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Grokking The Gimp
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8.4 Shadows

A shadow is just a dark silhouette of an object, but with a somewhat fuzzy edge to account for the diffraction of the illuminating light source.  Furthermore, depending on the location of the source of light, a shadow is somewhat displaced with respect to the object. You can construct very convincing shadows in the GIMP. These are surprisingly useful rendering tools in image manipulation, and this section explains how to make them.

To make a shadow for an image object you must have a selection of it. The following describes the steps needed to create the selected region's shadow:

1.
Cut the selected region by typing C-x in the image window. This places the selection into the default buffer.
2.
Create a new transparent layer by clicking on the New Layer button in the Layers dialog and choosing the Transparent option.
3.
Paste the contents of the default buffer by typing C-v in the image window. This places the paste into a floating selection. Anchor the float to the new layer by clicking on the Anchor button in the Layers dialog.
4.
Duplicate the new layer by clicking on the Duplicate Layer button in the Layers dialog. The duplicated layer is placed above the original layer in the layer stack.
5.
Name the duplicated layer Object and the original layer Shadow.
6.
Make the Shadow layer active by clicking on its thumbnail in the Layers dialog, toggle on the Keep Trans. checkbox in the Layers dialog, and use the Bucket Fill tool with its Threshold set to 255 to fill the image object with black or some other appropriate, dark color.
7.
Toggle off the Keep Trans. checkbox in the Layers dialog, use Gaussian Blur (IIR)  found in the Image:Filters/Blur menu to blur the Shadow layer, and use Offset  from the Image:Image/Transforms menu to shift it.
8.
Use the Opacity slider in the Layers dialog to give the shadow an appropriate degree of transparency.
This procedure is often referred to as making a drop shadow.  

An example of creating a drop shadow is now presented using the preceding recipe. Figure  8.16(a)

  
Figure 8.16: A Daisy Selection
Figure 8.16

illustrates a photo of a daisy. Using techniques from Chapters  3 and 4 a selection of the daisy is made and, as shown in Figure  8.16(b), this is used to cut away the daisy's background. (Note: the cut produces a transparent background only if the original image layer has an alpha channel. For more on alpha channels see Section  4.2.1.) The Layers dialog in Figure  8.16(c) shows that the Daisy layer has been duplicated and that the lower layer has been labeled Daisy Silhouette.

The remaining steps in the creation of the shadow are now easy. The Daisy Silhouette layer is filled with black using the Bucket Fill tool (don't forget to set Threshold to 255 in the Bucket Fill dialog). The blurring  can be performed with any of the blur functions from the Image:Filters/Blur menu (but make sure that the Keep Trans. button in the Layers dialog is toggled off before applying one). Here, Gaussian Blur (IIR) is used with a radius of 20.8.1 This is followed by using Offset , which can be applied by typing C-S-o in the image window. The offset parameters are set to 15 for both the X and Y components, and the Wrap-Around radio button is toggled off. The result is shown in Figure  8.17(a).

  
Figure 8.17: Filling, Blurring, and Offsetting Creates the Shadow
Figure 8.17

Figure  8.17(b) and (c) show the dialogs for the Gaussian Blur (IIR) and Offset filters used in this example.

All that remains is to place the flower and shadow over an appropriate background. This could be anything: a solid color, an image pattern, or a photograph. Figure  8.18(a)

  
Figure 8.18: The Final Drop Shadow
Figure 8.18

illustrates the daisy on a light blue background. The Layers dialog in Figure  8.18(b) shows the placement of the blue layer at the bottom of the image stack. This layer was created by clicking on the New Layer button in the Layers dialog, positioning it to the bottom of the layer stack, and using the Bucket Fill tool to give it the desired color.

By the way, the shadow produced using this technique can be made to look more diffuse by making it more transparent. Simply make the shadow layer active in the Layers dialog and set the desired value of transparency using the Opacity slider.

A technique very similar to making drop shadows is that of making punchouts.   A drop shadow creates the illusion of an image object floating above a background. The punchout is also a shadow technique but gives the illusion that part of the background has been cut away casting a shadow on yet another background behind. This is the effect you would see by holding a stencil slightly in front of a wall. The light shining through the stencil casts a shadow that can be seen through the stencil's hole, against the wall.

