March 9, 2005

Rev up your presentations with masks and movement

Author: Rob Reilly

We all appreciate well-thought-out slide shows that logically step through a topic, especially when they're not dull and boring. When creating presentations, many of us are tempted to toss in every little feature the software supports. Unfortunately, cluttered slides can be hard to follow, and obnoxious design elements look cheap. One good technique to enhance your presentations is to use the GIMP's mask feature to make interesting text and cut-out objects, and make those objects move on an OpenOffice.org Impress slide.

Suppose you are trying to convince a client that he needs to switch over to a remote support model for his customers. His company currently sends its technicians out in old 1948 CJ-2A Willys Jeeps, which, while unique, certainly are not the most practical mode of transportation. Let's illustrate how you could create a slide showing a technician in the Jeep traveling from the office to the customer locations and back. The next slide could show how remote support would have just electrons traveling back and forth.

To begin, snap a quick picture of one of the Jeeps with a digital camera and upload it to a file on your Linux machine. Using the GIMP's masking feature to create a picture of just the Jeep, you can then animate that picture in your Impress slide show with the "move along a line" feature. Masking is just a super-powerful way to select regions of the screen for editing. In this case it would let us keep the image of the Jeep and get rid of everything else -- otherwise known as a cut-out.

Create a cut-out

Here's how to create a cut-out, using a picture of my old Jeep as an example (see Figure 1). When you're done, you'll have a cut-out image with a transparent background that's perfect for Impress slides and Web pages.

  • Start the GIMP.
  • Create a new file using the File and New Image tabs.
  • Make sure to click the Transparent button on the New Image tab.
Fig. 1: Image to cut-out.

Open the graphic file with the image that you want to cut out as a second image.Press Ctrl-A in the car image window to select the whole frame.Press Ctrl-C to copy the car image to the GIMP's buffer.Move to the new file window and Ctrl-V to paste the image into the new file.Minimize the car image window so you don't start working on it by mistake.Click the Select Tab and then the Toggle Quickmask. A red "mask" will cover your car image.Click the Eraser tool and begin erasing the red mask to reveal the car underneath. You'll know it's working because as you erase, the color and features of the car will shine through the mask. If you go outside the lines, click Select and then Invert, then click Select and Toggle Quickmask to "un-erase" the mask. So, instead of choosing what you want the mask to uncover, you're actually adding the mask back in.

You can use the zoom feature under the View tab to get a closer look at what you're doing. You can change the brush size under the Eraser Options. You can also use the Bucket-Fill tool for masking of large areas. When making fine adjustments to the mask, use a small pencil point brush and take short strokes. You can use the Undo feature under Edit to back up a stroke or two if you make a mistake.

When you're finished with the mask, click Select and Toggle Mask one last time. That should make the outline of your selection move -- often called "marching ants." Your car will be highlighted with the marching ants selection outline around its periphery. If you accidentally click on a selection tool and the outline of your car disappears, just use Edit / Undo to get back. To erase the background behind the car, bring up the Layers dialog box and highlight (blue line) the Pasted Layer, then click Edit and Cut to perform the erasure. If you've been careful in your masking, you'll now have a sharp, clear, individual image of the car, without a background (see Figure 2). You should see a checkboard grey and black pattern behind the Jeep image, which indicates a transparent background..

Fig. 2: Cut-out from image

Save the file for later use. I saved the file as car1.png. Although the .png format doesn't support layers, if you use the default values in the save box, it will smash all the layers down into one and still keep the transparent background. A transparent background makes it possible to use only the irregularly shaped cut-out image without any kind of square-shaped background color behind it.

Masked text how-to

You might want to try masking to make letters that have a background image showing through, instead of the usual boring black or white text color. Use the steps above to select and copy the image you want to use as a background (the "fill" of the text). Then:

  • Use the Text dialog to select a suitable text size and font. I chose the Helmet Bold font with a size of 1.300 inches. Did you know that you don't have to work with just point sizes when it comes to text?
  • Type in your text. In my case I used the words "Use Linux."
  • Click Select, then By Color.
  • Click anywhere on the black text to select the outline of the text, turning its outline to marching ants.
  • Turn visibility off (click on the eyeball) for the "Use Linux" text on the Layers dialog.
  • Click the Select Tab and then the Toggle Quickmask. The red mask will cover your background image.
  • Click on the Background image layer on the Layers dialog.
  • Click the Move icon (crossed arrows) on the main GIMP dialog menu.
  • Click back in the red mask area to move the background image underneath the mask. Situate the background image for a pleasing appearance.
  • On the Select tab again Toggle Quickmask to off.
  • On the Select tab click the Invert menu item to allow selection of everything except the text outline.
  • To get rid of the background, leaving the cool new masked text, click the Cut menu item under the Edit tab.
Fig. 3: Masked Text

Once you have the effect you like, save the file as a .png file (see Figure 3). You could use the filled text as an artistic touch on the opening slide in your presentation.

At this point we could just put the static image of the Jeep and some filled text into the Impress slide show and we'd be done. But why not add a little motion to the Jeep and let it putter from the office to the client site? Here's how to get that Jeep moving.

Move along a line

Impress lets you add motion to elements in your presentation. I made my Jeep travel from the office to the client. Here's how you can do it.

  • Start Impress.
  • Create a new presentation using File, then New. Choose the defaults while in the autopilot to get to a blank first slide.
  • Select the Rectangle icon on the left and insert a square toward the upper left corner of the slide.
  • Copy and paste another square toward the lower right corner.
  • By double-clicking each square, you can edit its text. For the upper left box I used "Client," and for the lower right box "Office."
  • Next, choose the Curve icon and free form unfilled line to draw a serpentine line between the office and client boxes. Don't use a connector line, because graphics can't be made to follow that type.
  • Import your car into the slide using the Graphics menu's Insert tab. The line will represent the path the car will follow.
  • Click on the graphics handles to resize the car so it's proportional to the boxes.
  • Again, click the freeform line icon and add another line, roughly on top of the original path. It doesn't have to be exact.
  • Boost the line width up a little bit to make it bold so it looks like a road. You need the road because the original path line will not be visible when the animation runs.
  • To make the car follow the line, highlight the car, and while holding the Shift key, highlight the path line. You should be able to grab the path where it peeks out from under the road.
  • Open the animation effects dialog (the moving little "e" on the left) and select the "Move Along Line" icon. Set the speed at the bottom to "slow" and click the check box to apply.
  • To get the car on top of the road, right-click the car, then choose the Arrange and Bring to Front menu items. This will make the car travel on top of the road, instead of the road going over the car.
Fig. 4: Motion in Impress

See Figure 4 for a picture of my Jeep on the road, within Impress.

To run the car down the road click the Slide Show icon at the lower left, then click on the slide to start it moving.

Now it's your turn

Using masks and animating the resultant graphics along a path is an appealing way of getting an idea across to your audience. It's straightforward, clean, and high-impact. Now that you have the basics, get out there and give those presentations some go.

Rob Reilly is a consultant, writer, and commentator who advises clients on business and technology projects. His Linux, portable computing, and public speaking skills-related articles regularly appear in various high-end Linux and business media outlets.

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