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87-405: The scenario described by Welch's 1984 paper encodes sequences of 8-bit data as fixed-length 12-bit codes. The codes from 0 to 255 represent 1-character sequences consisting of the corresponding 8-bit character, and the codes 256 through 4095 are created in a dictionary for sequences encountered in the data as it is encoded. At each stage in compression, input bytes are gathered into a sequence until

174-483: A lossless format makes a TIFF file a useful image archive, because, unlike standard JPEG files, a TIFF file using lossless compression (or none) may be edited and re-saved without losing image quality. This is not the case when using the TIFF as a container holding compressed JPEG. Other TIFF options are layers and pages. TIFF offers the option of using LZW compression, a lossless data-compression technique for reducing

261-469: A lossless compression scheme, or compressed using a lossy compression scheme. The lossless LZW compression scheme has at times been regarded as the standard compression for TIFF, but this is technically a TIFF extension, and the TIFF6 specification notes the patent situation regarding LZW. Compression schemes vary significantly in at what level they process the data: LZW acts on the stream of bytes encoding

348-408: A compression ratio of 10.9, for a data-rate saving of 0.91, or 91%. When the uncompressed data rate is known, the compression ratio can be inferred from the compressed data rate. Lossless compression of digitized data such as video, digitized film, and audio preserves all the information, but it does not generally achieve compression ratio much better than 2:1 because of the intrinsic entropy of

435-497: A consequence, Baseline TIFF features became the lowest common denominator for TIFF. Baseline TIFF features are extended in TIFF Extensions (defined in the TIFF 6.0 Part 2 specification) but extensions can also be defined in private tags. The TIFF Extensions are formally known as TIFF 6.0, Part 2: TIFF Extensions . Here are some examples of TIFF extensions defined in TIFF 6.0 specification: A baseline TIFF file can contain

522-457: A file's size. Use of this option was limited by patents on the LZW technique until their expiration in 2004. The TIFF 6.0 specification consists of the following parts: When TIFF was introduced, its extensibility provoked compatibility problems. The flexibility in encoding gave rise to the joke that TIFF stands for Thousands of Incompatible File Formats . To avoid these problems, every TIFF reader

609-431: A limited time period rather than over infinite time). A high-level view of the decoding algorithm is shown here: The decoding algorithm works by reading a value from the encoded input and outputting the corresponding string from the dictionary. However, the full dictionary is not needed, only the initial dictionary that contains single-character strings (and that is usually hard coded in the program, instead of sent with

696-551: A medium-independent version. TIFF/IT is based on Adobe TIFF 6.0 specification and both extends TIFF 6, by adding additional tags, and restricts, it by limiting some tags and the values within tags. Not all valid TIFF/IT images are valid TIFF 6.0 images. TIFF/IT defines image-file formats for encoding color continuous-tone picture images, color line art images, high-resolution continuous-tone images, monochrome continuous-tone images, binary picture images, binary line-art images, screened data, and images of composite final pages. There

783-576: A number of tiles. All tiles in the same image have the same dimensions and may be compressed independently of the entire image, similar to strips (see above). Tiled images are part of TIFF 6.0, Part 2: TIFF Extensions, so the support for tiled images is not required in Baseline TIFF readers. According to TIFF 6.0 specification (Introduction), all TIFF files using proposed TIFF extensions that are not approved by Adobe as part of Baseline TIFF (typically for specialized uses of TIFF that do not fall within

870-439: A pixel next to each other within a single strip/tile (PlanarConfiguration = 1) but also different samples in different strips/tiles (PlanarConfiguration = 2). The default format for a sample value is as an unsigned integer, but a TIFF extension allows declaring them as alternatively being signed integers or IEEE-754 floats, as well as specify a custom range for valid sample values. TIFF images may be uncompressed, compressed using

957-710: A registered developer's private tags are guaranteed not to clash with anyone else's tags or with the standard set of tags defined in the specification. Private tags are numbered in the range 32,768 and higher. Private tags are reserved for information meaningful only for some organization, or for experiments with a new compression scheme within TIFF. Upon request, the TIFF administrator (currently Adobe) will allocate and register one or more private tags for an organization, to avoid possible conflicts with other organizations. Organizations and developers are discouraged from choosing their own tag numbers arbitrarily, because doing so could cause serious compatibility problems. However, if there

