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2.  Image structure related dialogs

Revision History
Revision $Revision$ 2006-03-09 lexa

2.1.  Layers dialog

Revision History
Revision $Revision: 1.50 $ 2006-03-09 lexa

Figure 9.1.  Layer Dialog

Layer Dialog

The Layers dialog is the main interface to edit, modify and manage your layers. You can think of layers as a stack of slides or clothes on your body. Using layers, you can construct an image of several conceptual parts, each of which can be manipulated without affecting any other part of the image. Layers are stacked on top of each other. The bottom layer is the background of the image, and the components in the foreground of the image come above it.

Figure 9.2.  An image with layers

An image with layers

Layers of the image

An image with layers

Resulting image:

2.1.1.  Activate Dialog

The Layer dialog can be called in many ways :

  • from the toolbox-menu: File->Dialog->Layers

  • from the image-menu: Dialog->Layers

  • from an other dialog-menu: Add Tab->Layers

  • from the (default) shortcut: Ctrl-L

2.1.2.  Using the Layerdialog


Every layer appears in the dialog in the form of a thumbnail. When an image has multiple layers as components, they appear as a list. The upper layer in the list is the first one visible, and the lowest layer the last visible, the background. Above the list one can find characteristics related individually to each layer. Under the list one can find management buttons for the layer list. A right-click in a layer thumbnail opens the Layer menu.

Layer attributes

Every layer is shown in the list along with its attributes. The main attribute is the name of the layer. You can edit this by a double-click on the name or the thumbnail of the layer. In front of the thumbnail is an icon showing an eye . By clicking on the eye, you toggle whether the layer is visible or not. (Shift-clicking on the eye causes all other to be temporarily hidden.) Another icon, showing a chain , allows you to group layers for operations on more than one layer at a time (for example with the Move tool).

[Tip] Tip

In the case of an animation layer (GIF or MNG), the name of the layer can be used to specify certain parameters : Layer_name (delay in ms) (combination mode), for example Frame-1 (100 ms) (replace). The delay sets the time during which the layer is visible in the animation. The combination mode sets whether you combine the layer with the previous layer or replace it: the two modes are (combine) or (replace).

Layers characteristics

Above the layer list, it is possible to specify some properties for the active layer. The active layer is the one highlighted in blue. The properties are : "Layer mode", "Keep transparency", and "Opacity".

Layer modes

Figure 9.3.  Layer modes

Layer modes

The layer mode determines how the layer interacts with the other layers. From the combo box you can access all the modes provided by GIMP. The layer modes are fully detailed in the Glossary.

Keep transparency

Figure 9.4.  Keep transparency

Keep transparency

If you check this option the transparent areas of the layer will be kept, even if you have checked the Fill transparent areas option for the Bucket fill tool.


Figure 9.5.  Opacity


By moving the slider you give more or less opacity to the layer. With a 0 opacity value, the layer is transparent and completely invisible. Don't confuse this with a Layer Mask, which sets the transparency pixel by pixel.

Layer management

Under the layer list a set of buttons allows you to perform some basic operations on the layer list.

Edit layer attributs

Here you can change the name of the active layer in the list.

New layer

Here you can create a new layer. A dialog is opened where you can enter the Layer name, perhaps change the default Height and Width, and choose the Layer fill type that will be the new layer's background.

Raise layer

Here you can move the layer up a level in the list. Press the Shift key to move the layer to the top of the list.

Lower layer

Here you can move the layer down a level in the list. Press the Shift key to move the layer to the bottom of the list.

[Tip] Tip

To move a layer at the bottom of the list, it may first be necessary to add a transparency channel (also called Alpha channel) to the Background layer. To do this, right click on the Background layer and select Add Alpha channel from the menu.

Duplicate layer

Here you can create a copy of the active layer. Name of new layer is suffixed with a number.

Anchor layer

When the active layer is a temporary layer (also called floating selection) shown by this icon , this button anchors it to the previous active layer.

Delete layer

Here you can delete the active layer.

More layer functions

Other functions about layer size are available in the Layer Drop down menu you get by right clicking on the Layer Dialog. You can find them also in the Layer sub-menu of the image menu.

You will find merging layers functions in the Image submenu of the Image menu.

Clicking-and-dragging layers

Click and hold on layer thumbnail: it enlarges and you can move it by dragging the mouse.

  • So you can put this layer down somewhere else in the layer list.

  • You can also put the layer down into Toolbox : a new image is created that contains this layer only.

  • Finally, you can put the layer down into another image : this layer will be added to the layer list, above existing layers.

2.1.3.  Layer masks

Revision History
Revision $Revision: 1.29 $ 2006-03-09 lexa

Figure 9.6.  Dialog add mask

Dialog add mask

A transparency mask can be added to each layer, it's called Layer mask. A layer mask has the same size and same pixel number as the layer to which it is attached. Every pixel of the mask can then be coupled with a pixel at the same location in the layer. The mask is a set of pixels in gray-tone on a value scale from 0 to 255. The pixels with a value 0 are black and give a full transparency to the coupled pixel in the layer. The pixels with a value 255 are white and give a full opacity to the coupled pixel in the layer.

To create a layer mask start with a right click on the layer to call the context menu and select Add layer mask in the menu. If the menu item is grayed first select Add Alpha channel in the same menu. A dialog appears where you can initialize the content of the mask:

  • White (full opacity): the mask has no effect, all layer pixels are full visible.

  • Black (full transparency): the mask gives a full transparency to the layer which becomes invisible.

  • Layer's alpha channel: the mask is initialized according to the content of layer Alpha channel. If the layer still contains transparency it's copied in the mask.

  • Transfer layer's alpha channel: Does the same thing as the previous option, except that it also resets the layer's alpha channel to full opacity.

  • Selection : the mask is initialized according to pixel values found in the selection.

  • Grayscale copy of layer: the mask is initialized according to pixel values of the layer.

When the mask is created it appears as a thumbnail right to the layer thumbnail. By clicking alternatively on the layer and mask thumbnail you can enable one or other. The active item is highlighted by a white border (which is not well visible around a white mask). To view mask content instead of its effect in image window, press Ctrl-Alt and then on mask thumbnail. Its borber turns to red. To return to normal view redo last operation.

[Caution] Caution

The layer mask acts like a transparency mask on a particular layer. Since you have many layers it becomes different from the image Alpha channel which represents transparency applied to the whole image.

  Published under the terms of the GNU General Public License Design by Interspire