1<?xml version="1.0" encoding="UTF-8"?>
2<!DOCTYPE sect2 PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
3                       "http://www.docbook.org/xml/4.3/docbookx.dtd">
4<!-- section history:
5  2017-04-01 elle stone: add enable-color-management.xml
6-->
7<sect2 id="gimp-image-enable-color-management">
8  <title>Enable Color Management</title>
9
10  <indexterm>
11    <primary>Image</primary>
12    <secondary>Color Management</secondary>
13    <tertiary>Enable Color Management</tertiary>
14  </indexterm>
15  <indexterm>
16    <primary>Color Management</primary>
17    <secondary>Enable Color Management</secondary>
18  </indexterm>
19  <indexterm>
20    <primary>Enable Color Management</primary>
21  </indexterm>
22
23  <para>
24    If unchecked, <guimenuitem>Enable Color Management</guimenuitem>
25    assigns a GIMP built-in sRGB color space to your image.
26  </para>
27
28  <para>
29    Also, if you've selected to
30    display the image's assigned ICC color profile on the title or status bar,
31    unchecking Enable Color Management prints
32    the phrase "not color managed" to the title or status bar in place
33    of the previously assigned color profile.
34  </para>
35
36  <note>
37    <para>Enable Color Management is checked by default. It's best to leave
38    this option checked.
39    </para>
40  </note>
41
42  <sect3>
43    <title>Activating the command</title>
44        <para>
45          You can access this command from the image menu bar through
46          <menuchoice>
47            <guimenu>Image</guimenu>
48            <guisubmenu>Color Management</guisubmenu>
49            <guimenuitem>Enable Color Management</guimenuitem>
50          </menuchoice>.
51        </para>
52  </sect3>
53
54
55  <sect3>
56    <title>
57      Use Notes regarding unchecking
58      <guimenuitem>Enable Color Management</guimenuitem>
59    </title>
60    <para>
61      The best possible advice is to <emphasis role="bold">never uncheck <guimenuitem>Enable Color Management</guimenuitem></emphasis>.
62    </para>
63  </sect3>
64<!--    <para>
65      If your image is already in one of GIMP's built-in sRGB color spaces,
66      unchecking Enable Color Management makes no difference whatsoever in your
67      editing results or in the appearance of your image.
68    </para>
69    <para>
70      If your image is not already in one of GIMP's built-in sRGB color
71      spaces, then the only time unchecking Enable Color Management won't change
72      your image's appearance is if the ICC profile assigned to your image has:
73    </para>
74    <orderedlist>
75      <listitem>
76        <para>
77          The same channel encoding as the channel encoding that
78          GIMP happens to be using at the time you uncheck Enable Color Management.
79        </para>
80      </listitem>
81      <listitem>
82        <para>
83          The same chromaticities as the chromaticities of the
84          built-in GIMP sRGB profiles.
85        </para>
86      </listitem>
87    </orderedlist>
88    <para>
89      In the above case unchecking Enable Color Management is the
90      functional equivalent of assigning the built-in sRGB profile to your image,
91      except that simply assigning the built-in sRGB profile to your image
92      doesn't produce a misleading status or title bar message that the image is
93      "not color managed".
94    </para>
95  </sect3>-->
96
97  <sect3>
98      <title>
99        What does GIMP do when
100        <guimenuitem>Enable Color Management</guimenuitem> is unchecked?
101      </title>
102      <para>
103        When you uncheck the option to
104        <guimenuitem>Enable Color Management</guimenuitem>, GIMP does
105        two things:
106      </para>
107      <orderedlist>
108        <listitem>
109          <para>
110            Whatever ICC profile is currently assigned to the image
111            file is at least temporarily stored (pending subsequent editing,
112            Precision, and Color Management actions), but isn't used.
113            And then a built-in GIMP profile is assigned in place of the previously
114            assigned ICC profile:
115          </para>
116          <itemizedlist>
117            <listitem>
118              <para>If the image is at Perceptual gamma (sRGB) precision,
119                the ICC profile "GIMP built-in sRGB" is assigned.
