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<title>colord - What is colord?</title>
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<p>Back to the <a href="index.html">main page</a></p>
<h1>How it works:</h1>
<h2>Mapping the device to the profile</h2>
<p>
Preferences are per-user and are stored in GConf in GNOME 2-30, or GSettings in newer versions.
There is need for configuration of devices to profiles, and to store metadata about each device.
This is stored in the colord mapping database, which is
<code>/var/lib/colord/mapping.db</code> by default.
The schema is really simple, and as follows:
</p>
<pre>
CREATE TABLE mappings (id TEXT PRIMARY KEY,device TEXT,profile TEXT);
</pre>
<p>
Multiple profiles can of course be assigned to the same device.
Persistent devices and profiles can also be saved to the storage database, which is
<code>/var/lib/colord/storage.db</code> by default.
The schema is really simple, and as follows:
</p>
<pre>
CREATE TABLE devices (device_id TEXT PRIMARY KEY,device TEXT);
CREATE TABLE properties (device_id TEXT,property TEXT,value TEXT);
</pre>
<h3>Comparison to UCMM</h3>
<p>
<a href="http://www.argyllcms.com/doc/ucmm.html">ucmm</a> (Unix micro Color Management Module) is a color management config file designed just to handle the necessary configuration needed to track the installation and association of ICC profiles with X11 displays.
</p>
<pre>
{
"devices": {
"display": {
"1": {
"EDID": "0x00FFFFFFFFFFFF0034A1731751720000150901010C1F17CDE8A11E9E554A982712474FA4CE0045598180315961590101010101010101000000FE004D6F6E69746F720A2020202020000000FE004D6F6E69746F720A2020202020000000FE004D6F6E69746F720A2020202020000000FE004D6F6E69746F720A2020202020003D",
"ICC_PROFILE": "/home/graeme/.local/share/color/devices/display/mon1.icc"
},
"2": {
"NAME": ":0.1",
"ICC_PROFILE": "/home/graeme/.local/share/color/devices/display/mon2.icc"
}
}
}
}
</pre>
The colord database differs from UCMM in the following ways:
<ul>
<li>
UCMM is a <a href="http://www.json.org/">JSON</a>
(JavaScript Object Notation) file format, whilst colord is a
<i>key=value</i> style store
</li>
<li>
UCMM allows mapping from a monitor EDID or display name to a device
profile, where colord maps <i>device IDs</i> to <i>profile IDs</i>.
</li>
<li>
UCMM stores the EDID in the file as a huge hex number, but colord
stores other "junk" details such as a the device colorspace and
device serial number which are useful to some GUI tools.
</li>
<li>
UCMM is a well documented standard used for a long time by ArgyllCMS
whilst colord has only ever been used by GCM for a short time.
</li>
<li>
UCMM has to be parsed using a parser such as JNCF, whilst colord can
bequeried by any client that speaks <code>DBus</code>.
</li>
<li>
UCMM only supports one profile per device, unlike colord which
supports an ordered list of profiles with optional qualifiers.
</li>
</ul>
<p>
All that said, UCMM is already used by ArgyllCMS and we should probably
import the existing files on the first run of GCM.
</p>
<h3>Using Elektra</h3>
<p>
Oyranos puts device settings in the session and system
<a href="http://elektra.g4ii.com/Main_Page">Elektra</a> database.
Elektra is not a well supported library in any mainstream distribution
and is not used by many open source projects.
colord will not import settings from Elektra nor can it propagate
settings back into the Oyranos configuration system.
</p>
<p>
The colord author is willing to work with the Oyranos developers to
define a standard compatible with both systems.
</p>
<h2>Setting the system default</h2>
<p>
One user may want to set the default for all users.
We cannot reference files in <code>/home/foo/.icc/</code> when logged in
as user bar, as the user will not have access permissions, or in the
worst case, <code>/home/foo</code> may be encrypted and inaccessible even as root.
For this reason, colord copies the ICC profiles to a systemwide directory,
<code>/usr/lib/color</code> that is per-machine and accessible to all users.
</p>
<p>
It is <a href="http://lists.freedesktop.org/archives/openicc/2010q2/002167.html">encouraged</a> that other CMS implementations also read ICC profiles from the per-machine
<code>/usr/lib/color</code> directory.
</p>
<h2>What the binaries do</h2>
<p>
GCM ships quite a few data files and binary files. Most users will interact with ICC files by double clicking on them, and with color management using ''System->Preferences->Color Profiles''. It's not expected that users should need to run any command line programs at all.
</p>
For interest, the different binaries are listed here.
<h3>GTK programs</h3>
<ul>
<li><code>gcm-import</code> - Helper to import an ICC file. This is normally run by the <code>gcm-import.desktop</code> file.</li>
<li><code>gcm-picker</code> - Simple program to pick a spot color using a photospectrometer.</li>
</ul>
<h3>Command line tools</h3>
<ul>
<li><code>gcm-inspect</code> - Command line tool to inspect settings and test the DBus API.</li>
<li><code>gcm-fix-profile</code> - Tries to fix a corrupted or invalid ICC profile file.</li>
<li><code>gcm-session</code> - DBus session service that is started on demand.</li>
<li><code>gcm-dump-edid</code> - Debugging program that dumps the EDID to a file.</li>
<li><code>gcm-dump-profile</code> - Debugging program that dumps all details about a profile.</li>
</ul>
<p>Back to the <a href="index.html">main page</a></p>
<p class="footer">
Copyright <a href="mailto:richard@hughsie.com">Richard Hughes 2011</a><br/>
<a href="http://validator.w3.org/check/referer">Optimized</a>
for <a href="http://www.w3.org/">standards</a>.
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