6. Using Filters

This chapter gives you the opportunity to explore Filter effects such as blur, distort, enhance, and use artistic and map filters.

Anyone who’s ever gone to the movies or seen a television show is aware of the concept of special effects and visual effects. This is the process by which a visual, mechanical, or computer-generated image is integrated into the overall filmed narrative, with the goal of having the audience accept the effect as “real”. The effect can be completely illusionary, such as inserting the CGI of the Incredible Hulk into an actual filmed environment, or used to enhance an actual person or object, such as making it seem as if actor Elijah Wood is really the size of the hobbit Frodo Baggins.

The use of filter effects in GIMP is more of the latter for the most part; an application of different GIMP features to produce an overall visual modification to an existing image element. You’ve already seen how Gaussian Blur and Hurl noise effects can create a desired outcome. That’s only the start.

Getting to Know Filters

Many, but not all, GIMP filters use Script-Fu or what the Windows world calls macros. This is a method of creating a rule or set of rules that automates a repetitive task. When you apply a particular Script-Fu, you are actually applying a number of pre-set GIMP features that run in a particular order to produce a specific result.

As already mentioned, not all Filter effects rely on Script-Fu. A very commonly used effect, Gaussian Blur, is not an applied set of different features, but rather a specific blur method, although Gaussian Blur is sometimes used as part of a Script-Fu.

Regardless of the nature of one filter or another, filters, like layers, are a primary tool in the creation and modification of a wide variety of image effects you’ll use repeatedly in GIMP. It would be impossible to survey all of the available filters within the scope of this book, so the following collection of exercises will demonstrate only a selected sample.

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Polar Coordinates Filter

In this exercise, you’ll learn how to apply an effect to text (though it works with any image) to create a logo or part of a logo. As part of the exercise, you’ll also get some additional experience using the Text tool and Patterns. If GIMP is not already open, launch it now.

1. Open a new, blank canvas with a white background, with a width of 1000 pixels and a height of 150 pixels.
2. Click Layer, New Layer, and add a new layer called something like “new background” with a white Layer Fill Type.
3. In the Layers tab, select the original Background layer, right-click, and then select Delete Layer.
   

   The original background layer cannot be deleted unless there’s at least one other layer for the graphic. If the original background layer were not deleted, it might inadvertently cover the new background where the pattern is added.

4. On the Image Window toolbar, click Windows, Dockable Dialogs, and then click Patterns.
5. When the Patterns dialog opens, select one with a blue color such as Electric Blue, and then drag it to the blank canvas to bucket fill the background with that pattern as in Figure 6.1, then close the Patterns dialog. (Note that the Pattern name is displayed in italic type above the swatches when you click on a Pattern swatch in the dialog box.)
   

   Figure 6.1. The Patterns dialog is available for you to fill an image layer with a particular pattern.

   

6. Click on the Text tool in the Main Toolbox, and on the Text tool tab, change the font size to 110 pixels, and then choose an interesting font type. For this example, I’m using Forte, but any font will work.
7. Click in the Image Window to open the Text Editor, enter the words “Having the Blues” or something similar, and then close the Text editor.
8. Use the Move tool to center the text layer in the Image Window.
9. Select the text layer on the Layer tab, right-click and select Alpha to Selection.
10. Select the new background layer in the Layers tab, then on the Image Window, click Select and then Invert.
11. Press the Delete key on your keyboard to remove the patterned background.
12. On the text layer in the Layers tab, turn off the view of the layer by clicking the “eye” button, so you can see the pattern preserved in the text.
13. Right-click the text layer in the Layer’s tab and then select Delete Layer, leaving only the new background layer which contains the text.
14. Click Select and then click None to remove all selections, leaving the patterned text against a transparent background.
15. Open a new image window measuring 1000 pixels wide by 150 pixels in height and give it a white background.
16. Copy the text from the first image into the new image window, and click Layer and then New Layer to add the text layer.
17. On the new image, click Filters, Distorts, and then click, Polar Coordinates.
18. In the Polar Coordinates dialog, select the Map Backwards check box and then click OK.
19. Select the Crop tool and crop an area around the curved text that contains it in a square as shown in Figure 6.2.
    

    Figure 6.2. The Polar Coordinates feature curves an image around the polar center of the image.

    

    You may have to resize the window or change the view percentage after cropping to view the drawing at an optimal size. In Figure 6.2, the view is magnified to 200%.

20. If desired, save the image and either save or discard the original, blue text image.

Admittedly, the desired Filters feature wasn’t presented until nearly the end of the exercise, but it’s a realistic scenario of how filters are used after a drawing has otherwise been created and prepared for the effect.

