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Grokking The Gimp
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7.2 Project 2: Through the Looking Glass

Blending modes, discussed in Chapter  5, are very useful tools for compositing. They can be used to give the illusion of one image element not just being delimited by another but of being fused right into it. This is a very powerful device because it allows the artist to convey a message about the relationship of the fused images, which simple juxtaposition does not. The objective of the project in this section is to illustrate this type of effect.

The images shown in Figures  7.7

  
Figure 7.7: A Tin Can Discarded as Trash
Figure 7.7

and 7.8
  
Figure 7.8: A Flower and a Visiting Friend
Figure 7.8

are the raw materials for this project. They will be fused together to make the tin can seem to reflect the flower and insect. A summary of the procedure used to achieve the effect is as follows:
1.
Place the flower image into a new layer above the layer of the tin can image.
2.
Position, scale, and orient the flower layer to juxtapose it with the can in the desired manner.
3.
Mask the upper layer to the limits of the tin can's borders.
4.
Apply an appropriate blending mode to the upper layer.
5.
Adjust the upper layer's brightness using the Curves tool.

Figure  7.9

  
Figure 7.9: The Flower Layer Pasted and Oriented over the Tin Can Layer
Figure 7.9

illustrates the flower copied and pasted into a layer over the tin can image. As the Layers dialog in Figure  7.9(a) indicates, the flower layer is in a floating selection where it will stay until it is positioned, scaled, and oriented. The Opacity slider in the Layers dialog has been set to 60%, which allows the tin can to be seen through this floating selection.

The Transform tool is used to rotate the flower layer. The flower image is aligned with the longitudinal axis of the tin can, which requires 59o of rotation. The partial transparency of the floating selection is invaluable, while using the Move  tool, for correctly positioning the flower layer over the tin can. This is the stage of the project seen in Figure  7.9(b).

Before moving to the next stage of the project, let's discuss how the rotation value of -59.00, shown in Figure  7.9(c), was determined. This angle was computed using the Measure  tool, as is illustrated in Figure  7.10.

  
Figure 7.10: Using the Measure Tool to Compute the Correct Angle of Rotation
Figure 7.10

Figure  7.10(a) shows how the angle of the longitudinal axis of the insect's back is measured, and Figure  7.10(b) does the same for the lateral axis of the tin can. As shown in the two figures, the insect's back measures 68.43o with respect to the horizontal axis, and the tin can measures 9.40o. To make the insect align with the can after rotation requires $(9.40^o-68.43^o) \approx -59^o$.

An alternative technique to using the Measure tool to get an accurate estimate of the amount of rotation needed is to make use of the Path Transform Lock in the Paths dialog (see Section  3.4.1). This feature locks a path to the active layer so that when the layer is transformed with the Transform tool, the path is too. Figures  7.11 and 7.12 illustrate how this helps. Figure  7.11(a)

  
Figure 7.11: Using a Bezier Path to Delineate the Insect's Outline, and Toggling On the Path Transform Lock
Figure 7.11

shows a Bezier path outlining the insect, and Figure  7.11(b) shows that the Path Transform Lock for this path is toggled on. In addition, the insect's layer has been made partially transparent, allowing the tin can to be seen through it from behind.

Figure  7.12(a)

  
Figure 7.12: Bezier Path Outline Rotating with Transform Grid
Figure 7.12

shows the Tool Options  window for the Transform tool. The Rotation radio button is shown checked, and, take note, the Show Path checkbox is toggled on. This means that the locked Bezier path will be shown with the transform grid lines when the mouse is first clicked in the image window. An accurate transformation of the insect layer can now be performed because the locked path moves visibly with the grid lines as they are transformed by the mouse.

Figure  7.12(b) shows the result of rotating the grid lines, and it can be seen that the insect's outline is also rotated. This is a very powerful technique for getting accurate transforms. In particular, it is the only technique for effectively visualizing how to warp one object to another when using the Perspective option of the Transform tool.

