In this glossary we have listed terms that you may come across in the Shutha resource that you may not be familiar with, or that you may not be exactly sure what they mean. We have tried to define their meaning as clearly as possible to aid your grasp of the material. This glossary was originally developed for the ASMP's dpBestFlow.org web site and was edited by Greg Barnett. We have simply added relevant terms to it and subtracted terms that do not appear in the Shutha text. Click here to view the original which includes lots of technical terms outside the scope of Shutha.
One of the four rendering intents specified by the ICC for handling out-of-gamut colors when converting from one color space to another. Absolute colorimetric preserves the white of the source (by adjusting the white of the destination) and then reproduces all in-gamut colors exactly. Out-of-gamut colors are clipped to the closest reproducible hue. Absolute colorimetric is primarily designed for proofing since it will simulate the output of one device (printer or press) to another by laying down the appropriate ink to reproduce the source (paper) white.
Applying tonal or color adjustment such as levels or curves directly on a raster layer mathematically redefines the pixel data the moment you hit save. Adjustment layers allow you to preview those same changes without actually applying them to the pixel data. Tonal and color adjustments made with adjustment layers remain non-destructive until they have been applied to the pixel layers below through merging or flattening.
A device independent color space (also commonly called a “working” space) developed by Adobe. It provides a relatively large gamut (that encompasses most CMYK print devices) that is gray balanced and perceptually uniform. It is widely used for image editing.
In the context of digital imaging or photography, an algorithm is computer software code that performs a finite set of unambiguous instructions in a prescribed sequence. For example, raw file converters use algorithms to perform color filter array interpolations (demosaicing) or other complex mathematical computations.
A device that converts continuous analog signals into discrete digital numbers. In the case of digital cameras, this signal would be the electrical charge (voltage) generated by photons striking sensor sites that is then converted in digital data.
This is an optical filter (also known as low-pass filter) placed on the sensor to create a slight blur or softening that helps counteract aliasing or moiré interference. These patterns are created when the sensor cannot properly resolve high frequency elements in the image. Capture sharpening can be used to help restore initial image sharpness lost by this process.
The process of transferring an image from the capture source (digital camera or scanner) to a computer. Acquire modules (sometimes in the form of a plug-in) are often supplied by equipment manufacturers to import images into an image editing program such as Photoshop.
A collection of images kept in secure, long-term storage. Archiving can take place at different stages of the workflow: original captures prior to processing and optimization, the master files which contain image optimization, and working files and their derivatives at the completion of job.
Also see Preservation.
An image that has been processed in such as way to prepare it for permanent storage and preservation. In the context of a digital image or photograph, this would typically be an original or master file that has been saved using a documented standard open file format such as TIFF or DNG that preserves all of the original image data.
The acronym for American Standard Code for Information Interchange, which is a standard commonly used for encoding English characters with a corresponding number. ASCII codes are used by computers to display, store, and transfer text in a human readable format. This formatting provides nearly universal access to the contents of the file and is widely used for text files that are intended for cross-platform use.
In workflow terms, this refers to operations that are automated to make them more efficient, consistent, and require less human intervention. Also commonly referred to as batch processing, these steps can take the form of scripts, actions, droplets, or dedicated applications.
A system whereby copies of applications, image files, and other digital assets are preserved to ensure restoration of the data in the event of corruption, media, or system failure. Backups can be created at various stages in the workflow to ensure that image files are preserved. There are a number of different approaches and strategies employed in making backups, which include incremental, a mirror (or clone), or additive. There are also a wide variety of both software and hardware solutions available depending on the size and scope of your backup needs.
A term widely used to describe the speed and throughput of a device or communication network. The related term Broadband refers to a high-speed Internet connection.
Batch processing automates repetitive tasks so that they can be to be done in an efficient and consistent manner. Rather than handle each file individually, when batched, a number of files are collected (or selected) together and sent for processing at the same time. Common examples of batch processes include renaming, ingestion, application of pre-sets and metadata, or conversion to DNG.
Also know as a Bayer Filter, is a mosaic color filter array (CFA) that is in wide use on most digital camera sensors. The pattern is comprised of individual RGB filters that align with the sensor elements (pixels) in a pattern of 50% green, 25% red, and 25% blue, with each pixel recording only one color value. A demosaicing algorithm is employed to interpolate the colors and create a photographic image.
A numbering system employed by computers using only two digits, zero and one.
Short for a binary digit using a value of either zero or one. It is the smallest unit of data used by computers.
Defines how many bits of tonal or color data is associated with each pixel or channel. For example, 2 bits per pixel only allows for black or white. 8 bits provides 256 grayscale tones or colors. When referring to an 8-bit color image, 256 is multiplied (256x256x256) by the three primary (RGB) channels to create what is commonly called 24-bit color (with a possible 16,777,266 colors).
A pixel-by-pixel representation of an image where each bit is mapped to a corresponding pixel or dot. Also commonly referred to as a raster image because the pixels are laid out in a rectangular grid or array.
Typically, either an external or additional internal hard drive that is an exact duplicate of a computer’s main (system) drive. It allows the user to boot the computer from this drive instead of the main drive.
Original images that were created by a digital camera or scanner (scan-o-grams) as opposed to images scanned from film or prints.
In image editing, the tonal adjustment that sets the point at which the deepest shadow detail in the histogram is clipped to black.
The next generation of optical storage media that uses a blue-violet laser, allowing for a higher density of data on a disc that is the same diameter as CD/DVD. Single-layer Blu-ray disks have capacity of 25GB and dual-layer can hold up to 50GB. There are three formats: BD-ROM is read-only, BD-R is recordable or write once, read many (worm), and BD-RE is rewriteable. The RE format is not recommended for archiving digital image files because they can be accidentally over-written or erased.
The overall intensity of an image, or the degree to which a color sample (or tone) appears to reflect light.
Software applications such as Adobe Bridge or PhotoMechanic that allows the user to view, edit, and make various modifications to digital images or other assets. They can also be referred to as organizers. A browser works by pointing it at a live folder or drive containing images but it does not keep track (unlike a cataloging application) of the files and corresponding metadata in a permanent fashion. They are not considered optimal for digital asset management.