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1044-562: A sequence of images (IFD). Typically, all the images are related but represent different data, such as the pages of a document. In order to explicitly support multiple views of the same data, the SubIFD tag was introduced. This allows the images to be defined along a tree structure . Each image can have a sequence of children, each child being itself an image. The typical usage is to provide thumbnails or several versions of an image in different color spaces. A TIFF image may also be composed of

1131-541: A sequence ω until ω + next character is not in the dictionary. Emit the code for ω, and add ω + next character to the dictionary. Start buffering again with the next character. (The string to be encoded is "TOBEORNOTTOBEORTOBEORNOT#".) Using LZW has saved 29 bits out of 125, reducing the message by more than 23%. If the message were longer, then the dictionary words would begin to represent longer and longer sections of text, sending repeated words very compactly. To decode an LZW-compressed archive, one needs to know in advance

1218-455: A signed 32-bit offset, running into issues around 2 GiB. BigTIFF is a TIFF variant file format which uses 64-bit offsets and supports much larger files (up to 18 exabytes in size). The BigTIFF file format specification was implemented in 2007 in development releases of LibTIFF version 4.0, which was finally released as stable in December 2011. Support for BigTIFF file formats by applications

1305-685: A strip or tile (without regard to sample structure, bit depth, or row width), whereas the JPEG compression scheme both transforms the sample structure of pixels (switching to a different color model) and encodes pixels in 8×8 blocks rather than row by row. Most data in TIFF files are numerical, but the format supports declaring data as rather being textual, if appropriate for a particular tag. Tags that take textual values include Artist, Copyright, DateTime, DocumentName, InkNames, and Model. The MIME type image/tiff (defined in RFC 3302) without an application parameter

1392-514: A telefax they typically would not be equal). A baseline TIFF image divides the vertical range of the image into one or several strips , which are encoded (in particular: compressed) separately. Historically this served to facilitate TIFF readers (such as fax machines) with limited capacity to store uncompressed data — one strip would be decoded and then immediately printed — but the present specification motivates it by "increased editing flexibility and efficient I/O buffering". A TIFF extension provides

1479-404: A two- byte indicator of byte order : " II " for little-endian (a.k.a. "Intel byte ordering", c.  1980 ) or " MM " for big-endian (a.k.a. "Motorola byte ordering", c.  1980 ) byte ordering. The next two-byte word contains the format version number, which has always been 42 for every version of TIFF (e.g., TIFF v5.0 and TIFF v6.0). All two-byte words, double words, etc., in

1566-406: A viable format for scientific image processing where extended precision is required. An example would be the use of TIFF to store images acquired using scientific CCD cameras that provide up to 16 bits per photosite of intensity resolution. Storing a sequence of images in a single TIFF file is also possible, and is allowed under TIFF 6.0, provided the rules for multi-page images are followed. TIFF

1653-466: Is a flexible, adaptable file format for handling images and data within a single file, by including the header tags (size, definition, image-data arrangement, applied image compression ) defining the image's geometry. A TIFF file, for example, can be a container holding JPEG (lossy) and PackBits (lossless) compressed images. A TIFF file also can include a vector -based clipping path (outlines, croppings, image frames). The ability to store image data in

1740-512: Is a popular format for deep-color images. The first version of the TIFF specification was published by the Aldus Corporation in the autumn of 1986 after two major earlier draft releases. It can be labeled as Revision 3.0. It was published after a series of meetings with various scanner manufacturers and software developers. In April 1987 Revision 4.0 was released and it contained mostly minor enhancements. In October 1988 Revision 5.0

1827-438: Is defined as the ratio between the uncompressed size and compressed size : Thus, a representation that compresses a file's storage size from 10 MB to 2 MB has a compression ratio of 10/2 = 5, often notated as an explicit ratio, 5:1 (read "five" to "one"), or as an implicit ratio, 5/1. This formulation applies equally for compression, where the uncompressed size is that of the original; and for decompression, where

