forked from openkylin/gimp
317 lines
12 KiB
Plaintext
317 lines
12 KiB
Plaintext
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PARASITE REGISTRY
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=================
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This document describes parasites in GIMP.
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Table of contents
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-----------------
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Parasite registry
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Table of contents
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Audience
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1. Namespace
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2. Known prefixes
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3. Known global parasites
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4. Known image parasites
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5. Known layer/drawable parasites
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6. Parasite format
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Audience
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--------
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This document is designed for the convenience of GIMP developers.
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It does not need to concern users.
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>>>> If your plug-in or script writes parasites, please
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>>>> amend this file in the Git repository or submit patches to
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>>>> gimp-developer-list@gnome.org
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1. NAMESPACE
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============
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Plug-in-specific data should be prefixed by the plug-in function name and
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a slash, i.e. private data of plug_in_displace should be named like:
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plug_in_displace/data1
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plug_in_displace/data2
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etc.
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Global data follows no strict rules.
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2. KNOWN PREFIXES
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=================
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"tiff" : The standard GIMP TIFF plugin
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"jpeg" : The standard GIMP JPEG plugin
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"png" : The standard GIMP PNG plugin
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"dcm" : The standard GIMP DICOM plugin
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"gimp" : For common and standard parasites
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3. KNOWN GLOBAL PARASITES
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=========================
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"jpeg-save-defaults" (GLOBAL, PERSISTENT)
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Default save parameters used by the JPEG plug-in.
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"png-save-defaults" (GLOBAL, PERSISTENT)
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Default save parameters used by the PNG plug-in.
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"<plug-in>/_fu_data" (GLOBAL, IMAGE, DRAWABLE, PERSISTENT)
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The Gimp::Fu module (Perl) might store the arguments of the
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last plug-in invocation. It is usually attached to images,
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but might also be found globally. The data format is either
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pure character data (Data::Dumper) or a serialized data
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stream created by Storable::nfreeze.
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"exif-orientation-rotate" (GLOBAL, PERSISTENT)
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Whether a load plug-in should automatically rotate the image
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according to the orientation specified in the EXIF data. This
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has values "yes" or "no". If the parasite is not set, the
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plug-in should ask the user what to do. This parasite may be
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removed in a future version (assuming always yes).
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4. KNOWN IMAGE PARASITES
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========================
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"gimp-comment" (IMAGE, PERSISTENT)
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Standard GIF-style image comments. This parasite should be
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human-readable text in UTF-8 encoding. A trailing \0 might
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be included and is not part of the comment. Note that image
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comments may also be present in the "gimp-metadata" parasite.
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"gimp-brush-name" (IMAGE, PERSISTENT)
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A string in UTF-8 encoding specifying the name of a GIMP brush.
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Currently, the gbr plug-in uses this parasite when loading and
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saving .gbr files. A trailing \0 might be included and is not
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part of the name.
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"gimp-brush-pipe-name" (IMAGE, PERSISTENT)
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A string in UTF-8 encoding specifying the name of a GIMP brush
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pipe. Currently, the gih plug-in uses this parasite when loading and
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saving .gih files. A trailing \0 might be included and is not
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part of the name.
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"gimp-brush-pipe-parameters" (IMAGE, PERSISTENT)
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This is all very preliminary:
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A string, containing parameters describing how an brush pipe
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should be used. The contents is a space-separated list of
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keywords and values. The keyword and value are separated by a
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colon.
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This parasite is currently attached to an image by the psp
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plug-in when it loads a .tub file (Paint Shop Pro picture
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tube). It is used (first attached with values asked from the
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user, if nonexistent) by the gpb plug-in when it saves a .gih
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file. The .gih file contains the same text in it.
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The keywords are:
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ncells: the number of brushes in the brush pipe
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step: the default spacing for the pipe
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dim: the dimension of the pipe. The number of cells
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in the pipe should be equal to the product
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of the ranks of each dimension.
