Numbers in parentheses indicate the pages on which the term appears in the text.
Aberration These are unexpected inaccuracies when lenses create images. They may be edge effects, abnormal color, ect.
Absorption (45) Capturing energy when light strikes a surface and the energy enters the material that does not pass through.
Algorithm (79) Set of mathematical methods, rules, and/or procedures used to solve a problem.
Aliasing (83) Occurs when the shape or attitude of a detail in an image changes faster than an acceptable sampling rate and jagged or step-like artifacts form along the contour of the detail.
Analog-to-digital converter (ADC) (71) Provides a link between the analog world of light capture and the digital world of signal processing by analyzing the incoming analog signal and changing it to digital code.
Anti-Aliasing This is a software application that introduces tonal variations into the image to soften the edges and optically reduce aliasing (the jaggies).
Anti-blooming technology (31) In order to reduce blooming, modern sensors have electrical microcircuits located next to photosites that “drain” excess light-produced charge from the active sites without polluting nearby sites.
Aperture (54) Size of the opening in a lens that allows the light through—larger apertures allow more light to reach the sensor. The aperture is commonly described by the ratio of the f-number.
Apochromatic lenses (51) Compound lenses with higher curvature elements that reduce chromatic aberration. They often have special coatings to further reduce chromatic aberrations.
Array processor (75) Calculates and establishes the colors for each pixel within the digital camera system.
Arrays (35) Arrangements of capture or memory elements in one or more planes.
Autofocus lenses (58) Automatic focus. Automatic focusing lenses use a linear pattern in the sensor to determine focus by movement of lens elements to a point at which the fewest number of sites capture the light.
Banding (76) Occurs when an image has too little color variation; colors tend to become flat and have distinct lines at their borders. Often caused by a limited color space or effects of compression and decompression of the image file.
Basic daylight exposure (BDE) (94) Basic daylight or sunny-day exposure is based on the lighting conditions of a bright, sunny day with the subject in the sunlight. Sometimes this is called the “sunny 16 rule,” which states that on a sunny day the exposure will be f16 at a shutter speed of 1/ISO. BDE is an exposure calculated by adding or subtracting f-stops from f16 at a shutter speed of 1/ISO to adjust for various lighting situations.
Batch processing (115) When an image has been adjusted to a desired look, the steps used to make the adjustments can be saved, and the algorithm can be used on succeeding images made under the same conditions. If all the images use this algorithm at one time, then they have been batch processed.
Bayer array (35) A type of filter matrix used in color imaging for many image sensors. The pattern is alternating rows of filters ordered red–green–red–green and green–blue–green–blue. These filters are arranged so that a green site is never next to another green site.
Binary (134) In a binary numbering system (base two), only two numbers make up all the values. Such a numbering system works exceptionally well in the computer environment, as the number 0 can apply to the power being off while the number 1 represents a charge. This base unit—0 or 1—is a bit.
Blooming (31) When the energy exposing a photosite is greater than can be held in the potential well, it can migrate to nearby sites and is called “blooming.” The effect is of the lightness spreading or streaking from the oversaturated site.
Camera obscura (11) The term camera obscura is Latin for “darkened room.” The original camera obscura was a darkened room with a hole at one end. An image would be projected through this small hole onto the opposite wall. The image would be inverted. The camera obscura evolved into smaller darkened boxes that used lenses, mirrors, and/or ground glass to aid artists and early photographers.
Capture Capturing, as used in this book, is the act of taking and saving a picture.
Charge-coupled device (CCD) (4, 27) An electronic device made up of light-sensitive sites arranged to process the output in a linear process. The charges recorded and output from each site are proportional to the light intensity at each site.
Chromatic aberrations (49) Caused by lights of different wavelengths focusing at different points. Aberrations can be reduced by the use of multicoatings and compound lens elements.
Circle of confusion (54) Circle of light created when light from a point source is focused on the surface of the sensor. The size is determined by the size of the aperture and the fineness of the focus. If the circle is acceptably small to the viewer, then the image is considered to be in focus.
Clipping (104) When the amount of light exposing the sensor exceeds its ability to record all the energy, the system eliminates these higher energy levels or software eliminates higher digital number values from the image file.
Collimators (61) Lenses used to form light into a column. Similar to a lighthouse beacon, the light has little spread. These are helpful in digital systems as they bring light into the sensor perpendicularly.
Color electronic prepress system (CEPS) or digital prepress (4) The process of using computers or other electronic equipment to prepare plates for the printing press.
Color management Color management is the concept of control that matches the output of the digital process to the input (captured) color. This is one of the most difficult and demanding portions of the digital work flow.
Commission Internationale de L’Éclairage (CIE) (135) The color measuring and numbering system created by the CIE is based on human perception and is heavily used in digital imaging.
Complementary metal oxide semiconductor (CMOS) (27) Computer chips that can be repurposed to act as a sensor. Because they are not specifically a sensor, as in the case of the CCD chip, they can handle many functions of the digital photographic process beyond capturing the light.
Compression (18) A method to reduce a file size by performing mathematical operations on the data file.