120              </para>
121            </listitem>
122            <listitem>
123              <para>
124                If the image is at Linear light precision, the ICC
125                profile "GIMP built-in Linear sRGB" is assigned.
126              </para>
127            </listitem>
128          </itemizedlist>
129          <para>
130            You can confirm that one of GIMP's built-in sRGB color spaces has
131            been assigned by checking "Image/Image Properties/Color Profile".
132          </para>
133        </listitem>
134        <listitem>
135          <para>
136            If you have set up the title or status bar to show the
137        image's color space, then the title or status bar will display a message
138        that the image is "not color managed". <emphasis>In reality the image is
139        still color managed</emphasis>, but now the image is color managed
140        "as if" it were in one of GIMP's built-in sRGB color spaces instead of
141        whatever color space it's actually in.
142            </para>
143        </listitem>
144      </orderedlist>
145  </sect3>
146
147  <sect3>
148    <title>
149      When <guimenuitem>Enable Color Management</guimenuitem>
150      is unchecked, what happens to the image
151      and the image appearance?
152    </title>
153    <note>
154      <para>
155        Assigning a new profile to an image doesn't change the image's
156      actual channel values. Assigning a new ICC profile only changes the meaning
157      of the channel values, which means the image appearance will change (unless
158      the original and new profile are functionally equivalent).
159      </para>
160    </note>
161    <para>
162      When <guimenuitem>Enable Color Management</guimenuitem> is unchecked,
163      GIMP assigns one of GIMP's
164      built-in sRGB profiles to the image. Assigning a new ICC profile to an image
165      doesn't change the image's channel values, but it does more or less
166      drastically change the image's appearance:
167    </para>
168    <orderedlist>
169      <listitem>
170        <para>If the image was already in one of GIMP's built-in color
171          spaces (or if the assigned ICC profile is a profile that is functionally
172          equivalent to the assigned GIMP built-in sRGB profile) then the image's
173          appearance will not change.
174        </para>
175      </listitem>
176      <listitem>
177        <para>
178          If the image was not already in one of GIMP's built-in
179          color spaces (and is not in a color space that is functionally
180          equivalent to the assigned GIMP built-in sRGB profile),
181          the image's appearance will change more
182          or less drastically depending on three things:
183        </para>
184        <itemizedlist>
185          <listitem>
186            <para>
187              What GIMP Precision channel encoding &mdash;
188              Linear light or Perceptual gamma (sRGB) &mdash; the image was in
189              before the <guimenuitem>Enable Color Management</guimenuitem> box was unchecked.
190            </para>
191          </listitem>
192          <listitem>
193            <para>
194              How far the image's originally assigned ICC profile's
195              channel encoding ("TRC") is from the GIMP Precision channel encoding.
196            </para>
197          </listitem>
198          <listitem>
199            <para>
200              How far the image's originally assigned ICC profile's
201              Red, Green, and Blue chromaticities are from GIMP's built-in sRGB
202              chromaticities.
203            </para>
204          </listitem>
205        </itemizedlist>
206      </listitem>
207    </orderedlist>
208  </sect3>
209
210  <sect3>
211    <title>
212      Two screenshots showing examples of correct and incorrect image
213      appearances after unchecking
214      <guimenuitem>Enable Color Management</guimenuitem>
215    </title>
216    <para>
217      In both screenshots shown below, the image is color
218      managed: An ICC profile is assigned to the image, and that profile is being
219      used to send the image colors to the screen.
220    </para>
221    <para>
222      But in the second screenshot, after unchecking Enable Color
223      Management, one of GIMP's built-in sRGB profiles has been incorrectly
224      assigned to the image, so the colors look wrong.
