[gimp-help] Adapted and added Elle's gimp.org tutorial to XML so that it can be translated to all languages
- From: Julien Hardlin <jhardlin src gnome org>
- To: commits-list gnome org
- Cc:
- Subject: [gimp-help] Adapted and added Elle's gimp.org tutorial to XML so that it can be translated to all languages
- Date: Fri, 16 Nov 2018 17:46:54 +0000 (UTC)
commit 117aaf066bc6055bcec71d7ae9e1ad5f7d556f92
Author: Julien Hardelin <jhardlin orange fr>
Date: Fri Nov 16 18:45:49 2018 +0100
Adapted and added Elle's gimp.org tutorial to XML so that it can be translated to all languages
.directory | 6 +
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diff --git a/src/annexes/tone-mapping/tone-mapping-tutorial.xml
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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook XML V4.3//EN"
+ "http://www.docbook.org/xml/4.3/docbookx.dtd";>
+
+<sect1 id="tone-mapping-tutorial">
+ <title>
+ Tone Mapping and Shadow Recovery Using GIMP’s ‘Colors/Exposure’
+ </title>
+
+ <para>
+ This tutorial comes from www.gimp.org/tutorials and was created by Elle
+ Stone. It is presented here for translations.
+ </para>
+
+ <para>
+ A very common editing problem is how to lighten the shadows and midtones of
+ an image while retaining highlight details, a task sometimes referred to as
+ “shadow recovery” and more generally speaking as “tone mapping”. This
+ step-by-step tutorial shows you how to use high bit depth GIMP’s floating
+ point “Colors/Exposure” operation to add one or more stops of positive
+ exposure compensation to an image’s shadows and midtones while retaining
+ highlight details.
+ </para>
+
+ <para>
+ Page Contents
+ <orderedlist>
+ <listitem>
+ <para>
+ <xref linkend="tone-mapping-introduction"/>
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <xref linkend="tone-mapping-example"/>
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <xref linkend="tone-mapping-notes"/>
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <xref linkend="tone-mapping-conclusion"/>
+ </para>
+ </listitem>
+ </orderedlist>
+ </para>
+
+ <sect2 id="tone-mapping-introduction">
+ <title>
+ High bit depth GIMP’s floating point “Colors/Exposure”: much better than
+ Curves for lightening the shadows and midtones of an image without
+ blowing the highlights
+ </title>
+ <para>
+ A very common editing problem is how to lighten the shadows and midtones
+ of an image without blowing out the highlights, which problem is very
+ often encountered when dealing with photographs of scenes lit by direct
+ sunlight. Precanned algorithms for accomplishing this task are often
+ referred to as “shadow recovery” algorithms. But really these algorithms
+ are special-purpose tone-mapping algorithms, which sometimes work pretty
+ well, and sometimes not so well, depending on the algorithm, the image,
+ and your artistic intentions for the image.
+ </para>
+ <para>
+ This step-by-step tutorial shows you how to use GIMP’s unbounded floating
+ point “Colors/Exposure” operation to recover shadow information—that is,
+ add one or more stops of positive exposure compensation to an image’s
+ shadows and midtones—without blowing out or unduly compressing the image
+ highlights. The procedure is completely “hand-tunable” using masks and
+ layers, and is as close as you can get to non-destructive image editing
+ using high bit depth GIMP 2.9/2.10.
+ </para>
+
+ <para>
+ <emphasis role="bold">Figure 1:</emphasis> power lines at noon
+ </para>
+ <para>
+ Before and after tone mapping (aka “shadow recovery”) using high bit
+ depth GIMP’s floating point “Colors/Exposure”.
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+fileref="images/tutorials/tone-mapping/before-auto-stretch-contrast.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para>
+ <emphasis>Scene-referred interpolated raw file.</emphasis>
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata fileref="images/tutorials/tone-mapping/power-lines.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para>
+ <emphasis>After tone mapping/shadow recovery using GIMP unbounded
+ Levels.</emphasis>
+ </para>
+ <para>
+ High bit depth GIMP is my primary image editor, and I’ve used the
+ procedure described below for the last couple of years as my “go to”
+ way to modify image tonality. The same general procedure can be used to
+ darken as well as lighten portions of an image, again controlling the
+ effect using a layer mask. This isn’t exactly nondestructive editing
+ because at some point you need to make a “New from Visible” layer. But
+ unlike using Curves, using high bit depth GIMP’s floating point
+ “Colors/Exposure” doesn’t clip RGB channel values and allows you to
+ fine-tune the results by modifying and re-modifying the layer mask
+ until you are completely happy with the resulting tonality.