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cols: number of columns in each layer of the image,
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to be used when editing the pipe as a GIMP image
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rows: ditto for rows. Note that the number of columns and rows
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not necessarily are identical to the ranks of the
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dimensions of a pipe, but in the case of two-
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and three-dimensional pipes, it probably is.
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rank0, rank1, ...: (one for each dimension): the index range
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for that dimension
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placement: "default", "constant" or "random". "constant" means
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use the spacing in the first brush in the pipe.
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"random" means perturb that with some suitable
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random number function. (Hmm, would it be overdoing it
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if the pipe also could specify what random function
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and its parameters...?)
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sel0, sel1, ...: "default", "random", "incremental", "angular",
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"pressure", "velocity", and whatever else suitable we might
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think of ;-) Determines how one index from each dimension is
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selected (until we have pinpointed the brush to use).
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"gimp-image-grid" (IMAGE, PERSISTENT)
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The GimpGrid object serialized to a string. Saved as parasite
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to keep the XCF files backwards compatible. Although gimp-1.2
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does not know how to handle the image grid, it keeps the grid
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information intact.
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"gimp-pattern-name" (IMAGE, PERSISTENT)
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A string in UTF-8 encoding specifying the name of a GIMP pattern.
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Currently, the pat plug-in uses this parasite when loading and
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saving .pat files. A trailing \0 might be included and is not
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part of the name.
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"tiff-save-options" (IMAGE)
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The TiffSaveVals structure from the TIFF plugin.
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"jpeg-save-options" (IMAGE)
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The JpegSaveVals structure from the JPEG plugin.
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"jpeg-exif-data" (IMAGE) (deprecated)
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The ExifData structure serialized into a uchar* blob from
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libexif. This is deprecated in favor of "exif-data".
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"jpeg-original-settings" (IMAGE, PERSISTENT)
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The settings found in the original JPEG image: quality (IJG),
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color space, component subsampling and quantization tables.
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These can be reused when saving the image in order to minimize
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quantization losses and keep the same size/quality ratio.
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"gamma" (IMAGE, PERSISTENT)
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The original gamma this image was created/saved. For JPEG; this is
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always one, for PNG it's usually taken from the image data. GIMP
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might use and modify this. The format is an ascii string with the
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gamma exponent as a flotingpoint value.
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Example: for sRGB images this might contain "0.45454545"
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"chromaticity" (IMAGE, PERSISTENT)
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This parasite contains 8 floatingpoint values (ascii, separated by
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whitespace) specifying the x and y coordinates of the whitepoint, the
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red, green and blue primaries, in this order.
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Example: for sRGB images this might contain
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"0.3127 0.329 0.64 0.33 0.3 0.6 0.15 0.06"
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wx wy rx ry gx gy bx by
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"rendering-intent" (IMAGE, PERSISTENT)
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This specifies the rendering intent of the image. It's a value
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between 0 and 3, again in ascii:
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0 - perceptual (e.g. for photographs)
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1 - relative colorimetric (e.g. for logos)
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2 - saturation-preserving (e.g. for business charts)
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3 - absolute colorimetric
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"hot-spot" (IMAGE, PERSISTENT)
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Use this parasite to store an image's "hot spot". Currently
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used by the XBM plugin to store mouse cursor hot spots.
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Example: a hot spot at coordinates (5,5) is stored as "5 5"
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"exif-data" (IMAGE, PERSISTENT)
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The ExifData structure serialized into a character array by
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libexif (using exif_data_save_data). If a "gimp-metadata"
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parasite is present, it should take precedence over this one.
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"gimp-metadata" (IMAGE, PERSISTENT)
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The metadata associated with the image, serialized as one XMP
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packet. This metadata includes the contents of any XMP, EXIF
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and IPTC blocks from the original image, as well as
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user-specified values such as image comment, copyright,
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license, etc.
