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621 lines
22 KiB
621 lines
22 KiB
<chapter id="layers">
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<title>Layers</title>
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<para>
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This chapter gives an overview of how layers work in &chalk;.
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</para>
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<sect1 id="layers-background">
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<title>Background information on layers</title>
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<para>
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Extensive use of &chalk; will almost require you to have some knowledge of
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layers. Using layers, you can work on one part of the image without touching
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the rest of it, and most effects are best applied on a layer, instead of on
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the whole image. Of course, if you do want to apply an effect to an entire
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image, &chalk; does offer you that possibility, and there is nothing against
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it.
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</para><para>
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The idea behind layers is quite simple. As the name suggests, layers lie on
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top of each other, and together form the layer stack. The final resulting
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image is that what you see when looking through the stack from top to bottom.
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This means that usually the upper layers of your image will have more or less
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transparency, since you cannot look through a layer which has no transparency.
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(&chalk; works with opaqueness instead of transparency. A layer that is 100
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percent opaque is 0 percent transparent, and vice versa.) A layer higher in
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the stack gets applied later than one lower in the stack. For example, if your
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image contains four layers, numbered from 1 (lowest) to 4 (highest), the
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effect that layer number 4 adds to the image, is applied to the result from
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applying layers 1 through 3.
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</para><para>
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Every image you edit in &chalk; contains layers. When you create a new image,
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the layer box (usually shown at the bottom right of your screen, see <link
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linkend="commands-palettes-layers-layers">this section</link>) will contain
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one layer. The painting and editing you do is then applied to that layer. Once
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you add more layers, you can choose on which part of the image you want to
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work, by selecting the respective layer. All further painting is then applied
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to that layer, until you select another one.
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</para><para>
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Layers are also an excellent way to check whether adding certain effects (or
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applying certain image modifications) come out right. Add a layer which
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contains what you want to try out, and show or hide it with the eye icon in
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the layer box. You can especially profit from this method if you have multiple
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effects to check out: show and hide them in any combination, and decide which
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you like best. And since you can move the layers around, you can also
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experiment with the order in which the effects are applied.
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</para><para>
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See the <link linkend="tutorial-select-layer">Selections and layers
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tutorial</link> for a small hands-on introduction.
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</para>
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</sect1>
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<sect1 id="layers-layerbox">
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<title>The layer box</title>
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<para>The layer box is the instrument you will use most to work with layers. It
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gives an overview of the layers that are present in your image, and using it
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you can manage layers by adding, removing, reordering or modifying them.
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</para><para>
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The layer box consists of three parts. The middle part gives an overview of the
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layers in the image. At the top, you can set some properties for the current
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layer. At the bottom, a couple of layer management options can be found. The
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next sections describe these three parts in more detail.
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</para>
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<sect2 id="layers-layerbox-overview">
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<title>Layer overview</title>
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<para>This part shows you which layers are present in your image. In a tree-like
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structure, the layer group hierarchy is shown: layers that are contained within
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a layer group are displayed a bit to the right to indicate their belonging to
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that group.
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</para><para>
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For each layer, a thumbnail preview and its name are shown. The layer name
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is preceded by a folder icon if it is a group layer. Furthermore, two
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indicators are present: the eye icon shows whether the layer is currently
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visible (an open eye indicates that the layer is visible, a closed eye
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indicates that it is not), and the lock icon shows whether the layer is
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locked. No changes can be made to a locked layer.
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</para><para>
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When you click on a layer's eye icon, its visibility is switched from on to
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off or vice versa. Clicking on the lock icon enables or disables editing of
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that layer. You can click on the name of the current layer to rename it.
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Note that to rename a layer, it has to be the current one. You do not need to
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activate a layer in order to make it (in)visible or (un)locked via the eye and
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lock icons, respectively: these work directly.
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</para><para>
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Doubleclick on a layer entry in the list to open the <link
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linkend="commands-dialogs-layers-layerproperties"><guilabel>Layer
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Properties</guilabel></link> dialog. This dialog shows a layer's colorspace and
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profile. You can also change its name, opacity and composite mode here.