Like for drop shadows, to make a punchout for an image object you must have a selection of it. The procedure for making a punchout is similar to that for making a drop shadow, but with a couple of twists. To make a punchout in the shape of a selected image region follow these steps:

1.
Set the default colors by typing d in the image window.
2.
Create a new layer by clicking on the New Layer button in the Layers dialog, and select Foreground as the Layer Fill Type in the New Layer Options dialog. This fills the new layer with black.
3.
Make sure that the new layer is active in the Layers dialog, and fill the selected region with white using the Bucket Fill tool. Label this layer Shadow.
4.
Cancel the selection by typing C-S-a in the image window, and create a layer mask for the Shadow layer by choosing Add Layer Mask  from the Layers menu.
5.
Make the Shadow layer active by clicking on its thumbnail in the Layers dialog, and copy it to the default buffer by typing C-c in the image window.
6.
Make the layer mask of the Shadow layer active by clicking on the layer mask's thumbnail in the Layers dialog, paste the default buffer's contents by typing C-v in the image window, and anchor the resulting float to the layer mask by typing C-h in the image window.
7.
Make the Shadow layer active, blur it with Gaussian Blur (IIR),  and shift it with Offset. 
This creates the punchout effect.

An example of making a punchout is now presented. The example deviates slightly from the steps described in the preceding list. Figure  8.19

  
Figure 8.19: Lightning Strike!
Figure 8.19

shows an impressive flash of lightning across a deep purple sky. You can just imagine the powerful clap of thunder that's coming. But in case you can't, we're going to drive the message home by punching it out of the photo.

We begin by setting the default colors by typing d and then switching the background and foreground colors by typing x in the image window. A new layer is created by opening the Layers dialog and clicking on the New Layer button. The Background radio button is selected from the New Layer Options dialog. This sets the new layer to black. For this example the new layer is labeled Inverse Text.

The Text tool is now invoked by clicking on its icon in the Toolbox and then clicking in the image window. This brings up the Text tool dialog shown in Figure  8.20(c).

  
Figure 8.20: Placing Some Text
Figure 8.20

The Brushstroke font has been chosen with a height of 100 pixels, and, because the goal of choosing this font is to get a rough punchout effect, the Antialiasing option has been turned off, as shown in the Text tool's Tool Options dialog (Figure  8.20(d)). Clicking on the OK button in the Text tool dialog places the text into a floating selection. Because the Active Foreground Color is white, so is the newly created text.

Cutting the floating selection with C-x and then pasting it back with C-v centers the text before it is anchored into the layer below by clicking on the Anchor button in the Layers dialog. This makes a layer with white text on a black background. Figure  8.20(a) shows the image window, and Figure  8.20(b) shows the corresponding Layers dialog at this stage in the example.

The procedure is almost complete. If we were making a drop shadow, the new layer would be blurred and offset. However, for the punchout, we first copy the Inverse Text layer into its own layer mask. This is done in the following steps:

1.
Make the Inverse Text layer active by clicking on its thumbnail in the Layers dialog.
2.
Copy the Inverse Text image contents to the default buffer by typing C-c in the image window.
3.
Create a layer mask by choosing Add Layer Mask  from the Layers menu.
4.
Paste the default buffer contents by typing C-v in the image window.
5.
Anchor the resulting floating selection to the layer mask by clicking on the Anchor button in the Layers dialog.
The result is shown in Figure  8.21(a).
  
Figure 8.21: Creating the Layer Mask
Figure 8.21

Figure  8.21(b) shows the corresponding Layers dialog.

The final step is to blur and offset the text in the Inverse Text layer. To do this, the Inverse Text layer is made active by clicking on its thumbnail in the Layers dialog. This layer is then blurred using the Gaussian Blur (IIR) filter with a radius of 8 and shifted using Offset with values of 4 for both X and Y. The result is shown in Figure  8.22(a).

  
Figure 8.22: The Final Punchout
Figure 8.22

The blurred and offset inverted text now appears as a shadow seen through a stencil punched out of the photo. Figures  8.22(b) and (c) show the dialogs for the Gaussian Blur (IIR) and Offset filters used in this example.




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