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This tutorial simulates lighting that comes from behind text. It also illustrates one of the more interesting uses of the Polar Coordinates filter. Most GIMP users ignore this filter because its purpose isn’t obvious. It converts linear effects into circular ones—and it does that extremely well.
In this tutorial we’ll take black text on a white background and transform it into a dazzling, colorful effect. We’ll even take a detour along the way to see how GIMP can turn wind into light.
Creating the Text
Start with a black canvas set to the default size (640×400 pixels).
- Choose the Text tool from the toolbox. Choose a thick sans-serif font—I’ve used FacetBlack Thin sized to 120 pixels—and set the font color to white. Whenever you work with textures inside text, you want to use thick fonts so that it’s easier to see the texture.
- Click in the canvas and type OpenSource .
- Use the Align tool to center the text layer manually.
- Expand the layer size to fit the canvas (Layer->Layer to Image Size).
The Align tool requires that you click in the canvas to select layers to include in the alignment, then set the Relative To option in the Tool Options dialog. To center a layer, click on it and then choose to align it relative to the image.
- Create a selection of the text by choosing Layer->Transparency->Alpha to Selection. Save the selection to a channel (Select->Save to Channel). Double-click the channel name and change it to Outline. We’ll come back to the saved channel in a moment.
- Click the Open Source layer in the Layers dialog to make that layer active again and then clear the selection (Select->None).
The selection is saved to a channel so we can easily recover it, even after we’ve made changes to the text layer.
- Click the text layer in the Layers dialog to make it active again.
- Open the Gaussian Blur filter and apply a blur of 10 pixels to the text layer. In the Gaussian Blur dialog, specify the IIR blur method. (The IIR setting works better with text, whereas the RLE setting works better with photographs.) Apply this setting to the layer.
- Merge the text layer with the Background layer (Layer->Merge Down).
- If you’d like, you can enhance the whiteness in the image by applying the Autolevel option. Just choose Colors->Levels and then click the Auto button.
Autoleveling is optional, but it will enhance some of the white areas of the image. How dramatic a change this will make depends on the thickness of the font you choose.
Adding the Light Burst
- Open the Polar Coordinates filter (Filters->Distorts->Polar Coordinates). Set the Circle Depth slider to 0 percent and set the Offset Angle slider to 0 degrees. Check the box next to the words Map from top and uncheck the boxes next to the words To polar and Map backwards. Click OK to apply these settings to the image.
The Circle Depth setting changes the nature of the effect from rectangular (at the low end) to circular (at the high end). The Angle setting rotates the effect around the layer’s central point. Mapping the effect from the top causes each row of the layer, top to bottom, to be mapped from the center of a circle to the outside, with the bottom row mapped to the outermost edge of the effect. This setup allows us to produce a sunburst effect that seems to radiate from the center of the text.
Applying the Polar Coordinates filter to the image produces an interesting effect, but this is just the start.
- Rotate the image clockwise by 90 degrees (Image->Transform->Rotate 90 degrees clockwise). If you’re not using the Single Window mode then press ctrl-E to so you can see the entire image. If you are using Single Window mode, use ctrl-shift-J.
- Open the Wind filter (FiltersDistortsWind). Set the Style to Wind, the Direction (from which the wind blows) to Right, and the Edge Affected to Leading. The Wind setting produces softer streaks than the Blast setting, and the streaks originate on the side of the image that is facing the wind.
- Set the Threshold to 5 so that more of the white pixels are streaked, and then set the Strength to 40 to create longer streaks. Click OK to apply these settings to the image.
- Repeat this process by pressing ctrl-F two more times to strengthen the effect.
Pressing ctrl-F reapplies the last filter used. This comes in handy when you need to apply a filter several times in a row.
The long streaks created by the Wind filter eventually become bursts of light.
- Rotate the image counterclockwise by 90 degrees (Image->Transform->Rotate 90 degrees counter-clockwise). Again use ctrl-E or ctrl-shift-J if necessary to fit the image on your screen.
- Open the Polar Coordinates filter again (Filters->Distorts->Polar Coordinates). Set the Circle Depth to 0 percent and set the Angle to 0 degrees. Uncheck the box next to the words Map backwards and then check the boxes next to the words To polar and Map from top. Click OK to apply these settings. Now you have something that is beginning to look like a real light burst.
- Add a new transparent layer by choosing Layer->New Layer and setting the Layer Fill Type to Transparency.
- Open the Channels dialog (Windows->Dockable Dialogs->Channels) and click the Outline channel at the bottom of the window to make that channel active. Click the Channel to Selection button in the Channels dialog.
- Return to the Layers dialog and click the uppermost layer to make that layer active. Fill the selection you just created with white and then deselect all (Select->None).
- Open the Motion Blur filter (Filters->Blur->Motion Blur). Set the Blur Type to Zoom and set the Length to 66 pixels. This long blur will stretch the effect toward the edges of the image. Click OK to apply these settings.
Reversing the polar coordinates gives us a light-burst effect.
Enhancing the Text Over the Background
- We’d like to make the text stand out a bit against the sunburst background. We’ll do that by outlining the text and simulating some depth.
- Add another new layer (Layer->New Layer). Name it Stroke.
- Make sure black is the current foreground color by pressing D in the canvas to reset the foreground and background colors to black and white, respectively.
- Click the channel you saved earlier, the one you named Outline and create another selection from it. Return to the new layer in the Layers dialog.
- Stroke it by 1.5 pixels to outline the text (Edit->Stroke).
- Deselect all (Select->None).
- Duplicate the layer in which you stroked the outline (Layer->Duplicate Layer) and then invert the colors in that layer (Colors->Invert).
- Click on the original stroked layer to make it active. Open the Gaussian Blur filter and apply a blur of 3 pixels to this layer.
- To give the appearance of depth, offset this layer by choosing Layer->Transform->Offset and setting the Offset X and Offset Y values to 1 pixels.
Outlining the selection with black makes the text easier to read.
Inverting the colors and offsetting the layer gives the lettering an embossed appearance.
Adding a Color Gradient
- Add a new transparent layer by choosing Layer->New Layer named Color and setting the Layer Fill Type to Transparency. Move this layer to the top of the layer stack in the Layers dialog.
- Choose the Blend tool from the toolbox. In the Tool Options dialog, select the Yellow Orange gradient and choose Square from the Shape drop-down menu. Click the middle of the layer and drag toward any corner of the canvas to apply the gradient. Set the layer mode for this layer to Color so you’ll be able to see through to the text.
- Add another layer (Layer->New Layer) named Overlay.
- Choose the saved Outline channel and convert it to a selection again. Return to the new layer and fill the selection with black.
- Set the layer mode to Overlay and then deselect all (Select->None).
Choosing Square from the Shape drop-down menu maps the darker colors over the light streaks while adding lighter colors toward the center, where the light source is supposed to be.
- Click the Background layer in the Layers dialog to make that layer active.
- Open the Curves dialog (Color->Curves) and adjust the curve as shown here.
Use the Curves dialog to produce all kinds of bizarre bursts.
Congratulations! You’ve created the basic light burst. To test your skills, try adjusting the curves in the Background layer. Doing so will have a dramatic effect on the appearance of the light burst. Also, duplicating the black letter layer at the top of the Layers dialog can enhance the letter coloring to improve its visibility.