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Pascal/Delphi Source File | 1996-09-04 | 24.2 KB | 633 lines

--------I-TIFF------------------------------ The TIFF file format was designed jointly by Aldus and Microsoft with leading scanner vendors to faciliate incorporating scanned images into publishing. The described TIFF specification is TIFF 5.0. A TIFF file consists of several different blocks which define the palette data or the LZW-compressed body among other things. TIFF files can be in Motorola _or_ Intel byte order, depending on the first word. If it is 'II', the byte order is in Intel order, if it is 'MM', then you have Motorola byte ordering. Each TIFF file begins with a image file header which points to one or more image file directories, which contain the image data and image information. The format of the image header : OFFSET Count TYPE Description 0000h 2 char ID='II', ID='MM' This is the identification, 'II' stands for Intel byte order, 'MM' for Motorola byte order. The following data must be interpreted accordingly ! 0002h 1 word TIFF "version number". This version number never changed and the value (42) was choosen for its deep philosophical value. In fact, if the version number ever changes, this means that radical changes to the TIFF format have been made, and a TIFF reader should give up immediately. You can consider this word to be a part of the header ID. 0004h 1 dword Offset of first image directory in file form start of file. The first image directory must begin on an even byte boundary. The image directory may follow the image data it describes. The image directory is described below. An organization may wish to store information that is meaningful to only that organization in a TIFF file. Tags numbered 32768 or higher are reserved for that purpose. Upon request, the administrator will allocate and register a block of private tags for an organization. Private enumerated values can be accommodated in a similar fashion. The format of the image file directory (IFD) : All entries are sorted in ascending order by the tag field. OFFSET Count TYPE Description 0000h 1 word Number of entries ="NUM" 0002h "NUM" rec Field descriptor 1 word Field tag, see below 1 word Field type 1 - byte 2 - ASCII string, counted in length. Most often an ASCIIZ string, the trailing zero is counted with the data length. 3 - word 4 - dword / uword 5 - rational (2 dwords, numerator and denominator) 1 dword Length of the field in units of the data type. A single 16-bit word has the length 1. 1 dword Data offset of the field. The data starts on a word boundary, thus the dword should be even. The data for the field may be anywhere in the file, even after the image data. If the data size is less or equal to 4 bytes (determined by the field type and length), then this offset is not a offset but instead the data itself, to save space. If the data size is less than 4 bytes, the data is stored left-justified within the 4 bytes of the offset field. 0002h+ "NUM"*12 1 dword Offset of next IFD in file, 0 if none follow If a certain field in the IFD does not exist, you have to presume the default values. The different fields are : --- BitsPerSample Tag = 258 (102) Type = word N = SamplesPerPixel Default = 1 Number of bits per sample. Note that this tag allows a different number of bits per sample for each sample corresponding to a pixel. For example, RGB color data could use a different number of bits per sample for each of the three color planes. --- ColorMap Tag = 320 (140) Type = word N = 3 * (2**BitsPerSample) No default.ColorMap must be included in all palette color images. This tag defines a Red-Green-Blue color map for palette color images. The palette color pixel value is used to index into all 3 subcurves. The subcurves are stored sequentially. The Red entries come first, followed by the Green entries, followed by the Blue entries. The width of each entry is 16 bits, as implied by the type of word. 0 represents the minimum intensity, and 65535 represents the maximum intensity. --- ColorResponseCurves Tag = 301 (12D) Type = word N = 3 * (2**BitsPerSample) Default: curves based on the NTSC recommended gamma of 2.2. This tag defines three color response curves, one each for Red, Green and Blue color information. The Red entries come first, followed by the Green entries, followed by the Blue entries. The length of each subcurve is 2**BitsPerSample, using the BitsPerSample value corresponding to the respective primary. The width of each entry is 16 bits, as implied by the type of word. The purpose of the color response curves is to refine the content of RGB color images. --- Compression Tag = 259 (103) Type = word N = 1 Default = 1. 1 = No compression, but pack data into bytes as tightly as possible, with no unused bits except at the end of a row. The bytes are stored as an array of bytes, for BitsPerSample <= 8, word if BitsPerSample > 8 and <= 16, and dword if BitsPerSample > 16 and <= 32. The byte ordering of data >8 bits must be consistent with that specified in the TIFF file header (bytes 0 and 1). Rows are required to begin on byte boundaries. 2 = CCITT Group 3 1-Dimensional Modified Huffman run length encoding. See ALGRTHMS.txt BitsPerSample must be 1, since this type of compression is defined only for bilevel images (like FAX images...) 