[babl] docs: add separate pages for CMYK, ColorManagement and alpha
- From: Øyvind "pippin" Kolås <ok src gnome org>
- To: commits-list gnome org
- Cc:
- Subject: [babl] docs: add separate pages for CMYK, ColorManagement and alpha
- Date: Mon, 22 Jul 2019 02:23:17 +0000 (UTC)
commit 0476f8b8fee2019c54d2302d6009dfa6d07f1dc5
Author: Øyvind Kolås <pippin gimp org>
Date: Mon Jul 22 04:06:26 2019 +0200
docs: add separate pages for CMYK, ColorManagement and alpha
docs/CMYK-static.html | 61 +++++++++++++++++++
docs/CMYK.html | 87 ++++++++++++++++++++++++++
docs/ColorManagement-static.html | 64 ++++++++++++++++++++
docs/ColorManagement.html | 90 +++++++++++++++++++++++++++
docs/Makefile.am | 47 +++++++++++---
docs/SymmetricAlpha-static.html | 102 +++++++++++++++++++++++++++++++
docs/SymmetricAlpha.html | 128 +++++++++++++++++++++++++++++++++++++++
docs/Vocabulary-static.html | 107 ++++++++++++++++++++++++++++++++
docs/index-static.html.in | 47 +-------------
docs/toc | 26 ++++++++
tools/babl-html-dump.c | 4 +-
11 files changed, 707 insertions(+), 56 deletions(-)
---
diff --git a/docs/CMYK-static.html b/docs/CMYK-static.html
new file mode 100644
index 0000000..27cbe66
--- /dev/null
+++ b/docs/CMYK-static.html
@@ -0,0 +1,61 @@
+<?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='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-0.1.67' title='babl-0.1.67'
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>
diff --git a/docs/CMYK.html b/docs/CMYK.html
new file mode 100644
index 0000000..6a8539a
--- /dev/null
+++ b/docs/CMYK.html
@@ -0,0 +1,87 @@
+<?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='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='Vocabulary.html'> Vocabulary</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-0.1.67' title='babl-0.1.67'
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>
diff --git a/docs/ColorManagement-static.html b/docs/ColorManagement-static.html
new file mode 100644
index 0000000..57c5516
--- /dev/null
+++ b/docs/ColorManagement-static.html
@@ -0,0 +1,64 @@
+<?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='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-0.1.67' title='babl-0.1.67'
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>
diff --git a/docs/ColorManagement.html b/docs/ColorManagement.html
new file mode 100644
index 0000000..5bb8482
--- /dev/null
+++ b/docs/ColorManagement.html
@@ -0,0 +1,90 @@
+<?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='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='Vocabulary.html'> Vocabulary</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-0.1.67' title='babl-0.1.67'
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>
diff --git a/docs/Makefile.am b/docs/Makefile.am
index bea1654..4a0e2cc 100644
--- a/docs/Makefile.am
+++ b/docs/Makefile.am
@@ -13,16 +13,20 @@ DIST_SUBDIRS= graphics
#
#
HTML_FILES = index-static.html \
- index.html
+ index.html \
+ CMYK.html \
+ ColorManagement.html \
+ SymmetricAlpha.html \
+ Vocabulary.html
EXTRA_DIST= \
babl.css \
tools/xml_insert.sh \
tools/changelog2rss \
index-static.html.in \
- ColorManagement.html \
- CMYK.html \
- SymmetricAlpha.html \
+ ColorManagement-static.html \
+ CMYK-static.html \
+ SymmetricAlpha-static.html \
COPYING \
toc \
COPYING.LESSER \
