home *** CD-ROM | disk | FTP | other *** search
- <?xml version="1.0" encoding="UTF-8" standalone="no"?>
- <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
- <html xmlns="http://www.w3.org/1999/xhtml">
- <head>
- <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
- <title>Chapter 8.  Combining Images</title>
- <link rel="stylesheet" href="gimp-help-plain.css" type="text/css" />
- <link rel="stylesheet" href="gimp-help-screen.css" type="text/css" />
- <link rel="stylesheet" href="gimp-help-custom.css" type="text/css" />
- <link rel="alternate stylesheet" href="gimp22.css" type="text/css" title="gimp22" />
- <meta name="generator" content="DocBook XSL Stylesheets V1.73.2" />
- <link rel="start" href="index.html" title="GNU Image Manipulation Program" />
- <link rel="up" href="pt02.html" title="Part II.  How do I Become a GIMP Wizard?" />
- <link rel="prev" href="gimp-using-rectangular.html" title="13.2.  Creating a Basic Shape" />
- <link rel="next" href="gimp-concepts-layer-modes.html" title="2.  Layer Modes" />
- </head>
- <body>
- <div class="navheader">
- <table width="100%" summary="Navigation header">
- <tr>
- <th colspan="3" align="center">Chapter 8. 
- <span lang="en" xml:lang="en">Combining Images</span>
- </th>
- </tr>
- <tr>
- <td width="20%" align="left"><a accesskey="p" href="gimp-using-rectangular.html"><img src="../images/prev.png" alt="Prev" /></a> </td>
- <th width="60%" align="center">Part II. 
- <span lang="en" xml:lang="en">
- How do I Become a <acronym class="acronym">GIMP</acronym> Wizard?
- </span>
- </th>
- <td width="20%" align="right"> <a accesskey="n" href="gimp-concepts-layer-modes.html"><img src="../images/next.png" alt="Next" /></a></td>
- </tr>
- </table>
- <hr />
- </div>
- <div class="chapter" lang="en" xml:lang="en">
- <div class="titlepage">
- <div>
- <div>
- <h2 class="title"><a id="gimp-image-combining"></a>Chapter 8. 
- <span lang="en" xml:lang="en">Combining Images</span>
- </h2>
- </div>
- </div>
- </div>
- <div class="toc">
- <p>
- <b>Table of Contents</b>
- </p>
- <dl>
- <dt>
- <span class="sect1">
- <a href="gimp-image-combining.html#gimp-concepts-layers">1.
- <span lang="en" xml:lang="en">Introduction to Layers</span>
- </a>
- </span>
- </dt>
- <dd>
- <dl>
- <dt>
- <span class="sect2">
- <a href="gimp-image-combining.html#gimp-layer-properties">1.1.
- <span lang="en" xml:lang="en">Layer Properties</span>
- </a>
- </span>
- </dt>
- </dl>
- </dd>
- <dt>
- <span class="sect1">
- <a href="gimp-concepts-layer-modes.html">2.
- <span lang="en" xml:lang="en">Layer Modes</span>
- </a>
- </span>
- </dt>
- <dt>
- <span class="sect1">
- <a href="gimp-using-layers.html">3.
- <span lang="en" xml:lang="en">Creating New Layers</span>
- </a>
- </span>
- </dt>
- <dt>
- <span class="sect1">
- <a href="gimp-concepts-text.html">4.
- <span lang="en" xml:lang="en">Text and Fonts</span>
- </a>
- </span>
- </dt>
- <dt>
- <span class="sect1">
- <a href="gimp-using-text.html">5.
- <span lang="en" xml:lang="en">Text</span>
- </a>
- </span>
- </dt>
- <dd>
- <dl>
- <dt>
- <span class="sect2">
- <a href="gimp-using-text.html#id2603987">5.1.
- <span lang="en" xml:lang="en">Embellishing Text</span>
- </a>
- </span>
- </dt>
- <dt>
- <span class="sect2">
- <a href="gimp-using-fonts.html">5.2.
- <span lang="en" xml:lang="en">Adding Fonts</span>
- </a>
- </span>
- </dt>
- <dt>
- <span class="sect2">
- <a href="font-problems.html">5.3.
