What Is the Term for Pixel-based Images That Map Bits to a Display Space?
Tagged Image File Format
File Analysis
Cory Altheide , Harlan Carvey , in Digital Forensics with Open Source Tools, 2011
Tiff
The Tagged Prototype File Format (TIFF) is an image file format used commonly in publishing and graphic design. It is the default file format for many applications on OS X, including the default screen capture utility Grab. TIFF was created originally as a unified format for scanned documents and is even so mutual for fax and scanning applications to generate TIFF images. Equally the name suggests, TIFF epitome files support internal metadata tags. There are besides extended versions of TIFF, such as GeoTIFF (used to shop geographical image data) and the Microsoft Certificate Imaging format used to store scanned or faxed documents. In improver, many of the "Raw" formats used as lossless storage by digital cameras are TIFF-based. Metadata from TIFF files can be processed using exiftool.
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Data Hiding Using Steganographic Techniques
Nihad Ahmad Hassan , Rami Hijazi , in Information Hiding Techniques in Windows Os, 2017
TIFF
Tagged Prototype File Format (TIFF) has a TIFF or TIF extension. It creates very large image size as it contains a large volume of image data (TIFF stores its storage algorithm every bit a part of the image file). TIFF images are ordinarily saved using 24-bit or 48-flake (in the terminal case each RGB color shop 16 bit alone). This format is rarely used online as it is not widely supported by all web browsers.
It unremarkably comes uncompressed although it supports both lossy and lossless pinch (some programs compress TIFF files using a lossless compression algorithm called LZW but information technology is not widely supported).
This blazon is very flexible equally it can be stored as a colored RGB image, grayscale, or CMYK for impress. Furthermore, TIFF images can be extended to include proprietary tags according to vendor needs.
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Systems, Disks, and Media
In The Official CHFI Study Guide (Exam 312-49), 2007
TIFF
TIFF is an acronym for Tagged Image File Format, an image format that has been commonly used for print since its introduction. TIFFs are oft used for desktop publishing and graphic pattern, although the format was originally developed in the 1980s as a standard file format in which scanned images could be saved. The goal was to avoid proprietary file formats when a moving picture or certificate was scanned, with the assumption that all scanners would eventually support the TIFF format. Equally scanners grew more powerful, the TIFF file format evolved to support grayscale and color images. Because the image quality was then high, even images that weren't scanned were saved in this format and used in printed materials.
TIFFs back up a wide range of colors, and can be exported as 8-bit, 16-bit, 24-bit, or 32-bit color modes. Because higher-quality images are also larger, this affects its portability to other systems, and its use on the Internet. When TIFFs are saved, they are generally high-resolution graphics that are larger in size than JPEGs or other file formats. Every bit such, Internet browsers generally don't support this format. However, in improver to images created or modified in graphics programs, many digital cameras support TIFF every bit a format in which photos are stored on the photographic camera.
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Digitising material
Allison B. Zhang , Don Gourley , in Creating Digital Collections, 2009
TIFF
TIFF (Tagged Image File Format) is ane of the most popular and flexible of the current public domain file formats. It is a container format for storing all kinds of images. Information technology tin can handle multiple images and data in a single file through the inclusion of 'tags' in the file header. Information technology allows for a wide range of different compression schemes and colour spaces. TIFF is primarily designed for the interchange of raster data (i.e. pixel-based images). Its principal strengths are a highly flexible and platform-independent format that is supported by numerous paradigm-processing applications.
Image data in a TIFF can use lossy or lossless compression or no compression at all. The ability to store image data in a lossless format makes TIFF useful for archiving images. Nevertheless, the image format is non widely supported by web browsers. In addition, uncompressed TIFFs are generally very big, and therefore not proficient for delivering and distributing over the internet.
TIFF filenames utilise .tif or .tiff extensions.
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Metadata
Ian H. Witten , ... David Thousand. Nichols , in How to Build a Digital Library (2nd Edition), 2010
Image metadata: TIFF
The Tagged Image File Format, TIFF, described in Section 5.iii, incorporates all-encompassing facilities for descriptive metadata. It is used to describe image data that comes from scanners, frame-grabbers, pigment programs, and photo-retouching programs. It is a rich format that can take advantage of many prototype requirements but is not tied to particular input or output devices. It provides numerous options—for example, several different compression schemes and comprehensive information for color calibration. It is designed so that individual and special-purpose information can be included.
A unmarried TIFF file can include several images, each of which is characterized past tags whose values define particular properties of the image. Near tags contain integers, merely some incorporate ASCII text—and provision is fabricated for tags containing floating-point and rational numbers. Baseline TIFF has a dozen or then mandatory tags that give concrete characteristics and features of images: their dimensions, pinch, various metrics associated with the colour specification, and information most where they are stored in the file.