@@ -35,8 +39,25 @@ DISTCLEANFILES = index-static.html $(BUILT_EXTRA_DIST)
all: $(HTML_FILES)
+SymmetricAlpha.html: SymmetricAlpha-static.html toc
+ echo -n "HTML: $@"
+ cp $< $@
+ $(SHELL) $(top_srcdir)/docs/tools/xml_insert.sh $@ TOC $(top_srcdir)/docs/toc
+ echo " [OK]"
+
+CMYK.html: CMYK-static.html toc
+ echo -n "HTML: $@"
+ cp $< $@
+ $(SHELL) $(top_srcdir)/docs/tools/xml_insert.sh $@ TOC $(top_srcdir)/docs/toc
+ echo " [OK]"
+
+ColorManagement.html: ColorManagement-static.html toc
+ echo -n "HTML: $@"
+ cp $< $@
+ $(SHELL) $(top_srcdir)/docs/tools/xml_insert.sh $@ TOC $(top_srcdir)/docs/toc
+ echo " [OK]"
+
index.html: index-static.html \
- $(babl_html_dump) \
$(top_srcdir)/AUTHORS \
$(top_srcdir)/TODO \
$(top_srcdir)/NEWS \
@@ -44,14 +65,24 @@ index.html: index-static.html \
Makefile.am
echo -n "HTML: $@"
cp $< $@
+ $(SHELL) $(top_srcdir)/docs/tools/xml_insert.sh $@ AUTHORS $(top_srcdir)/AUTHORS
+ $(SHELL) $(top_srcdir)/docs/tools/xml_insert.sh $@ TODO $(top_srcdir)/TODO
+ $(SHELL) $(top_srcdir)/docs/tools/xml_insert.sh $@ NEWS $(top_srcdir)/NEWS
+ $(SHELL) $(top_srcdir)/docs/tools/xml_insert.sh $@ TOC $(top_srcdir)/docs/toc
+ echo " [OK]"
+
+
+Vocabulary.html: Vocabulary-static.html \
+ $(babl_html_dump) \
+ toc \
+ Makefile.am
+ echo -n "HTML: $@"
+ cp $< $@
(which mktemp > /dev/null 2>&1 && TMPFILE=`mktemp` || TMPFILE="/tmp/babl_build_tempfile" ;\
export BABL_PATH="$(top_builddir)/extensions:$(top_builddir)/extensions/.libs"; $(babl_html_dump) >
$$TMPFILE;\
$(SHELL) $(top_srcdir)/docs/tools/xml_insert.sh $@ BablBase $$TMPFILE;\
rm -f $$TMPFILE )
echo -n "."
- $(SHELL) $(top_srcdir)/docs/tools/xml_insert.sh $@ AUTHORS $(top_srcdir)/AUTHORS
- $(SHELL) $(top_srcdir)/docs/tools/xml_insert.sh $@ TODO $(top_srcdir)/TODO
- $(SHELL) $(top_srcdir)/docs/tools/xml_insert.sh $@ NEWS $(top_srcdir)/NEWS
$(SHELL) $(top_srcdir)/docs/tools/xml_insert.sh $@ TOC $(top_srcdir)/docs/toc
echo " [OK]"
diff --git a/docs/SymmetricAlpha-static.html b/docs/SymmetricAlpha-static.html
new file mode 100644
index 0000000..4aca2d3
--- /dev/null
+++ b/docs/SymmetricAlpha-static.html
@@ -0,0 +1,102 @@
+<?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='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-0.1.67' title='babl-0.1.67'
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>
diff --git a/docs/SymmetricAlpha.html b/docs/SymmetricAlpha.html
new file mode 100644
index 0000000..26ef6df
--- /dev/null
+++ b/docs/SymmetricAlpha.html
@@ -0,0 +1,128 @@
+<?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='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='Vocabulary.html'> Vocabulary</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-0.1.67' title='babl-0.1.67'
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>
diff --git a/docs/Vocabulary-static.html b/docs/Vocabulary-static.html
new file mode 100644
index 0000000..34b7b8c
--- /dev/null
+++ b/docs/Vocabulary-static.html
@@ -0,0 +1,107 @@
+<?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-0.1.67</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>
+
+ <script type='text/javascript'>
+ function hide(id)
+ {
+ (document.getElementById(id)).style.display = "none";
+ }
+ function show(id)
+ {
+ (document.getElementById(id)).style.display = "block";
+ }
+ function get_visible (id)
+ {
+ var element = document.getElementById(id);
+