In a camera, memory that can hold a number of images while the camera writes them to the media card in the background. The buffer allows for bursts of images to be captured while files are being written.
A binary unit computer data that typically consists of 8 bits.
In computers, a bank of high-speed RAM used for temporary storage of data that is likely to be reused. This provides increased performance by not having to read the data or instructions from a slower source. In software applications, it can be either RAM or disk based storage that serves a similar purpose.
Adjusting or modifying the behavior of a device (such as a printer or monitor) to bring it into a known specification or state. Calibration is often performed as the first step in building a color profile for the device.
Provides slider-based controls in Adobe Camera Raw and Lightroom that allow the user to adjust the behavior of the built-in, default camera profiles. Another tool provided by Adobe, the DNG Profile Editor provides a more flexible method for creation or adjustment of camera profiles. These should not be confused with ICC profiles, rather, they are an Adobe specific solution to camera profiling.
Proprietary raw file formats designed to hold image data and metadata generated by digital cameras. These formats are non-standard and undocumented, although they are usually based on the TIFF/EP file format standard.
A setup that utilizes a digital camera to copy film originals as opposed to using a conventional film scanner.
A unit of luminance which is defined as the luminous intensity of light that is either emissive or reflective. In digital photo imaging, it is used as the measure of a computer monitor's brightness level. (See Nit)
The process of acquiring/recording data in a digital format. This could be in the form of a photographic, moving image, or audio recording. Also see image capture.
The initial image sharpening step that compensates for blurring created by anti-aliasing filters, other optical defects, or softness introduced during raw conversion. Capture sharpening is not intended to be the ultimate or final sharpening of the image. Also see Sharpening Output Sharpening.
A non-volatile memory device that is used to store images and data for digital cameras. There are a variety of formats currently in use such as compact flash (CF), secure digital (SD), smart media (SM), and memory sticks. Each format can come in difference capacities and access speeds.
Parametric Image Editing (PIE) applications, which provide cataloging (DAM - digital asset management) capabilities by use of an underlying database structure. Adobe Lightroom and Apple Aperture are examples. Also see PIEware.
Also known as digital asset management (DAM) applications. Microsoft Expression Media, Extensis Portfolio, and Cantos Cumulus are examples. They are designed to build catalogs (databases) of images (and other assets), associated metadata, and previews. They also provide further utility by creating organizational sets or groups that can associate files, independent of the original storage hierarchy. These applications also differ from a browser in that they do not necessarily show the live contents of a drive or folder. The actual files being displayed do not have to be connected to the computer in order to display their catalog record.
A type of image sensor commonly employed in digital cameras and scanners. It is a light-sensitive integrated circuit that converts light into an electrical charge (analog signal), which is then further processed by an analog to digital converter (ADC). CCD architecture differs from the other common sensor type (CMOS) in the way that it processes the electrical charges captured by the sensor elements (pixels).
Digital images separate color information into individual channels that represent the components such as Red, Green, and Blue (RGB). If viewed individually, the pixel information contained in the channel is a grayscale representation for that color. When all of the channels are combined, a full color image results.
Also known as color fringing or halos, is caused when a camera lens does not focus the different wavelengths of light onto the exact same focal plane. The effect is visible as a thin colored halo around objects in the scene, often the border between dark and light objects.
A color model (or space) that was designed to represent all of the colors encompassed by human vision. It is based on color opponency with three primaries: L* representing lightness, a* represents red-greenness, and b* represents yellow-blueness. It was intended designed to be as close to perceptually uniform (meaning an change in a primary or color will yield a visual change of the same degree) as possible. CIELAB is an important component of color management systems in that it typically acts as the PCS (profile connection space) that serves as the intermediary in color transformations between profiles.
The loss or either highlight or shadow details when tonal information is driven to pure white or black. For example, over exposure can produce clipping by driving highlights that should contain detail to pure white. Clipping can also be introduced in the image processing stage either intentionally as a creative effect or unintentionally as a result of excessive corrections. Saturation clipping can occur when colors are pushed beyond the gamut of a color space.
A type of image sensor commonly employed in digital cameras and scanners. It is a light-sensitive integrated circuit that converts light into an electrical charge (analog signal), which is then further processed by an analog to digital converter (ADC). CMOS architecture differs from the other common sensor type (CCD) in the way that it processes the electrical charges captured by the sensor elements (pixels).
Also commonly referred to as process color, it is a subtractive color model using cyan, magenta, yellow, and black inks in color printing.
A mosaic array of color filters placed over the pixel elements of an image sensor to record color information. The Bayer pattern is most commonly used and is comprised of 50% green, 25% red, and 25% blue filters. There are variations on the pattern that include other color filters in an attempt achieve better accuracy. An entirely different approach has been developed by Foveon, which uses three layers of sensors that respond to the way light wavelengths penetrate to different depths of the silicon. This allows the sensor to capture full color at every pixel and does not require demosaicing.
A system designed to specify color information numerically; RGB, CMYK, and CIELAB are examples.
Also known as an ICC profile, it defines the information required to by a color management system (CMS) to make the color transforms between color spaces. They can be device specific (such as monitors, scanners, or printers) spaces or abstract editing (or working) spaces.
Commonly referred to as the process for conversion of RGB color into CMYK for printing. It is the process of separating the original color components of an image in preparation for conversion to the destination.
A geometric (usually three-dimensional) representation of colors that can be produced by a color model. Multiple color spaces can share the same color model. Color spaces can be further defined as device dependent or device independent.
A widely used type of optical storage media for digital files and data with a capacity of up to 700MB. There are three formats: CD-ROM is read-only, CD-R is recordable or write once, read many (worm), and CD-RW is rewriteable. The RW format is not recommended for archiving digital image files because they can be accidentally over-written or erased.
When an image is used to promote a brand or a product in any way whether through advertising, promotion, public relations production or in any other way. Examples include use in a product brochure, a magazine advertisement or on a bill board in association with a product or brand.
The process of re-encoding digital information using fewer bits than the original file or source. This reduces transmission time and storage requirements. There are number of different algorithms in use that provide either lossy or lossless compression. JEPG is a common file format that employs lossy compression to achieve significantly smaller file sizes but at the expense of image quality.
