July 20, 2007

I found this glossary online in a magazine, unfortunately the authors name didn't copy and I haven't been able to find where I copied it from. Sorry. Also, it would not copy here without problems so I retyped it to word myself. I am not a typist, far from it and by the time I finished and realized the authors name wasn't there it was too late. I couldn't find the website at all.

That said, I found this glossary to be very helpful to me. I haven't been using my digital camera for very long and have been confused by the terms used when trying to learn how to set the camera. It works wonderfully on auto, but with all of the features included I feel the need to at least achieve a basic understanding of what can be accomplished with the camera.

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Aberration

Essentially, an aberration is anything in an image that isn’t supposed to be there. For example, optical imperfections within a lens may cause distortions such as barrel distortion or pincushioning. Barrel distortion, the outward curvature or bowing of straight lines, is most noticeable in wide-angle lenses or at the extreme wide-angle end of zoom lenses. Pincushioning, the inward curvature or bowing of straight lines is most common in telephoto lenses or the extreme telephoto end of zoom lenses. When corrective elements are incorporated into the lense design, most spherical aberrations can be minimized. Additionally, these spherical aberrations can often be adjusted with image editing software.

AD Converter

The analog to digital converter (ADC) converts the light waves that are absorbed by the photodiode (pixel) on an image sensor in the digital code. This digital information is then processed into image data that is then stored on the camera’s media card or internal memory. This image data can then be read as a photograph by a camera or computer.

Aperture

Measured in f-stop numbers, it is the variable opening in a lens that controls the amount of light that hits the image sensor, thereby affecting exposure. A small f-stop number (i.e., f/2.8) represents a wide lens opening, which allows more light to pass through the lens to the sensor and is beneficial in low light conditions. A larger f-stop number (i.e., f/8.0) narrows the lens opening allowing less light to hit the sensor. The latter provides a broader depth of field, while the former decreases the depth of field.

APO (Apochromatic)

Lenses that use internal elements to bring all colors of the visible spectrum to a common point of focus, creating a sharp image and minimizing chromatic aberrations, are referred to as APO lenses. These lenses are generally more expensive than non-APO lenses.

Artifacts

Digital image anomalies caused by the image sensor, optics or internal image processing of the camera. These anomalies include: blooming (brightened highlights usually visible along high-contrast edges); maze or moiré artifacts (as the name implies, maze artifacts appear in a maze-like pattern, while moiré artifacts occur as wavy lines); chromatic aberrations; jaggies (pixels visible in a stair-stepping pattern); noise; and sharpening halos (a bright or white area similar to blooming appears along an edge when an image has been over sharpened).

Autofocus (Active & Passive)

Active autofocus cameras bounce infrared beams off the subject to determine what the focal length of the lens should be. Passive autofocus cameras use the k\light falling on photocells to determine the correct focus. When a scene is out of focus, the intensity of light on each adjacent photocell is very similar. The microprocessor moves the lens until the contrast of light between each adjacent photocell is at its maximum.

Autofocus (Continuous)

Available on some digital cameras, this AF option signals the camera to constantly focus on whatever object is in front of the lens. While some cameras perform better than others, continuous AF is helpful when photographing a moving subject.

Bit

A bit is the smallest data unit of binary computing, being either a 1 or 0. eight bits make up one byte.

Bit-Depth

Also referred to as color-depth, bit-depth determines the maximum number of shades or intensities of colors that can be represented at a time. Camera sensors typically have 12 bits per channel color (red, green and blue) for a 36 bit image (which JPEG compression reduces to 8 bits per channel). Although more bit-depth is preferable, there are diminishing returns beyond 8 bits per channel (8 bits x 3 channels = 24 bit-depth). Image file sizes increase dramatically, and not all devices (printers, monitors) will benefit from higher bit-depth. Additionally, some image editing may have limited - or no - capabilities of working beyond 8 bits.

