+++ /dev/null
-<?xml version="1.0" encoding="utf-8"?>
-<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
-
-
-<!-- The babl webpage is partially autogenerated
--->
-<html>
- <head>
- <title>CMYK - babl</title>
- <meta http-equiv="content-type" content="text/html;charset=utf-8" />
- <link rel="icon" href="graphics/babl-16x16.png" type="image/png" />
- <link rel="shortcut icon" href="graphics/babl-16x16.png" type="image/png" />
- <style type='text/css'>
- @import url(babl.css);
- </style>
- </head>
- <body>
-
- <div class='print'>
- <div class='print_title'>
- <h1>Babl-0.1.67</h1>
- </div>
- </div>
-<!--TOC-->
- <div class='toc'>
- <div class='print'>
- <h3>Contents</h3>
- </div>
- <ul>
- <li><a href='index.html#Download'> Download</a></li>
- <li><a href='index.html#Features'> Features</a></li>
- <li><a href='Reference.html'> Reference</a></li>
- <li><a href='Glossary.html'> Glossary</a></li>
- <li><a href='ColorManagement.html'> Color Management</a></li>
- <li><a href='SymmetricAlpha.html'> Symmetric-Alpha</a></li>
- <li><a href='CMYK.html'> CMYK</a></li>
- <!--<li><a href='#Background'>Background</a></li>-->
- <li><a href='index.html#Usage'> Usage</a></li>
- <!--<li><a href='index.html#Data-types'> Data types</a></li>
- <li><a href='index.html#Color-models'> Color models</a></li>
- <li><a href='#Pixel-formats'> Pixel formats</a></li>-->
-
- <li><a href='index.html#Environment'> Environment</a></li>
- <li><a href='index.html#Extending'> Extending</a></li>
- <li><a href='index.html#DirectoryOverview'> Directory Overview</a></li>
- <li><a href='index.html#TODO'> Todo</a></li>
-
- <li><a href='index.html#Copyright'> Copyright</a></li>
- <li><a href='index.html#Authors'> Authors</a></li>
- </ul>
- </div>
-
- <div class='paper'>
- <div class='content'>
-
- <h2>CMYK</h2>
-
- <p>CMYK handling is done using babl-spaces created with ICC profiles
-containing CMYK profiles. BablSpaces for these ICC profiles handle color conversions using lcms2 - or if compiled without lcms2 support a naive profile independent fallback.</p>
- <p>When a babl space derived from a CMYK ICC profile is used to instantiate
-RGB formats, the resulting formats are using the default/NULL space for
-primaries and TRCs.</p>
-
- <p>The CMYK formats that use lcms2 for color interchange with the rest of
-babl are the following, which are available for all data types, u8, u16, half
-and float:</p>
- <dl>
- <dt>CMYK</dt><dd>Cyan Magenta Yellow Key, with 0 being white and 1.0 full ink coverage.</dd>
- <dt>CMYKA</dt><dd>as previous, with separate alpha channel</dd>
- <dt>CaMaYaKaA</dt><dd>as previous but associated alpha</dd>
- <dt>cmyk</dt><dd>inverted CMYK, where 0.0 is full ink coverage and 1.0 is none</dd>
- <dt>cmykA</dt><dd>as previous, with separate alpha channel</dd>
- <dt>camayakaA</dt><dd>as previous but associated alpha</dd>
- </dl>
-
-
- <a href='graphics/index.html'><img class='BablFish' alt='/babl' title='babl' src='graphics/babl-48x48.png'/></a>
- </div>
- </div>
-
- <div class='graphic'>
- <div class='print'>
- <img src='graphics/babl-a4poster.png' alt=' '/>
- </div>
- </div>
-
- </body>
-</html>
+++ /dev/null
-<?xml version="1.0" encoding="utf-8"?>
-<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
-
-
-<!-- The babl webpage is partially autogenerated
--->
-<html>
- <head>
- <title>babl color management</title>
