, use 3 1/4-inch CD-R or CD-RW discs.
To save images, you transfer them to a computer, typically by connecting the camera to the computer's USB or FireWire port or inserting the memory card into a special reader. Some printers can take memory cards and make prints without putting the images on a computer first. Image-handling software, such as Adobe Photoshop Elements, Jasc Paint Shop, Microsoft Picture It, and ACDSee, lets you size, touch up, and crop digital images using your computer. Most digital cameras work with both Windows and Macintosh machines.
The file format commonly used for photos is JPEG, which is a compressed format. Some cameras can save photos in uncompressed TIFF format, but this setting yields enormous files. Other high-end cameras have a RAW file format, which yields the image data with no processing from the camera.
Digital cameras typically have both an optical viewfinder and a small color LCD viewer. LCD viewers are very accurate in framing the actual image you get--better than most of the optical viewfinders--but they use more battery power and may be hard to see in bright sunlight. You can also view shots you've already taken on the LCD viewer. Many digital cameras provide a video output, so you can view your pictures on a TV set.
Certain cameras let you record an audio clip with a picture. But these clips use additional storage space. Some allow you to record limited video, but the frame rate is slow and the resolution poor.
A zoom lens provides flexibility in framing shots and closes the distance between you and your subject--ideal if you want to quickly switch to a close shot. The typical 3x zoom on mainstream cameras goes from a moderately wide-angle view (35mm) to moderate telephoto (105mm). You can find cameras with extended zoom ranges between 8x and 12x, giving added versatility for outdoor photography. Other new cameras go down to 24 or 28 mm at the wide-angle end, making it easier to take in an entire scene in close quarters, such as a crowded party.
Optical zooms are superior to digital zooms, which magnify the center of the frame without actually increasing picture detail, resulting in a somewhat coarser view.
Sensors in digital cameras are typically about as light-sensitive as ISO 100 film, though some let you increase that setting. (At ISO 100, you'll likely need to use a flash indoors and in low outdoor light.) A camera's flash range tells you how far from the camera the flash will provide proper exposure: If the subject is out of range, you'll know to close the distance. But digital cameras can tolerate some underexposure before the image suffers noticeably.
Red-eye reduction shines a light toward your subject just before the main flash. (A camera whose flash unit is farther from the lens reduces the risk of red eye. Computer editing of the image may also correct red eye.) With automatic flash mode, the camera fires the flash whenever the light entering the camera registers as insufficient. A few new cameras have built-in red-eye correction capability.
Some cameras that have powerful telephoto lenses now come with image stabilizers. These compensate for camera shake, letting you use a slower shutter speed than you otherwise could for following movement. But an image stabilizer won't compensate for the motion of subjects.
Most new 6- to 8-megapixel cameras come with full manual controls, including independent controls for shutter and aperture. That gives serious shutterbugs control over depth of field, shooting action, or shooting scene with tricky lighting.
HOW TO CHOOSE
The first step is to determine how you will use the camera most of the time. Consider these two questions:
How much flexibility to enlarge images do you need? If you mainly want to make 4x6 snapshots, a camera with a 3- or 4-megapixel resolution will be fine. Such a camera will also make an 8x10 print of an entire image without alteration that looks as sharp as one from a 6- or 8-megapixel model. But to enlarge the image more or enlarge only part of it, you'll want a 6- to 8-megapixel camera.
How much control do you want over exposure and composition? Cameras meant for automatic point-and-shoot photos, with a 3x-zoom lens, will serve snap shooters as well as dedicate hobbyists much of the time. The full-featured cameras in the 6- to 8-megapixel range offer capabilities that more-dedicated photographers will want to have. Two of the more important capabilities are a zoom range of 5x to 10x or more, which lets you bring distant outdoor subjects close and also lets you shoot candid portraits without getting right in your subject's face, and a full complement of manual controls that you determine the shutter speed and lens opening. '
Once you've established the performance priorities that you need from a camera, you can narrow your choices further by considering these convenience factors:
Size and weight. The smallest, lightest models aren't necessarily inexpensive 3-megapixel cameras. And the biggest and heaviest aren't necessarily found at the high end. If possible, try cameras at the store before you buy. That way, you'll know which one fits you hand best and which can be securely gripped. In our tests, we have found that some of the smallest don't leave much room even for small fingers.
Battery type and life. All digital cameras can run on rechargeable batteries of one of two types: an expensive battery pack or a set of AA batteries. In our tests of the cameras, neither battery type had a clear performance advantage. The best-performing cameras offer upward of 300 shots on a charge, while the worst manage only about 50. We think it's more convenient to own a camera that accepts AA batteries. You can buy economical, rechargeable cells (plus a charger) and drop in a set of disposable lithium or alkaline batteries if the rechargeable run down in the middle of the day's shooting.
Camera speed. With point-and-shoot cameras like the ones we tested, you must wait after each shot as the camera processes the image. Most models let you shoot an image every few seconds, but a few make you wait 5 seconds or more. They may frustrate you when you're taking photos in sequence.
Your other cameras. If you're adding a camera to your lineup or trading up to a more versatile model, look first for one that's compatible with the other cameras. If it is, you can share memory cards and batteries. Designs within a camera brand line are often similar. So staying wit the brand you have lowers the learning curve on the new camera for family members who switch between cameras.
Copyright © 2002-2006 Consumers Union of U.S., Inc.
For the latest information on this and many other products and services, visit www.ConsumerReports.org.
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