CCD (Charge-Coupled Device)

CMOS (Complimentary Metal Oxide Semiconductor)

The two types of sensors used in digital cameras are CCD and CMOS. These sensors are the equivalent of film in that, as the light enters the camera through the lens; the light waves are focused on the sensor, recorded electronically and then processed into the digital image. The CCD is the most common electronic image sensor used in digital cameras and is noted for its high quality but also for its extensive power requirements. CMOS is a sensor technology that encompasses all required camera circuits on a single chip. In the early days of digital photography, CMOS sensors were used in low-end digital cameras because they were less expensive to manufacture. However, more recently, because of technological advancements and the low power requirements of CMOS technology, a number of high-resolution, high-quality digital cameras now use CMOS sensors.

Chromatic Aberration

A fringe or outline of any color generated when the lens does not focus all light waves at the same focal point. While chromatic aberration can be purple, the term “purple fringing” – a purple/blue fringe along high-contrast edges - refers to a separate phenomenon that is generally caused by characteristics of the sensor.

Color Spaces

Every device that produces measures or captures color has its own way of reproducing all the colors in the visible spectrum, which is known as its color space. The most common color spaces in digital photography are Adobe RDB 1998 and Adobe sRGB. The former has broader color gamut (range of colors/tones), while sRGB has a smaller color gamut.

Compression

Compression is the process of encoding files through an algorithm, which decreases the size of the file for storage or transmission over the internet. There are two types of compression: lossy and lossless. Lossy compression (JPEG is an example) can result in visible degradation of image quality, especially when saving the image as a JPEG multiple times, because some image data is lost in each compression process. Lossless compression (like LZW compression) preserves all image data.

Depth of Field

Depth of field is the degree to which the scene remains in acceptably or perceived sharp focus in front of and beyond the focal plane. A larger aperture number (i.e., f/16) produces a broader depth of field. A smaller aperture number (i.e., f/2.8) can be used to throw the background out of focus, drawing the viewer’s eye to the main subject.

Digital Zoom

Digital zoom is a simulated zoom effect that enlarges the image on a portion of the image sensor. Akin to cropping, fewer pixels are used to capture the image, and although you end up with a closer view of the subject, the final image is generally of significantly lower resolution. With lower resolution, the ability to enlarge the photograph without affecting image quality is reduced.

Dynamic Range

The range of tones, from lightest to darkest, that can be recorded, displayed or reproduced by devices such as image sensors, scanners, printers and monitors are known as the dynamic range. The term is also used to describe the light-sensitivity range of film and the range of reflected light of a print. A photograph produced by a camera with a high dynamic range, for example, will retain image detail in both the shadows and highlights.

Effective Pixels

Effective pixels are the pixels on the sensor actually used to capture an image. Often, not all of the pixels on a sensor can be used because: 1) some pixels on the surrounding edges of a sensor are masked off to determine a black point; or 2) some cameras, especially compact ones, have lenses that are unable to cover the entire sensor area. The difference between actual and effective pixels is usually minimal, i.e., a 5.2 megapixel camera, for example, will provide 5.0 effective megapixels.

Exposure

A controlled amount of light projected to an image sensor or a frame of film is the exposure. This determines the lightness or darkness of an image and can be controlled manually by the photographer or automatically by the camera or by a combination of the two. If the aperture is too large and /or the shutter speed is too slow, an image will be too light, i.e., overexposed and vice versa.

Focal Length

The degree to which light from a scene is magnified by the lens is focal length. A short focal length, such as 28mm, will have a wider angle of view compared to the tight or telephoto focal length of a large 300mm lens. Zoom lenses have the ability to move through a range of focal lengths, while prime lenses are fixed at a specific focal length.