- <meta http-equiv="content-type" content="text/html;charset=utf-8" />
- <link rel="icon" href="graphics/babl-16x16.png" type="image/png" />
- <link rel="shortcut icon" href="graphics/babl-16x16.png" type="image/png" />
- <style type='text/css'>
- @import url(babl.css);
- </style>
-
- </head>
- <body>
-
-<!--TOC-->
- <div class='toc'>
- <div class='print'>
- <h3>Contents</h3>
- </div>
- <ul>
- <li><a href='index.html#Download'> Download</a></li>
- <li><a href='index.html#Features'> Features</a></li>
- <li><a href='Reference.html'> Reference</a></li>
- <li><a href='Glossary.html'> Glossary</a></li>
- <li><a href='ColorManagement.html'> Color Management</a></li>
- <li><a href='SymmetricAlpha.html'> Symmetric-Alpha</a></li>
- <li><a href='CMYK.html'> CMYK</a></li>
- <!--<li><a href='#Background'>Background</a></li>-->
- <li><a href='index.html#Usage'> Usage</a></li>
- <!--<li><a href='index.html#Data-types'> Data types</a></li>
- <li><a href='index.html#Color-models'> Color models</a></li>
- <li><a href='#Pixel-formats'> Pixel formats</a></li>-->
-
- <li><a href='index.html#Environment'> Environment</a></li>
- <li><a href='index.html#Extending'> Extending</a></li>
- <li><a href='index.html#DirectoryOverview'> Directory Overview</a></li>
- <li><a href='index.html#TODO'> Todo</a></li>
-
- <li><a href='index.html#Copyright'> Copyright</a></li>
- <li><a href='index.html#Authors'> Authors</a></li>
- </ul>
- </div>
-
-
- <div class='paper'>
- <div class='content'>
- <h2>Color Management</h2>
-
- <p>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.
- </p>
-
- <p>babl has API for creating a format for a specific space:
- <tt>babl_format_with_space("R'G'B' u16", babl_space ("Rec2020"))</tt> 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.
- </p>
-
- <p>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.
- </p>
-
- <p>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) sometimes also do
- relative-colorimetric transfer for the "perceptual" intent CLUTs, but with
- a more flexible and possibly higher accuracy conversions.</p>
-
- <p>Handling of <a href='CMYK.html'>CMYK is in a separate document</a>.</p>
-
- <a href='graphics/index.html'><img class='BablFish' alt='/babl' title='babl' src='graphics/babl-48x48.png'/></a>
- </div>
- </div>
-
- <div class='graphic'>
- <div class='print'>
- <img src='graphics/babl-a4poster.png' alt=' '/>
- </div>
- </div>
-
- </body>
-</html>
+++ /dev/null
-<?xml version="1.0" encoding="utf-8"?>
-<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
-
-
-<!-- The babl webpage is partially autogenerated
--->
-<html>
- <head>
- <title>Symmetric Alpha - babl</title>
- <meta http-equiv="content-type" content="text/html;charset=utf-8" />
- <link rel="icon" href="graphics/babl-16x16.png" type="image/png" />
- <link rel="shortcut icon" href="graphics/babl-16x16.png" type="image/png" />
- <style type='text/css'>
- @import url(babl.css);
- </style>
- </head>
- <body>
-
- <div class='print'>
- <div class='print_title'>
- <h1>Babl-0.1.67</h1>
- </div>
- </div>
-<!--TOC-->
- <div class='toc'>
- <div class='print'>
- <h3>Contents</h3>
- </div>
- <ul>
- <li><a href='index.html#Download'> Download</a></li>
- <li><a href='index.html#Features'> Features</a></li>
- <li><a href='Reference.html'> Reference</a></li>
- <li><a href='Glossary.html'> Glossary</a></li>
- <li><a href='ColorManagement.html'> Color Management</a></li>