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</para>
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</sect2>
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<sect2 id="layers-layerbox-options">
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<title>Layer options</title>
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<para>
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The top of the layer box contains two controls for setting properties of the
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currently selected layer. The list box at the left allows you to quickly set
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the layer's composite mode. The spin field and slider at the right can be used
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to change the layer's opacity.
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</para><para>
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At the bottom of the layer box, there are five buttons. From left to right,
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these are as follows. The <guibutton>New Layer</guibutton> icon brings up a
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submenu from which you can choose which type of layer you want to add. This
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menu can also be opened by clicking with the &RMB; on the layer box. The
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<guibutton>Move Layer Down</guibutton> and <guibutton>Move Layer Up</guibutton>
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buttons move the current layer one level down and up, respectively, within the
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current layer group. If the layer is already the last or first within the
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layer group, trying to move it further will move it out of the layer group.
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The <guibutton>Layer Properties</guibutton> button opens the <link
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linkend="commands-dialogs-layers-layerproperties"><guilabel>Layer
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Properties</guilabel></link> dialog, just as when you would have doubleclicked
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on the layer. The <guibutton>Delete Layer</guibutton> button deletes the
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current layer.
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</para>
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</sect2>
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</sect1>
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<sect1 id="layers-working">
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<title>Working with layers</title>
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<para>
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Because layers are quite important when extensively using &chalk;, you can
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perform a lot of operations on them. These are all available via the <link
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linkend="commands-menus-layer"><guimenu>Layer</guimenu> menu</link>. Some of
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the possibilities:
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</para>
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<variablelist>
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<varlistentry><term></term><listitem><para>Add, remove, and duplicate layers;</para></listitem></varlistentry>
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<varlistentry><term></term><listitem><para>Create and edit layer masks;</para></listitem></varlistentry>
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<varlistentry><term></term><listitem><para>Flip, rotate, scale and shear layers;</para></listitem></varlistentry>
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<varlistentry><term></term><listitem><para>Convert layers between colorspaces;</para></listitem></varlistentry>
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<varlistentry><term></term><listitem><para>Save layers as images;</para></listitem></varlistentry>
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<varlistentry><term></term><listitem><para>View layer histograms.</para></listitem></varlistentry>
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</variablelist>
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</sect1>
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<sect1 id="layers-adjustment">
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<title>Adjustment Layers</title>
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<para>Adjustment layers are layers that consist of a filter and an optional
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selection. The filter effect is applied to the composite image of all
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layers under the adjustment layer in the current layer group. The big
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thing is, adjustment layers apply these effects non-destructively. The
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original image data is not modified.
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</para><para>
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Almost all &chalk; filters are suitable for use in adjustment
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layers -- even filters that would downgrade the image quality. For instance,
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the raindrops filter converts to 8-bit RGB before working its magic. If you
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would try to use this filter directly on a 16-bit L*a*b* layer, &chalk; would
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warn you about the conversion to RGB and back again this filter would cause.
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Not so with adjustment layers: the original data isn't touched, so applying
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the filter is safe.
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</para><para>
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What about the colorspace of an adjustment layer then? In order to examine
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this issue, you need to know what happens when &chalk; renders an adjustment
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layer.
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</para>
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<sect2 id="layers-adjustment-selections">
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<title>Adjustment layers and selections</title>
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<para>If the currently active layer has an active selection, then that selection
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will be copied and used as a mask for the adjustment layer. If there is no
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active selection, then there will be no mask and the adjustment will apply to
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the entire extent of the layers under the adjustment layer in the current
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group. There is <emphasis>no</emphasis> way of adding a mask to an existing
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adjustment layer.
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</para><para>
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If there is a mask in the adjustment layer, you can edit the mask using the
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ordinary painting tools and painting operations.