+ </para>
+ </sect2>
+
+ <sect2 id="tone-mapping-example">
+ <title>
+ A step-by-step example showing how to recover shadow information using
+ high bit depth GIMP’s floating point “Colors/Exposure”
+ </title>
+ <para>
+ <emphasis role="bold">Figure 2</emphasis>
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+fileref="images/tutorials/tone-mapping/tree-exposed-for-sky-ground-is-dark.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para>
+ Using high bit depth GIMP’s “Colors/Exposure” to lighten the ground
+ by one stop without blowing out portions of the sky.
+ </para>
+ <itemizedlist>
+ <listitem>
+ <para>
+ <emphasis>Left</emphasis>: The original image, an
+ interpolated camera raw file that was deliberately
+ underexposed in camera to avoid blowing out the sky. It might
+ not appear to be the case, but this image is already very
+ close to having out of gamut RGB channel values in the sky,
+ and a simple Auto Stretch Contrast won’t lighten the image at
+ all.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <emphasis>Right</emphasis>: The same image after using high
+ bit depth GIMP’s “Colors/Exposure” at 32-bit floating point
+ linear precision to add one stop of positive exposure
+ compensation. An inverse grayscale mask was used to keep the
+ highlights from blowing out.
+ </para>
+ </listitem>
+ </itemizedlist>
+ <para>
+ This step-by-step example provides a sample image and is broken down into
+ five steps, starting with downloading the image. Steps 3, 4, and 5
+ describe the actual procedure.
+ </para>
+ <procedure>
+ <step>
+ <para>
+ <emphasis role="bold">Download</emphasis> <ulink
+url="https://www.gimp.org/tutorials/Tone_Mapping_Using_GIMP_Levels/tree.png";>
+tree.png</ulink>,
+ which is a 16-bit integer sRGB image. High bit depth GIMP really is
+ an “sRGB only” image editor, so it’s best if you don’t even try to
+ edit in other RGB working spaces.
+ </para>
+ </step>
+ <step>
+ <para>
+ <emphasis role="bold">Open tree.png with GIMP and assign the GIMP
+ built-in sRGB profile (the image colors won’t change a bit). Then
+ convert the image to 32-bit floating point linear
+ precision</emphasis>: Go to “Image/Precision”, select “32-bit
+ floating point”, and when the Dither dialog pops up, select “Linear
+ light” (this ensures that the Normal blend mode produces
+ radiometrically correct results).
+ </para>
+ </step>
+ <step>
+ <para>
+ Make a copy of the “tree.png” layer, and label it “+1 stop exposure
+ comp”. Then use “Colors/Exposure” to add one stop of positive
+ exposure compensation—Figure 3 below shows the proper settings for
+ the “Colors/Exposure” dialog, and Figure 4 shows the result:
+ </para>
+ <para><emphasis role="bold">Figure 3</emphasis></para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+ fileref=
+"images/tutorials/tone-mapping/add-one-stop-positive-exposure-compensation.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para>
+ <emphasis>Using “Colors/Exposure” to add one stop of positive
+ exposure compensation.</emphasis>
+ </para>
+ <para>
+ When using “Colors/Exposure” to add one stop of positive exposure
+ compensation, make sure the image really is at floating point
+ precision, because integer precision will clip the highlights.
+ </para>
+ <para>
+ <emphasis role="bold">Figure 4</emphasis>
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+ fileref=
+"images/tutorials/tone-mapping/1-stop-positive-exposure-compensation-added.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para>
+ At floating point precision, GIMP’s “Colors/Exposure”
+ operation is unbounded. This means you can use
+ “Colors/Exposure” to add positive exposure compensation
+ without blowing out the highlights.