Tabular array half dozen.5 shows some TIFF tags, all of which except the final group are mandatory. The commencement group specifies the paradigm dimensions in pixels, along with enough data to allow conversion to physical units where possible. All images are rectangular. The second group gives colour information. For bilevel images, the colour group defines whether they are standard black-on-white or reversed; for grayscale it gives the number of bits per pixel; for palette images, information technology specifies the colour palette. The third group specifies the compression method—baseline TIFF allows merely extremely unproblematic schemes. Finally, a TIFF image tin can exist cleaved into strips for efficient input/output buffering, and the last group of mandatory tags specifies their location and size.
Table half dozen.v:. TIFF tags
| Dimensions |
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| Color |
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| Compression |
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| Location of the data |
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| Optional fields |
|
Boosted features go far across the baseline illustrated in Table 6.5 and users tin can define new TIFF tags and compression. This makes the TIFF format fifty-fifty more flexible than the official listing of extensions given in the standard, although naturally intendance needs to be taken to ensure that the software used to read and write prototype files is conversant with the tags they use. To avoid disharmonize, a registration process is provided for allocating individual tags. There are over 70 such tag sets, including support for EXIF (see next subsection). More radical extensions include GeoTIFF, which permits the addition of geographic data associated with cartographic raster data and remote sensing applications, such every bit projections and datum reference points. Many digital cameras produce TIFF files, and Kodak has a PhotoCD file format based on TIFF with proprietary color space and compression methods.
Nearly digital library projects of images utilize the TIFF format to store and annal the original captured images, even though they may convert them to other formats for brandish. At the bottom of Tabular array 6.5 are some optional fields that are widely used in digital library work. Some, such as the name of the plan that generated the image and the date and fourth dimension it was generated, are usually filled in automatically by scanner programs and other image-creation software. Digital library projects frequently establish conventions for the apply of the other fields. For case, in a digitization project, the Document name field might comprise the catalog ID of the original document. These fields are coded in ASCII, just there is no reason why they should not comprise information that is farther structured. For example, the Prototype clarification field might incorporate an XML specification that itself includes several subfields.
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rRNA Gene Restriction Design Decision (Ribotyping) and Computer Interpretation
Patrick A.D. Grimont , Francine Grimont , in New Approaches for the Generation and Analysis of Microbial Typing Data, 2001
(i) Epitome capture
The gel image is captured past either a CCD (charged couple device) camera or a flatbed scanner connected to a estimator, as described in Chapter 3 . Both should requite a TIFF (tagged image file format) prototype that can be opened by unlike software programs on various computers (Macintosh, PC, workstations). When only nylon membranes or photographs are to be digitised (i.due east., dry out material), a flatbed scanner is sufficient. Cameras and flatbed scanners must produce TIFF images with 256 shades of greyness and optical (not extrapolated) resolution up to 300 dpi (dots per inch). Prototype file size should betwixt 200 kilobytes and one megabyte. College resolution yields image files that can merely be handled by a express number of software programs for an insignificant gain in information precision. A few programs may handle more gray levels. Withal, the higher precision in gray levels is not justified when reproducibility is considered. Colour images are just a nuisance as far as ribotyping is concerned. The captured image tin can be printed on a loftier resolution printer and saved on a hard drive. In an agile ribotyping laboratory, the hard drive on which images are saved will speedily become saturated. Files should be efficiently compressed or stored on removable supports (magneto-optical disks, writable CDs).
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Selective Restriction Fragment Amplification by AFLP™
Paul J.D. Janssen , in New Approaches for the Generation and Assay of Microbial Typing Data, 2001
A. Digitisation of AFLP data
A common theme in the non-automated processing of AFLP data is the generation of epitome files from the electrophoresis patterns (e.g., those obtained by autoradiography, by phosphor imaging, etc.). These image files are ordinarily saved in 'tagged prototype file format' (TIFF), which is a generally accepted computer file format and supported by most epitome processing tools for both workstations and personal computers. A TIFF file consists of a number of labels (tags) which depict certain properties of the file (such equally gray levels, colour tabular array, byte format, compression size, etc.). After the inital tags comes the information, which may be interrupted past more than descriptive tags. The size of each TIFF file is predetermined past the resolution in which the digital image was created (i.e., past the specifications of the scanner). A typical resolution of an AFLP epitome obtained from a 35 × 43 cm polyacrylamide slab gel is 1200 by 2000 datapoints. The image is used for defining 'tracks' for each lane of involvement. Within the boundaries of these tracks, data points are resampled and average densitometric values are lined out as a office of the run-time, resulting in electrophoresis 'pinnacle profiles'. These profiles are then used for comparative assay (cf. the Pearson product-moment correlation coefficient). Images can also be used to define the bands for each lane that will participate in the comparative assay. Similarities are then calculated from the presence and absence of bands (cf. the band-based similarity coefficient of Dice). However, it may sometimes exist difficult to assign bands correctly because of the high complexity of the AFLP banding patterns, in which case the Pearson correlation coefficient is often preferred.