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</para>
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</sect2>
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<sect2 id="layers-adjustment-projection">
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<title>A note on projections</title>
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<para>
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&chalk; composites the layers bottom to top, within each layer group. The
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aggregate -- or the projection as it is also called -- is then filtered by
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the adjustment layer. If there are layers on top of the adjustment layer,
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those are composited onto the projection. &chalk; converts all layer data before
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compositing, so if the bottom-most layer in an image is grayscale, all layers
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are converted to grayscale before compositing -- and that means that the
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adjustment layer projection will be grayscale, too.
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</para><para>
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With this knowledge you'll understand why &chalk; can often offer better
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performance working with layers on top of an adjustment layer which is on top
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of a complex layer structure: &chalk; uses the projection and doesn't even look
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anymore at the layers under the adjustment layer. Unless, of course, you
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change one of them.
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</para>
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</sect2>
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</sect1>
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<sect1 id="layers-composite">
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<title>Compositing modes</title>
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<para>
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Layers can be composited in various ways, each yielding a different effect.
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This section describes the available compositing modes. Each description is
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accompanied by an example: on top of an original image (see below), a rainbow
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gradient is added.
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</para>
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<para>
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<screenshot>
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<screeninfo>The original image</screeninfo>
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<mediaobject>
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<imageobject>
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<imagedata fileref="mountains-original.png" format="PNG" />
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</imageobject>
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<textobject>
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<phrase>The original image</phrase>
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</textobject>
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<caption><para>The original image</para></caption>
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</mediaobject>
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</screenshot>
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</para>
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<sect2 id="layers-composite-normal">
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<title><guilabel>Normal</guilabel></title>
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<para>
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The <guilabel>Normal</guilabel> mode does nothing special. It adds the layer
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to the image, and if no other special effects like opacity are changed, the
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underlying layers will only be visible at places where the new layer is
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itself transparent.
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</para>
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<para>
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<screenshot>
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<screeninfo>The gradient applied with the <guilabel>Normal</guilabel> compositing
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mode</screeninfo>
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<mediaobject>
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<imageobject>
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<imagedata fileref="mountains-normal.png" format="PNG" />
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</imageobject>
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<textobject>
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<phrase>The gradient applied with the <guilabel>Normal</guilabel> compositing
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mode</phrase>
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</textobject>
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<caption><para>The gradient applied with the <guilabel>Normal</guilabel> compositing
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mode</para></caption>
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</mediaobject>
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</screenshot>
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</para>
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</sect2>
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<sect2 id="layers-composite-multiply">
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<title><guilabel>Multiply</guilabel></title>
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<para>
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The <guilabel>Multiply</guilabel> mode blends the two layers so that the
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bottom layer gets <quote>colorized</quote> by the new layer. The resulting
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image is generally quite dark.
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</para>
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<para>
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<screenshot>
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<screeninfo>The gradient applied with the <guilabel>Multiply</guilabel> compositing
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mode</screeninfo>
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<mediaobject>
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<imageobject>
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<imagedata fileref="mountains-multiply.png" format="PNG" />
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</imageobject>
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<textobject>
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<phrase>The gradient applied with the <guilabel>Multiply</guilabel> compositing
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mode</phrase>
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</textobject>
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<caption><para>The gradient applied with the <guilabel>Multiply</guilabel> compositing
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mode</para></caption>
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</mediaobject>
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</screenshot>
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</para>
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</sect2>
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<sect2 id="layers-composite-burn">
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<title><guilabel>Burn</guilabel>, <guilabel>Dodge</guilabel>,
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<guilabel>Divide</guilabel> and <guilabel>Screen</guilabel></title>
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<para>
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The <guilabel>Burn</guilabel>, <guilabel>Dodge</guilabel>,
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<guilabel>Divide</guilabel> and <guilabel>Screen</guilabel> modes all add an
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extra <quote>burning</quote> effect by following contours instead of using
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straight lines. In addition, <guilabel>Burn</guilabel> and
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<guilabel>Divide</guilabel> use the inverted colors instead of the actual
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colors of the composited layer.