Crown glass (49) A type of glass used for making fine optics that consists mostly of lime and silicate of soda or potash, with no lead.
Curves (157) Curves are graphs in imaging software that show how inputs are related to outputs. In most software packages, the curves can be changed to alter the look of the image.
Daguerreotype (4) The first successful photographic process, introduced in 1839, in which an image is exposed directly onto a highly polished silver plate; the image is developed using a vapor of mercury that condenses on the plate to form an amalgam producing an image.
Decibel (dB) (78) Unit of measure expressing the relative difference in power or intensity. It is commonly used to compare two acoustic or electric signals and is equal to ten times the common logarithm of the ratio of the two levels.
Depletion layer (28) Region between the positive and negative semiconductors of the photodiode. This area is free of electrons or positive “holes.” Without free or exposed charges, this region is considered depleted.
Diffraction (51) Changes in the direction and intensity of light as the lightwaves pass by an edge or through a small aperture.
Digital imaging (1) Using digital computing devices and processes for producing photographs.
Doping (28) Treating the photosite with an impurity. The dopant causes positive “holes” to be formed that allow the photodiode to collect light.
Dynamic range (78) Measure of the tonal range of light, from brightest to darkest, that an imaging device can capture.
Electromagnetic spectrum (EMS) (28) Range of energy, from long-wavelength radiowaves to extremely short gamma rays, including human observable light. Digital imaging sensors are capable of capturing the visible light and a portion of the infrared energy.
Electronic prepress systems (CEPS) or digital prepress CEPS is the process of using computers or other electronic equipment to prepare publications for the printing press.
Electroplating (33) A manufacturing process used to create sensors (such as CCD and CMOS) that utilizes electronic energy to deposit a layer of metal to specific locations or pathways within the sensor structure.
Exposure (91) A measure of the light captured on the sensor. Exposure is calculated with the equation H = E × T, where H is the exposure, E is illumination (the amount of light), and T indicates time (shutter speed).
File format (134) The file format contains instructions on how to encode, save, and extract data in a file.
Fill factor (33) The ratio of the light-sensitive surface to the overall size of the sensor.
Flare (47) Unwanted reflection within an optical system that is seen as fogging or bright spots on an image.
Four-Thirds standard (4/3rds) (48) A standard for digital camera lenses that allows optimal performance in these digital systems. Sensors do not respond well to light striking at a high angle of incidence, so the Four-Thirds standard uses only the light projected from the lens.
f-stop (54) The ratio for a lens or lens system computed by dividing the effective diameter or aperture by its focal length; used to define lens aperture for exposure calculation.
Gamma adjustment (116) The slope of the curve formed by graphing the input values of the captured image compared to its output values is referred to as gamma. A gamma adjustment is a computer control that changes the relationship between input and output values.
Gate (28) Acts as a control in a digital imaging sensor that allows electrical charge or light energy to have an effect on the operation of the photosite. The gate both allows energy to enter the photodiode and restricts energy flow.
Histogram (114) The histogram is a graph that shows how the light values in the image are distributed. The height of the lines in the histogram represents the number of pixels that are found in the image at any particular value.
Hot mirror (37) Filter used to block infrared light from the sensor that works by reflecting the nonvisible wavelengths and allowing visible light to pass through.
Hyperfocal distance (55) Focusing distance that provides the maximum focus that includes infinity at any given aperture.
Incident meters (96) The dome on an incident meter covers a photocell that evaluates the amount of light transmitted through the dome. This allows a determination of the amount of light falling on the subject.
Indium tin oxide (ITO) (28) A material often used in place of silicon to produce the gates of sensors. ITO tends to provide a better color range because it is optically more transparent than polysilicon.
Input All methods of acquiring an image into the computer, whether with a camera or other data generation methods, is known as input.
ISO (International Standards Organization) (75) Not just an acronym; instead, the name derives from the Greek word iso, which means “equal.” Photographers are most familiar with ISO ratings of film speeds which are used for sensors.
Levels (157) Levels are used to modify the distribution of tones in an image in relation to output by changing the white point, black point, and gamma (slope of the curve).
Liquid-crystal display (LCD) (12) A display technology often used on digital camera backs and computer monitors.
Lossless compression (136) If a file format can compress encoded data and then decompress the information in the data without degradation, then it is lossless; this is a reversible compression concept.
Lossy (136) Lossy is any type of file compression that shows a loss of data when opened after saving.
Metadata (135) Metadata are information attached or stored within a file format that is not part of the image.
Metal oxide semiconductor (MOS) (27) A family of semiconductors constructed of metal oxides (such as silicon oxides) that are used to construct digital imaging sensors.
Micro-lenses (37) Part of an image sensor above the filters that are used to concentrate light through the filter.
Mosaic or filter matrix (35) A pattern of filters used to gather all colors simultaneously in a color sensor.
Multicoatings (47) Multiple optical enhancing and protective layers used on and between lenses and lens elements.
Noise (40) Unwanted electronic information. Noise is common to all electronic equipment and shows up in a digital image as lighter pixels in otherwise dark-toned areas.