3 = Facsimile-compatible CCITT Group 3, exactly as specified in "Standardization of Group 3 facsimile apparatus for document transmission," Recommendation T.4, Volume VII, Fascicle VII.3, Terminal Equipment and Protocols for Telematic Services, The International Telegraph and Telephone Consultative Committee (CCITT), Geneva, 1985, pages 16 through 31. Each strip must begin on a byte boundary. (But recall that an image can be a single strip.) Rows that are not the first row of a strip are not required to begin on a byte boundary. The data is stored as bytes, not words - byte-reversal is not allowed. See the Group3Options field for Group 3 options such as 1D vs 2D coding. 4 = Facsimile-compatible CCITT Group 4, exactly as specified in "Facsimile Coding Schemes and Coding Control Functions for Group 4 Facsimile Apparatus," Recommendation T.6, Volume VII, Fascicle VII.3, Terminal Equipment and Protocols for Telematic Services, The International Telegraph and Telephone Consultative Committee (CCITT), Geneva, 1985, pages 40 through 48. Each strip must begin on a byte boundary. Rows that are not the first row of a strip are not required to begin on a byte boundary. The data is stored as bytes, not words. See the Group4Options field for Group 4 options. 5 = LZW Compression, for grayscale, mapped color, and full color images. See ALGRTHMS.txt 32773 = PackBits compression, a simple byte oriented run length scheme for 1-bit images. See Appendix C. Data compression only applies to raster image data, as pointed to by StripOffsets. --- GrayResponseCurve Tag = 291 (123) Type = word N = 2**BitsPerSample The purpose of the gray response curve and the gray units is to provide more exact photometric interpretation information for gray scale image data, in terms of optical density. --- GrayResponseUnit Tag = 290 (122) Type = word N = 1 For historical reasons, the default is 2. However, for greater accuracy, 3 is recommended. 1 = Number represents tenths of a unit. 2 = Number represents hundredths of a unit. 3 = Number represents thousandths of a unit. 4 = Number represents ten-thousandths of a unit. 5 = Number represents hundred-thousandths of a unit. --- ImageLength Tag = 257 (101) Type = word or dword N = 1 No default. The image's length (height) in pixels (Y:vertical). The number of rows (sometimes described as "scan lines") in the image. --- ImageWidth Tag = 256 (100) Type = word or dword N = 1 No default. The image's width, in pixels (X:horizontal). The number of columns in the image. --- NewSubfileType Tag = 254 (FE) Type = dword N = 1 Default is 0. A general indication of the kind of data that is contained in this subfile. This field is made up of a set of 32 flag bits. Unused bits are expected to be 0. Bit 0 is the low-order bit. Currently defined values for the bitmap are: 0 - Image is reduced of another TIFF image in this file 1 - Image is a single page of a multi-page 2 - Image is a transparency mask for another image in this file --- PhotometricInterpretation Tag = 262 (106) Type = word N = 1 No default. 0 = For bilevel and grayscale images: 0 is imaged as white. 2**BitsPerSample-1 is imaged as black. If GrayResponseCurve exists, it overrides the PhotometricInterpretation value. 1 = For bilevel and grayscale images: 0 is imaged as black. 2**BitsPerSample-1 is imaged as white. If GrayResponseCurve exists, it overrides the PhotometricInterpretation value. 2 = RGB. In the RGB model, a color is described as a combination of the three primary colors of light (red, green, and blue) in particular concentrations. For each of the three samples, 0 represents minimum intensity, and 2**BitsPerSample - 1 represents maximum intensity. For PlanarConfiguration = 1, the samples are stored in the indicated order: first Red, then Green, then Blue. For PlanarConfiguration = 2, the StripOffsets for the sample planes are stored in the indicated order: first the Red sample plane StripOffsets, then the Green plane StripOffsets, then the Blue plane StripOffsets. 3 = "Palette color." In this mode, a color is described with a single sample. The sample is used as an index into ColorMap. The sample is used to index into each of the red, green and blue curve tables to retrieve an RGB triplet defining an actual color. When this PhotometricInterpretation value is used, the color response curves must also be supplied. SamplesPerPixel must be 1. 4 = Transparency Mask. This means that the image is used to define an irregularly shaped region of another image in the same TIFF file. SamplesPerPixel and BitsPerSample must be 1. PackBits compression is recommended. The 1-bits define the interior of the region; the 0-bits define the exterior of the region. The Transparency Mask must have the same ImageLength and ImageWidth as the main image. PlanarConfiguration Tag = 284 (11C) Type = word N = 1 Default is 1. 