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1914-404: Is initialized with these 27 values. As the dictionary grows, the codes must grow in width to accommodate the additional entries. A 5-bit code gives 2 = 32 possible combinations of bits, so when the 33rd dictionary word is created, the algorithm must switch at that point from 5-bit strings to 6-bit strings (for all code values, including those previously output with only five bits). Note that since

2001-603: Is limited. The Exif specification builds upon TIFF. For uncompressed image data, an Exif file is straight off a TIFF file with some private tags. For JPEG compressed image data, Exif uses the JPEG File Interchange Format but embeds a TIFF file in the APP1 segment of the file. The first IFD (termed 0th in the Exif specification) of that embedded TIFF does not contain image data, and only houses metadata for

2088-695: Is little or no chance that TIFF files will escape a private environment, organizations and developers are encouraged to consider using TIFF tags in the "reusable" 65,000–65,535 range. There is no need to contact Adobe when using numbers in this range. The TIFF Tag 259 (0103 16 ) stores the information about the Compression method. The default value is 1 = no compression. Most TIFF writers and TIFF readers support only some TIFF compression schemes. Here are some examples of used TIFF compression schemes: The TIFF file formats use 32-bit offsets , which limits file size to around 4 GiB . Some implementations even use

2175-415: Is made up of one or several samples ; for example an RGB image would have one Red sample, one Green sample, and one Blue sample per pixel, whereas a greyscale or palette color image only has one sample per pixel. TIFF allows for both additive (e.g. RGB, RGBA ) and subtractive (e.g. CMYK ) color models. TIFF does not constrain the number of samples per pixel (except that there must be enough samples for

2262-441: Is needed to get 1080i video into a 20 Mbit/s MPEG transport stream . The data compression ratio can serve as a measure of the complexity of a data set or signal. In particular it is used to approximate the algorithmic complexity . It is also used to see how much of a file is able to be compressed without increasing its original size. TIFF Tag Image File Format or Tagged Image File Format , commonly known by

2349-639: Is no MIME type defined for TIFF/IT. The MIME type image/tiff should not be used for TIFF/IT files, because TIFF/IT does not conform to Baseline TIFF 6.0 and the widely deployed TIFF 6.0 readers cannot read TIFF/IT. The MIME type image/tiff (defined in RFC 3302) without an application parameter is used for Baseline TIFF 6.0 files or to indicate that it is not necessary to identify a specific subset of TIFF or TIFF extensions. The application parameter should be used with image/tiff to distinguish TIFF extensions or TIFF subsets. According to RFC 3302, specific TIFF subsets or TIFF extensions must be published as an RFC. There

2436-522: Is no such RFC for TIFF/IT. There is also no plan by the ISO committee that oversees TIFF/IT standard to register TIFF/IT with either a parameter to image/tiff or as new separate MIME type. TIFF/IT consists of a number of different files and it cannot be created or opened by common desktop applications. TIFF/IT-P1 file sets usually consist of the following files: TIFF/IT also defines the following files: Some of these data types are partly compatible with

2523-474: Is not in the dictionary. When such a string is found, the index for the string without the last character (i.e., the longest substring that is in the dictionary) is retrieved from the dictionary and sent to output, and the new string (including the last character) is added to the dictionary with the next available code. The last input character is then used as the next starting point to scan for substrings. In this way, successively longer strings are registered in

2610-404: Is the same as the first character of the current string), and updates the dictionary with the new string. The decoder then proceeds to the next input (which was already read in the previous iteration) and processes it as before, and so on until it has exhausted the input stream. If variable-width codes are being used, the encoder and decoder must be careful to change the width at the same points in

2697-402: Is to encode a multipage telefax in a single file, but it is also allowed to have different subfiles be different variants of the same image, for example scanned at different resolutions. Rather than being a continuous range of bytes in the file, each subfile is a data structure whose top-level entity is called an image file directory (IFD). Baseline TIFF readers are only required to make use of

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2784-425: Is used for Baseline TIFF 6.0 files or to indicate that it is not necessary to identify a specific subset of TIFF or TIFF extensions. The optional "application" parameter (Example: Content-type: image/tiff; application=foo) is defined for image/tiff to identify a particular subset of TIFF and TIFF extensions for the encoded image data, if it is known. According to RFC 3302, specific TIFF subsets or TIFF extensions used in