Broadly defined, content management systems are used to create, view, edit, index, review, search, publish, and archive various forms of digital assets. This is often done in a collaborative format. Widely used on the Web, applications such as WordPress have popularized the use of content management for blogging and websites. Digital Asset Management (DAM) is also a type of CMS.
A structured approach to developing a consistent vocabulary of terms and or phrases that are used to aid and improve upon searches. As it relates to a digital photography workflow, a controlled vocabulary is commonly used build a hierarchical keyword system or catalog. Creating and using a CV can help ensure that keywords will be applied in a consistent manner that when combined with digital asset management, significantly aids in the search and retrieval of images.
An electronic circuit that can execute computer programs, often simply referred to as the processor. Most current desktop/laptop computers use either Intel or Advanced Micro Devices (AMD) CPU’s.
A largely obsolete computer display (monitor) device that has been replaced by Liquid Crystal Display (LCD) and most recently, Light Emitting Diode (LED) display technology.
Additional files created from an original or master file, which have been prepared for final print output, web display, or some other form of repurposing.
The process of reconstructing (interpolation) color images captured with CCD or CMOS sensors using color filter arrays (CFA). Different demosaicing algorithms are used by the various raw converter applications. Because of this, each algorithm/converter combination will provide different results with the same image. Digital cameras also employ on-board demosaicing algorithms in the process of creating JEPG files.
A color model or color space, which describes the unique characteristics of a specific device. Building a color profile of a device is a method by which this description can be created.
A color model or color space, which uses unambiguous color numbers that do not depend on a specific device. CIELAB is device independent because a specific set of numbers always represents the same color regardless of the device.
Any digital content (photograph, video, text, music, etc.) which you have the right to use by virtue of being the creator or having been granted permission or a license.
Can be broadly defined as the decisions, workflow, and tasks that involve: ingesting, editing, organization, annotating, cataloguing, storage, and retrieval of digital assets. This can be done with a dedicated asset management solution or a workflow employing multiple software applications.
A digital connection between a computer display (monitor) that allows a suitably designed graphics adapters to adjust monitor parameters such as brightness and color balance.
A publicly documented, royalty free, open standard file format developed by Adobe Systems that provides a standardized alternative to proprietary camera raw files. The DNG specification incorporates rich metadata support along with imbedded previews, camera profiles, and “maker notes” (private or proprietary metadata). DNG can employ lossless compression that can result in a significant file size reduction over the original proprietary raw. It is also being promoted as an archival image format since it is fully documented and has been submitted to the ISO.
A free utility provided by Adobe Systems to aid in the creation or customization DNG camera profiles used in their Camera Raw and Lightroom applications. These should not be confused with ICC profiles, rather, they are an Adobe specific solution to camera profiling.
Typically described as the unwanted color or luminance variations of pixels that degrade the overall quality of an image. Digital noise is often equated with excessive film grain in analog photography. Noise can result from a number of different sources including a low signal-to-noise ratio, the use of high ISO settings, long exposures, stuck sensor pixels, and demosaicing artifacts. It can range in appearance from random color speckles (sometimes called the Christmas lights effect) to a luminance based grain-like effect, or banding. There are a variety of in-camera and software based noise reduction solutions available. Digital noise can also be intentionally added to an image to enhance the effect of grain or to reduce banding (caused by posterization or the failure of an output device to render subtle tones) in large areas of continuous tone or color such as a blue sky.
A widely used type of optical storage media for digital files and data with a capacity of up to 4.7GB.
There are three formats: DVD-ROM is read-only, DVD-R is recordable or write once, read many (worm), and DVD-RW is rewriteable. The RW format is not recommended for archiving digital image files because they can be accidentally over-written or erased.
The measurement of print resolution expressed in how many dots of ink are laid down either horizontally or vertically per inch. A higher number indicates a greater amount of output resolution. Not to be confused with pixel per inch (PPI). There is not necessarily a direct correlation between DPI and PPI.
In the context of photography, describes the difference (ratio) between the brightest and darkest measurable light intensities of a scene or image. From initial capture to final output, there can be an extremely large difference in the size of the dynamic range that each device is capable capturing or reproducing. Dynamic range is commonly expressed in the number of f-stops that can be captured or the contrast ratio of the scene or device.
The process of selecting, ranking, and organizing images. This can include deleting outtakes, applying star ratings, color labels, and metadata to files, along with sorting according to content. The term edit is also used to generally describe the process of applying image-processing steps.
The total amount of light that strikes the sensor (or film) during an image capture. An “optimal” exposure in digital terms would take full advantage of the dynamic range of the sensor without under exposing the shadows or overexposing the highlights. Under exposure can result in the possibility of clipping shadow details to black and introducing digital noise. Over exposure runs the risk of clipping highlight details to pure white.
An exposure technique used with raw image capture in digital photography. ETTR takes into account the linear response of sensors when capturing light, allowing for the maximum use of the dynamic range. Additionally, this technique can improve the signal-to-noise ratio (SNR) that in turn, reduces digital noise. A raw file records linear data where the brightest f-stop can potentially contain up to one half of all tonal information within the image. The object of ETTR is to expose the image so that the raw data fully populates the right-hand side of the histogram without clipping highlights to pure white. Most cameras provide a certain amount of headroom that provides a cushion should the exposure be a little too aggressive with the brightest highlights. PIEware is used to post process the image in such a way as to restore a pleasing visual balance.
The hand-off of digital image files in a finished format. This can range from optimized, sized, and sharpened press-ready images, to low-res JPEGs for a designer’s layout. File Delivery can be in a physical format such as optical media (CD/DVD) or a hard drive. Delivery can also take place electronically via FTP (file transfer protocol) or through a web-based service such as YouSendIt.com.
The structure of how information is stored (encoded) in a computer file. File formats are designed to store specific types of information, such as JPEG and TIFF for image or raster data, AI for vector data, or PDF for document exchange.
A software application (and the accompanying ActionScript programming language) and file format (SWF) for the development of vector and bitmap based interactive, cross-platform, media. In wide use on the Web, Flash is used to create interfaces, web galleries, and entire web sites. Flash objects or “movies” can be embedded in web pages and other file formats or run in a standalone player.