With 'automatic' AFLP technology, fluorescently labelled amplicons are detected with a laser while they migrate downwards through the gel. The detection signals are collected, digitised and sent to the computer for storage and processing. These raw data are converted to the TIFF format with software that is ordinarily included in the automatic sequencing apparatus package. The actual size of the paradigm file depends on the conversion settings used, with a typical vii- to 10-fold reduction of the original vertical resolution (as divers by the run-time and signal detection interval). Although TIFF images obtained by classical or fluorescent AFLP are processed in the same way, the bodily banding patterns obtained by the two different approaches differ in one important aspect. Classically obtained patterns (i.eastward., via a scan of an autoradiogram) contain large bands that are compressed together and smaller bands that are relatively diffuse as compared to the larger bands. In contrast, fAFLP patterns contain many minor discrete bands while the larger bands are diffuse, simply because the smaller fragments migrate much faster through the gel and are detected very early, with little fourth dimension in between each detection. A possible improvement to overcome the 'stacking' of pocket-sized bands in fAFLP patterns would be the employ of a signal detection interval that is initially very modest (eastward.g., 500 ms) and gradually increases during the runtime; i.e., more than data points are created at the start of the run and then that the design is somewhat stretched and small bands can be assigned more than accurately. Alternatively, Stoffel fragment of DNA polymerase (which has a low rate of processivity) may exist added to facilitate the discrimination of small (50–100 bp) PCR products (Hookey et al., 1999).
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Digital image nuts
Margot Annotation , in Managing Image Collections, 2011
File formats
File formats ensure that data is stored according to a predictable set of rules that will allow for device independence, so that files can be shared or accessed on other systems. Information professionals must consider the long-term usefulness and accessibility of the images and choose a file format that is a non-propriety industry standard. Doing so will ensure the indelible viability of the digital images, which is important because, due to the costs of digitization, it is unlikely that the procedure will be repeated in the short term. Additionally, standard formats ensure the maximum re-usability of images across projects and over time, and enable institutions to have role of cooperative projects and to brand the best utilize of staff expertise. Adopting open international standards also enables the establishment to make all-time apply of external sources such as advisory boards, contractors, and consultants.
Despite the range of file formats, but a few are recommended for paradigm collections. The most common formats include TIFF (Tagged Image File Format), JPEG or JFIF (Joint Photographic Experts Group File Interchange Format), PNG (Portable Network Graphics), and GIF (Graphic Interchange Format). Many digital imaging projects use TIFF principal files and JPEG derivative files.
The 'tagged' in TIFF refers to the internal structure of the format, which allows for arbitrary additions, such as custom metadata fields, without affecting general compatibility with photo editing and management programs. These tags describe the size of the paradigm or define how the image data is arranged and identify the pinch algorithm that is used. TIFF supports several types of image information pinch, allowing an organization to select the most advisable for its needs. Many users of TIFF opt for a lossless compression scheme such as Lempel-Ziv-Welch (LZW) encoding, to avert deposition of image quality during compression. Users frequently avoid any compression at all, so every bit to ensure that image data will be unproblematic to decode. TIFF is the best file format for archiving high-quality images because files can exist edited and saved without damage to the epitome due to pinch loss.
JPEG is a lossy compression format that allows epitome data to be compressed by assigning a compromise color value to a cake of pixels rather than to each separate pixel. The extent of this procedure can exist controlled, but there is irretrievable deterioration in image quality, nearly noticeably in polish-gradient areas. JFIF specifies how to produce a file suitable for computer storage and manual over the internet from a JPEG stream. JFIF does not allow for the storage of associated metadata, which has led to the development of SPIFF (Still Moving picture Interchange File Format), which can be read by JPEG-compliant readers while providing storage for more robust metadata. JPEG is all-time used with continuous tone photographic images, destined for electronic mail and web use, or for storage when space is limited. It is not suitable for use with line drawings or text because its compression method does non perform well with these types of image.
PNG (pronounced 'ping') is an open up source standard that was introduced to overcome the possible patent bug associated with the GIF format. Information technology is used either as an 8-chip indexed version, a 24-scrap color version, or an infrequently used 48-bit version. A versatile format, it offers the advantages of lossless compression in full color and a GIF replacement in 8-scrap form. However, it cannot compete with JPEG in terms of producing high-quality images for web viewing. The pinch available from PNG in 24-bit mode creates a file of about 60 to 75 percent of the original size.
GIF is an 8-bit (and under) indexed file blazon with a range of 256 colors. It works best with simple images using block colors, such as graphics, logos, and banners. GIF uses lossless LZW compression, just the amount of pinch will depend on the blazon of epitome existence saved. A full colour, continuous tone paradigm is unlikely to compress to less than 30 percent of its original size. The GIF file format also supports layers, assuasive for both transparency and animation.