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Creating a Text Logo Using Multiple Filters

While a single filter can produce desirable and even dramatic effects, it’s more likely that you’ll use multiple filters and other techniques to achieve the look you desire. The next exercise is also working with text, but in a very different way.

1. Create a new, blank canvas, measuring 800 pixels wide and 200 pixels in height, with a white background.
2. Click Layer and then click Duplicate Layer to create a second, identical background.
3. Click Filters, Render, Nature, and then click Flame.
4. When the Flame dialog appears, on the Rendering tab, use the Gamma slider to set the value to about 3.80.
5. Click the Camera tab, and use the Zoom slider to set the value to about 0.50, and then click OK.
   

   You can feel free to experiment with any of the other settings to alter the effect, but the settings listed in these steps are those used to produce the exercise’s final outcome.

6. Click Filters, Noise, and then click Hurl.
7. When the Hurl dialog appears, use the Randomization slider to set the value to 15, and then click OK.
8. Select the Text tool, choose an interesting font. For this example, I’m using Broadway, but any font will work and set the font size to about 75 pixels.
9. Click in the image to open the Text Editor, and type in a logo name such as “Wiredwriter.net”.
10. Close the Text Editor, and use the Move tool to center the text in the image window or otherwise place it against the “noisiest” part of the background.
11. With the text layer selected, right-click and then select Alpha to Selection.
12. Select the Background Copy layer, click Select and then click Invert.
13. Right-click the original background layer and select Delete Layer.
14. Click the “eye” next to the text layer to make the layer invisible.
15. Select the Background Copy layer and press the Delete key on your keyboard, to make the text appear with the flame and hurl effects against a white background.
16. Click Select and then click Invert again to make sure only the text is selected.
17. Click Filters, Decor, and then click Add Bevel.
18. When the Add Bevel dialog appears, use the Thickness slider to set the value to its maximum of 30, accept the default settings, and then click OK.
19. When the second image opens with the beveled text, create another blank image of the same dimensions but using the Advanced Options in this dialog box to define the background as transparent.
20. With the beveled text still selected, copy it to the canvas with the transparent background as seen in Figure 6.3.
    

    Figure 6.3. Using the Bevel filter creates a second, duplicate image of the beveled object.

    

21. Save the transparent image with the pasted text and discard the other created images.

You now have a text logo that you can paste against any sort of background. In the case of this exercise, the text is rather light, so a black or dark background would be most suitable. The Flame filter can be adjusted using the Colormap menu on the Render tab to select a different color, and on the Camera tab, the X, Y, and Zoom sliders can change the apparent size and location of the effect on the canvas, thus changing the appearance of the effect in the text. The Hurl and Bevel effects can also be modified to create a different presentation and finally, the choice of font size and type can give many sorts of impressions.

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Reducing Noise in a Photo

While GIMP is good at creating images such as logos or banners for a website, its real strength is as an image editor and particularly as a tool to enhance photographs. There are a wide variety of ways that an otherwise good image can have imperfections. Often the image will contain noise that detracts from the subject. There are a number of filters that can help correct this problem. The result may not be perfect, since even GIMP has to work within the reality of what’s contained in the photo, but they’ll certainly be better.

For this exercise, choose any photo that contains unwanted noise, such as graininess, and open it in GIMP.

1. On the Image Window toolbar, click Filters, Enhance, and then click Despeckle.
2. When the Despeckle dialog appears, use the slider bars on the Preview window to center the main subject of the photo, review the preview image as shown in Figure 6.4, accept the defaults, and then click OK.
   

   Figure 6.4. The Despeckle filter reduces noise seen as RGB color “flecks’ by softening the image.

   

   Unfortunately, the Despeckle filter often softens the image to the point of reducing sharpness and clarity, so other filters have to be used in conjunction to maintain image quality.

3. Click Filters, Enhance, and then click Unsharp Mask.
4. When the Unsharp Mask dialog appears, accept the default settings, and click OK.
5. Click Filters, Enhance, and then click Sharpen.
6. When the Sharpen dialog appears, use the Sharpness slider to adjust the preview image to the desired level, and then click OK.
7. Save your changes. The image should look something like the photo in Figure 6.5.
   

   Figure 6.5. The finished product is a mix of filters that reduce noise and enhances sharpness in the image.

   

As you can see, this sort of enhancement is a compromise between reducing noise, which requires reduction of detail, and attempting to maintain or improve sharpness. Like any compromise, both competing elements don’t get everything they want, but the overall effect is usually an improvement.