A standard network protocol used to transfer digital files between computers and servers via the Internet or a local area network. Typically, an FTP client application is used to connect to the server or destination (host) computer to initiate the transfer. FTP connections can be configured to require password authentication or anonymous user connections.
In digital imaging, the term gamma is commonly used to describe the non-linear behavior of a device’s tonal response. Gamma curve is used to describe a curve (sometimes called a tone reproduction curve - TRC) that effects the relationship between the shadow, midtones, and highlights of an image or device. Gamma encoding is used to describe the process of converting linear data (raw capture) into a non-linear color space. Also see monitor gamma.
The range of color (and density/tonal values) that can be produced by a capture or output device or represented by a color space.
Graphics Interchange Format is a bitmap image format, but it only supports 8-bits per pixel, so it is not really suitable for color photographic images unless they are used in small animations or low resolution film clips. Photographers seldom need to delivery images as GIF files.
A binary unit of computer data or storage that consists of 1024 megabytes. Hard drive manufacturers have standardized 1 gigabyte at 1000 megabytes of storage.
A monochromatic digital image file with pixel values that use shades of gray to represent tonal information. The term grayscale is often used to describe a digital black and white photograph.
A process that combines multiple exposure variations of an image to achieve a dynamic range exceeding that of a single exposure. Tone mapping algorithms are used to blend the exposures into a high-bit (typically 32 bits) file format that can them be converted down to either 8 or 16 bit for printing or web display. Depending on the type of tone mapping and the degree to which it is employed, the resulting images can range from natural looking to very surreal.
A graphical representation of tonal and color distribution in a digital image. This is typically based on a particular color or working space by plotting the number of pixels for each tonal/color value. It can be used to interpret photographic exposure and reveal shadow or highlight clipping.
A markup language that uses a defined set of tags to create and publish web pages. These tags define elements such as links, paragraphs, lists, and other attributes of text and images. The World Wide Web Consortium (WW3) maintains the HTML specification.
Many PIE applications provide a highlight recovery function that will attempt to recover (reconstruct) any highlights lost to clipping. It requires that at least one channel is not clipped to pure white. Most cameras provide a certain amount of exposure headroom that can assist in the recovery.
The international organization that is responsible for the development and continued advancement of the ICC Profile Specification. This specification defines the architecture and formatting that is the foundation for open, vendor-neutral, cross-platform color management systems (CMS) and color-managed workflows.
See Color Profile.
The process of downloading digital camera image files from media cards that can include renaming, applying metadata, image processing presets, DNG conversion, and performing initial backups. There are dedicated applications (sometimes called downloaders) such as ImageIngester or PhotoMechanic which fully automate the process and provide a wide variety of options. Or PIEware such as Lightroom or Aperture that can perform ingestion as part of their overall workflow.
The process of using devices such as digital cameras or scanners to capture images in a digital format. The resulting files are then further processed to arrive at a final image.
See Lossy or Lossless Compression.
See Raster Image Editor and PIEware.
A term that broadly describes the use of a proxy image in a variety of applications. These can range from small thumbnails used as image links in web pages to full, screen-sized JPEGs rendered out by PIEware using image-processing parameters. Camera Raw files contain embedded previews created by the camera, which, can then be displayed by various applications. DNG files have the ability to embed image previews of varying sizes.
A file structure and set of metadata elements developed in the early 1990’s by the IPTC and Newspaper Association of America to standardize the exchange of news information and data. These metadata elements are referred to as the IPTC header (or more commonly known as the IPTC metadata) in digital image files. Although the Adobe Extensible Metadata Platform (XMP) has largely replaced the IIM structure, the IIM attributes are defined in the “IPTC Core Schema for XMP.” Most applications that read and write metadata can keep the XMP and IIM metadata attributes synchronized.
In the context of digital photography, interpolation is most often referred to as the process of re-sampling an image to either add or remove pixels. There are several algorithms (nearest neighbor, bicubic, bicubic sharper, etc.) that can be employed depending on the type of image data and whether the goal is to increase or reduce file/image size. The Image Size dialog box in Photoshop is commonly used for this process although there are several other standalone products or plug-ins available as alternatives. A different type of interpolation is used in the demosaicing stage of raw file processing which reconstructs the color information from the camera sensor’s color filter array.
The international organization that develops and maintains technical standards for news exchange. They are responsible for the IPTC Photo Metadata Standard, which consists of the IPTC Core and Extension schemas.
A non-governmental organization that develops and publishes international standards. In photography, ISO refers to the standard for measurement of the sensitivity of film or digital sensors to light. ISO also publishes and maintains the specifications for several standard open file formats used in digital photography.
A data storage configuration that typically consists of a multiple-disk enclosure where each hard drive is independent. Benefits include the ability to mix drives of different sizes, scalability, and most enclosures allow for hot swapping. Although it does not provide automated redundancy like certain RAID configurations, it is a reliable and flexible storage solution.
A computer scripting language commonly used to provide interactivity in web pages. It is also used to provide extensibility in software applications such as Adobe Photoshop or Bridge.
A standard created by the Joint Photographic Experts Group (a joint committee of the ISO and IEC) for the compression of photographic or photo realistic images and the accompanying file format. It employs a lossy compression algorithm that can significantly reduce file size but at the expense of image quality and detail. It is not well suited to non-photographic images due to compression artifacts that become readily apparent in line drawings or artwork and text with straight lines or sharp contrasting edges. Caution should be exercised when using JEPG to re-save original JEPG files because of the cumulative effect of compression artifacts that can significantly degrade the image quality.
A standard created by the Joint Photographic Experts Group for a wavelet-based, image compression algorithm and the accompanying file format. It uses a sliding scale of lossy to lossless compression that can significantly reduce file size without artifacts or image degradation.
An element of descriptive IPTC metadata that is used to add value to a digital image or file by making it more discoverable to searches. Keywords can be individual words or short phrases employing either a flat or hierarchical structure. The use of a controlled vocabulary is highly recommended when developing keyword lists or catalogs to ensure a consistent and structured approach. Keywords can be both public and or private depending on the nature of the term and how it used by the photographer to organize or reference the image.
A binary unit of computer data or storage that consists of 1024 bytes. It is typically expressed as 1000 bytes when referring to hard drive storage.