- <span lang="en" xml:lang="en">Font Problems</span>
- </a>
- </span>
- </dt>
- </dl>
- </dd>
- </dl>
- </div>
- <div class="sect1" lang="en" xml:lang="en">
- <div class="titlepage">
- <div>
- <div>
- <h2 class="title" style="clear: both"><a id="gimp-concepts-layers"></a>1. 
- <span lang="en" xml:lang="en">Introduction to Layers</span>
- </h2>
- </div>
- </div>
- </div>
- <a id="id2599016" class="indexterm"></a>
- <p>
- A good way to visualize a GIMP image is as a stack of transparencies: in
- GIMP terminology, each individual transparency is called a
- <span class="emphasis"><em>layer</em></span>. There is no limit, in principle, to the number
- of layers an image can have: only the amount of memory available on the
- system. It is not uncommon for advanced users to work with images
- containing dozens of layers.
- </p>
- <p>
- The organization of layers in an image is shown by the Layers dialog,
- which is the second most important type of dialog window in GIMP, after
- the Main Toolbox. The appearance of the Layers dialog is shown in the
- adjoining illustration. How it works is described in detail in the
- <a class="link" href="gimp-dialogs-structure.html#gimp-layer-dialog" title="2.1.  Layers Dialog">Layers Dialog</a>
- section, but we will touch on some aspects of it here, in relation to the
- layer properties that they display.
- </p>
- <p>
- <a id="id2599061" class="indexterm"></a>
- Each open image has at any time a single
- <span class="emphasis"><em>active drawable</em></span>. A “<span class="quote">drawable</span>”
- is a GIMP concept that includes layers, but also several other types of
- things, such as channels, layer masks, and the selection mask. (Basically,
- a “<span class="quote">drawable</span>”
- is anything that can be drawn on with painting tools). If a layer is
- currently active, it is shown highlighted in the Layers dialog, and its
- name is shown in the status area of the image window. If not, you can
- activate it by clicking on it. If none of the layers are highlighted, it
- means the active drawable is something other than a layer.
- </p>
- <p>
- In the menubar above an image window, you can find a menu called
- <span class="guimenu">Layer</span>, containing a number of commands that
- affect the active layer of the image. The same menu can be
- accessed by right-clicking in the Layers dialog.
- </p>
- <div class="sect2" lang="en" xml:lang="en">
- <div class="titlepage">
- <div>
- <div>
- <h3 class="title"><a id="gimp-layer-properties"></a>1.1. 
- <span lang="en" xml:lang="en">Layer Properties</span>
- </h3>
- </div>
- </div>
- </div>
- <p>
- Each layer in an image has a number of important attributes:
- </p>
- <div class="variablelist">
- <dl>
- <dt>
- <span class="term">Name</span>
- </dt>
- <dd>
- <p>
- Every layer has a name. This is assigned automatically when the
- layer is created, but you can change it. You can change the name
- of a layer either by double-clicking on it in the Layers dialog,
- or by right-clicking there and then selecting the top entry in the
- menu that appears,
- <span class="guimenuitem">Edit Layer Attributes</span>.
- </p>
- </dd>
- <dt>
- <span class="term">Presence or absence of an alpha channel</span>
- </dt>
- <dd>
- <a id="id2599168" class="indexterm"></a>
- <a id="id2599176" class="indexterm"></a>
- <p>
- An alpha channel encodes information about how transparent a layer
- is at each pixel. It is visible in the Channel Dialog: white is
- complete opacity, black is complete transparency and grey levels
- are partial transparencies.
- </p>
- <p>
- The background layer is particular. If you have just created a
- new image, it has still only one layer which is a background
- layer. If the image has been created with an opaque Fill type,
- this one layer has no Alpha channel. If you add a new layer,
- even with an opaque Fill type, an Alpha channel is automatically
- created, which applies to all layers apart from the background
- layer. To get a background layer with transparency, either you
- create your new image with a transparent Fill type, or you use
- the
- <a class="link" href="gimp-layer-alpha-add.html" title="10.32.  Add Alpha Channel">Add an Alpha Channel</a>.
- </p>
- <p>
- Every layer other than the bottom layer of an image has
- automatically an Alpha channel, but you can't see a grayscale
- representation of the alpha values. See
- <a class="link" href="glossary.html#glossary-alpha" title="Alpha">Alpha</a> in Glossary for
- more information.