+ </para>
+ <para>
+ Notice the RGB channel values for the four sample points:
+ the channel information that would have been clipped using
+ integer precision is encoded using channel values that are
+ greater than 1.0 floating point.
+ </para>
+ <para>
+ The image in Figure 4 clearly has “blown” highlights in the sky.
+ But the highlights aren’t really blown (that is, clipped to 1.0 in
+ one or more channels). Instead the highlight information is still
+ there, but the RGB channel values fall outside the RGB <ulink url=
+"http://ninedegreesbelow.com/photography/display-referred-scene-referred.html";>
+ display channel value</ulink> range of 0.0f to 1.0f. The sample
+ points dialog in Figure 4 above shows four sample points that have RGB
+ channel values that are greater than 1.0. As shown in Figure 5 below,
+ adding a mask allows you to recover these highlights by bringing
+ them back down into the display range.
+ </para>
+ <para>
+ If you had used integer precision instead of floating point, the
+ highlights really would be blown: The sample points would have a
+ maximum channel values of 255, 65535 or 4294967295, depending on
+ the bit depth. And masking would only “recover” a solid expanse of
+ gray, completely lacking any details (try for yourself and see what
+ happens).
+ </para>
+ </step>
+ <step>
+ <para>
+ <emphasis role="bold">Add an inverse grayscale layer mask</emphasis>:
+ Right-click on the layer and select “Layer/Mask/Add Layer Mask”, and
+ when the “Add a mask to the Layer” dialog pops up, choose “Grayscale
+ copy of layer” and check the “Invert mask” box.
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+fileref="images/tutorials/tone-mapping/add-inverse-grayscale-mask.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para>
+ As shown in Figure 5 below, at this point the highlights will be
+ brought back into the display range, meaning all RGB channel values
+ are between 0.0f and 1.0f. But the image will probably look a little
+ odd (sort of cloudy and flat), and depending on the image, the
+ brightest highlights might actually have dark splotches—don’t worry!
+ this is temporary.
+ </para>
+ <para>
+ <emphasis role="bold">Figure 5</emphasis>
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+ fileref="images/tutorials/tone-mapping/inverse-grayscale-mask-added.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para>
+ Result of adding an inverse grayscale layer mask to bring the
+ highlights back into the display range.
+ </para>
+ <para>
+ Adding an inverse grayscale layer mask brings the highlights
+ back into the display range, but at this point most images will
+ look flat and cloudy, and some images will have dark splotches
+ in the highlights. The next step—“Auto Stretch Contrast”
+ performed on the mask—will take care of this problem.
+ </para>
+ </step>
+ <step>
+ <para>
+ <emphasis role="bold">Click on the layer mask to select it for
+ editing, and then select “Colors/Auto/Stretch Contrast”</emphasis>:
+ <mediaobject>
+ <imageobject>
+ <imagedata
+fileref="images/tutorials/tone-mapping/auto-stretch-contrast-mask.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ </para>
+ <para><emphasis>
+ “Keep Colors” should be checked (though it doesn’t really
+ matter on grayscale images such as layer masks).</emphasis>
+ </para>
+ <para>
+ <emphasis role="bold">Figure 6</emphasis> below shows the final
+ result:
+ <mediaobject>
+ <imageobject>
+ <imagedata
+fileref="images/tutorials/tone-mapping/gegl-exposure-mask-auto-stretched.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ </para>
+ <para><emphasis>
+ Doing “Auto/Stretch Contrast” on the layer mask removes the
+ “cloudy” appearance, leaving a nicely brightened image with
+ intact highlights.</emphasis>
+ </para>
+ <para>
+ “Auto/Stretch Contrast” on the mask is necessary because just like
+ the image layer has out of gamut RGB channel values, the inverted
+ grayscale mask contains out of gamut grayscale values.
+ “Auto/Stretch Contrast” brings all the mask grayscale values back
+ into the display range, allowing the mask to proportionately
+ compensate for the layer’s otherwise out-of-gamut RGB channel
+ values, masking more in the layer highlights and less/not at all in
+ the image’s shadows and midtones.