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Adding Lighting Effects and a Lens Flare

On occasion, when you take a photo, a lens flare (wanted or unwanted) will appear in the image. If you want to add one to an image for artistic effect, GIMP easily provides that ability. Lighting effects in general, enhance images of objects that are metallic or glass, making them look sharper, shinier, or just plain cool.

For the purpose of the exercise, I’m using a photo of a very sleek sports car, but you can use whatever photo or graphic you deem suitable.

1. On the Image Window toolbar, click Filters, Light and Shadow, and then click Lighting Effects.
2. In the Lighting Effects dialog, click on the Light tab.
3. In the Preview window, drag the blue “star” to the position where you want to place the lighting effect, accept the default settings as shown in Figure 6.6, and click OK.
   

   Figure 6.6. The Lighting Effects dialog contains a number of tabs and controls that let you configure how light effects are modified in an image.

   

4. Click Filters, Light and Shadow, and then click Lens Flare.
5. When the Lens Flare dialog opens, in the preview window, click on the point in the image where you want to place the flare effect, which should be where you placed the Lighting Effect, and then click OK.
6. Save and close the image.

The Gradient Flare filter is different from other filters including the somewhat similar Lens Flare filter. The Lens Flare filter creates the effect of you shooting an object that was being hit by sunlight creating a strong reflection. The Gradient Flare filter creates the effect of a photograph being taken of a brilliant light source, complete with halo and radiant light being emitted from around the source. Both filters are found in the Filters menu under Light and Shadow and may sometimes be used together.

As you can see, with just a very few steps, you can take a very slick photo of a sports car or other object and make it truly great. Both effects use a variety of GIMP features to apply the desired results, so it takes a few moments for you to achieve the final product, but it’s certainly worth it.

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Creating a Dynamic Desktop Image

The last few tutorials have shown you examples about how to correct and enhance photos, but sometimes you may want to create a completely different type of art. Many people like to personalize the desktop of their computers. Most of the time, a person will either select a pre-loaded wallpaper image on their computer or download something from the web. The following tutorial shows how to make a personalized wallpaper using filters.

Assuming you plan to actually use the wallpaper created in this tutorial on your computer’s desktop, you’ll need to know your screen resolution, so that you can create an image of the same size. In Windows XP, right-click on the desktop, select Properties, and in the Properties dialog, click the Settings tab to see the screen res settings. In Windows 7 (and I assume Windows Vista, though I’ve never owned a Vista machine), Click Start, Control Panel, Display, and in the Display dialog, click Adjust resolution to see the settings.

1. Open a new, blank canvas with a white background, giving it the same dimensions in pixels as your computer’s screen resolution.
2. In the Main Toolbox, select the Blend tool, and on the Blend tool tab, click Gradient, and select a Gradient type such as Caribbean Blues.
3. Drag your cursor from one side of the blank image to another in any desired direction, such as left to right, and then release the mouse button to apply the gradient.
4. Click Filters, Render, Clouds, and then click Plasma.
5. In the Plasma dialog, use the Turbulence slider to achieve the desired effect, select the Randomize check box, and then click OK.
6. Click Filters, Blur, and then click Motion Blur.
7. In the Motion Blur dialog, select Radial under Blur Type, and then click OK.
   

   The Motion Blur effect may take a few moments to apply, so be patient.

8. Click Layer, New Layer, and create a new transparent layer, calling it something like “logo”.
9. Select the Rectangle Select tool and create a rectangular selection as a banner completely across the top of the image window as shown in Figure 6.7.
   

   Figure 6.7. Use the Rectangle Select tool to create a banner across the top of your customized, abstract wallpaper.

   

10. With the logo layer selected, use the bucket fill tool to fill the rectangular selection with white.
11. With the logo layer still selected, use the Opacity slider to set a value of about 40.
12. Click Filters, Light and Shadow, and then click Drop Shadow.
13. When the Drop Shadow dialog appears, clear the Allow resizing check box, accept the other default values, and click OK.
14. On the Image Window toolbar, click File, New, Create, Logos, and then select any item in the list.
15. Create a logo using the logo type and settings you believe will enhance your wallpaper background.
    

    You may have to go through something of a trial-and-error process to find a logo that will be suitable.

16. Resize the logo as necessary, deselect the background layer, and from the Image Window Toolbar, Edit, Copy Visible, then paste your new logo graphic into logo layer of the main image, using the Move tool to place it in the banner area.
17. Remove any remaining selections and save the image as shown in Figure 6.8.
    

