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<div class="titlepage">
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<h3 class="title"><a id="gimp-layer-mask"></a>2.2. Layer masks</h3>
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<h3 class="title"><a id="id3333822"></a>2.2. Using the Layerdialog</h3>
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<div class="mediaobject">
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<img src="../images/dialogs/dialogs-layer-addmask.png" />
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<div class="variablelist">
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A transparency mask can be added to each layer, it's called Layer
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mask. A layer mask has the same size and same pixel number as
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the layer to which it is attached. Every pixel of the mask can
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then be coupled with a pixel at the same location in the layer.
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The mask is a set of pixels in graytone on a value scale from 0
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to 255. The pixels with a value 0 are black and give a full
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transparency to the coupled pixel in the layer. The pixels with
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a value 255 are white and give a full opacity to the coupled
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To create a layer mask start with a right click on the layer to
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call the context menu and select <span class="guilabel">Add layer
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mask</span> in the menu. If the menu item is grayed first
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select <span class="guilabel">Add Alpha channel</span> in the same menu.
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A dialog appears where you can initialize the content of the
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<div class="itemizedlist">
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<span class="guilabel">White</span>: the mask has no effect,
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all layer pixels are full visible.
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<span class="guilabel">Black</span>: the mask gives a full
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to the layer which becomes invisible.
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<span class="guilabel">Layer's Alpha channel</span>: the mask is
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initialized according to the content of layer Alpha
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channel. If the layer still contains transparency it's
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<span class="guilabel">Selection</span> : the mask is initialized
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according to pixel values found in the selection.
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<span class="guilabel">Grayscale copy of layer</span>: the mask
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initialized according to pixel values of the layer.
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When the mask is created it appears as a thumbnail right to the
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layer thumbnail. By clicking alternatively on the layer and mask
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thumbnail you can enable one or other. The active itemis
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highlighted by a white border (which is not well visible around a
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white mask). To view mask content instead of its effect in image
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window, press <span><b class="keycap">Ctrl Alt</b></span> and then on mask
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thumbnail. To return to normal view redo last operation.
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<div class="caution" style="margin-left: 0.5in; margin-right: 0.5in;">
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<table border="0" summary="Caution">
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<span class="term">Overview</span>
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Every layer appears in the dialog in form of a thumbnail. When
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an image has many layers as components then it appears like a
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list. The upper layer in the list is the first one visible and
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the lowest layer the last visible, the background. Above the
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list one can find characteristics related individually to each
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layer. Under the list one can find managements buttons for the
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layer list. A right-click in a layer thumbnail opens the layer
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<a href="ch05s07.html" title="7. Layers">menu</a>.
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<span class="term">Layer attributes</span>
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Every layer is shown in the list with its own attributes. The
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main attribute is the name of the layer itself. You can edit it
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by a double-click on the name or the thumbnail of the layer. In
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front of the thumbnail is an icon showing an eye
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<span class="guiicon">
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<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-eye.png" /></span>
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</span>. By clicking on the eye, you toggle whether the layer is
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visible or not. (Shift-clicking on the eye causes all
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<span class="emphasis"><em>other</em></span> to be temporarily hidden.) An
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other icon showing a chain <span class="guiicon">
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<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-vchain.png" /></span>
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</span> enables to group layers for operations on multiples
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layers (for example with the Move tool).
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<div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
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<table border="0" summary="Tip">
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<td rowspan="2" align="center" valign="top" width="25">
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<img alt="[Caution]" src="../images/caution.png" />
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<img alt="[Tip]" src="../images/tip.png" />
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<th align="left">Caution</th>
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<th align="left">Tip</th>
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<td colspan="2" align="left" valign="top">
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The layer mask acts like a transparency mask on a particular
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layer. Since you have many layers it becomes different from the
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image Alpha channel which represents transparency applied to the
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In case of an animation layer GIF or MNG the name of the
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layer can be used to specify some parameters : Layer_name
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(delay in ms) (combination mode), for example Frame-1 (100
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ms) (replace). The <span class="guilabel">delay</span> set the time
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during the layer is visible in the animation. The combination
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mode set if you combine with the previous layer or replace
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it: the two modes are (combine) or (replace).