Some cameras employ unprocessed RAW formats. These files include the original data captured by the sensor without alteration, and adjustments tin be made on the estimator to the white balance, exposure, and sharpness before saving them in a non-proprietary format. Raw processing combines maximum flexibility with epitome brightness and white balance and removes the limitations of stock-still, in-photographic camera processing, such every bit sharpening. RAW files unremarkably incorporate higher scrap depths than the equivalent JPEGs and TIFFs produced by the camera. The RAW format is oftentimes called a 'digital negative' considering little photographic camera processing has been applied to the epitome. Since no standards be, the RAW files must exist opened in that format with an image editor capable of translating them.
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Digitization of text and still images
Iris Xie PhD , Krystyna One thousand. Matusiak PhD , in Detect Digital Libraries, 2016
Technical factors
A range of technical factors play a role in the digitization process and relate to the quality and size of captured images. Paying close attention to epitome measures, such as resolution, chip depth, and color mode is critical during the conversion process, equally these directly impact the quality of digital master files. Other factors, such as compression, need to be determined during the processing phase in the production of derivative files. Technical specifications, including resolution, bit depth, and fashion of capture, take to be considered in the pick of the scanners and digital cameras.
Resolution is one of the near important factors, as it refers to the number of times an epitome is sampled and consequently relates to the amount of detail captured during the scanning procedure. Resolution specifically refers to the number of dots, or pixels (motion picture elements), used to correspond an image. It is expressed in a number of ways, DPI (dots per inch) or PPI (pixels per inch). PPI refers to the number of pixels captured in a given inch and is used when discussing scanning resolution and on-screen display. DPI comes from the print environs in reference to the optical resolutions for images and hardware. DPI more accurately refers to output devices, or how many dots of ink per inch a printer puts on the newspaper or onscreen monitor display. Nonetheless, the ii terms are often used interchangeably. Digitization guidelines recommend scanning at the highest resolution affordable to accurately and fully capture the visual content of the original materials. Scanning resolution depends on the technical specifications of capture devices, then it is of import to select a scanner or camera with sufficient optical resolution. Depending on the camera's lenses and support, the achieved resolution tin can sometimes exist unlike from the optical resolution. FADGI (2010) provides helpful guidelines on sampling frequency. Items scanned at high resolution volition issue in big digital master files. However, there is no "i size fits all" ideal or standard resolution. The resolution should be adjusted according to the type of source particular, its physical dimensions, and the corporeality of detail that needs to be captured. Digitization guidelines provide a range of recommended resolution measures relative to the types of sources materials and dimensions. For example, a minimum resolution for textual materials without images is 300 ppi, while a photographic viii × 10 in. print will benefit from scanning at 600 ppi (ALCTS, 2013). College resolution provides more pixels and volition more often than not return more than detail, but there is also a signal when increasing resolution does not yield any additional information.
Pixel scrap depth influences the representation of images, rendered in a grayscale tone or a range of colors. Information technology is a measure that "defines the number of shades that can actually be represented by the corporeality of information saved for each pixel" (Puglia, 2000, p. 85). Depending on the number of bits per pixel, images are represented as black or white, grayscale, or true colour. One-flake images are bitonal—either black or white. Eight-bit images are necessary to represent 256 shades of gray tones in photographic images. Most colour images require 24 bits per pixel to provide truthful representation of colour. The greater the chip depth, the more information nearly the source is captured by the scanning device, resulting in a more accurate digital representation of the original. A chip depth of 8 tin can capture enough information to represent 256 colors or shades of gray. A bit depth of 24 captures over sixteen 1000000 colors or shades of gray. It is worth remembering that at that place is a relationship between bit depth and file size. Scanning at a higher bit depth increases the overall file size. The usage of the term has evolved as institutions have moved from legacy scanning to modern raw capture. Currently, an 8-flake file means a 3-channel file with 8 bits per channel, which used to be referred to as a 24-bit image.
Color mode refers to the representation of color in images. Color images consist of 3 or more channels that correspond color information. Several different systems are used to represent color images, with RGB existence one of the about common. RGB stands for blood-red, green, and blue, the three channels used to represent digital color images. Estimator software combines the iii channels for each pixel to decide the final color. An RGB color digital image file consists of 3 channels, each with 8 bits of information (iii channels × 8 bits = 24 bits). Many cultural heritage institutions process to 16 $.25 per channel to reach subtle gradations of color.
Modes of capture refer to the fashion digitization equipment captures images in relation to the ii measures: chip depth and color fashion.
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Bitonal mode is appropriate for printed text materials without illustrations. Text can be scanned in bitonal mode where one bit per pixel volition correspond black or white values. Bitonal scanning was used in early digitization projects merely now is used infrequently.