225    </para>
226    <para>
227      In screenshot 1 below, the image is already in a GIMP built-in sRGB
228      color space. So unchecking <guimenuitem>Enable Color Management</guimenuitem>
229      makes no difference in the appearance of the image. In this
230      particular case unchecking <guimenuitem>Enable Color Management</guimenuitem> actually makes
231      no difference at all, except that if you've selected to show the
232      image's assigned ICC profile in the title or status bar, then instead
233      of showing the assigned ICC profile, the title or status bar will
234      show the words "not color managed". But in reality the image is still
235      color managed:
236    </para>
237    <mediaobject>
238      <imageobject>
239        <imagedata fileref="images/menus/image/color-management/enable-cm-gimp-built-in-perceptual-srgb-color-space-enabled-disabled.png" format="PNG"/>
240      </imageobject>
241    </mediaobject>
242
243    <para>
244      In screenshot 2 below, the channel encoding of the original profile
245      matches the GIMP channel encoding (both are linear), but the
246      LargeRGB-elle-V4-g10.icc profile chromaticities don't match the GIMP built-in
247      sRGB chromaticities. So after unchecking
248      <guimenuitem>Enable Color Management</guimenuitem>, the tonality
249      is correct but the colors are wrong. The image is still color managed,
250      but it's color managed using the wrong ICC profile:
251    </para>
252    <mediaobject>
253      <imageobject>
254        <imagedata fileref="images/menus/image/color-management/enable-cm-linear-precision-mismatched-chromaticities.png" format="PNG"/>
255      </imageobject>
256    </mediaobject>
257    <caution>
258      <para>
259        If your image's originally assigned ICC profile doesn't have the same
260        channel encoding and chromaticities as the GIMP built-in sRGB profile, and
261        you uncheck and then immediately change your mind
262        and recheck <guimenuitem>Enable Color Management</guimenuitem>,
263        the originally assigned ICC profile
264        will be reassigned to your image and your image channel values will be
265        unchanged.
266      </para>
267      <para>
268        Otherwise, whether or not you can recover the originally
269        assigned ICC profile and correct colors for your image depends on what
270        else you've done between the unchecking and rechecking of
271        <guimenuitem>Enable Color Management</guimenuitem>.
272      </para>
273      <para>
274        Again, the best possible advice is to <emphasis role="bold">never uncheck <guimenuitem>Enable Color Management</guimenuitem></emphasis>.
275      </para>
276    </caution>
277<!--
278    <para>In screenshot 3 below, the chromaticities match, but the channel
279    encoding does not match:</para>
280    <mediaobject>
281      <imageobject>
282        <imagedata fileref="images/menus/image/color-management/enable-cm-linear-precision-mismatched-channel-encoding.png" format="PNG"/>
283      </imageobject>
284    </mediaobject>
285    <para>In screenshot 3 above, the sRGB-elle-V4-srgbtrc.icc chromaticities
286    match the chromaticities of the GIMP built-in linear sRGB profile, but the
287    sRGB-elle-V4-srgbtrc.icc profile channel encoding doesn't match the current
288    GIMP linear channel encoding. So after unchecking Enable Color
289    Management, the colors are correct but the tonality is wrong.</para>
290    <para>In screenshot 4 below, both the channel encoding and chromaticities
291    are mismatched:</para>
292    <mediaobject>
293      <imageobject>
294        <imagedata fileref="images/menus/image/color-management/enable-cm-mismatched-chromaticities-and-channel-encoding.png" format="PNG"/>
295      </imageobject>
296    </mediaobject>
297    <para>In Screenshot 4 above, the channel encoding of the original
298    LargeRGB-elle-V4-g10.icc profile is linear, but GIMP is using the
299    Perceptual gamma (sRGB) encoding. Also the LargeRGB-elle-V4-g10.icc
300    chromaticities don't match the GIMP built-in sRGB chromaticities.
301    So after unchecking Enable Color Management, the tonality is
302    wrong (it's too dark) and the colors are wrong.</para>-->
303  </sect3>
304
305</sect2>
306