Pixel Editing applications use of layers to stack one “page” of data on top of another. Layers may contain data from a variety of sources, including duplicate pixels from a layer above or below. Photoshop currently supports 4 types of layers: Raster, Vector, Adjustment and Smart Object. Layers may optionally house embedded special effects such as smart filters, drop shadows, embossing and more.
A display technology used in computer monitors (also called flat panels) that has largely replaced CRT devices. Typically they use a cold cathode fluorescent (CCFL) backlight to illuminate the screen, which is made up of a layer of liquid crystal, further layered with positive and negative electrodes, polarizing film, and protective glass. LCD computer monitors can range from consumer-grade displays with reduced contrast, sharpness and color gamut to high-bit, wide-gamut, TFT (thin-film transistors) active matrix displays designed for digital photography and graphics applications. LCDs are also used on the back of digital cameras to provide an image preview.
LED technology is coming into wider use in computer monitors, replacing the cold cathode fluorescent (CCFL) backlights that have until recently (2009) been standard. Providing higher brightness levels, they are also considered more environmentally friendly because they do not contain Mercury (CCFL does) along with reduced energy consumption. OLED (organic light emitting diode), is an emerging, next-generation display technology that shows great promise and could replace LCD/LED backlit computer monitors in the future.
Raw files contain the linear data recorded by a digital camera’s image sensor. This data is logarithmic in nature and the tonal values are either doubled or halved as they relate to each f-stop of exposure. For example, if a camera has a dynamic range of 8 f-stops and records 12 bits per pixel, the capture has a maximum of 4096 (212 ) possible tonal levels spread out over the 8 stops. Because the distribution from one stop to another is linear, the first (brightest) stop would contain fully half of all the tonal information or levels (if the full dynamic range of the sensor was used). Following this rule the progression would be: 2048 (1st stop), 1024 (2nd), 512 (3rd), and so forth until reaching the 8th stop with only 16 levels available.
Digital sensors see and record light in a linear fashion, which is very different than the non-linear nature of human vision. Sensors are effectively counting the photons that strike the pixels or sensor elements. This luminance information is recorded in a linear format and requires a significant amount of image processing to turn it into a recognizable image. Color information is added in during the demosiacing process along with compression and tone mapping, rendering a final image that we would interpret as a photograph. Also see ETTR (expose to the right) for an explanation of the exposure implications of linear capture.
A measurement unit of print resolution that relates to the frequency of the half-tone screening. Common LPI numbers are 85 for newsprint, 133 for magazines, and 150, 175, or 200 for high quality reproduction. Not to be confused with dots per inch (DPI).
LUTs are used to translate input values to output values by means of a table of numbers that matches input numbers to corresponding output values. The LUT saves computer processing time that would otherwise be needed to compute the output values. LUT's are used in certain types of color profiles such as CMYK profiles. LUT's are also built into video cards and some computer monitors and are used to determine the colors and intensity values with which digital images are displayed by the monitor.
Software algorithms (and accompanying file formats) used for reducing files sizes were data is not discarded during compression and can be fully restored when decompressed. Lossless compression usually results in larger file sizes when compared to lossy. RLE (run-length encoding) and LZW (Lempel-Zif-Welch) are commonly used algorithms along with ZIP, which also has several file format variants. JEPG 2000, GIF, PNG, TIFF, and DNG are all examples of file formats that employ lossless compression.
Software algorithms (and accompanying file formats) used for reducing files sizes were data (often targeting redundant data) is discarded during compression and is not fully restored when decompressed. High amounts or repeated re-saving with lossy compression can introduce artifacts and degrade image quality. But lossy compression can provide significant savings in file sizes and is especially useful for images intended for web display or digital camera applications where storage capacity may be limited. JPEG and MP3 are examples of formats file formats that use lossy compression.
The intensity of light as emitted or reflected by an object/surface. This is usually expressed in candelas per square meter (cd/m2). It is a measurement of the brightness of an object or light source.
In image processing or publishing applications, a mask is a defined area used to limit the effect of editing/processing operations. There are a number of different types and techniques that include channel, clipping, layer, raster, and vector masks. A wide variety of selection tools can be employed in software such as Photoshop to aid in the creation of masks. There are also dedicated applications and plug-ins for the express purpose of masking.
Commonly defined as a high-value, duplicate of the original source or capture file that has been permanently renamed, had basic metadata, capture sharpening, dust-busting, and basic image/color corrections applied. Depending on your workflow this could be a DNG (un-rendered) or rendered file (with layers) such as a TIFF. This file can be both archived and held in a “working” location. All subsequent derivative files are created from the master.
A binary unit of computer data or storage that consists of 1024 kilobytes. Hard drive manufacturers have standardized 1 megabyte at 1000 kilobytes of storage.
A term commonly used in reference to digital camera resolution, 1 megapixel equals one million pixels or sensor elements. To calculate the megapixel value for a camera, multiply the horizontal by the vertical pixel counts. In general, a higher megapixel number indicates increased resolution but is not an absolute measurement of image quality. Other factors such as the size of the individual pixels, the presence of an anti-aliasing filter, and the noise characteristics of the sensor, along with image processing all play a role in determining the final perceived resolution or image quality.
Commonly defined as “data about data,” metadata is embedded or associated information describing a file’s contents, both technically and conceptually. There are several metadata container formats such as EXIF, IIM, IPTC Core, Dublin Core, DICOM, and XMP. The way metadata is structured is referred to as a schema, an example being IPTC Core which is an standardized structure to hold information about a digital image file, such as authorship details, description, keywords, copyright status, usage, etc. Parametric image editing (PIE) instructions saved in the XMP format are another type of metadata, which is comprised of the image processing parameters from a PIEware application.
The phenomenon where two spectrally different colors appear to visually match under one light source or condition but differ under another. These two colors would be called a metameric pair. Metamerism can be a problem with certain combinations of ink/pigments and substrates.