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Grayscale mode requires multiple $.25 per pixel (eight $.25 minimum) to represent shades of grayness and is advisable for scanning photographic black-and-white film negatives, black-and-white photographic prints, or books and newspapers with grayscale images. Increasingly, colour RGB mode is recommended for black-and-white photographic materials since it captures more data from an analog source. More often than not, blackness-and-white prints and negatives will benefit considerably from scanning in RGB. If storage of these files is an consequence, they may be converted to grayscale after scanning.
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RGB color mode is recommended for items with continuous tone colour information. RGB way is used for all textual and visual resources where color is nowadays in the source item. In addition, archival textual materials or rare books are scanned in color when it is of import to capture the crumbling nature of paper or other artifacts (handwritten notes, stamps, etc.).
Compression is the process of reducing the file size by discarding a certain amount of information. The process is, in near cases, irreversible. Compression is closely related to the quality of images and their size.
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Lossless compression discards redundant information and does not touch on the quality of images. It allows for storing data in a more compact form. Lossless pinch is supported by TIFF and JPEG 2000 formats and tin can be used for service masters—images created as a result of processing and image enhancement techniques. However, it should not be applied to digital chief files. Digital archival masters should be saved equally uncompressed files. No compression is different from lossless compression. Digital principal files should retain all information captured during the conversion procedure.
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Lossy compression creates file sizes that are smaller, merely it besides contributes to the loss of paradigm data and decreases quality (the corporeality of discarded data depends on the level of compression). It is important to remember that when a compressed image is decompressed, it is no longer identical to the original image. JPEG format applies lossy compression. JPEG file sizes can be reduced past applying compression, which makes them suitable for online access and distribution.
Formats provide a standardized method of encoding and organizing data into files. The digital conversion of textual and photographic materials results in even so raster (bitmap) images, a 2-dimensional grid of pixels. A variety of formats can be used for storing raster images. The distinction between digital master files and derivatives in the digitization of cultural heritage materials provides a foundation for the choice of formats. TIFF has been recommended as a principal format for all the same images. TIFF has been widely adopted, and, as a recent report of file formats for raster nevertheless images indicates, it "has been the format of selection for the cultural heritage community" (FADGI, 2014, p. 3). JPEG and JPEG 2000 have been recommended equally derivative formats for photographic images, newspapers, manuscripts, and maps. JPEG 2000 has also been considered as an archival format for principal files (Buckley, 2008; Buonora and Liberati, 2008; Van der Knijff, 2011). PDF is recognized equally a suitable derivative format for textual documents. PDF/A is a format recommended for archiving digital documents.
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TIFF (Tagged-Prototype File Format) is a stable and widely adopted file format for chief files of raster still images. Used since the early on days of digitization, TIFF has get the de facto standard for digital masters of digitized static cultural heritage materials. Fleischhauer (2014a) notes, "its endurance in time tin can exist seen as a strength, especially because the wide array of applications that tin read it" (pp. 2–3). Highly flexible and platform-independent, information technology tin be used for storing bitonal, grayscale, and colour still images. TIFF combines raster image data with a flexible tagged field construction for metadata. TIFF supports lossy and lossless compression. It is recommended that digital masters be saved as uncompressed TIFF files, only lossless pinch, such as LZW pinch, can be used for service masters. Uncompressed TIFF files require a considerable amount of storage space. TIFF is an open and well-documented standard, with the specifications of TIFF Revision 6.0 maintained by the Adobe Systems. The TIFF filenames use .tif or .tiff extensions.
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JPEG (Joint Photographic Experts Group) is designed for compressing and thus reducing the size of grayscale and color raster however images. The JPEG standard was published in 1992 and is normally used on the spider web and in digital cameras. In digitization, JPEG is used primarily for derivative images to exist displayed in digital collections. JPEG applies a lossy compression method, which reduces the file size. The corporeality of compression tin be adjusted. The typical ratio of 10:i results in very little perceptible loss in image quality. JPEG works particularly well with photographic images of continuous tone, while images with lettering or line drawings may suffer some degradation in quality. The effective compression makes JPEG a particularly suitable format for online brandish and transfer over the Internet. However, considering of the loss of data associated with compression, this file format should not exist used for master files. The JPEG format is supported by all browsers. The JPEG file extensions are .jpg or .jpeg.
