[gnome-user-docs] Add page about colorspace conversion

[Richard Hughes <rhughes src gnome org>]

commit fbe425fffe3e689362a810280b0d14f902fffd36
Author: Richard Hughes <richard hughsie com>
Date:   Thu Aug 25 13:04:15 2011 +0100

    Add page about colorspace conversion

 gnome-help/C/color-whatisspace.page  |   96 ++++++++++++++++++++++++++++++++++
 gnome-help/C/figures/color-space.png |  Bin 0 -> 43641 bytes
 gnome-help/Makefile.am               |    2 +
 3 files changed, 98 insertions(+), 0 deletions(-)
---
diff --git a/gnome-help/C/color-whatisspace.page b/gnome-help/C/color-whatisspace.page
new file mode 100644
index 0000000..b87f244
--- /dev/null
+++ b/gnome-help/C/color-whatisspace.page
@@ -0,0 +1,96 @@
+<page xmlns="http://projectmallard.org/1.0/";
+      type="topic"
+      id="color-whatisspace">
+
+  <info>
+    <link type="guide" xref="color#profiles"/>
+    <link type="seealso" xref="color-whatisprofile"/>
+    <desc>A color space is a defined range of colors.</desc>
+    <credit type="author">
+      <name>Richard Hughes</name>
+      <email>richard hughsie com</email>
+    </credit>
+    <include href="legal.xml" xmlns="http://www.w3.org/2001/XInclude"/>
+  </info>
+
+  <title>What is a color space?</title>
+
+  <p>
+    A colorspace is a defined range of colors.
+    Well known colorspaces include sRGB, AdobeRGB and ProPhotoRGB.
+  </p>
+
+  <p>
+    The human visual system is not a simple RGB sensor, but we can
+    approximate how the eye responds with a CIE 1931 chromacity diagram
+    that shows the human visual response as a horse-shoe shape.
+    You can see that in human vision there is many more shades of green
+    detected than blue or red.
+    With a trichromatic colorspace like RGB we represent the colors
+    on the computer using three values, which restricts up to encoding
+    a <em>triangle</em> of colors.
+  </p>
+
+  <note>
+    <p>
+      Using models such as a CIE 1931 chromacity diagram is a huge
+      simplification of the human visual system, and real gamuts are
+      expressed as 3D hulls, rather than 2D projections.
+      A 2D projection of a 3D shape can sometimes be misleading, so if
+      you want to see the 3D hull, use the <code>gcm-viewer</code>
+      application.
+    </p>
+  </note>
+
+  <figure>
+    <desc>sRGB, AdobeRGB and ProPhotoRGB represented by white triangles</desc>
+    <media type="image" mime="image/png" src="figures/color-space.png"/>
+  </figure>
+
+  <p>
+    First, looking at sRGB, which is the smallest space and can encode
+    the least number of colors.
+    It it an approximation of a 10 year old CRT display, and so most
+    modern monitors can easily display more colors than this.
+    sRGB is a standard <em>least-common-demoninator</em> standard and
+    is used in a large number of applications (including the Internet).
+  </p>
+  <p>
+    AbodeRGB is frequently used as an <em>editing space</em>.
+    It can encode more colors than sRGB, and means you adjust colors in
+    a photograph without worrying too much that the brightnest colors
+    are being clipped or the blacks crushed.
+  </p>
+  <p>
+    PhoPhoto is the largest space available and is frequently used for
+    document archival.
+    It can encode nearly the whole range of colors detected by the human
+    eye, and even encode colors that the eye cannot detect!
+  </p>
+
+  <p>
+    Now, if PhoPhoto is clearly better, why don't we use it for everything?
+    The answer is to do with <em>quantisation</em>.
+    If you only have 8 bits (256 levels) to encode each channel, then a
+    larger range is going to have bigger steps between each value.
+  </p>
+  <p>
+    Bigger steps mean a larger error between the captured color and the
+    stored color, and for some colors this is a big problem.
+    It turns out that key colors, like skin colors are very important,
+    and even small errors will make untrained viewers notice that something
+    in a photograph looks wrong.
+  </p>
+  <p>
+    Of course, using a 16 bit image is going to leave many more steps and
+    a much smaller quantisation error, but this doubles the size of each
+    image file.
+    Most content in existance today is 8bpp, i.e. 8 bits-per-pixel.
+  </p>
+  <p>
+    Color managment is a process for converting from one colorspace to
+    another, where a color space can be a well known defined space like
+    sRGB, or a custom space such as your monitor or printer profile.
+  </p>
+
+</page>
diff --git a/gnome-help/C/figures/color-space.png b/gnome-help/C/figures/color-space.png
new file mode 100644
index 0000000..3b07671
Binary files /dev/null and b/gnome-help/C/figures/color-space.png differ
diff --git a/gnome-help/Makefile.am b/gnome-help/Makefile.am
index 722957a..2ff90ba 100644
--- a/gnome-help/Makefile.am
+++ b/gnome-help/Makefile.am
@@ -10,6 +10,7 @@ HELP_MEDIA = \
 	figures/color-display.png \
 	figures/color-printer.png \
 	figures/color-profile-default.png \
+	figures/color-space.png \
 	figures/gnome.png \
 	figures/gnome-searchtool.png \
 	figures/nautilus.png \
@@ -78,6 +79,7 @@ HELP_FILES = \
 	color-notspecifiededid.page \
 	color-virtualdevice.page \
 	color-whatisprofile.page \
+	color-whatisspace.page \
 	color-why-calibrate.page \
 	color-whyimportant.page \
 	clock.page \