2871-546: Is used to represent a stop code: a code outside the plaintext alphabet that triggers special handling. We arbitrarily assign these the values 1 through 26 for the letters, and 0 for the stop code '#'. (Most flavors of LZW would put the stop code after the data alphabet, but nothing in the basic algorithm requires that. The encoder and decoder only have to agree what value it has.) A computer renders these as strings of bits . Five-bit codes are needed to give sufficient combinations to encompass this set of 27 values. The dictionary

2958-624: The United States and other countries for LZW and similar algorithms. LZ78 was covered by U.S. patent 4,464,650 by Lempel, Ziv, Cohn, and Eastman, assigned to Sperry Corporation , later Unisys Corporation, filed on August 10, 1981. Two US patents were issued for the LZW algorithm: U.S. patent 4,814,746 by Victor S. Miller and Mark N. Wegman and assigned to IBM , originally filed on June 1, 1983, and U.S. patent 4,558,302 by Welch, assigned to Sperry Corporation, later Unisys Corporation, filed on June 20, 1983. In addition to

3045-429: The 1980s, many images had small color tables (on the order of 16 colors). For such a reduced alphabet, the full 12-bit codes yielded poor compression unless the image was large, so the idea of a variable-width code was introduced: codes typically start one bit wider than the symbols being encoded, and as each code size is used up, the code width increases by 1 bit, up to some prescribed maximum (typically 12 bits). When

3132-841: The LZ77-based DEFLATE algorithm, but as of 2008 at least FreeBSD includes both compress and uncompress as a part of the distribution. Several other popular compression utilities also used LZW or closely related methods. LZW became very widely used when it became part of the GIF image format in 1987. It may also (optionally) be used in TIFF and PDF files. (Although LZW is available in Adobe Acrobat software, Acrobat by default uses DEFLATE for most text and color-table-based image data in PDF files.) Various patents have been issued in

3219-517: The TIFF file are assumed to be in the indicated byte order. The TIFF 6.0 specification states that compliant TIFF readers must support both byte orders ( II and MM ); writers may use either. TIFF readers must be prepared to encounter and ignore private fields not described in the TIFF specification. TIFF readers must not refuse to read a TIFF file if optional fields do not exist. Many TIFF readers support tags additional to those in Baseline TIFF, but not every reader supports every extension. As

3306-521: The TIFF specification (June 1992) by introducing a distinction between Baseline TIFF (which all implementations were required to support) and TIFF Extensions (which are optional). Additional extensions are defined in two supplements to the specification which were published in September 1995 and March 2002 respectively. A TIFF file contains one or several images, termed subfiles in the specification. The basic use case for having multiple subfiles

3393-510: The United Kingdom, France, Germany, Italy, Japan and Canada all expired in 2004, likewise 20 years after they had been filed. Data compression ratio Data compression ratio , also known as compression power , is a measurement of the relative reduction in size of data representation produced by a data compression algorithm. It is typically expressed as the division of uncompressed size by compressed size. Data compression ratio

3480-443: The abbreviations TIFF or TIF , is an image file format for storing raster graphics images, popular among graphic artists, the publishing industry, and photographers. TIFF is widely supported by scanning , faxing , word processing , optical character recognition , image manipulation, desktop publishing , and page-layout applications. The format was created by the Aldus Corporation for use in desktop publishing. It published

3567-650: The above patents, Welch's 1983 patent also includes citations to several other patents that influenced it, including two 1980 Japanese patents ( JP9343880A and JP17790880A ) from NEC 's Jun Kanatsu, U.S. patent 4,021,782 (1974) from John S. Hoerning, U.S. patent 4,366,551 (1977) from Klaus E. Holtz, and a 1981 German patent ( DE19813118676 ) from Karl Eckhart Heinz. In 1993–94, and again in 1999, Unisys Corporation received widespread condemnation when it attempted to enforce licensing fees for LZW in GIF images. The 1993–1994 Unisys-CompuServe controversy ( CompuServe being