- </p>
- <p><a id="alpha-channel-example"></a><b>
- <span lang="en" xml:lang="en">Example for Alpha channel</span>
- . </b><a id="id2599251" class="indexterm"></a>
- </p>
- <div class="figure">
- <a id="id2599262"></a>
- <p class="title">
- <b>Figure 8.1. 
- <span lang="en" xml:lang="en">Alpha channel example: Basic image</span>
- </b>
- </p>
- <div class="figure-contents">
- <div class="mediaobject">
- <img src="../images/glossary/alpha-channel-0.png" alt="Alpha channel example: Basic image" />
- <div class="caption">
- <p>
- This image has three layers painted with pure 100% opaque
- Red, Green, and Blue. In the Channel Dialog, you can see
- that an alpha Channel has been added. It is white because
- the image is not transparent since there is at least one
- 100% opaque layer. The current layer is the red one : since
- it is painted with pure red, there is no green and no blue
- and the corresponding channels are black.
- </p>
- </div>
- </div>
- </div>
- </div>
- <p><br class="figure-break" />
- </p>
- <div class="figure">
- <a id="id2599317"></a>
- <p class="title">
- <b>Figure 8.2. 
- <span lang="en" xml:lang="en">
- Alpha channel example: One transparent layer
- </span>
- </b>
- </p>
- <div class="figure-contents">
- <div class="mediaobject">
- <img src="../images/glossary/alpha-channel-1.png" alt="Alpha channel example: One transparent layer" />
- <div class="caption">
- <p>
- The left part of the first layer has been made transparent
- (Rectangular selection, Edit/Clear). The second layer,
- green, is visible. The Alpha channel is still white, since
- there is an opaque layer in this part of the image.
- </p>
- </div>
- </div>
- </div>
- </div>
- <p><br class="figure-break" />
- </p>
- <div class="figure">
- <a id="id2599360"></a>
- <p class="title">
- <b>Figure 8.3. 
- <span lang="en" xml:lang="en">
- Alpha channel example: Two transparent layers
- </span>
- </b>
- </p>
- <div class="figure-contents">
- <div class="mediaobject">
- <img src="../images/glossary/alpha-channel-2.png" alt="Alpha channel example: Two transparent layers" />
- <div class="caption">
- <p>
- The left part of the second layer has been made
- transparent. The third layer, blue, is visible through the
- first and second layers. The Alpha channel is still white,
- since there is an opaque layer in this part of the image.
- </p>
- </div>
- </div>
- </div>
- </div>
- <p><br class="figure-break" />
- </p>
- <div class="figure">
- <a id="id2599402"></a>
- <p class="title">
- <b>Figure 8.4. 
- <span lang="en" xml:lang="en">
- Alpha channel example: Three transparent layers
- </span>
- </b>
- </p>
- <div class="figure-contents">
- <div class="mediaobject">
- <img src="../images/glossary/alpha-channel-3a.png" alt="Alpha channel example: Three transparent layers" />
- <div class="caption">
- <p>
- The left part of the third layer has been made transparent.
- The Alpha channel is still white and the left part of the
- layer is white, opaque! The background layer has
- no Alpha channel. In this case, the Clear command works
- like the Eraser and uses the Background color of Toolbox.
- </p>
- </div>
- </div>
- </div>
- </div>
- <p><br class="figure-break" />
- </p>
- <div class="figure">
- <a id="id2599446"></a>
- <p class="title">
- <b>Figure 8.5. 
- <span lang="en" xml:lang="en">
- Alpha channel example: Alpha channel added to the Background
- </span>
- </b>
- </p>
- <div class="figure-contents">
- <div class="mediaobject">
- <img src="../images/glossary/alpha-channel-3b.png" alt="Alpha channel example: Alpha channel added to the Background" />
- <div class="caption">
- <p>
- We used the
- <span class="guimenu">Layer</span> ‚Üí <span class="guimenuitem">Transparency</span> ‚Üí <span class="guisubmenu">Add Alpha Channel</span>
- command, which is active on the Background layer only.
- Now, the left part of the image is fully transparent and
- has the color of the page the image is lying on. The left
- part of the Alpha Channel thumbnail is black (transparent)
- in the Channel Dialog.