+ </para>
+ <para>
+ <emphasis role="small">Notice that one of the sample points still
+ has a blue RGB channel value that is slightly out of gamut. The
+ easiest way to deal with this is to “Colors/Exposure” to make a
+ Gamma adjustment of 0.45 on the mask, not on the actual image
+ layer. You can make this Gamma adjustment either on the entire mask
+ (works well, less effort). Or else you can make the adjustment just
+ on the mask shadows (which correspond to the layer highlights), in
+ which case you’d load the mask as a selection, invert the
+ selection, and make the Gamma adjustment. Or if the remaining out
+ of gamut channel values are only very slightly out of gamut, make a
+ “New from Visible” layer and then “Auto/Stretch Contrast” the
+ result to bring the remaining channel values back into
+ gamut.</emphasis>
+ </para>
+ <para>
+ That’s the whole procedure for using “Colors/Exposure” to add a
+ stop of positive exposure compensation to the shadows without
+ blowing out the highlights. Now you can either fine-tune the mask,
+ or else just make a “New from Visible” layer and continue editing
+ your nicely brightened image. Depending on the image and also on
+ your artistic intentions for the image, the mask might not need
+ fine-tuning. But very often you’ll want to modify the resulting
+ tonal distribution by doing a “Colors/Exposure” gamma correction,
+ or perhaps a Curves operation on the mask, or else by painting
+ directly on the mask. And sometimes you’ll want to blur the mask to
+ restore micro contrast<xref linkend="restore-micro-contrast"/>.
+ </para>
+ </step>
+ </procedure>
+ </sect2>
+
+ <sect2 id="tone-mapping-notes">
+ <title>Use Notes</title>
+ <orderedlist>
+ <listitem><!--1-->
+ <para>
+ Depending on your particular artistic intentions for an image, some
+ images are more likely than others to benefit from being tone
+ mapped using floating point “Colors/Exposure”. Your mileage may
+ vary, but typically the procedure described on this page works best
+ for photographs of scenes with a pronounced tonal difference
+ between the highlights and shadows, as per typical sunny day
+ “sky-ground” photographs.
+ </para>
+ </listitem>
+ <listitem><!--2-->
+ <para>
+ <emphasis role="bold">For adding just one stop of positive exposure
+ compensation, the procedure described on this page works really
+ well</emphasis>. Depending on the image you might want to blur the
+ mask using an edge-respecting blur algorithm, and/or tweak the mask
+ using “Colors/Exposure”, Curves, etc. But only modify the mask
+ after using Auto Stretch Contrast on the mask. Otherwise results
+ will be unpredictable:
+<ulink url="http://ninedegreesbelow.com/photography/unbounded-srgb-levels-gamma-slider.html";>
+Gamma adjustments produce odd results when operating on out of gamut values</ulink>,
+ and Curves will summarily clip out of gamut values.
+ </para>
+ </listitem>
+ <listitem>
+ <para><!--3-->
+ <emphasis role="bold">For adding more than one stop of exposure
+ compensation, you can use one or more than one
+ positive-exposure-compensation layers</emphasis>. Either way the
+ layer mask(s) will need careful tweaking that’s very
+ image-specific and also specific to your intended result. Figure 7
+ shows an example of using two exposure compensation layers to add
+ two and a half stops of exposure compensation to the shadows and
+ midtones of an image:
+ </para>
+ <para>
+ Using GIMP’s floating point unbounded Levels plus layer masks
+ to add two stops of positive exposure compensation to the
+ shadows and midtones of a photograph of an apple orchard truck
+ that was taken in bright sunshine.
+ </para>
+ <para><emphasis role="bold">Figure 7</emphasis></para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+fileref="images/tutorials/tone-mapping/apple-orchard-truck-from-camera.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para><emphasis>
+ Image from the camera, underexposed to avoid blowing out
+ highlights.</emphasis>
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+fileref=
+"images/tutorials/tone-mapping/apple-orchard-truck-tone-mapped-with-Exposur.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para><emphasis>
+ After tone mapping/shadow recovery using high bit depth
+ GIMP's floating point "Color/Exposure".</emphasis>
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+fileref="images/tutorials/tone-mapping/truck-tone-mapped-using-gegl-mantuik.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para><emphasis>
+ For comparison, Mantuik tone mapping using the GEGL default
+ settings.</emphasis>
+ </para>
+ <para>
+ Using GIMP’s floating point “Colors/Exposure” plus layer masks to
+ add two and a half stops of positive exposure compensation to the
+ shadows and midtones of a “bright sun” photograph of an apple
+ orchard truck.