Picking up the project from where we left off, the rotated floating selection is now anchored to a new layer by clicking on the New Layer button in the Layers dialog, and the Opacity slider is set back to 100%. Before the next step, which is to mask the tin can, the flower layer is merged into a transparent layer that has the same size as that of the tin can. This is done as follows:

1.
In the Layers dialog the New Layer button is clicked and the Transparent layer option is chosen in the New Layer Options dialog.
2.
The resulting layer is positioned in the layer stack just below the Flower layer.
3.
With the flower layer active, the function Merge Down is selected from the Layers menu (or C-S-m is typed in the Layers dialog window). This merges the flower into the transparent layer.
At this point, it is useful to name the two layers in the Layers dialog. Let's label them Flower and Tin Can.

The next step in the process is to create a mask of the tin can. This is done by making a selection of the can, which is then converted to a layer mask. To facilitate the selection, the visibility of the Flower layer is toggled off. The selection is made using the Bezier Path tool and is illustrated in Figure  7.13.

  
Figure 7.13: Making a Selection of the Tin Can
Figure 7.13

After toggling the visibility of the Flower layer back on and making it active, the procedure for creating the layer mask from the selection is performed using these steps:

1.
Make the Flower layer active by clicking on its thumbnail in the Layers dialog.
2.
Create a layer mask for the Flower layer using the Add Layer Mask  function from the Layers menu, choosing the White (Full Opacity) option.
3.
Invert the selection by typing C-i in the image window.
4.
Make the Active Background Color black by typing d and then x in the image window.
5.
Making sure the layer mask is active in the Layers dialog by clicking on its thumbnail, and cut the selection by typing C-x in the image window.
Cutting the selection makes the the layer mask black outside the tin can's boundaries. Note that although the selection was made in the Tin Can layer, the cut is applied to the layer mask. This illustrates the important rule that regardless of where a selection is made, its effect is only applied to the active layer.

Figure  7.14

  
Figure 7.14: Flower Layer Masked by Tin Can
Figure 7.14

shows the result of creating the layer mask. The thumbnail of the mask can be seen in Figure  7.14(a), and its effect can be seen in Figure  7.14(b). Notice that the parts of the Flower layer extending outside of the boundaries of the tin can have been masked off.

Figure  7.14(b) is almost what we are looking for except that the flower image now looks is if it is pasted onto the outer surface of the can. The effect we are looking for is different. We want to make the flower look fused into the can, as if it is an integral part of it. For example, it would be interesting for the insect and flower to appear as if they were reflected off the can's shiny surface. To achieve this effect, we use a blending mode.

The blending mode used in this example is Multiply (Burn).  It is applied by making the Flower layer active and then selecting it from the Mode menu in the Layers dialog. You can see the choice of mode in Figure  7.15(a),

  
Figure 7.15: Using the Multiply Blending Mode on the Flower Layer
Figure 7.15

and you can see the result on the image in Figure  7.15(b). This mode multiplies the pixel values of the two layers, but only where the Flower layer is not transparent. Thus, the lighting variations of the tin can are impressed onto the flower and insect, making them look as if they are truly a part of the can. The overall result, however, is a little dark.

The final step, then, is to lighten the dark result in Figure  7.15. This is done by applying the perturbation technique  described in Section  6.2.5 to the Flower layer using the Value channel of the Curves tool. The Value channel is selected because we do not want to affect the colors, just the lightness of the image. Figure  7.16(a)

  
Figure 7.16: Final Composition
Figure 7.16

shows the Curves dialog after using the perturbation technique. The resulting effect on the final composition is shown in Figure  7.16(b). Using the perturbation technique, it was determined that it was the highlight part of the value range that needed to be lightened to obtain the best result. Thus, this effect could not have been achieved using the Levels or Brightness-Contrast tools.

To summarize, this project illustrates the use of blending modes and the Curves tool for compositing. Note that the use of the Multiply blending mode is not primordial to the technique. Other possibilities could have been Screen, Overlay, Lighten Only, Darken Only, and Color. It is important to experiment with the different modes and to do so in conjunction with the Opacity slider and the Curves tool. The final choice will depend on your aesthetic sensibilities.




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Grokking The Gimp
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