- <li><a href='SymmetricAlpha.html'> Symmetric-Alpha</a></li>
- <li><a href='CMYK.html'> CMYK</a></li>
- <!--<li><a href='#Background'>Background</a></li>-->
- <li><a href='index.html#Usage'> Usage</a></li>
- <!--<li><a href='index.html#Data-types'> Data types</a></li>
- <li><a href='index.html#Color-models'> Color models</a></li>
- <li><a href='#Pixel-formats'> Pixel formats</a></li>-->
-
- <li><a href='index.html#Environment'> Environment</a></li>
- <li><a href='index.html#Extending'> Extending</a></li>
- <li><a href='index.html#DirectoryOverview'> Directory Overview</a></li>
- <li><a href='index.html#TODO'> Todo</a></li>
-
- <li><a href='index.html#Copyright'> Copyright</a></li>
- <li><a href='index.html#Authors'> Authors</a></li>
- </ul>
- </div>
-
- <div class='paper'>
- <div class='content'>
-
- <h2>Symmetric transformations for floating point alpha</h2>
-
-
- <p> babl clamps the alpha used when going from separate alpha to associated
-alpha or from associated alpha to separate alpha to BABL_ALPHA_FLOOR. This
-replaces asymptotic behavior and direct precision loss of color precision when
-multiplying or dividing by alphas near 0.0 with a consistent symmetric
-transformation.</p>
-
-<p>Original intent of data as well as non-asymptotic precision loss is thus
-maintained when the processing chain might temporarily use the other alpha
-representation.</p>
-
-<pre>
- #define BABL_ALPHA_FLOOR (1.0/65536.0)
- #define BABL_ALPHA_FLOOR_F (1.0f/65536.0f)
-</pre>
-
-<p>The deviation from not clamping near 0.0 is within the quantization margin
-of 16bit integer alpha, thus no adaptations for any SIMD or and similar 8bit
-and 16bit extensions of pixel format conversions are needed.
- </p>
-
- <p>This is the clamping function in use:</p>
-<pre>
-static inline float
-babl_epsilon_for_zero_float (float value)
-{
- if (value <= BABL_ALPHA_FLOOR_F)
- {
- /* for performance one could directly retun BABL_ALPHA_FLOOR_F here
- and dropping handling negative values consistently. */
- if (value >= 0.0f)
- return BABL_ALPHA_FLOOR_F;
- else if (value >= -BABL_ALPHA_FLOOR_F)
- return -BABL_ALPHA_FLOOR_F;
- }
- return value; /* most common case, return input value */
-}
-</pre>
-<p>And an example use of this clamping function that is consistent with babls behavior:</p>
-<pre>
-static inline void
-associated_to_separate_rgba (const float *associated_rgba,
- float *separate_rgba)
-{
- float alpha = associated_rgba[3];
- float clamped_alpha = babl_epsilon_for_zero_float (alpha);
- float reciprocal_alpha = 1.0f / clamped_alpha;
-
- separate_rgba[0] = associated_rgba[0] * reciprocal_alpha;
- separate_rgba[1] = associated_rgba[1] * reciprocal_alpha;
- separate_rgba[2] = associated_rgba[2] * reciprocal_alpha;
- separate_rgba[3] = alpha;
-}
-</pre>
-
-
-<p>For more detils see <a href='https://gitlab.gnome.org/GNOME/babl/commit/a4d607843d3cab18745d547fc8a46dec51dcea5e'>the commit message of the most recent refinement</a> as well as <a href='https://www.patreon.com/posts/premultiplied-in-21014115'>blog post with further background</a>.</p>
-
-
-
- <a href='graphics/index.html'><img class='BablFish' alt='/babl' title='babl' src='graphics/babl-48x48.png'/></a>
- </div>
- </div>
-
- <div class='graphic'>
- <div class='print'>
- <img src='graphics/babl-a4poster.png' alt=' '/>
- </div>
- </div>
-
- </body>
-</html>
projects / babl.git / commitdiff