The gamma correction applied to a computer monitor that describes the relationship between input voltage and output luminance. Adjusting the gamma setting is part of the calibration process that normally precedes building a color profile used by color management systems. A gamma of 2.2 (or thereabouts) is often regarded as optimal for smooth reproduction of tones and gradients. Higher-end displays designed for digital photography and graphics applications, will often have a factory calibrated gamma setting that will be automatically adjusted during the regular creation and updating of the display profile
A non-standard term sometimes used in place of cdm/2 (see cdm/2)
A file format that has published specifications describing the encoding of data, intended usage, royalty-free, and is managed by a standards organization such as the ISO or ICC. Examples include PDF, TIFF, DNG, and ICC profiles.
Software that provides the interface between computer hardware, applications, and the user. Current popular, and widely used OS’s include several variants of Windows NT and Vista, Mac OSX (actually Unix based), Unix, and Linux. In the context of digital photography workflow, Mac and Windows are the predominant platforms because of the large base of software applications that have become the de facto standards. Important OS level implications for imaging applications (including plug-ins) are whether they run in 32 or 64 bit memory space. 32 bit applications (or OS) although still widely in use, only allows for approximately 4GB of RAM allocation per application. This may seem like a lot but can be quickly consumed by editing large image files. In practical terms, 64 bit allows an almost unlimited amount of addressability but in reality, it will be limited by how much physical RAM a computer can hold and the associated cost of such amounts.
A theory of color vision which states that humans see in terms of opposing values of light-dark, red-green, and yellow-blue. This theory forms the basis of the CIELAB color model.
The maximum physical resolution that a device or system is capable of capturing without aid of interpolation. Often used to define the native resolution of scanners.
In the context of digital photography workflow, the process/steps of correcting tone and color, sharpening, retouching, and other output specific adjustments. Optimization can take place at the individual file level or be done as a batch process for multiple files and may be done in more than a single pass or round. Files that have been prepared for specific uses such as proofing, printing, and web, would be considered optimized.
All output devices have a fixed amount of color (or gamut) that they able to reproduce. When moving from one device (or color space) to another, colors that cannot be exactly reproduced between the source and destination are considered to be out-of-gamut. Rendering intents are used to manage the conversion process.
A broad-based term that refers to an end use/destination for a digital image. This could be print output using inkjet, press, laser writer devices, film, or other substrates. It could also be screen based for use on the web, multimedia and interactive applications, or video.
A final sharpening step that is intended to correct for softness introduced by the output process. It is optimized for a specific combination of output conditions at the final image size and resolution. This could include the type of device (i.e., inkjet, press, laser) combined with a DPI or LPI setting and a particular type of substrate. Images intended for screen display can also benefit from output sharpening. Typically, output sharpening is the last step performed on derivative images that have been tailored for a specific use. Also see Sharpening and Capture Sharpening.
One of the four rendering intents specified by the ICC for handling out-of-gamut colors when converting from one color space to another. Perceptual tries to preserve the overall color appearance or relationships between colors while compressing them to fit within the destination space. Because of this compression, all colors are remapped to some degree and accuracy is sacrificed to preserve the visual relationships. It is a good choice for images than have a significant amount of out-of-gamut color.
Developed by Adobe Systems, PDF is an open standard file format for cross-platform document exchange. PDF is highly extensible, preserves the integrity of the original document, is searchable, and provides document security. The Adobe Acrobat family of applications provides a platform for PDF creation and editing along with the free Acrobat reader to open and view files. Many popular software applications can write PDF files directly and there is a large base of third-party developers with DPF compliant editing and workflow solutions.
Settings available on many digital cameras that provide a variety of alternate renderings for camera generated JPEGs. Each camera manufacturer has their own terms to describe these styles or looks. They can be used to simulate the look of a particular film emulsion, create more pleasing skin tones for portraits, vivid colors for landscapes, or monochrome (B&W) images. These settings do not affect the underlying raw data and parametric image editors (other than the camera manufacturer’s own software) will ignore any associated metadata.
A non-destructive workflow where image edits are made using instructions (parameters) saved as metadata. Depending on the application, the metadata can be saved in a database, directly in the file (typically DNG, TIFF, or JPEG) or as a sidecar file. The editing instructions can then be rendered by the software (PIEware) into derivative versions of the file. The premise of PIE is that underlying image data is never directly edited or changed in the process.
A software application that edits image files by using instructions saved as metadata. Examples include Camera Raw,, Capture One Pro, and Nikon Capture. Also see Parametric Image Editing (PIE) and Cataloging PIEware.
Derived from the term picture element, this is the smallest unit of information in a digital image. Also commonly used to describe the individual senor elements on capture device.
The outline or schema for a project, where the outcomes and methods are decided upon before starting the process. In a digital photography workflow, planning is an essential element in the efficiency of the process and takes into account such issues as ease of use, repeatability, collaboration, final usages, sustainability, longevity, and preservation or the work.
A software application or module that provides extensibility and specific functionality from within a larger host application. Adobe Photoshop is an application with a programming architecture that supports a rich plug-in environment. One of the main advantages of supporting plug-ins is that enhancements or new functionality can be added without having to update the host application. The Adobe Camera Raw plug-in is an example since it is regularly updated with new camera support that would otherwise have to wait for a major release of Photoshop. Third-party software developers can also offer additional or enhanced features that may either be missing or lacking in the host.
A cooperative, multi-industry initiative whose focus is the development and management of a universal language for licensing image rights and the preservation of digital content. The components of the PLUS system include a picture licensing glossary, media matrix, and licensing format.
Portable Network Graphics format was designed to improve on GIF, and it does in many ways, supporting full color RGB images for instance. PNG, however, doesn't support embedded color profiles or EXIF data, so it's use is mostly limited to the web. Even then, JPEG is a more efficient format in terms of maintaining high quality at a small file size. PNG does support transparency, which JPEG doesn't, and PNG is a better choice than JPEG for images that contain text or line art, as it does better with sharp transitions. PNG uses non-lossy compression, so it doesn't suffer from increasing artifacts with subsequent edits and re-saves, as JPEG does.
A visual defect (also called banding) in an image created by insufficient amounts of data to maintain the appearance of continuous tone. Posterization can be result from overly aggressive image editing (typically curves or levels adjustments) that forces adjoining (but different) pixels values to all assume the same value. It can also be caused by color transforms and working with an insufficient bit depth to sustain the subtle gradations within an image. The effect often becomes visible first in shadow detail and large areas of continuous or uniform color (blue skies). Digital noise can also create or contribute to posterization as well as the failure of output devices to render subtle differences in tonality.