- </p>
- </div>
- </div>
- </div>
- </div>
- <p><br class="figure-break" />
- </p>
- </dd>
- <dt>
- <span class="term">Layer type</span>
- </dt>
- <dd>
- <a id="id2599526" class="indexterm"></a>
- <p>
- The layer type is determined by the image type (see previous
- section) and the presence or absence of an alpha channel. These
- are the possible layer types:
- </p>
- <div class="itemizedlist">
- <ul type="disc">
- <li>
- <p>RGB</p>
- </li>
- <li>
- <p>RGBA</p>
- </li>
- <li>
- <p>Gray</p>
- </li>
- <li>
- <p>GrayA</p>
- </li>
- <li>
- <p>Indexed</p>
- </li>
- <li>
- <p>IndexedA</p>
- </li>
- </ul>
- </div>
- <p>
- The main reason this matters is that most filters (in the
- <span class="guimenu">Filters</span>
- menu) only accept a subset of layer types, and appear grayed out
- in the menu if the active layer does not have an acceptable type.
- Often you can rectify this either by changing the mode of the
- image or by adding or removing an alpha channel.
- </p>
- </dd>
- <dt>
- <span class="term">
- <span class="guiicon">
- <span class="inlinemediaobject"><img src="../images/dialogs/stock-eye-20.png" /></span>
- </span>
- <span lang="en" xml:lang="en">Visibility</span>
- </span>
- </dt>
- <dd>
- <a id="id2599652" class="indexterm"></a>
- <p>
- It is possible to temporarily remove a layer from an image,
- without destroying it, by clicking on the symbol in the Layers
- dialog. This is called “<span class="quote">toggling the visibility</span>”
- of the layer. Most operations on an image treat toggled-off layers
- as if they did not exist. When you work with images containing
- many layers, with varying opacity, you often can get a better
- picture of the contents of the layer you want to work on by hiding
- some of the other layers.
- </p>
- <div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
- <table border="0" summary="Tip">
- <tr>
- <td rowspan="2" align="center" valign="top" width="25">
- <img alt="[Tip]" src="../images/tip.png" />
- </td>
- <th align="left">Tip</th>
- </tr>
- <tr>
- <td align="left" valign="top">
- <p>
- If you <span class="emphasis"><em>Shift</em></span>-click on the eye symbol, this
- will cause all layers <span class="emphasis"><em>except</em></span>
- the one you click on to be hidden.
- </p>
- </td>
- </tr>
- </table>
- </div>
- </dd>
- <dt>
- <span class="term">
- <span class="guiicon">
- <span class="inlinemediaobject"><img src="../images/dialogs/stock-vchain-24.png" /></span>
- </span>
- <span lang="en" xml:lang="en">Linkage to other layers</span>
- </span>
- </dt>
- <dd>
- <a id="id2599732" class="indexterm"></a>
- <a id="id2599746" class="indexterm"></a>
- <p>
- If you click between the eye icon and the layer thumbnail, you get
- a chain icon, which enables you to group layers for operations on
- multiple layers (for example with the Move tool or a transform
- tool).
- </p>
- <div class="figure">
- <a id="id2599764"></a>
- <p class="title">
- <b>Figure 8.6. 
- <span lang="en" xml:lang="en">Layer Dialog</span>
- </b>
- </p>
- <div class="figure-contents">
- <div class="mediaobject">
- <img src="../images/dialogs/link-visibility.png" alt="Layer Dialog" />
- <div class="caption">
- <p>
- Red: Linkage to others layers. Yellow: Visibility.
- </p>
- </div>
- </div>
- </div>
- </div>
- <br class="figure-break" />
- </dd>
- <dt>
- <span class="term">Size and boundaries</span>
- </dt>
- <dd>
- <a id="id2599819" class="indexterm"></a>
- <a id="id2599831" class="indexterm"></a>
- <p>
- In GIMP, the boundaries of a layer do not necessarily match the
- boundaries of the image that contains it. When you create text,
- for example, each text item goes into its own separate layer, and
- the layer is precisely sized to contain the text and nothing more.
- Also, when you create a new layer using cut-and-paste, the new
- layer is sized just large enough to contain the pasted item. In
- the image window, the boundaries of the currently active layer are
- shown outlined with a black-and-yellow dashed line.
- </p>
- <p>
- The main reason why this matters is that you cannot do anything to
- a layer outside of its boundaries: you can't act on what doesn't
- exist. If this causes you problems, you can alter the dimensions
- of the layer using any of several commands that you can find near
- the bottom of the <span class="guimenu">Layer</span> menu.