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JPEG 2000 is an international standard for the compression of digital still images. It was proposed by the Joint Photographic Experts Group in the year 2000 as an open file format and a compression method with the goal of improving or superseding the original JPEG format. JPEG 2000 provides a new compression algorithm with progressive brandish, multiresolution imaging, scalable image quality, and the ability to handle big and high-dynamic range images (Buckley, 2008). The JPEG 2000 file format also offers significant improvements over before formats by supporting both lossless and lossy paradigm compression. Because of its superior power to handle big content files and dynamic display with support for zooming and panning, JPEG 2000 has been used equally a derivative file format for maps, paper pages, and other large images (Fleischhauer, 2014b). At this signal, the format cannot exist viewed natively in near web browsers and requires a dedicated JPEG 2000 viewer. The potential of JPEG 2000 for storing large primary files and as an culling to uncompressed TIFFs files has also been explored due to its first-class compression performance (Buonora and Liberati, 2008; Van der Knijff, 2011). The credence of JPEG 2000 equally a preservation format, yet, has been slow and a subject of argue in the cultural heritage customs (Adams, 2013; Fleischhauer, 2014b). The report conducted by Van der Knijff (2011) also identifies some preservation risks, related to the current format specification in color infinite and in the handling of filigree resolution, which may atomic number 82 to the loss of some information in future migrations. JPEG 2000 uses .jp2 and .jpx extensions.
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PDF (Portable Document Format) is an admission format adult by Adobe Systems in 1993 to share and view digital documents. It remained a proprietary format until 2008 when information technology was released equally an open international standard. PDF is used to represent 2D documents in a fixed-layout format. PDF documents maintain the original structure and advent of source items and can be exchanged beyond many platforms. PDF is a universal format used to stand for both born digital and digitized documents. A pop format in the publishing manufacture, PDF became a de facto standard for scholarly publications, administrative documents, and many textual documents shared over the web. In digitization, PDF is used every bit a derivative format to represent multipage objects, such as manuscripts, books, journals, and archival documents. Full-text searching of digitized documents can be incorporated into PDF derivatives, but it requires additional processing of source images. At a minimum level, digitized historical documents are presented in the PDF format as images—digital facsimiles. Full-text searchability is available for digitized impress documents processed with Optical Character Recognition (OCR) software (Turró, 2008; Yongli, 2010). A gratis and widely bachelor PDF reader can be used as a standalone program or a browser plug-in. A PDF filename has a .pdf extension.
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PDF/A builds upon the specifications of PDF but was developed specifically as a standard format to ensure long-term accessibility and the preservation of electronic documents. PDF/A addresses the concerns of the archival customs and is recognized as a format for the digital archiving of documents (Dryden, 2008). PDF/A-ane was released in 2005, and the latest version, PDF/A-3, was fabricated available in 2012. Information technology provides "a mechanism for representing electronic documents in a manner that preserves their static visual advent over time, contained of the tools and systems used for creating, storing or rendering the files" (Lazorchak, 2014). The difference between PDF and PDF/A is in the preservation function, which in PDF/A is achieved past embedding all fonts and metadata within the file so that it tin can be consistently rendered regardless of the hardware and software used to create or view it.
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PNG (Portable Network Graphics) was designed to replace the older GIF format. PNG supports raster grayscale and color image files and offers lossless pinch. PNG is supported by all major web browsers and is a pop choice for transferring images over the spider web. The use of the PNG format in digitization projects is limited thus far. In a recent Library of Congress weblog, Fleischhauer (2014b) highlights PNG support for color management and lossless compression and wonders near the potential apply of PNG for master files. PNG uses a .png file extension.
The file formats used in the digitization of static media demonstrate a loftier degree of stability, especially in comparing to the notwithstanding-evolving formats for video recordings. A comparative study of TIFF, JPEG, JPEG 2000, PNG, and PDF, conducted by the Federal Agencies Digitization Guidelines Initiative, indicates that all formats accept viable sustainability, although they vary in attributes, capabilities, and cost of implementation (FADGI, 2014).
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Paradigm Analysis
JOHN DEMPSTER , in The Laboratory Computer, 2001
9.1 DIGITISATION OF IMAGES
Many of the concepts developed in earlier chapters employ also to image analysis. If an paradigm is to be stored in a computer organization it must exist converted into numerical data, and this implies quantisation using some course of counterpart-digital conversion procedure. A visual image is essentially a two-dimensional airplane – with spatial dimensions, tiptop and width – containing information in the form of variations in brightness and possibly colour. In society to represent such an paradigm in numerical course, both the intensity of the brightness and its spatial variation must exist quantised into a finite set of spatial locations and levels. This can be done by placing a rectangular grid over the image, dividing it up into an assortment of individual picture elements (pixels), measuring the brightness or intensity of each pixel, and storing this every bit a two-dimensional assortment of numbers in figurer memory.