The measurement of image resolution expressed in pixel density (or size) relative to inches. PPI can be used to calculate the final image size by dividing the image dimensions in pixels, by the PPI. The resulting numbers would be expressed in inches. Example: 2400x300 pixel image at 300 PPI would equal 8 by 10 inches. Not to be confused with dots per inch (DPI).
As it relates to digital images and data, it is the process of maintaining information in an error-free state to preserve its accessibility and usefulness. Due to the non-physical nature of digital information, this requires a constant process of upkeep, including refreshing storage mediums, migrating to new mediums and file formats, verifying and validating existing data, and maintaining redundant backups.
In digital imaging or photography, the steps and procedures that transform images or data through the use of software applications. PIE software such as Camera Raw processes raw image data into a recognizable photograph according to the user’s input and decisions.
File formats that may be protected by patent, copyright, and or other licensing agreements and generally are not publicly documented. Examples include Adobe PSD, and the vast majority of camera raw formats. Camera manufacturers and software vendors use proprietary formats to protect intellectual property or trade secrets. There is controversy surrounding their use since it raises user concerns of data ownership and longevity.
A number of data storage configurations that provide higher performance, redundancy, or both combined. RAID controllers can be software or hardware based, with hardware solutions typically providing higher levels of performance. There are potential of 8 RAID levels with 0,1, and 5 being the most widely used. Level 0 uses a technique known as striping to spread data over multiple drives that appear as a single volume. It provides high performance but with no redundancy of data. Level 1 writes the same data to multiple drives in a process called mirroring. It provides a high degree of redundancy but at the expense of performance. Level 5 uses multiple drives and provides the benefits of combining both striping and mirroring. The other levels are variations based on different levels of parity. RAID should not be confused as a backup in and of itself although it can be used as part of a backup process or system.
Chip based computer memory that stores temporary or dynamic data and instructions that can be accessed in any order. It is also known as volatile memory since the data it holds is lost when the computer is shut down or power is interrupted. RAM is considerably faster that disk-based memory and is an important component in computer performance. Modern operating systems can take advantage of large amounts of RAM, which can dramatically improve performance of software applications that have been designed or optimized accordingly. This allows an imaging editing application such as Photoshop to open large files directly into RAM (verses having to read from disk based virtual memory) and perform processing at much higher speeds.
A software application (also commonly called image editors) that works directly on the pixels of an image, Adobe Photoshop and Apple iPhoto are examples. Unlike PIEware, changes (edits) made by a raster application can be destructive in nature, permanently changing the pixel values.
Raster layers consist of an array of mathematically defined pixels, where each pixel describes a unique point on the image plane. The “Background” layer in flattened Photoshop files is always a raster layer. Raster layers can be duplicated and altered in a wide variety of ways. Changes applied to the pixel data in a raster layer become permanent with regards to that layer but do not affect the layers above or below it. Scaling raster layers is inherently destructive as upsampling requires new pixels to be invented and downsampling requires pixels to be thrown away.
A raw (or camera raw) file is the unprocessed linear data captured by a digital camera sensor and any associated metadata. It can be likened to the digital equivalent of a latent image but with the ability to be infinitely reprocessed or developed. In most cases, cameras write raw files using a proprietary file format. Raw files give the photographer the advantage of managing image processing during post-production rather than allowing the camera to make the processing decisions, as happens when shooting JPEG. Also see DNG and Linear Data.
One of the four rendering intents specified by the ICC for handling out-of-gamut colors when converting from one color space to another. Relative colorimetric maps the white of the source to the white of destination and then reproduces all in-gamut colors exactly. Out-of-gamut colors are clipped to the closest reproducible hue. Relative is considered to be a good choice for images when you are trying to achieve accurate reproduction and do not have a significant amount of out-of-gamut colors.
The four methods (Perceptual, Saturation, Relative Colorimetric, and Absolute Colorimetric) defined in the ICC profile specification by which out-of-gamut colors are handled when converting from one color space to another. Perceptual and Saturation use gamut compression to remap source colors to fit the destination. Relative and Absolute Colorimetric utilize gamut clipping to remap to the closest reproducible hue.
The process of creating derivative files or image components for a variety of alternate uses. Examples could include creating a web version of a file originally intended for CMYK reproduction, making a black and white version of a color image, stitching together several images to build a panorama, or taking elements from different images to create a montage.
A measurement of the ability of an optical, capture, or output system to record and reproduce detail. It can be defined in a number of different metrics such as Line Pairs, PPI, DPI, SPI, and LPI. Also see Optical Resolution, Dots Per Inch, Pixels Per Inch, Lines Per Inch.
A color model that uses the three primary (red, green, blue) additive colors, which can be mixed to make all other colors.
One of the four rendering intents specified by the ICC for handling out-of-gamut colors when converting from one color space to another. Saturation tries to produce vivid colors by mapping fully saturated colors from the source to the destination without regard for accuracy. It is not usually a good choice for photographic images but works well for business graphics or illustrations.
The process of using a flatbed scanner to create a photographic image of a three-dimensional object by laying it on the scanner bed (glass).
The process of increasing (or emphasizing) contrast around the edges of details (comprised of pixels) in an image. Sharpening is a workflow (pioneered by the late Bruce Fraser) unto itself with several different stages to compensate for softness introduced at various points in the image lifecycle. These stages are referred to as capture sharpening, creative sharpening, and output sharpening. Each uses different parameters and techniques to achieve optimum results tailored to that specific need. There are variety of different software tools, dedicated applications, and plug-ins available for sharpening. Pixel Genius is a software developer that has taken the workflow principals and research developed by Bruce (he was a founding member) and produced a product (Photokit Sharpener) along with licensing of technology to Abobe for use in Lightroom and the Camera Raw plug-in.
A text file that contains metadata associated with a parent file. Sidecars are typically used when the parent is a proprietary raw file that does not safely support the use of embedded metadata.
