About

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 @@ -99,8 +102,56 @@

News

+ -

Also see the ChangeLog in CVS.

+--> +

See the ChangeLog in CVS.

+ + +

Background

When creating various libraries and small tool that deal with + computer graphics I often have created conversion functions + transforming raster images between different representations.

+ +

Libraries to help with such conversions already do exist, but no + extendable candidate have surfaced in searches when looking. +

+ +

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 vocbulary of user + registered color models and data types. +

+ +

The need to provide your own reference conversions should be + unneccesary, since babl provides a good base vocabulary in BablBase, + as well as extensions.

+ +

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 + double. +

+ +

If what babls built in conversion isn't fast enough, you can provide + your own conversion between two formats, your registered conversion + will be taken into account when constructing other BablFishes as well. +

+ +

Babl extensions are shared objects, if you are already using a set + of conversion functions and you'd like to keep using them, as well as + the conversions babl provide, wrap your existing functions as an + extension. The code needed to wrap existing conversions is small. +

Features

@@ -114,11 +165,14 @@

Extendable and introspectable formats, color models, components and datatypes

Reference 64bit floating point conversions for - data types and color models. - -

+ data types and color models. + +

Vocabulary

+ + +

Extensions

At compile, load and runtime; babl is extendable with: @@ -137,6 +191,14 @@ +

Shortcut coverage

The diagram shown below is the coverage of shortcut conversions that already exist, + prior to the BablFishPath actually being operational, due to lack of testing of loss + against the reference conversions this is the most optimistic estimate. (DHTML version) +

+
+

Dependencies

@@ -169,7 +231,7 @@ buffers represented by an existing BablPixelFormat.

babl_process (babl_fish ("srgb", "lab-float"),
+>babl_process (babl_fish ("srgb", "CIE Lab float"),
               srgb_buffer, lab_buffer,
               pixel_count);

@@ -177,22 +239,22 @@ 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 ("rgb"),
+>babl_format_new (babl_model ("R'G'B'"),
                  babl_type ("u8"),
-                 babl_component ("B"),
-                 babl_component ("G"),
-                 babl_component ("R"),
+                 babl_component ("B'"),
+                 babl_component ("G'"),
+                 babl_component ("R'"),
                  NULL);

Instead of a linear buffer you can an image descriptor which desribes the start of the memory segment, the pitch in bytes between samples, and the rowstride (not used yet, use 0 to indicate unlimited for compatibility with future API.)

babl_process (babl_fish ("srgb", "y'cbcr420p"),
+>babl_process (babl_fish ("srgb", "Y'CbCr u8"),
               srgb_buffer,
               babl_image ("Y'", luma_buffer, 1, 0,
-                          "Cb", cb_buffer,  1, 0,
-                          "Cr", cr_buffer,  1, 0,
+                          "Cb", cb_buffer,   1, 0,
+                          "Cr", cr_buffer,   1, 0,
                           NULL);

@@ -207,35 +269,31 @@ 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. One way to deal with this is to register a custom color + model, that is backed by for instance lcms. (see the + lcms-lab extension) Then when using the newly registered color + model to create pixel formats, lcms will be used behind the scenes. +

TODO

Compile and/or runtime profiling. (The speed of conversions +
Compile-time instead of runtime profiling / storae 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 and vertical subsampling (for implementing 4:2:2 4:2:0 4:1:1 etc. chroma subsampling)

Thread safety for mutations of the type system.

Support for datatypes that are not a multiple of 8bit.
- - +
dithering
+
image resampling?

Contents

About

News

Background

How babl works

Features

Vocabulary

Extensions

Shortcut coverage

Dependencies

Color Management

TODO

Copyright