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Grokking The Gimp
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7.4 Project 4: The Call of the Mermaid

The fourth project is a bit more complicated than the third. It uses many of the techniques of the first three projects and adds several more. The objective is to actually combine image elements from two disparate sources, a young woman and a fish, to create a realistic and alluring mythological creature--the mermaid.

The raw image materials used to create the mermaid are shown in Figure  7.24.

  
Figure 7.24: Original Images of the Young Woman and the Fish
Figure 7.24

The first step of this project is to fuse together parts of the young woman and fish in a realistic way to create the mermaid. The second step is to place the mermaid composite into an appropriate underwater background scene.

To create the mermaid, the woman and the fish must be selected  and united into a single image but on separate layers. The woman is selected using the Decompose and Threshold technique described in Section  4.5.3. The HSV option of the Decompose function is chosen, and Threshold is applied to the resulting value component. The result is shown in Figure  7.25(a).

  
Figure 7.25: Using Threshold and the Lasso to Create a Mask for the Woman
Figure 7.25

The range of values used with the Threshold dialog is shown in Figure  7.25(b).

The image shown in Figure  7.25(a) has separated a large part of the subject from the background but requires a little more work to achieve the desired result. First, there are elements of the background that must be removed, and second, there are holes in the subject that must be filled. Both tasks are relatively easy to accomplish. The background is removed by following these steps:

1.
Draw a rough selection around the woman's silhouette using the Lasso tool. Make sure the path of the Lasso separates the background from the woman.
2.
Invert the resulting selection by typing C-i in the image window. This phase is shown in Figure  7.25(c).
3.
Choose white as the Active Background Color by typing d and then x in the image window.
4.
Cut the selection by typing C-x in the image window.
Figure  7.26(a)
  
Figure 7.26: Using the Paintbrush to Finish the Mask of the Woman
Figure 7.26

shows the result of having cut away the unwanted background. The remaining work is to fill in the holes seen in Figure  7.26(a) using the Paintbrush tool. As shown in Figure  7.26(b), a medium hard brush is chosen for this. Figure  7.26(c) shows the final mask. Although the lower portion of the woman's legs are not cleanly separated from the background, this is remedied shortly.

The next task is to create a layer mask  for the image in Figure  7.24(a) and to paste into it the grayscale image shown in Figure  7.26(b). This is done in the following steps:

1.
Invert the black and white regions of the image in Figure  7.26(b) using Invert from the Image:Image/Colors menu.
2.
Copy the resulting grayscale image to the default buffer by typing C-c in the image window.
3.
Create a layer mask for the image in Figure  7.24(a) by opening the Layers dialog and choosing Add Layer Mask  from the Layers menu.
4.
Paste the default buffer's contents into Figure  7.24(a) by typing C-v in the image window.
5.
Drop the resulting float into the layer mask by clicking on the Anchor button in the Layers dialog.
The effect of the layer mask on the image is shown in Figure  7.27(a),
  
Figure 7.27: Applying a Layer Mask to the Woman
Figure 7.27

and the thumbnail of the mask can be seen in the Layers dialog shown in Figure  7.27(b).

Now that the layer mask is in place, the remaining parts of the background around the woman's lower legs are removed by painting away the offending parts of the layer mask with black paint using the Paintbrush tool.

The Decompose and Threshold technique is the easiest method for selecting the woman. She presents a relatively difficult selection using any other tool. In particular, the outline of her hair would have been an especially thorny problem. In comparison, the parts of the fish that are needed for the project present a simple outline that can easily be selected using the Bezier Path tool. This step is not illustrated here, but the Bezier Path tool is described in detail in Section  3.1.1.

The selection of the woman and the fish are now united into a single image,  as shown in Figure  7.28(a).

  
Figure 7.28: Uniting the Pieces
Figure 7.28

Figure  7.28(b), which shows the Layers dialog, indicates that the woman and the fish each reside in separate layers. Note that both images have been rotated 90o with respect to their original orientations. This properly orients our mermaid in preparation for inserting her into her final underwater setting.

At this stage, we are ready to begin melding the two image components together. The strategy is to take pieces of the fish's tail and appropriately fuse them onto the woman's body. The fish's tail is too large to superimpose in one piece; thus, it is cut into two parts using the Lasso tool. Using the Move  tool, the bottom part, the tail fin, is repositioned over the lower part of the woman's legs. This is shown in Figure  7.29.