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</para>
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<para>
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<screenshot>
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<screeninfo>The gradient applied with the <guilabel>Burn</guilabel> compositing
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mode</screeninfo>
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<mediaobject>
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<imageobject>
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<imagedata fileref="mountains-burn.png" format="PNG" />
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</imageobject>
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<textobject>
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<phrase>The gradient applied with the <guilabel>Burn</guilabel> compositing
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mode</phrase>
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</textobject>
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<caption><para>The gradient applied with the <guilabel>Burn</guilabel> compositing
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mode</para></caption>
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</mediaobject>
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</screenshot>
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</para>
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<para>
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<screenshot>
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<screeninfo>The gradient applied with the <guilabel>Dodge</guilabel> compositing
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mode</screeninfo>
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<mediaobject>
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<imageobject>
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<imagedata fileref="mountains-dodge.png" format="PNG" />
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</imageobject>
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<textobject>
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<phrase>The gradient applied with the <guilabel>Dodge</guilabel> compositing
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mode</phrase>
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</textobject>
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<caption><para>The gradient applied with the <guilabel>Dodge</guilabel> compositing
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mode</para></caption>
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</mediaobject>
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</screenshot>
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</para>
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<para>
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<screenshot>
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<screeninfo>The gradient applied with the <guilabel>Divide</guilabel> compositing
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mode</screeninfo>
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<mediaobject>
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<imageobject>
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<imagedata fileref="mountains-divide.png" format="PNG" />
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</imageobject>
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<textobject>
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<phrase>The gradient applied with the <guilabel>Divide</guilabel> compositing
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mode</phrase>
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</textobject>
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<caption><para>The gradient applied with the <guilabel>Divide</guilabel> compositing
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mode</para></caption>
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</mediaobject>
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</screenshot>
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</para>
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<para>
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<screenshot>
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<screeninfo>The gradient applied with the <guilabel>Screen</guilabel> compositing
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mode</screeninfo>
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<mediaobject>
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<imageobject>
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<imagedata fileref="mountains-screen.png" format="PNG" />
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</imageobject>
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<textobject>
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<phrase>The gradient applied with the <guilabel>Screen</guilabel> compositing
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mode</phrase>
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</textobject>
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<caption><para>The gradient applied with the <guilabel>Screen</guilabel> compositing
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mode</para></caption>
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</mediaobject>
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</screenshot>
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</para>
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</sect2>
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<sect2 id="layers-composite-overlay">
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<title><guilabel>Overlay</guilabel></title>
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<para>
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Like <guilabel>Multiply</guilabel>, the <guilabel>Overlay</guilabel> mode
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colorizes the underlying layer. The resulting image is about as light as
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the original layer.
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</para>
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<para>
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<screenshot>
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<screeninfo>The gradient applied with the <guilabel>Overlay</guilabel> compositing
|
|
mode</screeninfo>
|
|
<mediaobject>
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|
<imageobject>
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|
<imagedata fileref="mountains-overlay.png" format="PNG" />
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</imageobject>
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<textobject>
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<phrase>The gradient applied with the <guilabel>Overlay</guilabel> compositing
|
|
mode</phrase>
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</textobject>
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<caption><para>The gradient applied with the <guilabel>Overlay</guilabel> compositing
|
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mode</para></caption>
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</mediaobject>
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</screenshot>
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</para>
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</sect2>
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<sect2 id="layers-composite-darken">
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<title><guilabel>Darken</guilabel></title>
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<para>
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The <guilabel>Darken</guilabel> mode darkens the underlying layer while
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colorizing it to match the colors in the composited layer.
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</para>
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<para>
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<screenshot>
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<screeninfo>The gradient applied with the <guilabel>Darken</guilabel> compositing
|
|
mode</screeninfo>
|
|
<mediaobject>
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|
<imageobject>
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|
<imagedata fileref="mountains-darken.png" format="PNG" />
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</imageobject>
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|
<textobject>
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<phrase>The gradient applied with the <guilabel>Darken</guilabel> compositing
|
|
mode</phrase>
|
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</textobject>
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<caption><para>The gradient applied with the <guilabel>Darken</guilabel> compositing
|
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mode</para></caption>
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</mediaobject>
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</screenshot>
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</para>
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</sect2>
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<sect2 id="layers-composite-lighten">
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<title><guilabel>Lighten</guilabel></title>
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<para>
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The <guilabel>Lighten</guilabel> mode lightens the underlying layer while
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colorizing it to match the colors in the composited layer.