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"icc-profile" (IMAGE, PERSISTENT | UNDOABLE)
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This contains an ICC profile describing the color space the
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image was produced in. TIFF images stored in PhotoShop do
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oftentimes contain embedded profiles. An experimental color
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manager exists to use this parasite, and it will be used
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for interchange between TIFF and PNG (identical profiles)
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"icc-profile-name" (IMAGE, PERSISTENT | UNDOABLE)
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The profile name is a convenient name for referring to the
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profile. It is for example used in the PNG file format. The
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name must be stored in UTF-8 encoding. If a file format uses
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a different character encoding, it must be converted to UTF-8
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for use as a parasite.
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"decompose-data" (IMAGE, NONPERSISTENT)
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Starting with GIMP 2.4, this is added to images produced by
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the decompose plug-in, and contains information necessary to
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recompose the original source RGB layer from the resulting
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grayscale layers. It is ascii; a typical example would be
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"source=2 type=RGBA 4 5 6 7". This means that layer 2 was
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decomposed in RGBA mode, giving rise to layers 4, 5, 6, and 7.
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"print-settings" (IMAGE, NONPERSISTENT)
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This parasite is stored by the Print plug-in and holds settings
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done in the Print dialog. It also has a version field so that
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changes to the parasite can be done. GIMP 2.4 used version 0.3.
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The format is GKeyFile. A lot of the contents are identical to
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what is stored in ~/.gimp-2.x/print-settings but the parasite
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has some additional image-related fields.
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"print-page-setup" (IMAGE, NONPERSISTENT)
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This parasite is stored by the Print plug-in and holds settings
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done in the Page Setup dialog. The format is GKeyFile as created
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from GtkPageSetup. The content is identical to what is stored in
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~/.gimp-2.x/print-page-setup.
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"dcm/XXXX-XXXX-AA" (IMAGE, PERSISTENT)
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These parasites are stored by the Dicom plug-in and hold the DICOM
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element information for that image. The format is raw binary data
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as read from the original image.
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where: XXXX is a 4-digit ascii encoded hexadecimal number
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AA is a two character ascii value representing the Dicom
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element's Value Representation (VR)
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5. KNOWN LAYER/DRAWABLE PARASITES
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=================================
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"gimp-text-layer" (LAYER, PERSISTENT)
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The associated GimpText object serialized to a string. For
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convenience the string is terminated by a trailing '\0'.
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The idea of using a parasite for text layers is to keep the XCF
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files backward compatible. Although gimp-1.2 doesn't know how
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to handle the text layer, it keeps the parasite intact.
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"gfig" (LAYER, PERSISTENT)
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As of GIMP 2.2, the gfig plug-in creates its own layers, and
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stores a representation of the figure as a layer parasite.
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The parasite contains a GFig save file, in an ascii format.
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If gfig is started while the active layer contains a "gfig"
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parasite, the contents of the parasite are loaded at startup.
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6. PARASITE FORMAT
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==================
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The parasite data format is not rigidly specified. For non-persistent
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parasites you are entirely free, as the parasite data does not survive the
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current gimp session. If you need persistent data, you basically have to
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choose between the following alternatives (also, having some standard for
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non-persistent data might be fine as well):
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- Cook your own binary data format
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You can invent your own data format. This means that you will either
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loose totally (consider endian-ness or version-ness issues) or you will
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get yourself into deep trouble to get it "right" in all cases.
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- Use character (string) data
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Obvious to Perl people but less so to C programmers: just sprintf your
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data into a string (e.g. "SIZE 100x200 XRES 300 YRES 300") and store
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that in the parasite, and later sscanf it again. This often solves most
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of the problems you might encounter, makes for easier debugging and
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more robustness (consider the case when you add more entries to your
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persistent data: older plug-ins might be able to read the relevant
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parts and your application can detect missing fields easily). The
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drawback is that your data is likely to be larger than a compact binary
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representation would be. Not much a problem for most applications,
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though.
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You could also use one parasite per field you store, i.e. foo-size,
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foo-offset-x, foo-offset-y etc...
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- Use the libgimpconfig serialize functions
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This is a special case of the previous one, using the convenience
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functions provided by libgimpconfig. If you are not concerned about
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the size of the string representation of your data, you can use
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gimp_config_serialize_to_string() and other functions to easily
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convert your data to/from a character string.
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