babl is a dynamic, any to any, pixel format translation library.
It allows converting between different methods of storing pixels known as pixel formats that have with different bitdepths and other data representations, color models, color spaces and component permutations.
A vocabulary to formulate new pixel formats from existing primitives is provided as well as the framework to add new color models, spaces and data types.
Features
- ANSI C without external dependencies, works on win32, linux and mac, 32bit and 64bit systems.
- Stable, small API, with singleton objects returned.
- Extendable with new formats, color models, components and datatypes.
- Can load color spaces from ICC v2 and v4 profiles containing RGB matrix + TRC.
- Reference 64bit floating point conversions for datatypes and color models.
- Self profiling and optimizing, optimizing accuracy and performance at runtime when the best performing single or multi-step conversion path is chosen.
GEGL through GeglBuffer provides tiled buffers with on disk storage as well as linear buffers with accessor functions for efficient data access transparently using babl fishes for translation to the desired pixel formats.
Download
The latest versioned development version of babl can be found in https://download.gimp.org/pub/babl/.
Babl uses git. The main repository is hosted by GNOME. It can be browsed online and cloned with:
git clone git://git.gnome.org/babl
NEWS
The following is a list of the major changes that have gone into each babl release. If there are significant improvements to babl when a GEGL release is done a babl release is most often put out just prior to the GEGL release.
For more news see git log.Documentation
When using BablFishes to do your conversions, you request a fish to convert between two formats, and an optimal fish to babls capability is provided that you can use to do your conversions. Babl also provides the capability to describe new formats based on a vocabulary of user registered color models and data types.
Babl provides a base vocabulary in BablBase and some extensions that are thought to be generally useful.
When performing further extensions to the vocabulary of babl, the internal consistency is governed by reference conversions that operate on double (64 bit floating point values). The only color model created during BablCore bootstrap is RGBA (linear light RGB, 0.0 - 1.0, with a linear 0.0 - 1.0 opacity channel) backed by the double datatype. Defined similarily to scRGB using 64bit floating point.
If babls conversion isn't fast enough, you can provide your own conversion shortcut between two formats. The registered shortcut might also be used by babl as an intermediate conversion when constructing BablFishes for other conversions.
Babl extensions are shared objects. If you have already developed some fast conversion functions, wrapping them as babl extensions should not take much time and will speed up babl for other users as well.
Usage
babl_process (babl_fish (source_format, destination_format), source_buffer, destination_buffer, pixel_count);
The processing operation that babl performs is copying including conversions if needed between linear buffers containing the same count of pixels, with different pixel formats.
int width = 123, height = 581, pixel_count = width * height; const Babl *srgb = babl_format ("R'G'B' u8"); const Babl *lab = babl_format ("CIE Lab float"); const Babl *srgb_to_lab_fish = babl_fish (srgb, lab); float *lab_buffer; unsigned char *srgb_buffer; babl_init (); srgb_buffer = malloc (pixel_count * babl_format_get_bytes_per_pixel (srgb)); lab_buffer = malloc (pixel_count * 3 * sizeof (float)); ...... load data into srgb_buffer ....... babl_process (srgb_to_lab_fish, srgb_buffer, lab_buffer, pixel_count); ...... do operation in lab space ........ babl_process (babl_fish(lab, srgb), lab_buffer, srgb_buffer, pixel_count); /* the data has now been transformed back to srgb data */
If the existing pixel formats are not sufficient for your conversion needs, new ones can be created on the fly. The constructor will provide the prior created one if duplicates are registered.
const Babl *format = babl_format_new (babl_model ("R'G'B'"), babl_type ("u16"), babl_component ("B'"), babl_component ("G'"), babl_component ("R'"), NULL);
Color Management
By default the babl API is assuming data to be (unbounded) sRGB data, data being sRGB defines the conversion to and from gray-scale as well as the gamma - or Transfer Response Curve, TRC, used for converting between linear and non-linear variants of the data.
There is also a babl API call for creating a format for a specific space. babl_format_with_space("R'G'B' u16", babl_space ("Rec2020")) creates a 16 bit integer format for the Rec2020 color space. Babl knows internally about "sRGB", "Rec2020", "Adobe", "Apple" and "ProPhoto" spaces, as they are defined with constants on their wikipedia pages.
Additional spaces can be loaded from monitor-class matrix+TRC ICC v2 and v4 profiles. Using babl_icc_make_space (see babl.h for details). The space of a babl format can also be queried with babl_format_get_space.
The conversions babl does with ICC profiles are according to what is known as the relative-colorimetric intent, monitor profiles containing both the matrices used by babl and 3d CLUTs (color look up tables) most often also do relative-colorimetric transfer for the "perceptual" intent CLUTs, but with a more flexible and possibly higher accuracy conversions. If babl adds support for loading and using CLUTs it will be thus the perceptual intent will by babl be considered a different albeit more accurate relative-colorimetric RGB space.
Vocabulary
Shortcut Coverage
The diagram shown below visualizes the coverage of current shortcut conversions. Dots indicate a direct conversion is provided for, the height of the bar indicates the number of conversions steps needed in a chain of conversions.
Environment
Through the environment variable BABL_TOLERANCE you can control a speed/performance trade off that by default is set very low (0.000001) values in the range 0.01-0.1 can provide reasonable preview performance by allowing lower numerical accuracy
.BABL_PATH contains the path of the directory, containing the .so extensions to babl.
Extending
For samples of how the current internal API specification of data types, color models, and conversions look in the extensions/ directory. The tables in this HTML file is directly generated based on the data registered by BablCore (double and RGBA), BablBase (core datatypes, and RGB models), extensions (CIE Lab, naive CMYK, various shortcut conversions).
Directory Overview
babl-dist-root
│
├──babl the babl core
│ └──base reference implementations for RGB and Grayscale Color Models,
│ 8bit 16bit, and 32bit and 64bit floating point.
├──extensions CIE-Lab color model as well as a naive-CMYK color model.
│ also contains a random cribbage of old conversion optimized
│ code from gggl. Finding more exsisting conversions in third
│ part libraries (hermes, lcms?, liboil?) could improve the
│ speed of babl.
├──tests tests used to keep babl sane during development.
└──docs Documentation/webpage for babl (the document you are reading
originated there.
Copyright
Babl is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 3 of the License, or (at your option) any later version.
Authors