The number of pixels within the filigree – or spatial resolution – of the digitised image determines the fineness of detail that is retained within the paradigm. For example, compare the photograph in Fig. 9.2(a), digitised using a grid containing 320 horizontal and 320 vertical divisions (320h × 320v), a total of 102 400 pixels, with (b), the aforementioned photograph digitised using a 32h × 32v grid (1024 pixels). The analogue intensity of each pixel is likewise quantised, being represented past the grayness level – an integer number proportional to the effulgence. The number of bachelor grayness levels determines the quality of the tonal rendition – the ability to distinguish shades of grey – within the digitised image. Effigy ix.2(a), digitised into 256 greyness levels, tin can return a much more realistic moving-picture show than (c), which has but four levels. The number of gray levels that can be produced by an imaging device is a part of its bit depth – the number of bits in the binary number generated by the A/D converter used to digitise pixel brightness. A pixel depth of viii $.25, providing 256 grey levels, is the minimum resolution used for scientific image analysis, and 10, 12, 14 or 16 flake depths are becoming mutual for many applications.
Figure 9.2. Digitising images: the writer at (a) 320h × 320v spatial resolution, eight $.25 (256 grey levels); (b) 32h × 32v, 8 bits; (c) 320h × 320v, two bits (4 grey levels).
The higher up principles, discussed so far in terms of monochrome images, can be readily extended to the digitisation of color images. Subjectively, any colour can represented by the addition of appropriate amounts of the three principal colours – cherry, green and blue (RGB). Prototype colour can thus be coded as triplets of pixel brightness levels, one for each RGB colour. Colour encoding schemes are oft described in terms of the total number of $.25 used to store the color. For case, 24-flake RGB colour implies the use of viii bits per red, light-green and blue component. Many imaging devices are now capable of producing 36-bit (12 levels per colour) or fifty-fifty 42-bit (14 levels) colour.
The additive RGB scheme is non the only way of representing colour and two others are in use in specialised fields – CYMK in press and HSB in television. Printed colours (inks, dyes) combine by absorption of lite, making a subtractive scheme more appropriate. Colour images intended for printed reproduction are defined in terms of the three secondary colours – cyan, yellow and magenta. These combined with black (to improve the reproduction of dark tones) form the basis of the CYMK colour scheme. The HSB scheme separates out the colour of the lite from its brightness, defining it in terms of: Hue (a standard colour drawn from a 0−360° circular colour palette containing all colours in the spectrum), Brightness (the intensity of the colour) and Southwardaturation (the purity of the colour), defined as the percent of grey mixed in with it. Still, where colour is relevant in a scientific context information technology would normally be expressed in RGB terms. For further details of the various ways of representing colour see Russ (1995).
ix.i.ane Image file formats
The computer-based handling of images has countless applications ranging from the desktop publishing of printed material, through electronic publishing via the world wide web and digitised video. In club to facilitate these activities, a large number of image file formats accept been developed. Both Microsoft with their DIB (Device Independent Bitmap) format and Apple with PICT developed standard image file formats for their respective operating systems. Quite a few suppliers of imaging hardware for the scientific market have also produced their own proprietary file formats – Bio-Rad's PIC format for their confocal microscope images and Hamamatsu's IMG format being only two examples. Some attempts accept also been made within the scientific customs to produce standard prototype formats, but these have tended to be restricted to particular disciplines. FITS (Flexible Image Transport Southwardystem), is used by the astronomical community and supported past NASA,* while DICOM (Digital Imaging and Communications in Grandedicine) was developed by the U.s. National Electrical Manufacturers Association (NEMA) as a standard for the exchange of radiological and other images in the clinical environment.
Of the many formats, ii take gained particularly widespread acceptance as a means of transferring digitised images between programs from different suppliers:
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Tagged Epitome File Format (TIFF)
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Joint Photographic Experts Grouping (JPEG)
TIFF originated with Aldus Corp. as a means of incorporating pictures into their Pagemaker program which started off calculator-based desktop publishing in the mid 1980s. Since then, it has go the de facto standard image file format in many fields, including epitome analysis. Virtually all image-treatment software has to be capable of reading and writing TIFF files to be taken seriously. The TIFF format is now supported by Adobe Systems (San Jose, CA, USA), the makers of Photoshop, the marketplace-leading epitome manipulating program, who bought Aldus in 1994. The JPEG format is almost as widespread, being the standard image format for digital photography.
9.1.2 Epitome compression
Digitised images can accept up a significant corporeality of storage space. The size of an image depends upon its spatial resolution, bit depth and number of colour channels,
[9.one]
where north h and northward v are the numbers of horizontal and vertical pixels in the image, n c is the number of colours, and north bpp is the number of bytes required to shop a single pixel intensity value. In general, storage space is allocated in units of 1 byte. Thus images with bit depths of 8 bits or less require 1 byte, and 9–16 bits require 2 bytes. A single monochrome image of 512 × 512 × eight $.25, typical of the sort acquired in many paradigm analysis applications, requires 256 kbyte of storage space. Storage demands chop-chop escalate with the introduction of colour and college spatial resolutions, to easily as high as 100 Mbyte for a unmarried image.