  
Figure 7.29: Flipping and Positioning the Tail Fin
Figure 7.29

Notice that I vertically flipped the tail fin (using the Flip tool) because that orientation looked better to me. The positioning of the tail fin over the woman's legs was facilitated by using the Opacity slider in the Layers dialog.

To convincingly fuse the tail fin to the woman's lower legs, a layer mask is needed. The layer mask, which is applied to the Tail Fin layer, is used to mask off the parts that extend beyond the boundaries of the woman's legs. Figure  7.30(a)

  
Figure 7.30: Fusing the Tail Fin to the Woman's Lower Legs
Figure 7.30

shows that the Tail Fin layer has been made partially transparent to allow the woman's legs to be seen through it. Figure  7.30(b) shows the corresponding Layers dialog. The Tail Fin layer mask is highlighted in the Layers dialog and the Opacity slider set to 56%.

The Paintbrush and Airbrush  tools were used to mask off parts of the tail fin in Figure  7.30(a). The Eraser  tool was used to remove the parts of the woman's feet that extend out beyond the tail fin. The result, after returning the Opacity slider to 100% in the Layers dialog, is shown in Figure  7.30(c). The tail fin now seems to be fused onto the woman's legs.

Figure  7.31

  
Figure 7.31: Fusing the Remainder of the Tail and Correcting for Image Inconsistencies
Figure 7.31

shows the image after performing a similar sequence of fusing the upper part of the fish's tail to the woman's body between her waist and her knees. As before, a layer mask is used to perform the fusion. Also, in order to better align the highlight in the scales of the tail with the axis of the woman's upper legs the Rotation option from the Transform tool is used.

In addition to fusing the tail to the woman's body, Figure  7.31 also shows that her wrist watch has been removed with the Clone  tool. Let's hope she wasn't too attached to it. The Clone tool was also used to remove some overly bright highlights in her face (for more on how to use the Clone tool see Section  6.3). Finally, the image was cropped to the dimensions seen in Figure  7.31.

It is now time to insert our siren of the sea into a scene reflecting her natural habitat, swimming with her faithful fishy companions along a reef, undoubtably somewhere in the south Pacific. The insertion of the mermaid into the scene was accomplished by first merging all the layers used to create Figure  7.31, applying the layer mask, and then copying and pasting the result into the underwater image. As usual, the paste gives rise to a floating selection, which is then dropped into a new layer using the New Layer button in the Layers dialog. The Move tool is used to position the Mermaid layer and the result is shown in Figure  7.32.

  
Figure 7.32: The Mermaid Placed into an Underwater Scene
Figure 7.32

Actually, the result in Figure  7.32 also displays an additional finesse. The obvious sunburn of our underwater beauty, as seen in Figure  7.31, has been color corrected to a tint more in keeping with her new environment. This is accomplished using the perturbation  technique for the Curves tool, as described in Section  6.2.5. The result is that her skin color has been changed to a mild bluish-green tint.

Looking at Figure  7.32, the edge between the mermaid's upper body and the blue of the background waters seems fine. However, the edge of her yellow tail seems a little too abrupt, too sharp. It looks as if this part of her body were cut out of another image and pasted into this one. Indeed, it was. So, as a final attention to detail, it would be nice to diminish the abruptness of this edge. You can do this using a clever technique based on the Border  function found in the Image:Select menu (see Section  3.3.9).

The idea is to blur  together the background and the mermaid in a narrow region around the mermaid's edge. To do this, follow these

  
Figure 7.33: Using Border and Gaussian Blur (IIR) to Soften the Cut-Out Look of the Mermaid's Edge
Figure 7.33

steps while referring to Figure  7.33:
1.
Activate the Mermaid layer by clicking on her thumbnail in the Layers dialog (shown in Figure  7.33(b)).
2.
Create a selection of the mermaid using Alpha to Selection  from the Layers menu.
3.
Use the selection to make a border 3 pixels wide using Border (Figure  7.33(c) shows the Border tool's dialog, and Figure  7.33(a) illustrates the selection result).
4.
Merge the Mermaid layer into the background by typing C-m in the Layers dialog or the image window.
5.
Apply Gaussian Blur (IIR)  with a radius of 3 pixels (Figure  7.33(d) shows the dialog for this filter).
6.
Remove the selection by typing C-S-a in the image window.
The final result gives a much softer edge between the mermaid and the background. This is shown in Figure  7.34.
  
Figure 7.34: The Final Mermaid Composition
Figure 7.34

To summarize, this project illustrates how layer masks, in conjunction with many other tools, can be used to literally fuse together image elements. This project also shows how the Border tool can be used to finesse the edges of composited images.




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