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3654-439: The all-zero code 00000 is used, and is labeled "0", the 33rd dictionary entry is labeled 32 . (Previously generated output is not affected by the code-width change, but once a 6-bit value is generated in the dictionary, it could conceivably be the next code emitted, so the width for subsequent output shifts to 6 bits to accommodate that.) The initial dictionary, then, consists of the following entries: Buffer input characters in

3741-410: The alternative of tiled images, in which case both the horizontal and the vertical ranges of the image are decomposed into smaller units. An example of these things, which also serves to give a flavor of how tags are used in the TIFF encoding of images, is that a striped TIFF image would use tags 273 (StripOffsets), 278 (RowsPerStrip), and 279 (StripByteCounts). The StripOffsets point to

3828-509: The application parameter must be published as an RFC. MIME type image/tiff-fx (defined in RFC 3949 and RFC 3950) is based on TIFF 6.0 with TIFF Technical Notes TTN1 (Trees) and TTN2 (Replacement TIFF/JPEG specification). It is used for Internet fax compatible with the ITU-T Recommendations for Group 3 black-and-white, grayscale and color fax . Adobe holds the copyright on the TIFF specification (aka TIFF 6.0) along with

3915-644: The blocks of image data, the StripByteCounts say how long each of these blocks are (as stored in the file), and RowsPerStrip says how many rows of pixels there are in a strip; the latter is required even in the case of having just one strip, in which case it merely duplicates the value of tag 257 (ImageLength). A tiled TIFF image instead uses tags 322 (TileWidth), 323 (TileLength), 324 (TileOffsets), and 325 (TileByteCounts). The pixels within each strip or tile appear in row-major order, left to right and top to bottom. The data for one pixel

4002-454: The chosen color model), nor does it constrain how many bits are encoded for each sample, but baseline TIFF only requires that readers support a few combinations of color model and bit-depth of images. Support for custom sets of samples is very useful for scientific applications; 3 samples per pixel is at the low end of multispectral imaging , and hyperspectral imaging may require hundreds of samples per pixel. TIFF supports having all samples for

4089-411: The clear code. Since the codes emitted typically do not fall on byte boundaries, the encoder and decoder must agree on how codes are packed into bytes. The two common methods are LSB-first (" least significant bit first") and MSB-first (" most significant bit first"). In LSB-first packing, the first code is aligned so that the least significant bit of the code falls in the least significant bit of

4176-412: The code for ω at width p (since that code does not require p  + 1 bits), and then increases the code width so that the next code emitted is p  + 1 bits wide. The decoder is always one code behind the encoder in building the table, so when it sees the code for ω, it generates an entry for code 2 − 1. Since this is the point where the encoder increases the code width,

4263-523: The compression ratio is defined in terms of uncompressed and compressed data rates instead of data sizes: and instead of space saving, one speaks of data-rate saving , which is defined as the data-rate reduction relative to the uncompressed data rate: For example, uncompressed songs in CD format have a data rate of 16 bits/channel x 2 channels x 44.1 kHz ≅ 1.4 Mbit/s, whereas AAC files on an iPod are typically compressed to 128 kbit/s, yielding

4350-651: The content and document management industry associated with the use of TIFF files arise when the structures contain proprietary headers, are not properly documented, or contain "wrappers" or other containers around the TIFF datasets, or include improper compression technologies, or those compression technologies are not properly implemented. Variants of TIFF can be used within document imaging and content/document management systems using CCITT Group IV 2D compression which supports black-and-white (bitonal, monochrome ) images, among other compression technologies that support color . When storage capacity and network bandwidth

4437-467: The corresponding definitions in the TIFF 6.0 specification. The Final Page (FP) allows the various files needed to define a complete page to be grouped together: it provides a mechanism for creating a package that includes separate image layers (of types CT, LW, etc.) to be combined to create the final printed image. Its use is recommended but not required. There must be at least one subfile in an FP file, but no more than one of each type. It typically contains

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4524-419: The creator of the GIF format) prompted a Usenet comp.graphics discussion Thoughts on a GIF-replacement file format , which in turn fostered an email exchange that eventually culminated in the creation of the patent-unencumbered Portable Network Graphics (PNG) file format in 1995. Unisys's US patent on the LZW algorithm expired on June 20, 2003, 20 years after it had been filed. Patents that had been filed in