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</para>
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<para>
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<screenshot>
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<screeninfo>The gradient applied with the <guilabel>Lighten</guilabel> compositing
|
|
mode</screeninfo>
|
|
<mediaobject>
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|
<imageobject>
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<imagedata fileref="mountains-lighten.png" format="PNG" />
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</imageobject>
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<textobject>
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<phrase>The gradient applied with the <guilabel>Lighten</guilabel> compositing
|
|
mode</phrase>
|
|
</textobject>
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<caption><para>The gradient applied with the <guilabel>Lighten</guilabel> compositing
|
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mode</para></caption>
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</mediaobject>
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</screenshot>
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</para>
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</sect2>
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<sect2 id="layers-composite-hue">
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<title><guilabel>Hue</guilabel>, <guilabel>Saturation</guilabel> and
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<guilabel>Value</guilabel></title>
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<para>
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The <guilabel>Hue</guilabel>, <guilabel>Saturation</guilabel> and
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<guilabel>Value</guilabel> modes respectively apply the hue, saturation and
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value components of the composited layer to the underlying layer.
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</para>
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<para>
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<screenshot>
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<screeninfo>The gradient applied with the <guilabel>Hue</guilabel> compositing
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|
mode</screeninfo>
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<mediaobject>
|
|
<imageobject>
|
|
<imagedata fileref="mountains-hue.png" format="PNG" />
|
|
</imageobject>
|
|
<textobject>
|
|
<phrase>The gradient applied with the <guilabel>Hue</guilabel> compositing
|
|
mode</phrase>
|
|
</textobject>
|
|
<caption><para>The gradient applied with the <guilabel>Hue</guilabel> compositing
|
|
mode</para></caption>
|
|
</mediaobject>
|
|
</screenshot>
|
|
</para>
|
|
|
|
<para>
|
|
<screenshot>
|
|
<screeninfo>The gradient applied with the <guilabel>Saturation</guilabel> compositing
|
|
mode</screeninfo>
|
|
<mediaobject>
|
|
<imageobject>
|
|
<imagedata fileref="mountains-saturation.png" format="PNG" />
|
|
</imageobject>
|
|
<textobject>
|
|
<phrase>The gradient applied with the <guilabel>Saturation</guilabel> compositing
|
|
mode</phrase>
|
|
</textobject>
|
|
<caption><para>The gradient applied with the <guilabel>Saturation</guilabel> compositing
|
|
mode</para></caption>
|
|
</mediaobject>
|
|
</screenshot>
|
|
</para>
|
|
|
|
<para>
|
|
<screenshot>
|
|
<screeninfo>The gradient applied with the <guilabel>Value</guilabel> compositing
|
|
mode</screeninfo>
|
|
<mediaobject>
|
|
<imageobject>
|
|
<imagedata fileref="mountains-value.png" format="PNG" />
|
|
</imageobject>
|
|
<textobject>
|
|
<phrase>The gradient applied with the <guilabel>Value</guilabel> compositing
|
|
mode</phrase>
|
|
</textobject>
|
|
<caption><para>The gradient applied with the <guilabel>Value</guilabel> compositing
|
|
mode</para></caption>
|
|
</mediaobject>
|
|
</screenshot>
|
|
</para>
|
|
|
|
</sect2>
|
|
|
|
<sect2 id="layers-composite-color">
|
|
<title><guilabel>Color</guilabel></title>
|
|
|
|
<para>
|
|
The <guilabel>Color</guilabel> mode colorizes the underlying layer, yielding
|
|
very strong colors.