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<span class="term">Layers characteristics</span>
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Above the layer list it's possible to specify some properties for
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the active layer. The active layer is the one highlighted in blue. The
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properties are : "Layer mode", "Keep transparency", and "Opacity".
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<div class="itemizedlist">
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<div class="mediaobject">
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<img src="../images/dialogs/dialogs-layer-modes.png" />
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<span class="guilabel">Layer modes</span>:
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The layer mode determines how the layer interact with the
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other layers. From the combo box you can access to all the
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mode provided by Gimp. The layer modes are full detailled
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in the <a href="go01.html#glossary-modes">Glossary</a>.
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<div class="mediaobject">
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<img src="../images/dialogs/dialogs-layer-keeptrans.png" />
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<span class="guilabel">Keep transparency</span>: If you check this
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option the transparent areas of the layer will be keeped,
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this even if you have checked the <span class="guilabel">Fill
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transparent areas</span> option for the Bucket fill
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<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-layer-opacity.png" /></span>
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<span class="guilabel"><a id="gimp-layer-dialog-opacity-scale"></a>Opacity</span>:
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By moving the slider you give less or more opacity to the
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layer. With a 0 opacity value the layer is transparent and
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full invisible. Don't mistake with the Layer mask (see
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chapter Layer mask) that sets the transparency pixel by
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<span class="term">Layer management</span>
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Under the layer list a set of buttons allows you to perform
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some basis operations on the layer list.
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<div class="itemizedlist">
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<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-edit.png" /></span>
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<span class="guilabel">Edit layer attributs</span>:
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You can change here the name of the active layer in the list.
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<a id="gimp-layer-new"></a>
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<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-new.png" /></span>
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<span class="guilabel">New layer</span>:
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You can create here a new layer. A dialog is opened where
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you have to fill the <span class="guilabel">Layer name</span>,
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perhaps change default <span class="guilabel">Height</span> and
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<span class="guilabel">Width</span> choose the <span class="guilabel">Layer fill
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type</span> which will be the new layer background.
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<a id="gimp-layer-raise"></a>
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<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-raise.png" /></span>
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<span class="guilabel">Raise layer</span>:
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You can here put the layer up a level in the list. Press the
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<span><b class="keycap">Shift</b></span> key to move the layer to the top of
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<a id="gimp-layer-lower"></a>
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<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-lower.png" /></span>
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<span class="guilabel">Lower layer</span>:
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You can here put the layer down a level in the list. Press the
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<span><b class="keycap">Shift</b></span> key to move the layer to the bottom of
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<div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;">
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<table border="0" summary="Tip">
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<td rowspan="2" align="center" valign="top" width="25">
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<img alt="[Tip]" src="../images/tip.png" />
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<th align="left">Tip</th>
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<td colspan="2" align="left" valign="top">
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To move a layer at the bottom of the list, first
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give a transparency channel to the Backgrpund layer
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(also called Alpha channel). Right click on the
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Background layer and select <span class="guilabel">Add Alpha
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channel</span> in the menu.
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<a id="gimp-layer-duplicate"></a>
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<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-duplicate.png" /></span>
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<span class="guilabel">Duplicate layer</span>:
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You can create here a copy of the active layer. Name of new
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layer is suffixed with a number.
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<a id="gimp-layer-anchor"></a>
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<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-anchor.png" /></span>
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<span class="guilabel">Anchor layer</span>:
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When the active layer is a temporary layer (also called floating
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selection) shown by this icon
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<span class="guiicon">
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<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-floating.png" /></span>
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this button anchors it in the previous active layer.
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<a id="gimp-layer-delete"></a>
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<span class="inlinemediaobject"><img src="../images/dialogs/dialogs-icon-delete.png" /></span>
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<span class="guilabel">Delete layer</span> :
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You can here delete the active layer.
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