4611-416: The data, the decoder mimics building the table as it sees the resulting codes. It is critical that the encoder and decoder agree on the variety of LZW used: the size of the alphabet, the maximum table size (and code width), whether variable-width encoding is used, initial code size, and whether to use the clear and stop codes (and what values they have). Most formats that employ LZW build this information into

4698-514: The data. Compression algorithms which provide higher ratios either incur very large overheads or work only for specific data sequences (e.g. compressing a file with mostly zeros). In contrast, lossy compression (e.g. JPEG for images, or MP3 and Opus for audio) can achieve much higher compression ratios at the cost of a decrease in quality, such as Bluetooth audio streaming, as visual or audio compression artifacts from loss of important information are introduced. A compression ratio of at least 50:1

4785-429: The data. This example has been constructed to give reasonable compression on a very short message. In real text data, repetition is generally less pronounced, so longer input streams are typically necessary before the compression builds up efficiency. The plaintext to be encoded (from an alphabet using only the capital letters) is: There are 26 symbols in the plaintext alphabet (the capital letters A through Z ). #

4872-493: The decoder must increase the width here as well—at the point where it generates the largest code that fits in p bits. Unfortunately, some early implementations of the encoding algorithm increase the code width and then emit ω at the new width instead of the old width, so that to the decoder it looks like the width changes one code too early. This is called "early change"; it caused so much confusion that Adobe now allows both versions in PDF files, but includes an explicit flag in

4959-416: The decoder receives a code Z that is not yet in its dictionary? Since the decoder is always just one code behind the encoder, Z can be in the encoder's dictionary only if the encoder just generated it, when emitting the previous code X for χ. Thus Z codes some ω that is χ + ?, and the decoder can determine the unknown character as follows: This situation occurs whenever the encoder encounters input of

5046-414: The dictionary and available for subsequent encoding as single output values. The algorithm works best on data with repeated patterns, so the initial parts of a message see little compression. As the message grows, however, the compression ratio tends asymptotically to the maximum (i.e., the compression factor or ratio improves on an increasing curve, and not linearly, approaching a theoretical maximum inside

5133-450: The domain of publishing or general graphics or picture interchange) should be either not called TIFF files or should be marked some way so that they will not be confused with mainstream TIFF files. Developers can apply for a block of "private tags" to enable them to include their own proprietary information inside a TIFF file without causing problems for file interchange. TIFF readers are required to ignore tags that they do not recognize, and

5220-408: The encoded data so they don't disagree on boundaries between individual codes in the stream. In the standard version, the encoder increases the width from p to p  + 1 when a sequence ω +  s is encountered that is not in the table (so that a code must be added for it) but the next available code in the table is 2 (the first code requiring p  + 1 bits). The encoder emits

5307-448: The encoded data). Instead, the full dictionary is rebuilt during the decoding process the following way: after decoding a value and outputting a string, the decoder concatenates it with the first character of the next decoded string (or the first character of current string, if the next one can't be decoded; since if the next value is unknown, then it must be the value added to the dictionary in this iteration, and so its first character

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5394-448: The encoder goes ahead and adds it. But what is the missing letter? It is the first letter in the sequence coded by the next code Z that the decoder receives. So the decoder looks up Z, decodes it into the sequence ω and takes the first letter z and tacks it onto the end of χ as the next dictionary entry. This works as long as the codes received are in the decoder's dictionary, so that they can be decoded into sequences. What happens if

5481-399: The end of data (a "stop code", typically one greater than the clear code). The clear code lets the table be reinitialized after it fills up, which lets the encoding adapt to changing patterns in the input data. Smart encoders can monitor the compression efficiency and clear the table whenever the existing table no longer matches the input well. Since codes are added in a manner determined by

5568-462: The entire image, and each begins on a byte boundary. If the image height is not evenly divisible by the number of rows in the strip, the last strip may contain fewer rows. If strip definition tags are omitted, the image is assumed to contain a single strip. Baseline TIFF readers must handle the following three compression schemes: Baseline TIFF image types are: bilevel, grayscale, palette-color, and RGB full-color images. Every TIFF file begins with