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+ fileref="images/tutorials/tone-mapping/orchard-truck-layer-stack.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para><emphasis>
+ A screenshot of the layer stack that I used to tone-map the
+ photograph of the apple orchard truck. Tone-mapping by hand
+ gives you complete control over the resulting image. Mantuik
+ and other “automagic” tone-mapping algorithms are
+ CPU-intensive, unpredictable, and often produce
+ unnatural-looking results.
+ </emphasis>
+ </para>
+ </listitem>
+
+ <listitem><!--4-->
+ <para>
+ Before using “Colors/Exposure” to add positive exposure
+ compensation, <emphasis>the base layer should already be stretched
+ to its maximum dynamic range</emphasis>. The easiest way to stretch
+ the base layer to its maximum dynamic range is to do
+ “Colors/Auto/Stretch Contrast” and make sure that “Keep colors” is
+ checked.
+ </para>
+ <para>
+ If you’ve never used an unbounded floating point image editor
+ before, “Colors/Auto/Stretch Contrast” can produce an unexpected
+ result: The image might actually end up with a severely reduced
+ dynamic range, having either lighter shadows or darker highlights
+ or both:
+ </para>
+ <para>
+ Before and after doing “Colors/Auto/Stretch Contrast” on the base
+ layer, plus the final image after tone mapping using
+ “Colors/Exposure”:
+ </para>
+ <para><emphasis role="bold">Figure 8</emphasis></para>
+ <para>1. Image from the camera</para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+ fileref="images/tutorials/tone-mapping/before-auto-stretch-contrast.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para>
+ 2. After doing "Colors/Auto/Stretch Contrast".
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+ fileref="images/tutorials/tone-mapping/after-auto-stretch-contrast.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para>
+ 3. Final "Power lines" image.
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+ fileref="images/tutorials/tone-mapping/power-lines.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <orderedlist>
+ <listitem>
+ <para>
+ This scene-referred interpolated raw file from the PhotoFlow
+ raw processor (which provides a GIMP plug-in for easy opening
+ of raw files) has out-of-display-range RGB channel values that
+ will be brought back into the display range by doing
+ “Colors/Auto/Stretch Contrast”.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ After doing “Colors/Auto/Stretch Contrast”, shadows are lighter
+ and highlights are darker because the dynamic range has been
+ compressed to fit within the display range. This looks like an
+ editing step in the wrong direction! but actually it’s
+ necessary.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Here’s the final “Power lines” image after tone mapping the
+ scene-referred interpolated raw file using the procedure
+ described in this tutorial.
+ </para>
+ </listitem>
+ </orderedlist>
+ <para>
+ As captured by the raw file, this picture of power lines marching
+ into the distance is a typical result of taking a photograph at
+ noon on a bright sunny day: The sky and clouds looked pretty good
+ right out of the camera, but the ground was far too dark. So the
+ image could benefit from some tone mapping to raise the shadows and
+ midtones. The first step is to do “Colors/Auto/Stretch Contrast” to
+ bring any channel values that are less than 0.0f or greater than
+ 1.0f back within the display range of 0.0 to 1.0 floating point.
+ </para>
+ <para>
+ Performing “Auto/Stretch Contrast” to bring the channel values back
+ inside the display range doesn’t exactly look like an editing step
+ in the right direction for tone-mapping this particular image! but
+ really it is. Using “Colors/Exposure” to add positive exposure
+ compensation to the shadows and midtones won’t work if the image
+ has channel values that fall outside the display range.