In digital photography, this defines the relationship between the incoming signal (light/photons striking the pixels/sensor elements) and the background electronic noise generated by the sensor. SNR is inherent in any electronic system. In relative terms, the higher the SNR, the cleaner the resulting data will be and in turn, this produces a higher quality image. Low SNR results in reduced separation between the signal and background noise and will increase the amount of visible image noise. This will degrade shadow detail and reduce the overall image quality. Increasing the ISO setting on a camera results in amplification of the signal and creates a corresponding increase in noise.
Since Smart Objects are references that don’t actually contain pixel data, pixel-altering filters cannot be applied to them directly. Instead, Smart Filters allow you to preview what certain filter functions will look like when applied to the pixel data represented by the Smart Object. Smart Filters are non-destructive and can be infinitely adjusted and edited. They only change the pixel data when the Smart Object is rasterized.
Smart Object layers (available in Photoshop CS2 and higher) serve as a visual reference to data residing in a separate file. While many types of files (Tiff, JPG) can be converted to Smart Objects, their true value lies in their ability to house RAW and Vector data. Smart Object layers preview the impact of editing adjustments while preserving the ability to update the smart object by non-destructively reprocessing, resizing or transforming the original RAW or Vector data. Any edits made within Photoshop remain non-destructive until the Smart Object is rasterized.
Another term used to describe how fine of a line (and their closeness) a particular imaging system can resolve. Also see Resolution.
As it relates to digital photography, the sensitivity and response of image sensors to the color spectrum and wavelengths of light. An example would be how different types of sensors may be more sensitive to certain wavelengths (colors) of light.
The term used to describe the material onto which an image (and or text) will be printed. Primarily this is paper but may be a variety of other materials including film, foil, plastic, ceramics, textiles and fabrics.
A binary unit of computer data or storage that consists of 1024 gigabytes. Hard drive manufacturers have standardized 1 terabyte at 1000 gigabytes of storage.
A small, low-resolution image preview used on the web to link to a high-resolution version of the file. Thumbnails can also be embedded in file formats such as TIFF and PSD. Previews that are generated by PIEware and browser applications are also occasionally described as thumbnails.
An open standard file format specifically designed for images. Although Adobe Systems owns the copyright for the TIFF specification, they maintain the format as an open standard, currently in revision 6. TIFF can incorporate several types of compression if desired, including LZW, JPEG, and ZIP. The format is particularly well suited for the storage of high quality, archive images. The DNG format is based on TIFF/EP (electronic photography), which is a subset of the main TIFF standard.
Used in image editing software, a graphical representation the relationship between the input and output values for the brightness levels of pixels that can be used to adjust the contrast of the image.
A URL is a computing term for a web site address such as http://www.shutha.org
The UI is a graphical front-end for the software or code that controls interaction between the user and the computer or device. These range from the complex GUIs (graphical user interface) of operating systems and applications like Photoshop, to button driven interfaces, like those found on the back of digital cameras.
Images that use mathematically described geometric shapes (arcs, curves, lines) and points rather than bitmapped pixels to create objects. Vector images or objects are compact (since they are a description rather than actual pixels), provide clean and crisp edges, and are infinitely saleable without being subject to the interpolation artifacts seen in bitmaps. Adobe Illustrator is an example of dedicated a vector graphics editor. Photoshop also has the ability to create and use vectors in conjunction with pixel based images.
Vector layer contents are defined by formulas describing the component geometric shapes - points, lines, curves and polygons – that make up the image. Typical uses for vector layers include typography, shapes and illustrations. Vector layers can be infinitely resized or altered until they are rasterized (converted to pixel data).
A process where the computer operating system (or software application) uses hard disk space to extend memory beyond the addressable RAM (random access memory). Also commonly called a page file or swap file (space), it extends the utility of a process but at the expense of slower access speeds. Depending on the operating system or application, it may be user-assignable and performance can be improved by locating it on a high-speed drive or RAID0.
A subjective term referring to any compression technique that reduces the file size by removing data of fine enough detail that the eye does not notice. A visual comparison between the original and the compressed file does not show any differences but a comparison of the binary code or actual pixels will.
In general, many photographic images can be compressed up to a ratio of 10:1 without a visually perceptible loss in image quality.
Also referred to as web proofs, they are simple web pages built using HTML or Flash to show and share images. Many DAM and PIEware applications are able to create web galleries from folders or collections of images.
In digital photography, the white balance establishes the color balance (and neutrality) of the image in relationship to color temperature of lighting conditions. Most digital cameras have several built-in white balance presets (tungsten, daylight, cloudy, fluorescent, etc.), along with an auto setting and the ability to set a custom WB. In raw capture, the white balance is recorded as a metadata tag but is not applied to the actual image data. PIEware provides tremendous flexibility for post-processing adjustment of WB in raw files. When shooting JEPG it is more critical to get the white balance “right” since it will in effect be backed into the pixels of the image and requires destructive image edits to correct.
A term used to describe color temperature as it relates to the luminance of the brightest white that a device can display. It also refers to the reference (or target) white of the illuminant. White point is commonly used to describe the calibration setting on a monitor that literally sets the color temperature (or illuminant) of how white is displayed. Common settings include 5000 or 6500k or the D50 or D65 references. Monitor white point settings are often determined by the viewing environment and color matching requirements of a workflow.
The processes and sequence of steps through which an image or other piece of work passes from inception to completion.
An RGB color space designed specifically for editing images. The properties would include being gray-balanced (equal amounts of R,G,and B produce neutrality), perceptual uniformity (meaning an change in a primary or color will yield a visual change of the same degree), and having a wide enough gamut to contain the colors of the image (or color values) being edited. Examples would include sRGB, Adobe 1998, and ProPhoto.
An acronym for optical media such as CD-R and DVD-R that is often recommended for archiving digital image files since it is not subject to accidental erasure, viruses, and overwriting of files.
Developed by Adobe Systems, the Extensible Metadata Platform is an open standard for processing and safely embedding metadata in a wide range of file formats. Based on XML, XMP is extensible, meaning that it can accept existing metadata schemas such as IPTC but can grow to accommodate emerging needs and technologies. Parametric image editing instructions along with proprietary metadata are also supported by XMP.
Is a specification for creating self-descriptive markup language for transporting and sharing data. XML has been recommended (the final stage of the ratification process) as an open standard by the W3C (world wide web consortium). XMP is an example of an XML based platform.