2.6.2.3 Layer Scaling
As has already been discussed in this section, it is possible to scale
an entire image. However, it is also possible to scale a single layer
within an image. There are two tools for doing this in the GIMP: the
Scale Layer function, found in the
Layers menu, and the Transform tool in the
Toolbox.
As for entire images, a layer can be scaled either smaller or larger.
The most typical use of layer scaling is to adjust the relative size
of an image on one layer with respect to an image in another. This is
needed for almost every compositing project (for examples, see
Chapter
7). When it is necessary to scale a layer
smaller, either the Scale Layer function or the scaling option
of the Transform tool will do the trick. However, the Transform tool might be preferable because it provides interactive
control of the scaling process. Scale Layer relies on entering
numbers into entry boxes in a dialog. It is difficult to choose the
correct dimensions, which leads to repeatedly applying Scale
Layer and Undo until the desired effect is achieved.
The problem of finding the right dimensions to scale a layer can
sometimes be solved using the Measure tool,
which is discussed in more detail in
Section
2.6.5. A good example of using the
Measure tool to determine the appropriate amount to rescale a
layer is given in Section
7.5. Alternatively, the Transform tool provides interactive visual feedback of the scaling
process. In addition, it can be used in conjunction with the Bezier Path tool and the Transform
Lock icon in the Paths dialog to get very
fine, interactive scaling control. The technique for this is
discussed in Section
3.4.1, and a relevant example is
shown in Section
7.2.
Scaling a layer larger should be avoided if possible, because this
operation requires the interpolation of
pixel values. Interpolation is
an approximation process that creates pixels where there were none
before and that, consequently, partially degrades the layer's image
quality. Thus, when adjusting the relative sizes of several image
components on different layers, it is preferable to scale down the
larger components to match the size of the smaller ones rather than
vice versa.
In the event that it is necessary to scale a layer larger, it is
important to know that a layer cannot be scaled to dimensions larger
than those of the existing image boundaries. To scale a layer to
dimensions greater than these limits, the image window must first be
resized larger using the function Canvas Size, previously
discussed.