Optics (45) The physical study of light and how it reacts to and with other materials.
Output Output is generally the final use of the image.
Pentaprisms (15) In single-lens reflex (SLR) cameras (both 35-mm and some medium format), pentaprisms allow an image to be viewed through the lens and reflected by a mirror without any reversal of the image.
Perceptual constancy (114) Our perceptual systems find it easier to hold things constant rather than relearn them continually. This means that when we have learned a color we will interpret it consistently regardless of minor fluctuations in the actual color simulation.
Photodiode (28) The portion of a sensor that actually accepts the light, this is a construction of positive and negative portions (di, meaning two) that allow the light to be captured. These are also called sites.
Photoetching (33) Digital imaging sensors are constructed on an etched surface. This is accomplished by using photographic resist (protection) to protect parts of the surface from chemical cutting. These relief portions on the sensor’s base material allow other manufacturing processes and electronic connections to be created.
Photons (30) Electromagnetic energy functions in either a wavelength or particle function, and the “photon” is the designation used when the electromagnetic energy is acting as a particle.
Photosite The part of the sensor that is sensitive to the light is a photosite. It is also called a site or photodiode.
Pixel (37) Smallest part or building block of a digital image. The name is derived from the words “picture” (pix) and “element” (el). Pixels are used to refer to both the individual parts of the image and the number of photosites on a sensor.
Point-and-shoot (12) An amateur camera that is simple to use.
Point processes (155) Point processes are the simplest computer adjustments; they perform the same operation on every pixel in the image or selected area.
Polaroid® dye migration process (4) Process in which dyes that form the print migrate from within the processing film to create an image on the print surface (i.e., “instant print”).
Potential well (30) Forms in the silicon base of the sensor when an electrical charge is applied to the photodiode. As the photons of the light are captured, a potential barrier is created that holds the captured energy until it can be discharged.
Profiles (116) Profiles are computer tools that coordinate the input of digital images to their output.
Prosumer (15) A blend of “professional” and “consumer,” this term is used to refer to systems that include many professional functions and are intended for use by advanced consumers.
Quantization (72) Process of converting a signal from a set of continuous linear values to a set of related unit values.
Reflection (45) Change of direction of energy as it returns from a surface.
Reflective meters (96) The photocell in a reflective meter reads the light reflected from the subject.
Refraction (45) Physical effect on light; as it passes from one medium to another, it bends.
Resampling (136) Resampling is changing the image file to increase or decrease the number of pixels that are in an image. When a file is permanently reduced in size, data are lost; however, if the file is increased in size, no new detail is added to the image.
Retrofocus lens (58) A lens that works as though it is a longer focal length lens mounted backwards to the camera, thus allowing the lens to have a wider angle of view than normal. It is positioned far enough away from the sensor to allow the mirror in the SLR design to operate without difficulty.
Sampling Sampling refers to the fineness of units captured compared to the detail in the scene.
Silver halide photography (1) Method used for film-based photography (both color and black and white) that utilizes silver halide crystals as the light-capturing element.
Single-lens reflex (SLR) (12) A camera viewing system that uses a mirror at a 45° angle in front of a sensor that projects the image onto a ground glass, thus allowing direct viewing of the image that will be captured.
Site (28) The basic unit of the sensor; it is also called a photosite, photodetector, or pixel.
Spectral energy distribution (SED) (150) This is a measure of how the energy of a particular light is distributed. When graphed as a spectral distribution curve, the height of the graph represents the amount of energy at any point in the spectrum.
Telephoto lenses (57) Lenses that give a magnified view, making distant objects look closer by narrowing the angle of view.
Tethered system (110) A tethered system uses a cable or tether to connect the camera to a computer or external control unit.
Through-the-lens (TTL) meters (96) Through-the-lens meters are reflective meters that read the light in the optic path after the light has passed through the lens.
Transfer (38) Refers to a type of architecture used in the processing of digital images on the sensor. The transfer moves the collected energy rapidly. Transfer types include frame, interline, and frame interline.
Transforms (155) These are complicated mathematical modifications of the image structure. The computer uses higher-level algorithms to change the image, often one point at a time. Applications such as rotating or warping and most software filters are transforms.
Transmission (45) Movement of radiant energy through lenses or other materials.
Tricolor photography (18) Tricolor or trichromatic systems are three-shot capture methods in cameras or scanners that utilize three colors of light (red, green, and blue).
Trilinear arrays (20) Sensors that use three-color filtered arrays over three parallel linear sensors. The simplest configuration has one line each of red, green, and blue filtered sensors.
Ultraviolet energy (UV) (151) These are wavelengths shorter than visible violet light but longer than x-rays.
Under-sampling (83) Occurs when the capture of an image uses fewer sites than the number required to accurately capture a detail.
Wavelengths (48) Distance between successive crests (the high points) of a wave of light—the shorter the wavelength, the greater the refraction. Violet is the shortest visible wavelength; red, the longest.
White balancing Neutral balancing of the light is an important advantage for digital imaging. The light can be balanced with any neutral tone, but is often refrred to as white balance.