    Figure 6.8. The final version of the personalized wallpaper.

    

As you can see from the tutorial, you could have adjusted the background image and logo in a wide variety of ways to achieve any number of different effects. The wallpaper created in this example is just one expression of how to manufacture one. You could also have created banner text manually and added an image to enhance your “brand” in the wallpaper. With just a slight variation, the image could also be suitable for a personal website as a background or background with logo and banner.

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Cartoonize Yourself Using Levels

In this age of social networking, we are all looking for new ways to “brand” ourselves in some manner or another. One way to do so is to create a customized avatar (no relation to the film) of your face. You may not want a realistic version of your face posted to the web, but what about a cartoon version of you? There are a number of services available on the web that will “cartoonize” your photograph for a fee, but you can do the same thing using GIMP.

For this exercise, you’ll need a “head shot” of yourself or at least of someone. For the purpose of this tutorial in this book, I’m using a photo of yours truly.

1. Open the desired photo in GIMP, click Layer and then click Duplicate Layer.
2. Select the duplicate layer; click Filter, Blur, and then click Gaussian Blur.
3. Set the Horizontal and Vertical Blur Radius values to 6.0 and then click OK.
4. With the duplicate layer still selected, click Colors and then click Invert.
5. Set the Opacity value for the duplicate layer to about 50, so that part of the original background layer is visible through the duplicate layer.
6. Right-click on the duplicate layer on the Layers tab and select Merge Down to merge the two layers.
7. Click Colors and then click Levels.
8. When the Levels dialog opens, set the Pick Black Point Input level to about 90 and set the Pick White Point level to about 160 as seen in Figure 6.9, and then click OK.
   

   Figure 6.9. The Levels tool is used to reduce color gradients and magnify details.

   

9. Click Colors and then click Desaturate.
10. When the Desaturate dialog appears, accept the defaults and click OK.
11. Open the Levels dialog again and set the Input values similarly to those you can see in Figure 6.10, and then click OK.
    

    Figure 6.10. Adjust the histogram levels to reduce the darkness of the image and increase contrast.

    

12. Save the image with a new name and, to use as an avatar, resize to the required measurements and then upload it to your favorite social networking venues.

You may have to tweak the settings in the Levels dialog for each of the occasions you use it to produce the desired effect. While you probably won’t look like your favorite anime character, the result is a simplified version of your (or someone’s) face with thicker lines and exaggerated details that are indicative of a cartoon. The general effect you applied in this exercise is called high-pass filtering.

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Cartoonize Yourself Using Colors

You may have noticed in the previous exercise that you didn’t go anywhere near the Filters menu. There’s a reason for this. There is a “cartoonize” filter option but it may not work as well, at least all by itself, as the previous method. Nevertheless, here’s a way to use that filter and the Levels utility to produce a similar image.

1. Open the original image of the desired face.
2. Click Filters, Artistic, and then click Cartoon.
3. When the Cartoon dialog opens, adjust the Mask radius and Percent black sliders until you achieve the effect you want in the Preview window, and then click OK to apply the result as seen in Figure 6.11.
   

   Figure 6.11. The Cartoon filter increases line thickness and contrast.

   

   This intermediate step in the process appears rather unattractive, which is why other tools besides the Cartoon filter are required to get the final result.

4. Click Colors and then click Levels.
5. When the Levels dialog opens, adjust the Input level settings to those similar to what you did in Step 11 of the previous exercise or otherwise, to those you desire, and then click OK.
6. Click Colors and then click Desaturate, and when the Desaturate dialog opens, click OK.
7. Click Colors, click Brightness-Contrast, and adjust the sliders to produce an effect similar to what you see in Figure 6.12, and then click OK.
   

   Figure 6.12. The Cartoon filter increases line thickness and contrast.

   

8. Save the image if you wish and, to use it as an avatar, resize it to the required dimensions and upload it to your favorite social networking venue.

I suppose it’s a matter of taste as far as which cartoon is better, so choose the one you like the best. You also probably realize that, with a bit of adjustment, you could use either method to generate identical cartoon images of the same photograph. If you feel daring, you can open the base photo again and reduce the number of colors in the image by clicking Colors and then Posterize. From there, use a variation of one of the two cartoon tutorials to see what you come up with.

Just opening the Filters menu produces a dizzying number of filter options and if you tried to explore the details under each selection, it could take you a great deal of time. This chapter has only introduced you to a small sample of filtering options and shown you how they work. Now that you’re familiar with some of them, continue to explore and see what else is available.