+ </para>
+ </listitem>
+ <listitem><!--5-->
+ <para>
+ <emphasis role="bold">Dispensing with “useless” shadow and
+ highlight information:</emphasis> Sometimes interpolated raw
+ files of photographs of high dynamic range scenes end up with a
+ sprinkling of highlight and shadow pixels that contains
+ essentially no useful information. The easiest thing to do with
+ such pixels is to use “Colors/Exposure” to set the desired black
+ and white points, and then clip the resulting out of gamut
+ channel information.
+ </para>
+ <itemizedlist mark="bullet">
+ <listitem>
+ <para>
+ <emphasis role="bold">Useless highlight information:</emphasis>
+ For the “Power lines” picture shown in Figure 8 above, after
+ doing “Color/Auto/Stretch Contrast”, a measly 48 pixels
+ occupied nearly half the tonal range (see the histogram to the
+ right). A little investigation with GIMP’s Threshold tool
+ revealed that all 48 pixels are the peak values of specular
+ highlights on the ceramic insulators on the power line pole in
+ the foreground.
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+ fileref="images/tutorials/tone-mapping/histogram-specular-highlights.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para>
+ In cases where nearly half the histogram is occupied by a
+ sprinkling of specular highlights, clipping the pixels is often
+ the best and easiest solution. For the “Power lines” image, the
+ 48 pixels in question carried essentially zero information. So
+ I used “Colors/Exposure” to raise the white point, and then
+ used “Tools/GEGL Operation/Clip RGB” to actually clip the
+ channel information in the highlights (this time making sure
+ the “Clip high pixel values” box was checked).
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ <emphasis role="bold">Useless shadow information:</emphasis>
+ Some raw processors can output images with negative channel
+ values. And previous edits using high bit depth GIMP might have
+ produced negative channel values. If doing an “Auto/Stretch
+ Contrast” on your base image layer makes the image a whole lot
+ lighter in the shadows, the problem is negative RGB channel
+ values. One solution is to use “Colors/Exposure” to move the
+ black point to where you want it to be, and then clip the
+ negative channel values. Here are two ways to clip negative
+ channel values:
+ </para>
+ <itemizedlist mark="opencircle">
+ <listitem>
+ <para>
+ Use “Tools/GEGL Operation/Clip RGB”, making sure to
+ uncheck the “Clip high pixel values” box.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Or else create a solid black layer above your base image
+ layer, set the blend mode to “Lighten only”, and make a
+ “New from Visible” layer.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </listitem>
+ </itemizedlist>
+ </listitem>
+ <listitem id="restore-micro-contrast"><!--6-->
+ <para>
+ <emphasis role="bold">Blurring the mask to restore micro
+ contrast:</emphasis> Putting an inverse mask on a layer that’s
+ used to add positive exposure compensation necessarily slightly
+ flattens micro contrast. Depending on your artistic intentions
+ for the image, you might want to blur the mask to restore micro
+ contrast. The trick is how to blur the mask without introducing
+ “halos” around the edges of objects in the image. Small radius
+ Gaussian blurs produce small but distressingly obvious halos
+ around dark edges. A large radius gaussian blur sometimes works
+ but just as often produces a large obvious halo separating the
+ brighter and darker portions of the image. For many images a
+ better solution is to blur the mask use an edge-respecting filter
+ such as the GIMP G’MIC bilateral smooth filter:
+ </para>
+ <para>
+ Adding exposure compensation with and without bilateral
+ smoothing of the mask.
+ </para>
+ <para><emphasis role="bold">Figure 9</emphasis></para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+fileref="images/tutorials/tone-mapping/without-bilateral-smoothing-of-mask.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para><emphasis>
+ Without applying bilateral smoothing to the mask, micro
+ contrast is flattened.</emphasis>
+ </para>
+ <mediaobject>
+ <imageobject>
+ <imagedata
+fileref="images/tutorials/tone-mapping/with-bilateral-smoothing-of-mask.jpg"
+ format="JPG"/>
+ </imageobject>
+ </mediaobject>
+ <para><emphasis>
+ After applying bilateral smoothing to the mask, micro
+ contrast is restored.</emphasis>
+ </para>
+ <para>
+ Adding exposure compensation combined with an inverse grayscale
+ mask does flatten micro contrast, which might or might not be
+ desirable depending on your artistic intentions for the image.