- </p>
- <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
- <table border="0" summary="Note">
- <tr>
- <td rowspan="2" align="center" valign="top" width="25">
- <img alt="[Note]" src="../images/note.png" />
- </td>
- <th align="left">Note</th>
- </tr>
- <tr>
- <td align="left" valign="top">
- <p>
- The amount of memory that a layer consumes is determined by its
- dimensions, not its contents. So, if you are working with large
- images or images that contain many layers, it might pay off to
- trim layers to the minimum possible size.
- </p>
- </td>
- </tr>
- </table>
- </div>
- </dd>
- <dt>
- <span class="term">Opacity</span>
- </dt>
- <dd>
- <p>
- The opacity of a layer determines the extent to which it lets
- colors from layers beneath it in the stack show through. Opacity
- ranges from 0 to 100, with 0 meaning complete transparency, and
- 100 meaning complete opacity.
- </p>
- </dd>
- <dt>
- <span class="term">Mode</span>
- </dt>
- <dd>
- <p>
- The Mode of a layer determines how colors from the layer are
- combined with colors from the underlying layers to produce a
- visible result. This is a sufficiently complex, and sufficiently
- important, concept to deserve a section of its own, which follows.
- See <a class="xref" href="gimp-concepts-layer-modes.html" title="2.  Layer Modes">Section 2, “
- <span lang="en" xml:lang="en">Layer Modes</span>
- ”</a>.
- </p>
- </dd>
- <dt>
- <span class="term">Layer mask</span>
- </dt>
- <dd>
- <a id="id2599949" class="indexterm"></a>
- <p>
- In addition to the alpha channel, there is another way to control
- the transparency of a layer: by adding a
- <span class="emphasis"><em>layer mask</em></span>,
- which is an extra grayscale drawable associated with the layer.
- A layer does not have a layer mask by default: it must be added
- specifically. Layer masks, and how to work with them, are
- described much more extensively in the
- <a class="link" href="gimp-dialogs-structure.html#gimp-layer-mask" title="2.1.3.  Layer masks">Layer Mask</a> section.
- </p>
- </dd>
- <dt>
- <span class="term">“<span class="quote">Lock alpha channel</span>” setting</span>
- </dt>
- <dd>
- <p>
- In the upper left corner of the Layers dialog appears a small
- checkbox that controls the “<span class="quote">Lock</span>”
- setting for the transparency of the layer (see the figure below).
- If this is checked, then the alpha channel for the layer is
- locked, and no manipulation has any effect on it. In particular,
- nothing that you do to a transparent part of the layer will have
- any effect.
- </p>
- <div class="figure">
- <a id="id2600016"></a>
- <p class="title">
- <b>Figure 8.7. 
- <span lang="en" xml:lang="en">Lock Alpha channel</span>
- </b>
- </p>
- <div class="figure-contents">
- <div class="mediaobject">
- <img src="../images/dialogs/lock-alpha.png" alt="Lock Alpha channel" />
- </div>
- </div>
- </div>
- <br class="figure-break" />
- </dd>
- </dl>
- </div>
- </div>
- </div>
- </div>
- <div class="navfooter">
- <hr />
- <table width="100%" summary="Navigation footer">
- <tr>
- <td width="40%" align="left"><a accesskey="p" href="gimp-using-rectangular.html"><img src="../images/prev.png" alt="Prev" /></a> </td>
- <td width="20%" align="center">
- <a accesskey="u" href="pt02.html">
- <img src="../images/up.png" alt="Up" />
- </a>
- </td>
- <td width="40%" align="right"> <a accesskey="n" href="gimp-concepts-layer-modes.html"><img src="../images/next.png" alt="Next" /></a></td>
- </tr>
- <tr>
- <td width="40%" align="left" valign="top"><a accesskey="p" href="gimp-using-rectangular.html">13.2. 
- <span lang="en" xml:lang="en">Creating a Basic Shape</span>
- </a> </td>
- <td width="20%" align="center">
- <a accesskey="h" href="index.html">
- <img src="../images/home.png" alt="Home" />
- </a>
- </td>
- <td width="40%" align="right" valign="top"> <a accesskey="n" href="gimp-concepts-layer-modes.html">2. 
- <span lang="en" xml:lang="en">Layer Modes</span>
- </a></td>
- </tr>
- </table>
- </div>
- </body>
- </html>
-