Histogram

A histogram is a sloping graph, resembling a mountain range with peaks and valleys, illustrating the exact ranges of tones the image sensor has captured for a particular shot. Anything past the left edge of the graph is pure black and anything beyond the right edge is pure white. The height of the graph represents the number of pixels for a given area. Some digital cameras have “live” histograms that are visible on the LCD when taking pictures to help the photographer determine the proper exposure. Other digital cameras have a histogram in the playback mode so the photographer can determine, albeit after the fact, if the image was properly exposed. Many image editing programs use histograms as a visual aid when adjusting image files during post processing.

Image Stabliziation

Optical image stabilization utilizes gyroscopic sensors within the lens to detect and compensate for motion or “camera shake.” Alternatively, some cameras achieve IS by moving the image sensor when camera movement is detected. But not all image stabilization is the same, nor as effective. For example, the latest trend in compact cameras is “image stabilization” that does nothing more than boost the ISO (light sensitivity) to achieve higher shutter speed to avoid blurry pictures. Unfortunately, this type of “stabilization” is usually compromised by high levels of image noise.

Interpolation (Resampling)

Artificially increasing or decreasing the number of pixels in an image through the use of an algorithm is known as interpolation. Some cameras increase the number of pixels automatically to compensate for digital zoom but this interpolation often results in degradation of image quality. Image editing software also interpolates pixels when enlarging an image beyond its core values of pixel count and resolution.

ISO (Light Sensitivity)

The ISO rating is an indication of light sensitivity in digital photography. Sensitivity is increased by amplifying sensor output, which also increases noise output, much like the increased grain in film with higher light sensitivity. ISO levels range from 50 to 6400. The higher the ISO, the less actual light is needed to achieve good exposure. At the same time, by increasing the ISO number, a higher shutter speed can be achieved, lessening the probability of a blurred image caused by camera shake, often at the expense of higher image noise levels.

JPEG (Joint Photographic Experts Group)

A common algorithm for the compression of image files, JPEG compression can vary from nearly lossless to highly lossy. All digital cameras are capable of capturing images in JPEG format, and because JPEG is standard, JPEG image files can be read by all image processing software.

LCD (Liquid Crystal Display)

In photography, Liquid Crystal Displays are typically a 1.5 to 2.5 inch screen comprised of liquid crystals that are stimulated by electric current to act as a viewfinder and/or preview screen of your frame. The LCD on most, but not all, digital SLRs is only used for viewing already captured images and navigating menus. Technology developed to allow a “live view” on digital SLRs is currently available only on a handful of cameras, but this feature may become more widely implemented in the near future.

LD, ED and UD Glass

(Low-Dispersion, Extra-Low-Dispersion and Ultra-Low-Dispersion Glass)

All of these terms refer to a glass type used in lenses. These formulated glasses correct the path of light rays as they pass through the lens, making all colors in the color spectrum focus at the same point. Lenses constructed with these types of glass eliminate or lessen the occurrence of aberrations and some kinds of artifacts.

Macro

Primarily used for close-up photography, macro refers to a one to one or higher magnification of a subject provided by optics (i.e., a macro lens). The focal length of a macro lens determines how close the lens must be to the subject to attain a one to one image capture. For example, a 60mm macro lens will require a shorter lens to subject distance than a 100mm lens.

Megapixel (one million pixels)

The number of photodiodes (also known as photosites or pixels) on an image sensor is expressed in megapixels, which in turn is the resolution of the device (a camera, scanner, etc.). Most sensors have one photodiode for each pixel in an image. For example, a 5 megapixel camera has five million photodiodes. Megapixels, however, are not the only factor that determines image quality. The lens, processing algorithms and other attributes are also critical factors.

Memory Card (Media Card)

A memory card is a digital camera storage medium. Although these cards are available in a number of different formats: SD (Secure Digital), CF (Compact Flash), Memory Stick (with several variations), xD-Picture Card, each camera can only accommodate only one (sometimes two) of these formats. All cards come in different capacities, measured in megabytes (i.e., 256 MB) or gigabytes (i.e., 2 GB). Some cards are also designed to facilitate high performance, decreasing the time it takes for the camera to write the mage data to the card. Card capacities continue to increase in all formats, although not all cameras may be able to use these large capacity cards. It’s also important to note that, with the exception of Micro Drives (CompactFlash Type II), which have movable parts like a hard drive, all other media cards are solid-state or flash memory cards and are, therefore, fairly nonvolatile.

