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Grokking The Gimp
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7.1 Project 1: Fish on Holiday!

A primary component of compositing is the assembling of different image elements and the subsequent positioning and scaling required to achieve the final desired composition. Assembling the image components consists of selecting them from their respective images. The selections are made using combinations of techniques from Chapters  3 and 4.

Because I'm often not sure exactly how I'll use selected image components in a project, I first like to assemble all of them into a kind of clip book.   A clip book is just a single image consisting of a layer for each image component. This makes an image palette from which the various components can be copied and then pasted into the target composition.

Figure  7.1(a)

  
Figure 7.1: Collection of Selected Sea Creatures
Figure 7.1

shows the image clip book used in this project. Each sea creature was obtained from a separate image source using a combination of selection and masking techniques. The Layers dialog in Figure  7.1(b) shows that each of the six separate images is contained in a separate layer. The project goal is to use these reef inhabitants to populate an eco-system not normally their own. The composition places our denizens of the deep among the palms of a tropical island beach scene. Sometimes even fish need a holiday...

The background image is shown in Figure  7.2(a).

  
Figure 7.2: Pasting an Image Component into the Holiday Scene Background
Figure 7.2

This scene will receive all the other image elements. The first element is the angel fish, which has been copied from Figure  7.1 and pasted into this one. The following procedure is used to accomplish this:
1.
Make the Angel Fish layer active by clicking on its thumbnail in the Layers dialog shown in Figure  7.1 (see Section  2.1.1 for more on active layers).
2.
Copy the Angel Fish layer to the default buffer by typing C-c  in the image window shown in Figure  7.1.
3.
Paste the Angel Fish layer into the target image by typing C-v in the image window shown in Figure  7.2. This loads the Angel Fish layer into a floating selection.
4.
Make the float into a new layer by clicking on the New Layer button in the Layers dialog.

There are two features worth noting in Figure  7.2. First, the Layers dialog shows that the new layer has been named Angel Fish to more easily identify it later. Second, the Angel Fish layer's boundaries (the yellow and black dashed line) are visible in the image window because it is the active layer in the image. The layer's boundaries can be toggled off by typing C-t in the image window. With respect to our composition, the first thing you might notice is that the angel fish seems too large for the background. This can be fixed by shrinking the angel fish or by enlarging the background. As already noted in Section  2.6.2, it is almost always preferable to shrink an image element that is too large rather than to enlarge the element that is too small. This is because enlarging an image requires interpolating pixel values, which introduces unpleasant image artifacts. Always avoid this--unless, of course, the artifacts are desirable as an artistic device.

Thus, our first task is to scale the Angel Fish layer to a more fitting size for our scene. This can be done in two ways, either with the Transform tool from the Toolbox or the Scale Layer  command found in the Layers menu. Section  2.6.2 describes both. The Transform tool is used here because it is interactive and gives some visual feedback to the scaling process. The Scaling option of the Transform tool is invoked by double-clicking on the Transform tool icon in the Toolbox, which brings up the Tool Options dialog. The Scaling option can then be selected from the dialog, as shown in Figure  7.3(b). Figure  7.3(a)

  
Figure 7.3: Scaling the Angel Fish
Figure 7.3

shows the result of using the Transform tool to scale the Angel Fish layer.

In scaling the Angel Fish layer, the aspect ratio has been preserved. This prevents the scaled layer from looking distorted. The aspect ratio can be maintained manually by watching the Scaling Information dialog  and keeping it manually adjusted during the scaling process. The Scaling Information dialog provides interactive feedback about the X and Y Scale Ratios while the transform is being performed. The aspect ratio is preserved by keeping the X Scale Ratio equal to the Y Scale Ratio. Alternatively, the Scaling option of the Transform tool can be constrained to preserve aspect ratio by pressing the Control and Alt keys while scaling. In this example, the angel fish has been scaled to 60% of her original dimensions. In the compositing process, however, this might be undone an redone several times to achieve the desired effect in the final result.

When the scaling of the angel fish is complete, she can be positioned  using the Move  tool. Her final location for this project is seen in Figure  7.4.

  
Figure 7.4: The Beginnings of a Composition
Figure 7.4

Also seen in this figure is the result of repeating the preceding operations for each of the angel fish's friends. Notice that it is not necessary for the repositioned image elements to be inside the boundaries of the background image window. In fact, having layers that extend partially outside the boundaries can create more interest in their subject elements.

The final procedure performed in this project adds an element of depth to our composition. The idea is to make the sea horse's tail look as if it is wrapped around a tree and to make the little red fish appear as if it is peaking out from behind another. This is done with layer masks (see Section  4.2). The elements of the procedure are shown in Figure  7.5.

  
Figure 7.5: Using a Layer Mask to Create the Illusion of Depth
Figure 7.5

Figure  7.5(a) shows a zoom of the image centered around the sea horse. As you can see from Figure  7.5(b), a layer mask  has been added to the Sea Horse layer in the Layers dialog, and the Opacity slider has been set to 50%. This allows the tree in the background image to be seen through the Sea Horse layer. In setting the Opacity slider, the goal is to be able to see the tree's boundaries through the sea horse.

Because the tree's boundaries can be seen, the Paintbrush tool can be used to paint away parts of the Sea Horse mask making the tree fully visible from behind. Figure  7.5(a) shows that this process has been started using a brush from the Brush Selection dialog and shown in Figure  7.5(c). The whole procedure is summarized in the following steps:

1.
A layer mask is added to the Sea Horse layer.
2.
The layer mask is made active by clicking on its thumbnail in the Layers dialog.
3.
The Opacity slider is set so that the tree can be seen through the Sea Horse layer.
4.
The Active Foreground Color is set to black by typing d in the image window.
5.
An appropriate brush type and size is selected. Here a small hard brush is chosen.
6.
Painting tools, such as the Paintbrush and the Airbrush, are used to reveal the tree from behind the sea horse by painting away the appropriate parts of the layer mask.

If too much of the layer mask is removed while painting, you can recover it by changing the Active Foreground Color to white by typing x in the image window and by painting over the erroneously removed parts of the mask. Close to the edge of the tree, it is probably worthwhile working with a smaller brush size in conjunction with the Airbrush tool, which is more effective at applying graded amounts of paint. See Section  4.5.1 for more details.

The result of applying layer masks to both the Sea Horse and the Red Fish layers is shown in Figure  7.6.

  
Figure 7.6: The Final Composition
Figure 7.6

The sea horse now seems to be well anchored, with its tail securely wrapped around the tree, against unforeseen, rapid air currents. The little red fish, surprisingly coy given its bright coloring, is peaking out from behind another.

The effects obtained with layer masks could have also been accomplished with selections applied in the image window. However, this would have required permanently cutting away parts of the Sea Horse and Red Fish layers. Alternatively, the layer masks used in conjunction with the painting tools simplified the work and produced a more robust solution. Because of the layer masks, nothing has been irrevocably lost in either the Sea Horse or Red Fish layers. Thus, these layers can be repositioned if need be--only the layer masks need be re-edited. This flexibility with positioning adjustments is not possible when using selections because the cut-away components are gone.

To summarize, this project reviewed cutting, pasting, scaling, and the positioning of layers for compositing. In addition, a simple application of layer masks was used to give our composition some illusion of depth. The next compositing project is more complicated because it makes use of the blending modes and the Curves tool.




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Grokking The Gimp
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