5655-468: The first one. There may be more than one Image File Directory (IFD) in a TIFF file. Each IFD defines a subfile. One use of subfiles is to describe related images, such as the pages of a facsimile document. A Baseline TIFF reader is not required to read any IFD beyond the first one. A baseline TIFF image is composed of one or more strips. A strip (or band) is a subsection of the image composed of one or more rows. Each strip may be compressed independently of

5742-452: The first stream byte, and if the code has more than 8 bits, the high-order bits left over are aligned with the least significant bits of the next byte; further codes are packed with LSB going into the least significant bit not yet used in the current stream byte, proceeding into further bytes as necessary. MSB-first packing aligns the first code so that its most significant bit falls in the MSB of

5829-448: The first stream byte, with overflow aligned with the MSB of the next byte; further codes are written with MSB going into the most significant bit not yet used in the current stream byte. GIF files use LSB-first packing order. TIFF files and PDF files use MSB-first packing order. The following example illustrates the LZW algorithm in action, showing the status of the output and the dictionary at every stage, both in encoding and decoding

5916-475: The first subfile, but each IFD has a field for linking to a next IFD. The IFDs are where the tags for which TIFF is named are located. Each IFD contains one or several entries , each of which is identified by its tag. The tags are arbitrary 16-bit numbers; their symbolic names such as ImageWidth often used in discussions of TIFF data do not appear explicitly in the file itself. Each IFD entry has an associated value , which may be decoded based on general rules of

6003-499: The first widely used universal data compression method on computers. A large English text file can typically be compressed via LZW to about half its original size. LZW was used in the public-domain program compress , which became a more or less standard utility in Unix systems around 1986. It has since disappeared from many distributions, both because it infringed the LZW patent and because gzip produced better compression ratios using

6090-414: The form cScSc , where c is a single character, S is a string and cS is already in the dictionary, but cSc is not. The encoder emits the code for cS , putting a new code for cSc into the dictionary. Next it sees cSc in the input (starting at the second c of cScSc ) and emits the new code it just inserted. The argument above shows that whenever the decoder receives a code not in its dictionary,

6177-470: The format specification or provide explicit fields for them in a compression header for the data. A high-level view of the encoding algorithm is shown here: A dictionary is initialized to contain the single-character strings corresponding to all the possible input characters (and nothing else except the clear and stop codes if they're being used). The algorithm works by scanning through the input string for successively longer substrings until it finds one that

6264-538: The format, but it depends on the tag what that value then means . There may within a single IFD be no more than one entry with any particular tag. Some tags are for linking to the actual image data, other tags specify how the image data should be interpreted, and still other tags are used for image metadata . TIFF images are made up of rectangular grids of pixels. The two axes of this geometry are termed horizontal (or X, or width) and vertical (or Y, or length). Horizontal and vertical resolution need not be equal (since in

6351-411: The header of each LZW-compressed stream to indicate whether early change is being used. Of the graphics file formats that support LZW compression, TIFF uses early change, while GIF and most others don't. When the table is cleared in response to a clear code, both encoder and decoder change the code width after the clear code back to the initial code width, starting with the code immediately following

6438-409: The initial dictionary used, but additional entries can be reconstructed as they are always simply concatenations of previous entries. At each stage, the decoder receives a code X; it looks X up in the table and outputs the sequence χ it codes, and it conjectures χ + ? as the entry the encoder just added – because the encoder emitted X for χ precisely because χ + ? was not in the table, and

6525-450: The latest version 6.0 in 1992, subsequently updated with an Adobe Systems copyright after the latter acquired Aldus in 1994. Several Aldus or Adobe technical notes have been published with minor extensions to the format, and several specifications have been based on TIFF 6.0, including TIFF/EP (ISO 12234-2), TIFF/IT (ISO 12639), TIFF-F (RFC 2306) and TIFF-FX (RFC 3949). TIFF was created as an attempt to get desktop scanner vendors of

6612-457: The main IFD. TIFF/IT is used to send data for print-ready pages that have been designed on high-end prepress systems. The TIFF/IT specification (ISO 12639) describes a multiple-file format, which can describe a single page per file set. TIFF/IT files are not interchangeable with common TIFF files. The goals in developing TIFF/IT were to carry forward the original IT8 magnetic-tape formats into