Metering

Metering is the processing of defining the light levels in a scene and providing a measurement for a proper exposure value. Popular modes include center-weighted metering (an average of the frame, with the emphasis on the center of the image), spot metering (generally 1 to 3 percent of the image), and evaluative or matrix metering (an average of independent areas of the image). Most digital cameras offer at least two, and generally three of these metering options.

Noise

Image artifacts caused by complex variations with color that manifest themselves as grain on an image is referred to as noise. Excessive noise, which is most often seen first in shadows, usually results in an objectionable looking image. High resolution digital cameras with small image sensors, where more pixels are forced to live in a smaller space and have physically smaller photodiodes are more subject to noise than sensors with larger photodiodes. High ISO (light sensitivity) also generates image noise. Most digital cameras are equipped with some form of noise reduction that is either automatically triggered with high ISOs or long exposures or, in higher end cameras, can be turned on and off manually. When noise reduction is applied in camera (or via image editing software), it can result in softened or blurred details to lessen the visibility of the noise.

RAW

RAW is an image capturing option containing the maximum information available from a sensor without the application of in-camera processing algorithms. This allows photographers to have more control over the final image by processing the image manually in a software program. The format is offered by many high-end compact digital cameras as well as D-SLRs. Each camera company has its own RAW format and corresponding software to support the software. Image editing applications like Adobe Photoshop are also capable of opening and processing images shot RAW.

Resolution

Camera resolution is expressed in the number of photodiodes (megapixels) on the image sensor. More megapixels equals higher resolution. It’s important to note that many factors go into image quality, and resolution is only one of them. If you have a poor lens on a high resolution camera, you’ll get a high resolution image of poor quality. Higher resolution image files can produce larger prints than lower resolution files.

RGB

RGB refers to the three primary colors of red, green and blue that our eyes perceive as the basis for every other color. When added together equally. They make pure white. Most, but not all, digital photography uses RGB color space. (see also Color Space)

Shutter Speed

Shutter speed is the amount of time the lens shutter remains open when the shutter is pressed. This controls, in conjunction with the aperture setting, the amount of light that hits the sensor, thereby determining the exposure. At the same time, the shutter speed can affect whether or not the image is in focus, especially if the subject is moving. Faster shutter speeds are measured in fractions of one second—averaging 1/4000 ^th of a second or higher. Many cameras also allow the shutter speed to be set in full seconds for longer exposures.

SLR/D-SLR

Modern D-SLRs are digital cameras based on the same mechanical and optical features of film SLR (Single Lens Reflex) cameras, minus the film. SLR cameras channel light through a lens and a mirror to a viewfinder that gives an exact preview of the shot to be captured.

TIFF (Tagged Image File Format)

TIFF is a standard file format for bitmapped graphics. TIFF files are uncompressed and, therefore, very large compared to compressed formats. Not only do TIFF files occupy more hard drive space for storage, it also takes longer for the camera to write these files to a media card, therefore slowing down some aspects of camera performance. Because TIFF is a standard, TIFF image files can be read by all image processing software.

White Balance

White balance is a calibration of color temperature to a degree on the Kelvin Scale where white reads as white, rather than the varying shades of white caused by different lighting conditions. White in the morning, for instance, is a cooler blue of white, especially when compared to the very warm yellow of afternoon sun. White balance settings can be changed within the digital camera to adjust for sun, shade, tungsten and fluorescent lighting; automatic white balance is also an option, although accuracy is generally inconsistent. Custom or manual white balance is available in many cameras and is accomplished by pointing the camera at a white surface and clicking the shutter. Higher end cameras have a variety of white balance options, including the ability to set Kelvin temperatures manually.