Babl-0.0.10

Babl is a dynamic, any to any, pixel format conversion library. It provides conversions between the myriad of buffer types images can be stored in. Babl doesn't only help with existing pixel formats, but also facilitates creation of new and uncommon ones.

News

xxxx-xx-xx babl-0.0.2 Green fish release

DRAFT Initial release.

2005-08-xx babl-0.0.1

Development release of babl, minimal working configuration for RGB, CMYK and YCbCr for 8bit 16bit float and double. Emphasis is on precision and clarity of code not speed.

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See the ChangeLog in Subversion.

Background

When creating various libraries and small tools that deal with computer graphics I have often created functions for converting raster images between different representations.

Libraries to help with such conversions already do exist, but no extendable candidates have surfaced in my searches.

The vocabulary developed in babl will most likely be part of GEGL's vocabulary to describe image buffers.

How babl works

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.

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.

Features

Core

• Small API for simple use cases
• Planar and linear buffers
• Thread safety for processing.
• Extendable and introspectable formats, color models, components and datatypes
• Reference 64bit floating point conversions for data types and color models.

Vocabulary

babl-db.c:98 babl_db_insert() Eeeeek Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1". 0xffffe410 in __kernel_vsyscall () #0 0xffffe410 in __kernel_vsyscall () #1 0x400fa933 in waitpid () from /lib/tls/i686/cmov/libc.so.6 #2 0x400a43c9 in strtold_l () from /lib/tls/i686/cmov/libc.so.6 #3 0x40022ae4 in babl_backtrack () at babl-internal.c:68 #4 0x40022b05 in babl_die () at babl-internal.c:74 #5 0x4001c292 in babl_db_insert (db=0x804bf78, item=0x0) at babl-db.c:98 #6 0x4001e021 in babl_extension_init () at babl-extension.c:197 #7 0x4001b94f in babl_init () at babl.c:40 #8 0x08048665 in main () at babl-html-dump.c:38

Extensions

At compile, load, and runtime; babl is extendable with:

• data types.
• color models.
• pixel formats.
• optimized conversion functions:

  SIMD instructions

  MMX, SSE, Altivec ...

  External libraries

  liboil, hermes, libavcodec, lcms, ...

Shortcut coverage

The diagram shown below visualizes the coverage of current shortcut conversions. A DHTML version is also available.

babl-db.c:98 babl_db_insert()
	Eeeeek
Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1".
0xffffe410 in __kernel_vsyscall ()
#0  0xffffe410 in __kernel_vsyscall ()
#1  0x400fa933 in waitpid () from /lib/tls/i686/cmov/libc.so.6
#2  0x400a43c9 in strtold_l () from /lib/tls/i686/cmov/libc.so.6
#3  0x40022ae4 in babl_backtrack () at babl-internal.c:68
#4  0x40022b05 in babl_die () at babl-internal.c:74
#5  0x4001c292 in babl_db_insert (db=0x8052f78, item=0x0) at babl-db.c:98
#6  0x4001e021 in babl_extension_init () at babl-extension.c:197
#7  0x4001b94f in babl_init () at babl.c:40
#8  0x080487f0 in main () at babl_fish_path_fitness.c:73

Dependencies

Babl is intended to be a low level infrastructure library and thus strives for few dependencies and thus portability.

• libdl (for loading extensions, babl is also reported to work on win32)

Download

The latest released version of babl can be found at: ftp://ftp.gimp.org/pub/babl/.

SVN

The latest development version is available in the babl module in GNOME Subversion. And can be checked out with the following command:

svn checkout http://svn.gnome.org/svn/babl/trunk/ babl

Usage

The simplest scenario for using babl is converting between linear buffers represented by an existing BablPixelFormat.

babl_process (babl_fish ("srgb", "CIE Lab float"),
              srgb_buffer, lab_buffer,
              pixel_count);

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.

babl_format_new (babl_model ("R'G'B'"),
                 babl_type ("u8"),
                 babl_component ("B'"),
                 babl_component ("G'"),
                 babl_component ("R'"),
                 NULL);

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). The API's used are very similar in style to the API's described under the Usage section.

Color Management

Babl is not a color management system, since it doesn't deal with ICC profiles. Babl is designed primarily for internal use when the color space is already known (sRGB, CIE Lab, Luminance or similar).

It is also possible to register new color models that are managed by a color management system like lcms, take a look at the lcms-lab extensions for an example.

TODO

• Validate that a created BablFishPath is actually faster than the BablFishReference it is a replacement for.
• Compile-time instead of runtime profiling / storage of profiling and loss data.. (The speed of conversions is bound to 'wobble', according to architecture, compiler flags, concurrently running processes and phase of moon.)
• Horizontal chroma subsampling (4:2:2 and 4:1:1)
• Thread safety (locking) for mutations of the type system.
• Support for datatypes that are not a multiple of 8bit.
• dithering

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 2 of the License, or (at your option) any later version.

Authors

Øyvind Kolås pippin@gimp.org

Maintainer and original author.

Sven Neumann sven@gimp.org

Build enviroment sanity.

Michael Schumacher schumaml@cvs.gnome.org

win32 support for dynamic extensions.

Kevin Cozens

Build environment fixes.