+ if (element &&
+ element.style.display &&
+ element.style.display != "none")
+ return true;
+ return false;
+ }
+ function set_visible (id, visible)
+ {
+ var element = document.getElementById(id);
+
+ if (element)
+ {
+ if (visible)
+ element.style.display = "block";
+ else
+ element.style.display = "none";
+ }
+ }
+ function toggle_visible (id)
+ {
+ if (get_visible(id))
+ set_visible(id, false);
+ else
+ set_visible(id,true);
+ }
+ </script>
+ </head>
+ <body>
+
+ <div class='print'>
+ <div class='print_title'>
+ <h1>Babl-0.1.67</h1>
+ </div>
+ </div>
+<!--TOC-->
+
+
+<div><a name='Babl'></a></div>
+ <div class='paper'>
+ <div class='content'>
+
+ <a name='Vocabulary'></a>
+ <h3 style='margin-bottom:0em;'>Vocabulary</h3>
+<!--BablBase-->
+
+<!--
+ <a name='Extensions'></a>
+ <h3>Extensions</h3>
+ <p>
+ At compile, load, and runtime; babl is extendable with:
+ </p>
+ <ul>
+ <li>data types.</li>
+ <li>color models.</li>
+ <li>pixel formats.</li>
+ <li>optimized conversion functions:
+ <dl>
+ <dt>SIMD instructions</dt>
+ <dd>MMX, SSE, Altivec ...</dd>
+ <dt>External libraries</dd>
+ <dd>liboil, hermes, libavcodec, lcms, ...</li>
+ </dl>
+ </li>
+ </ul>-->
+
+ <a href='graphics/index.html'><img class='BablFish' alt='/babl-0.1.67' title='babl-0.1.67'
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>
diff --git a/docs/index-static.html.in b/docs/index-static.html.in
index 5ffe554..e5ad863 100644
--- a/docs/index-static.html.in
+++ b/docs/index-static.html.in
@@ -1,7 +1,6 @@
<?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>
@@ -11,50 +10,10 @@
<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>
-
- <script type='text/javascript'>
- function hide(id)
- {
- (document.getElementById(id)).style.display = "none";
- }
- function show(id)
- {
- (document.getElementById(id)).style.display = "block";
- }
- function get_visible (id)
- {
- var element = document.getElementById(id);
-
- if (element &&
- element.style.display &&
- element.style.display != "none")
- return true;
- return false;
- }
- function set_visible (id, visible)
- {
- var element = document.getElementById(id);
-
- if (element)
- {
- if (visible)
- element.style.display = "block";
- else
- element.style.display = "none";
- }
- }
- function toggle_visible (id)
- {
- if (get_visible(id))
- set_visible(id, false);
- else
- set_visible(id,true);
- }
- </script>
</head>
<body>
@@ -234,10 +193,6 @@ lab_buffer = malloc (pixel_count * 3 * sizeof (float));
- <a name='Vocabulary'></a>
- <h3 style='margin-bottom:0em;'>Vocabulary</h3>
-<!--BablBase-->
-
<!--
<a name='Extensions'></a>
<h3>Extensions</h3>
diff --git a/docs/toc b/docs/toc
new file mode 100644
index 0000000..484d963
--- /dev/null
+++ b/docs/toc
@@ -0,0 +1,26 @@
+ <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='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='Vocabulary.html'> Vocabulary</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>
diff --git a/tools/babl-html-dump.c b/tools/babl-html-dump.c
index b685889..079b2d7 100644
--- a/tools/babl-html-dump.c
+++ b/tools/babl-html-dump.c
@@ -37,8 +37,8 @@ each_item (Babl *babl,
void *user_data);
static int
- show_item (Babl *babl,
- void *user_data);
+show_item (Babl *babl,
+ void *user_data);
static int
hide_item (Babl *babl,
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