1 = The sample values for each pixel are stored contiguously, so that there is a single image plane. See PhotometricInterpretation to determine the order of the samples within the pixel data. So, for RGB data, the data is stored RGBRGBRGB...and so on. 2 = The samples are stored in separate "sample planes." The values in StripOffsets and StripByteCounts are then arranged as a 2-dimensional array, with SamplesPerPixel rows and StripsPerImage columns. (All of the columns for row 0 are stored first, followed by the columns of row 1, and so on.) PhotometricInterpretation describes the type of data that is stored in each sample plane. For example, RGB data is stored with the Red samples in one sample plane, the Green in another, and the Blue in another. If SamplesPerPixel is 1, PlanarConfiguration is irrelevant, and should not be included. Predictor Tag = 317 (13D) Type = word N = 1 Default is 1. To be used when Compression=5 (LZW). 1 = No prediction scheme used before coding. 2 = Horizontal differencing. See Appendix I. ResolutionUnit Tag = 296 (128) Type = word N = 1 Default is 2. To be used with XResolution and YResolution. 1 = No absolute unit of measurement. Used for images that may have a non-square aspect ratio, but no meaningful absolute dimensions. The drawback of ResolutionUnit=1 is that different applications will import the image at different sizes. Even if the decision is quite arbitrary, it might be better to use dots per inch or dots per centimeter, and pick XResolution and YResolution such that the aspect ratio is correct and the maximum dimension of the image is about four inches (the "four" is quite arbitrary.) 2 = Inch. 3 = Centimeter. RowsPerStrip Tag = 278 (116) Type = word or dword N = 1 Default is 2**32 - 1, which is effectively infinity. That is, the entire image is one strip. Recomended is a strip size of 8K. The number of rows per strip. The image data is organized into strips for fast access to individual rows when the data is compressed - though this field is valid even if the data is not compressed. --- SamplesPerPixel Tag = 277 (115) Type = word N = 1 Default = 1. The number of samples per pixel. SamplesPerPixel is 1 for bilevel, grayscale, and palette color images. SamplesPerPixel is 3 for RGB images. --- StripByteCounts Tag = 279 (117) Type = word or dword N = StripsPerImage for PlanarConfiguration equal to 1. = SamplesPerPixel * StripsPerImage for PlanarConfiguration equal to 2 No default. For each strip, the number of bytes in that strip. The existence of this field greatly simplifies the chore of buffering compressed data, if the strip size is reasonable. --- StripOffsets Tag = 273 (111) Type = word or dword N = StripsPerImage for PlanarConfiguration equal to 1. = SamplesPerPixel * StripsPerImage for PlanarConfiguration equal to 2 No default. For each strip, the byte offset of that strip. The offset is specified with respect to the beginning of the TIFF file. Note that this implies that each strip has a location independent of the locations of other strips. This feature may be useful for editing applications. This field is the only way for a reader to find the image data, and hence must exist. --- XResolution Tag = 282 (11A) Type = RATIONAL N = 1 No default. The number of pixels per ResolutionUnit in the X direction, i.e., in the ImageWidth direction. --- YResolution Tag = 283 (11B) Type = RATIONAL N = 1 No default. The number of pixels per ResolutionUnit in the Y direction, i.e., in the ImageLength direction. --- Artist Tag = 315 (13B) Type = ASCII Person who created the image. Copyright notice. --- DateTime Tag = 306 (132) Type = ASCII N = 20 Date and time of image creation. Uses the format "YYYY:MM:DD HH:MM:SS", with hours on a 24-hour clock, and one space character between the date and the time. The length of the string, including the null, is 20 bytes. --- HostComputer Tag = 316 (13C) Type = ASCII "ENIAC", or whatever. --- ImageDescription Tag = 270 (10E) Type = ASCII For example, a user may wish to attach a comment such as "1988 company picnic" to an image. --- Make Tag = 271 (10F) Type = ASCII Manufacturer of the scanner, video digitizer, or whatever. --- Model Tag = 272 (110) Type = ASCII The model name/number of the scanner, video digitizer, or whatever. This tag is intended for user information only so format is arbitrary. --- Software Tag = 305 (131) Type = ASCII Name and release number of the software package that created the image. User information only. --- Group3Options Tag = 292 (124) Type = dword N = 1 Those options are for fax-images stored in TIFF format. This field is made up of a set of 32 flag bits. Unused bits are expected to be 0. It is probably not safe to try to read the file if any bit of this field is set that you don't know the meaning of. Bit map : 0 - 2-dimensional coding used. 1 - Image is uncompressed 2 - Fill bits have been added before EOL codes, so that EOL always ends on a byte boundary. --- Group4Options Tag = 293 (125) Type = dword N = 1 This field is made up of a set of 32 flag bits and is used for the images with fax group 4 compression. Unused bits are expected to be 0. It is probably not safe to try to read the file if any bit of this field is set that you don't know the meaning of. Gray scale and color coding schemes are under study, and will be added when finalized. For 2-D coding, each strip is encoded as if it were a separate image. In particular, each strip begins on a byte boundary; and the coding for the first row of a strip is encoded independently of the previous row, using horizontal codes, as if the previous row is entirely white. Each strip ends with the 24-bit end-of-facsimile block (EOFB). Bit map : 0 - reserved (unused) 1 - uncompressed mode is used 2-31 - reserved --- DocumentName