|
|
</para>
|
|
|
|
<para>
|
|
<screenshot>
|
|
<screeninfo>The gradient applied with the <guilabel>Color</guilabel> compositing
|
|
mode</screeninfo>
|
|
<mediaobject>
|
|
<imageobject>
|
|
<imagedata fileref="mountains-color.png" format="PNG" />
|
|
</imageobject>
|
|
<textobject>
|
|
<phrase>The gradient applied with the <guilabel>Color</guilabel> compositing
|
|
mode</phrase>
|
|
</textobject>
|
|
<caption><para>The gradient applied with the <guilabel>Color</guilabel> compositing
|
|
mode</para></caption>
|
|
</mediaobject>
|
|
</screenshot>
|
|
</para>
|
|
|
|
</sect2>
|
|
|
|
</sect1>
|
|
|
|
<sect1 id="layers-masks">
|
|
<title>Layer Masks</title>
|
|
|
|
<para>
|
|
Basically, a layer mask is a mask that you place on your paint layer. This
|
|
will literally mask areas of the layer, so that the content underneath shows
|
|
through. You can paint on it with greyscale colors: the more black the color,
|
|
the less the layer under it will shine through, the more white, the less the
|
|
layer under it will be shown. So complete white will let nothing through,
|
|
complete black will let everything through. Basically, it is a bit like
|
|
selecting a piece of your image, and then cutting it, so that the selected
|
|
bits go away. So what is the use for a mask here? The big advantage is that it
|
|
is non-destructive: if you decide that you masked out the wrong part of your
|
|
layer, you can easily remove the mask and start anew, something a lot harder
|
|
(not to say near impossible, especially in between sessions) with regular
|
|
selection-cutting.
|
|
</para><para>
|
|
So, how to create a mask? There are 2 ways:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
Start from scratch.
|
|
<menuchoice><guimenu>Layer</guimenu><guisubmenu>Mask</guisubmenu><guimenuitem>Create
|
|
Mask</guimenuitem></menuchoice>. The mask starts with everything being
|
|
retained, that is, a complete white mask. Basically you will not see any
|
|
changes as long as you do not paint on it.
|
|
</para></listitem>
|
|
<listitem><para>
|
|
Start from the current selection.
|
|
<menuchoice><guimenu>Layer</guimenu><guisubmenu>Mask</guisubmenu><guimenuitem>Mask
|
|
From Selection</guimenuitem></menuchoice>. The selectedness will be converted
|
|
to whiteness. This means that fully selected area will be visible, fully
|
|
unselected areas will be invisible, and the rest will be partially visible,
|
|
depending on how much the area was selected.
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
|
|
<sect2 id="layers-masks-editing">
|
|
<title>Editing the mask</title>
|
|
|
|
<para>
|
|
First, make sure you are editing the mask, not the layer, by making sure
|
|
<menuchoice><guimenu>Layer</guimenu><guisubmenu>Mask</guisubmenu><guimenuitem>Edit
|
|
Mask</guimenuitem></menuchoice> is checked. (This is checked by default.) Then
|
|
you can paint on the layer just like before, only now you are
|
|
painting on the mask, instead of on the layer itself. To stop painting on the
|
|
mask, you can uncheck the <guilabel>Edit Mask</guilabel> checkbox. There's
|
|
also the option to show the mask, through checking
|
|
<menuchoice><guimenu>Layer</guimenu><guisubmenu>Mask</guisubmenu><guimenuitem>Show
|
|
Mask</guimenuitem></menuchoice>. (This is not checked by
|
|
default). This option will render the entire layer as a visual representation
|
|
of the mask in greyscale, instead of the actual layer. This can be handy to
|
|
see where your mask is, but it might be not as handy when you want to edit it,
|
|
since you cannot look at the actual layer.
|
|
</para><para>
|
|
Other actions: you can also remove the mask if you are not satisfied with it,
|
|
and want to start over again, or just want to remove it, with
|
|
<menuchoice><guimenu>Layer</guimenu><guisubmenu>Mask</guisubmenu><guimenuitem>Remove
|
|
Mask</guimenuitem></menuchoice>. You can also <quote>apply</quote> the mask,
|
|
meaning that the mask will be made permanently. This means that the mask is
|
|
removed, but that its effect of transparency will be committed to the layer.
|
|
</para>
|
|
|
|
</sect2>
|
|
</sect1>
|
|
|
|
</chapter>
|