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Grokking The Gimp
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2.4 Layer Export and Import

Collecting separate, raw image elements into a single image window is one of the most-used layer operations in this book. This is a fundamental component of compositing, a subject discussed in great depth in Chapter  7. However, it is also useful for a wide range of core and advanced techniques in the GIMP.

The importation of layers into an image is accomplished using the Copy , Cut,  and Paste  editing functions (see Section  1.7). The technique for importing a layer is so important that this section develops an example in detail to illustrate the methodology. Study it well, because this technique is used often in this book.

To illustrate the process, we begin with the two images shown in Figure  2.8. Each image consists of a

  
Figure 2.8: Two Images to Illustrate the Use of Copy and Paste
Figure 2.8

single layer, and each will be imported into a third image that, on completion of the procedure, will contain three layers.

To begin, a new image is created that has width and height sufficient to accommodate the two single-layer images. Once open, the eagle image in Figure  2.8(a) is copied  and pasted into it. This is accomplished by moving the mouse cursor into the eagle image window and selecting the Copy  function from the Image:Edit menu. This can also be accomplished by simply typing C-c in the image window. This copies the active layer of the eagle image into the default buffer.   Note that for multiple-layer images, it is the active layer that is copied into the buffer. Thus, it would be prudent to verify which layer is active by inspecting the Layers dialog before copying. The whole procedure could also be performed by cutting the image instead of copying. Cutting puts a copy of the layer in the buffer and then deletes it from the image window. To cut the image, use the Cut  function from the Image:Edit menu. This function can be more easily employed by typing C-x in the image window.

Now that the eagle image is in the buffer, it can be pasted into the new image. This is done by moving the mouse cursor into the new image window and using the Paste function found in the Image:Edit menu, which can be more expeditiously accomplished by typing C-v in the image window. The result of the paste is shown in Figure  2.9(a).

  
Figure 2.9: Importing the First Pasted Image
Figure 2.9

The Layers dialog for this image is shown in Figure  2.9(b), and it shows that the pasted layer appears as a floating selection. The Background layer, the only other layer in the dialog, is grayed out, meaning that it cannot be selected as the active layer.

The pasted layer appears in Figure  2.9(a) as a selection with a moving dashed line around it. These moving dashes are referred to as the Marching Ants.   This floating selection can be positioned in the new image with the Move   tool from the Toolbox.

Once the layer is positioned, it can be anchored to the underlying layer by bringing up the Layers menu and selecting the Anchor Layer  function from the Layers menu or by typing C-h in either the Layers & Channels or image windows. It is also possible to simply click on the Anchor button in the Layers dialog. For this example, however, the layer is not anchored to the layer below it. Rather, it is converted into a new layer. This is done by using the New Layer function found in the Layers menu. Figure  2.10

  
Figure 2.10: Creation of New Layer
Figure 2.10

illustrates the result of the conversion. Figure  2.10(a) shows how the converted layer is smaller than the image window. Figure  2.10(b) illustrates the corresponding Layers dialog showing that the float was converted to a layer. A floating selection can also be converted to a new layer by typing C-n in the Layers & Channels window or by clicking on the New Layer icon in the button bar.

The sequence just described for importing the eagle image is used so often that it deserves to be memorized. Let's concisely recap the steps required...then bookmark this page! The following list of steps slightly generalizes the procedure by assuming that there is a multilayer source image window containing a layer to be exported and another multilayered destination image that will import it: 

1.
In the source image window, type C-l to bring up the Layers dialog.
2.
In the Layers dialog, make the source layer active by clicking on its thumbnail in the Layers Palette.
3.
Back in the source image window, type C-c to copy the active layer to the default buffer.
4.
In the destination image window, type C-v to paste the buffer contents into a floating selection. (Note that the context of the Layers dialog automatically changes to the destination image window when C-v is typed there.)
5.
Position the floating selection as desired with the Move tool.
6.
Type C-n in the Layers dialog (or click on the New Layer button) to anchor the float to a new layer. Otherwise, type C-h or click the Anchor button to anchor it to the last active layer of the destination image.

By the way, when the floating selection is converted to a new layer, the resulting dimensions of the layer are just large enough to contain the contents of the pasted layer. As shown in Figure  2.10(a) the resulting pasted eagle image layer is smaller than the image window. It is easy to put the pasted image into a separate layer having the same dimensions as the destination image window. Just create a new layer in the destination image before pasting from the buffer. After pasting, anchor the floating selection to this new layer by clicking the anchor icon in the button bar.

Repeating the import procedure for the airplane in Figure  2.8(b) produces the result shown in Figure  2.11.

  
Figure 2.11: Importing the Second Pasted Image
Figure 2.11

Note that the boundary  of the active layer in Figure  2.11(a) is visible as a black-and-yellow dashed line. Typically we are not aware of layer boundaries because often all the layers have the same dimensions. When this is the case, the layer boundary is coincident with the window edge. However, for the case illustrated in Figure  2.11(a), the layer boundary is apparent because the pasted layer is smaller than the image window.

The visible boundary of a layer can be a problem, especially when you're trying to adjust the relative position of two layers or when you're trying to carefully match colors at layer edges (for a particularly good example of this problem, see Section  7.5). When it is desirable to suppress the layer boundary, its visibility can be turned off with the function Toggle Selection, found in the Image:View menu or by typing C-t in the image window.




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