Tag = 269 (10D) Type = ASCII The name of the document from which this image was scanned. --- PageName Tag = 285 (11D) Type = ASCII The name of the page from which this image was scanned. --- PageNumber Tag = 297 (129) Type = word N = 2 This tag is used to specify page numbers of a multiple page (e.g. facsimile) document. Two word values are specified. The first value is the page number; the second value is the total number of pages in the document. Note that pages need not appear in numerical order. The first page is 0 (zero). --- XPosition Tag = 286 (11E) Type = RATIONAL The X offset of the left side of the image, with respect to the left side of the page, in ResolutionUnits. --- YPosition Tag = 287 (11F) Type = RATIONAL The Y offset of the top of the image, with respect to the top of the page, in ResolutionUnits. In the TIFF coordinate scheme, the positive Y direction is down, so that YPosition is always positive. --- White Point Tag = 318 (13E) Type = RATIONAL N = 2 Default is the SMPTE white point, D65: x = 0.313, y = 0.329. The white point of the image. Note that this value is described using the 1931 CIE xyY chromaticity diagram and only the chromaticity is specified. The luminance component is arbitrary and not specified. This can correspond to the white point of a monitor that the image was painted on, the filter set/light source combination of a scanner, or to the white point of the illumination model of a rendering package. The ordering is x, y. --- PrimaryChromaticities Tag = 319 (13F) Type = RATIONAL N = 6 Default is the SMPTE primary color chromaticities: Red: x = 0.635 y = 0.340 Green: x = 0.305 y = 0.595 Blue: x = 0.155 y = 0.070 The primary color chromaticities. Note that these values are described using the 1931 CIE xyY chromaticity diagram and only the chromaticities are specified.For paint images, these represent the chromaticities of the monitor and for scanned images they are derived from the filter set/light source combination of a scanner. The ordering is red x, red y, green x, green y, blue x, blue y. --- SubfileType Tag = 255 (FF) Type = word N = 1 A general indication of the kind of data that is contained in this subfile. Currently defined values are: 1 = full resolution image data - ImageWidth, ImageLength, and StripOffsets are required fields 2 = reduced resolution image data - ImageWidth, ImageLength, and StripOffsets are required fields. It is further assumed that a reduced resolution image is a reduced version of the entire extent of the corresponding full resolution data. 3 = single page of a multi-page image (see the PageNumber tag description). Continued use of this field is not recommended. Writers should instead use the new and more general NewSubfileType field. --- Orientation Tag = 274 (112) Type = word N = 1 Default is 1. 1 = The 0th row represents the visual top of the image, and the 0th column represents the visual left hand side. 2 = The 0th row represents the visual top of the image, and the 0th column represents the visual right hand side. 3 = The 0th row represents the visual bottom of the image, and the 0th column represents the visual right hand side. 4 = The 0th row represents the visual bottom of the image, and the 0th column represents the visual left hand side. 5 = The 0th row represents the visual left hand side of the image, and the 0th column represents the visual top. 6 = The 0th row represents the visual right hand side of the image, and the 0th column represents the visual top. 7 = The 0th row represents the visual right hand side of the image, and the 0th column represents the visual bottom. 8 = The 0th row represents the visual left hand side of the image, and the 0th column represents the visual bottom. It is extremely costly for most readers to perform image rotation "on the fly", i.e., when importing and printing; and users of most desktop publishing applications do not expect a file imported by the application to be altered permanently in any way. Threshholding Tag = 263 (107) Type = word N = 1 1 = a bilevel "line art" scan. BitsPerSample must be 1. 2 = a "dithered" scan, usually of continuous tone data such as photographs. BitsPerSample must be 1. 3 = Error Diffused. ColorImageType Tag = 318 (13E) Type = word N = 1 Default is 1. Gives TIFF color image readers a better idea of what kind of color image it is. There will be borderline cases. 1 = Continuous tone, natural image. 2 = Synthetic image, using a greatly restricted range of colors. Such images are produced by most color paint programs. See ColorList for a list of colors used in this image. ColorList Tag = 319 (13F) Type = BYTE or word N = the number of colors that are used in this image, times SamplesPerPixel A list of colors that are used in this image. Use of this field is only practical for images containing a greatly restricted (usually less than or equal to 256) range of colors. ColorImageType should be 2. See ColorImageType. The list is organized as an array of RGB triplets, with no pad. The RGB triplets are not guaranteed to be in any particular order. Note that the red, green, and blue components can either be a BYTE or a word in length. BYTE should be sufficient for most applications. EXTENSION:TIF,TIFF OCCURENCES:PC,MAC,UNIX PROGRAMS:Aldus Pagemaker, Paintbrush REFERENCE: SEE ALSO: VALIDATION: