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Glossary: P

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Panorama image
An image that displays a wider than normal horizontal field of view up to 360°. Although there are specialized cameras for creating single panorama images, they are more commonly created from multiple images that are stitched to form a single wide field image.…
PCM
See Pulse Code Modulation
PDF
Adobe's Portable Document Format (PDF) is a document encoding system that maintains the original content, structure and appearance of a document across many computer platforms and communications networks. Adobe has created a near universal document format that is device and resolution independent. A free and widely available PDF viewer allows users to open,…
Peak signal-to-noise ratio
The ratio between the maximum power of a signal and the power of noise contained in the signal. Often abbreviated as PSNR.…
See Signal-to-noise ratio
Persistent Uniform Resource Locator
See PURL
Photo montage
See Mosaic image
Photodiode
A type of photodetector that forms the basic component of imaging sensors. Photodiodes absorb photons of light to produce an electric potential that is then converted into a signal. In an imaging device, this signal is represented as areas of light and dark relative to the values of the original scene or object.…
Photometer
An instrument used to measure the intensity of light.…
Photometry
Photometry is the science of measuring the intensity of light (luminous intensity) in relation to the sensitivity of the human eye. Photometry is analogous to radiometry, weighted by the response function of the eye. The science of photometry does not deal with the perception of color, which is the realm of colorimetry.…
Photonics
The technology involved with the generation, detection, transmission and control of light and other electromagnetic radiation whose quantum unit is the photon. In digital imaging, this technology is involved in the area of sensor technology, both in imaging systems and devices used in quality control related to digital imaging.…
Photopic (general)
Having sensitivity characteristic similar to the human eye response.…
See Also Photopic sensitivity; Mesopic sensitivity; Scotopic sensitivity
Photopic sensitivity
Photopic sensitivity refers to visual sensitivity under conditions of bright light, where radiant energy stimulates the cones (retinal photo-receptors responsible for color perception). Photopic spectral sensitivity differs from scotopic spectral sensitivity (see scotopic sensitivity).…
See Also Photopic (general); Scotopic sensitivity; Mesotopic sensitivity
Physical replica
A physical copy of the original item, most often used for books. For many years, library and archive preservation programs made what were called preservation photocopies. In the first years of book scanning at Cornell University (circa 1990-95), the same outcome was sought: the digital images were printed back to paper and rebound, producing a…
See Also Virtual replica; Museum-quality facsimile or print; Copy negatives and transparencies; Interpositives, duplicate negatives and transparencies
Picture-referred
See Image state
Pixel
An abbreviation of picture element, this term may refer to a component of either a digital image or a digital sensor. In the case of a digital image, the pixel is the smallest discrete unit of information in the image\'s structure. Images based in raster data can be thought of as a grid in which…
See Also Bit depth (image); Megapixel; Pixel interpolation; Pixel misregistration; Pixellation; PPI; Raster data
Pixel interpolation
An image processing operation that attempts to estimate interstitial pixel positions.…
See Pixel
Pixel misregistration
The color-to-color spatial dislocation of otherwise spatially coincident color features of an imaged object.…
See Pixel
Pixellation
A term used to describe the an abrupt and unnatural transition over and edge feature. Also referred to as "staircasing" because of the jagged and abrupt transition.…
See Also Distortion; Aliasing; Pixel
Pixels per inch
See PPI
PPI
PPI stands for pixels per inch, commonly used in describing the resolution capabilities of an imaging device such as a scanner or the resolution of a digital image. The terms DPI (dots per inch) and PPI are used somewhat interchangeably today.…
See Pixel
Precision
The characteristic of measurement that relates to the consistency between multiple measurements of an identical item or process under uniform conditions. As opposed to accuracy, precision does not indicate how close a measurement is to a true value.…
See Accuracy
Preservation master file
See Archival master file
Preservation metadata
See Metadata, preservation
Printed halftone
Most photographs, paintings, or similar pictorial works reproduced in books, magazines and newspapers are printed as halftones. In a halftone, the continuous tones of the picture being reproduced are broken into a series of equally spaced dots of varying size, printed with only one color of ink. The outcome exploits an optical illusion: the…
Printing plate
In traditional offset lithography printing, a piece of film is produced (usually from a computer file today) on an imagesetter, which is then used to create a metal printing plate. This plate is then placed on the press and is used to create the printed impressions. If a photograph or otjher continuous tone image is…
Process metadata
See Metadata, process
Production master file
Files produced by processing the content in one or more archival master files, resulting in a new file or files with levels of quality that rival those of the archival master. The first type of processing consists of the assembly of a set of segments into a unified reproduction of an item. …
See Also Archival master file; Derivative file
ProPhoto RGB
ProPhoto RGB is a large gamut color space developed by Kodak primarily for photographic applications. The space encompasses 90% of the CIE L*a*b* color space - compared to Adobe RGB's coverage of about 50%. ProPhoto RGB is also known as ROMM RGB for Reference Output Medium Metric RGB…
Provenance metadata
See Metadata, process
Pulse code modulation
Type of encoding used for audio bitstreams. Pulse code modulation was originally developed in 1939 as a method for transmitting digital signals over analog communications channels. The same technique proved effective as a method of sampling and quantizing audio for encoding in digital form. Variants are based on different mathematical techniques for quantization, including linear,…
See Linear pulse code modulation
PURL
Acronym for Persistent Uniform Resource Locator. A PURL is technically a Uniform Resource Locator (URL), but rather than pointing directly to the internet site that it is refers to, it points to an intermediate resolution service. The resolution services associates the PURL with the actual URL and redirects the client to that URL. PURLs…