In gild to conserve storage space, digital information compression techniques are often used to shrink the digitised epitome earlier writing it to file. Quite significant reductions in file size can be achieved past a diverseness of techniques, of which there are ii main categories – lossy and loss-free compression. A loss-free compression technique exploits numerical redundancies with the data, reformatting it so as to take up less storage space, with no loss of data. Lossy compression, on the other, reduces epitome size by selectively discarding some of the less important information. An image compressed using a lossy technique cannot be restored exactly.
Loss-free information compression can exist achieved in a number of means. For instance, run-length coding replaces repeated sequences of the same number with 1 example of the number and a lawmaking indicating the number of repetitions. Huffman coding substitutes oft occurring number sequences with brusque codes. A refinement of Huffman coding, the LZW algorithm (Lempel-Ziv-Welch, named later the inventors), is used in GIF and TIFF file formats. With loss-gratis algorithms, the degree of compression is very dependent upon the amount of repetition with the epitome. Compression to 10% or less of the original file size can be achieved with images which comprise large areas of the exactly the same colour. However, with the more than variable grey-scale images, typical of scientific applications, l% pinch is the best that is commonly achieved, and with certain image/compression algorithm combinations almost no compression occurs at all.
Higher compression factors can only be achieved past using lossy compression techniques. Most lossy pinch techniques are based upon the JPEG standards adult past the Joint Photographic Experts Group, to provide an efficient and standardised ways of compressing colour and monochrome photographic images. The methodology is complex, merely essentially involves splitting the paradigm into eight × 8 blocks of pixels and converting these into a set of spatial frequency components using a two-dimensional equivalent of the Fourier transform. These components are then ordered into a sequence, quantised into detached groups (where the loss of detail arises) which are compressed using Huffman coding. Images tin can be compressed in this style to 20% or less of their original size with no visible loss of clarity and to as piffling as 2–iii% if some degradation is acceptable. 1 advantage of the JPEG approach is that it allows a compression versus paradigm quality trade-off. Most photographs incorporated into web pages are in JPEG format, equally are the images produced by the digital cameras which are replacing 35 mm moving-picture show cameras in the consumer market place.
Strictly speaking, JPEG defines a ready of four pinch standards (one of which is lossless, in fact) and not a particular epitome file format. However, JPEG has get largely synonymous with the JFIF (JPEG File Interchange Format) file type which implements lossy pinch simply. Details of JPEG and other image pinch techniques tin can be found in Miano (1999).
Table. 9.1 illustrates the compression doable by various pinch algorithms, using the image of the rat brain from Fig. nine.ane(a) as an example. The original uncompressed 512 × 512 × 8 chip epitome requires 258 Kbyte of storage space. Compression as a TIFF file, using the lossless LZW algorithm, produces a negligible reduction to 252 kbyte. Amend results are accomplished past saving it in Portable Network Graphics (PNG) format, a relatively new file format with a more efficient lossless algorithm which compresses the file to 172 kbyte (66%). Withal, JPEG pinch produces a file of only 61 kbyte (24%). It must be said, of course, that JPEG (or whatever kind of lossy pinch) should be practical with some caution to images intended for quantitative analysis. The JPEG techniques were designed to achieve a high caste of image compression with the minimum visual deposition, which does not necessarily guarantee that quantitative measurements of the paradigm will be unaffected. That said, no obvious differences could be seen between the JPEG-compressed and original rat brain image. Fifty-fifty the much more strict test of directly subtracting of the two images pixel by pixel revealed only minor variations from a uniform grey surface. Cox (1995) has fabricated like observations.
Table 9.one. Efficiency of standard file formats for compression of a 512 × 512 × 8-bit grey-scale paradigm (Fig. nine.1(a)). Maximum bit depth supported by format is as well shown
| Compressed file size (Kbyte) | Compression method | Lossless | Maximum bit depth | |
|---|---|---|---|---|
| TIFF | 252 | LZW | ✓ | sixteen |
| (97%) | ||||
| PNG | 172 | LZ77 | ✓ | xvi |
| (66%) | ||||
| JPEG | 61 | JPEG | ⨯ | viii |
| (24%) | ||||
| DIB | 257 | RLE | ✓ | 8 |
| (99.5%) |
One problem with the JPEG format is that in its currently well-nigh widely implemented form – baseline JPEG – information technology simply supports 8-bit grey scales. This prevents it from handling the 10–sixteen-bit images produced by the more modern digital cameras and scanners now used in many laboratories. TIFF, which is capable of handling images with chip depths upwardly to sixteen $.25, does not take this problem. An extended JPEG format capable of supporting 12 $.25 does be, only is rarely implemented. However, a number of new lossless, or near-lossless, standards are under evolution – JPEG-LS and office of JPEG-2000 – and may be incorporated into the DICOM standard. These accept the potential to provide a iv:one grey-scale compression similar to that seen here, only be applicable to xvi-bit depth medical and scientific images.
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