+ To restore micro contrast, try using an edge-respecting blur such
+ as G’MIC’s bilateral smoothing filter. GIMP G’MIC doesn’t work on
+ layer masks. A workaround is to to turn the unblurred mask into a
+ selection, save the selection as a channel, and then drag the
+ channel to the layer stack for blurring.
+ </para>
+ </listitem>
+ <listitem><!--7-->
+ <para>
+ An essential component of the procedure for using “Colors/Exposure”
+ to add positive exposure compensation to images with dark shadows
+ and midtones needs to be explicitly mentioned: Not only is the high
+ bit depth GIMP’s “Colors/Exposure” operation unbounded at floating
+ point precision —
+ <ulink url="https://bugzilla.gnome.org/show_bug.cgi?id=737925";>layer masks
+are also unbounded</ulink>.
+ </para>
+ <para>
+ If the inverted grayscale masks were summarily clipped (as is the
+ case when editing at integer precision), then the procedure
+ described in this tutorial wouldn’t work.
+ </para>
+ </listitem>
+ </orderedlist>
+ </sect2>
+ <sect2 id="tone-mapping-conclusion">
+ <title>Conclusion</title>
+ <para>
+ Photographs taken in bright direct sunlight typically are of high
+ dynamic range scenes, and the resulting camera file usually requires
+ careful tone mapping to produce a satisfactory final image. High bit
+ depth GIMP’s floating point floating point “Colors/Exposure” provides a
+ very useful tool for dealing with this type of image, and of course is
+ equally useful for any image where the goal is to raise the shadows and
+ midtones without blowing out the highlights.
+ </para>
+ <para>
+ High bit depth GIMP’s floating point “Colors/Exposure” combined with a
+ suitable layer mask can also be used to darken portions of the image,
+ either by moving the upper left Value slider to the right (darkens the
+ image by increasing contrast and also increases saturation; requires
+ careful masking to avoid producing regions of solid black), or moving
+ the lower right Value slider to the left (darkens the image by
+ decreasing contrast, useful for de-emphasizing portions of the image).
+ </para>
+ <para>
+ This is a GIMP-specific tutorial. However, the same technique can be
+ employed using the PhotoFlow raw processor and possibly other image
+ editors that allow for 32-bit floating point processing using unbounded
+ RGB channel values. The neat thing about using this technique in
+ PhotoFlow is that PhotoFlow uses nodes, which allows for completely
+ non-destructive editing of the inverted grayscale mask that’s used to
+ recover the highlight detail after applying positive exposure
+ compensation to raise the tonality of the shadows and midtones (even if
+ you close and reopen the image, if you save the image’s PFI file).
+ </para>
+ <para>
+ <subscript>
+ The original tutorial this was adapted from can be <!--linkfound
+ here--> and is reproduced courtesy of Elle Stone
+ <!--link>(http://ninedegreesbelow.com).--></subscript>
+ </para>
+ <para>
+ <subscript>
+ GIMP Tutorial - Tone Mapping Using GIMP Levels (text and images) by Elle
+ Stone is licensed under a Creative Commons Attribution-ShareAlike 3.0
+ Unported License.</subscript>
+ </para>
+ </sect2>
+</sect1>
+
+
diff --git a/src/gimp.xml b/src/gimp.xml
index 6ef17bf6c..fd2149897 100755
--- a/src/gimp.xml
+++ b/src/gimp.xml
@@ -201,14 +201,22 @@
<xi:include href="filters/web.xml"/>
<xi:include href="filters/animation.xml"/>
<!-- -->
+ </chapter>
+ </part>
+ <part id="Annexes">
+ <title>Annexes</title>
+ <chapter id="Tutorials">
+ <title>Tone-mapping</title>
+ <xi:include href="annexes/tone-mapping/tone-mapping-tutorial.xml"/>
</chapter>
-
</part>
+
<xi:include href="key-reference.xml"/>
<xi:include href="glossary/glossary.xml"/>
<!--
<xi:include href="dictionary/dictionary.xml"/>
-->
+
<xi:include href="appendix/bibliography.xml"/>
<xi:include href="appendix/history.xml"/>
<xi:include href="appendix/bugs.xml"/>
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