6699-404: The maximum code value is reached, encoding proceeds using the existing table, but new codes are not generated for addition to the table. Further refinements include reserving a code to indicate that the code table should be cleared and restored to its initial state (a "clear code", typically the first value immediately after the values for the individual alphabet characters), and a code to indicate

6786-465: The mid-1980s to agree on a common scanned image file format, in place of a multitude of proprietary formats . In the beginning, TIFF was only a binary image format (only two possible values for each pixel), because that was all that desktop scanners could handle. As scanners became more powerful, and as desktop computer disk space became more plentiful, TIFF grew to accommodate grayscale images, then color images. Today, TIFF, along with JPEG and PNG ,

6873-409: The next character would make a sequence with no code yet in the dictionary. The code for the sequence (without that character) is added to the output, and a new code (for the sequence with that character) is added to the dictionary. The idea was quickly adapted to other situations. In an image based on a color table, for example, the natural character alphabet is the set of color table indexes, and in

6960-470: The primary image. There may however be a thumbnail image in that embedded TIFF, which is provided by the second IFD (termed 1st in the Exif specification). The Exif audio file format does not build upon TIFF. Exif defines a large number of private tags for image metadata, particularly camera settings and geopositioning data, but most of those do not appear in the ordinary TIFF IFDs. Instead these reside in separate IFDs which are pointed at by private tags in

7047-597: The sequence of output symbols. Some package the coded stream as printable characters using some form of binary-to-text encoding ; this increases the encoded length and decreases the compression rate. Conversely, increased compression can often be achieved with an adaptive entropy encoder . Such a coder estimates the probability distribution for the value of the next symbol, based on the observed frequencies of values so far. A standard entropy encoding such as Huffman coding or arithmetic coding then uses shorter codes for values with higher probabilities. LZW compression became

7134-466: The situation must look like this. Although input of form cScSc might seem unlikely, this pattern is fairly common when the input stream is characterized by significant repetition. In particular, long strings of a single character (which are common in the kinds of images LZW is often used to encode) repeatedly generate patterns of this sort. The simple scheme described above focuses on the LZW algorithm itself. Many applications apply further encoding to

7221-580: The two supplements that have been published. These documents can be found on the Adobe TIFF Resources page. The Fax standard in RFC 3949 is based on these TIFF specifications. TIFF files that strictly use the basic "tag sets" as defined in TIFF 6.0 along with restricting the compression technology to the methods identified in TIFF 6.0 and are adequately tested and verified by multiple sources for all documents being created can be used for storing documents. Commonly seen issues encountered in

7308-423: The uncompressed size is that of the reproduction. Sometimes the space saving is given instead, which is defined as the reduction in size relative to the uncompressed size: Thus, a representation that compresses the storage size of a file from 10 MB to 2 MB yields a space saving of 1 - 2/10 = 0.8, often notated as a percentage, 80%. For signals of indefinite size, such as streaming audio and video,

7395-480: Was a greater issue than commonly seen in today's server environments, high-volume storage scanning, documents were scanned in black and white (not in color or in grayscale) to conserve storage capacity. The inclusion of the SampleFormat tag in TIFF 6.0 allows TIFF files to handle advanced pixel data types, including integer images with more than 8 bits per channel and floating point images. This tag made TIFF 6.0

7482-407: Was released and it added support for palette color images and LZW compression . TIFF is a complex format, defining many tags of which typically only a few are used in each file. This led to implementations supporting many varying subsets of the format, a situation that gave rise to the joke that TIFF stands for Thousands of Incompatible File Formats . This problem was addressed in revision 6.0 of

7569-437: Was required to read Baseline TIFF . Among other things, Baseline TIFF does not include layers, or compressed JPEG or LZW images. Baseline TIFF is formally known as TIFF 6.0, Part 1: Baseline TIFF . The following is an incomplete list of required Baseline TIFF features: TIFF readers must be prepared for multiple/multi-page images (subfiles) per TIFF file, although they are not required to actually do anything with images after

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