How to Use the Mask & Instant Alpha Tools in iWork for Mac - Part 1

In this two-part article, I want to talk to you about – perhaps even introduce you to – a pair of significant, yet poorly understood and far less utilized tools found in the iWork suite of apps for the Mac. These two tools are called the Mask Tool and the Instant Alpha Tool. They are available on all three iWork Mac apps: Pages, Keynote and Numbers.

The toolbar icons for the Mask and Instant Alpha tools in the iWork apps.

These are the toolbar buttons for the Mask tool and the Instant Alpha tool.

Here, in Part 1, I cover the Mask tool. For the sake of simplicity, I illustrate by using Keynote. However, you should note that the specifics of these tools – and how to use them – are identical in all three apps.

My two favorite and most-used Mac productivity apps are Keynote and Pages. In my current roles as presenter and educator, these two apps have been the most useful, powerful, and fun professional productivity apps in my thirty-five years of sitting at a keyboard and monitor. It's time now for me to get out of this chair and tell you that, while there are many practical tools available in the iWork suite, among the best are the Mask and Instant Alpha tools. These go a long way towards helping make your presentations and documents truly rise above all the mediocre ones out there.

Let's dive into the Mask tool. Think it as being similar to the crop tool you might already be familiar with in your work with an image editor like iPhoto.  The difference between the Mask tool and a crop tool is that, with the Mask tool, you can crop images without actually altering the image files. This is accomplished by "masking" the edges to hide unwanted parts or change the outline of the image. If you understand how masking tape works when taking on a room-painting project, you should quickly make sense of how the Mask tool works.

When activating the mask, the default shape is a rectangle, but you can use any of several stock shapes available in the app, including a custom shape that you can design with the Draw Tool, to mask the edges of your image.

Masking an Image with the Default Rectangular Mask

OK, here goes… Listed below are the steps you take to apply the default rectangular mask to an image:

1. Of course, you first need to import the image you wish to mask. In this example, I imported a photo of a pizza, but I don't want to show the whole pie; just a detail to help me make my point. Yet, I don't want to alter the image using a traditional crop.

2. Select the image, then click the Mask Button in the toolbar, or choose Format > Mask. You will notice a translucent mask appears over your image along with some controls. Any image area underneath the translucent part will not be visible when the slide is finalized.

By the way, if you do not see the Mask button in the toolbar, you can add it by going to View > Customize Toolbar. From the Customize Toolbar panel, drag the Mask button to the toolbar and position it anywhere you'd like.

An illustration showing how an image and its mask are manipulated on a Keynote slide.

There are lots of ways to manipulate the mask and the visible part of the image. Learn by doing

3. Dragging the selection handles in the masked image lets you resize the unmasked area – that area that you want appearing in your slide. Constrain the proportions by holding down the Shift key as you drag. If needed, you can also rotate the unmasked portion by holding down the Command key as you drag a corner selection handle on the mask.

4. To reposition the image, drag the unmasked portion to the desired location.

5. On the small black control bar that appears beneath the image, drag the slider to resize the image. Clicking on Edit Mask will toggle the masked area visible or hidden.

6. To reposition the part of the image you want visible, grab-and-drag inside the masked area. To reposition the unmasked area without repositioning the image click on the very edge of the visible area and drag.

Say, isn't this fun?

7. When you are satisfied with the position and size of your image and your visible area, you can commit your changes by pressing Return or clicking outside the image.

The same Keynote slide with the finished image, masked as desired.

I have the detail I need from the original image. The rest of the image is still there but hidden by the mask.

8. To resize or rotate the masked image, drag or Command-drag its selection handles.

9. To change the size of the masked image, double-click it first. Then click Edit Mask, and repeat the steps above as needed.

As you can see the beauty of the Mask tool is that you don't destroy any part of the original image, and you can make changes any time you need to. Non-destructive editing is a beautiful thing.

If you need to revert the image back to normal, make sure it's selected, then click on the Unmask Button in the toolbar, or choose Format > Unmask.

Masking an Image with a Custom Shape

A preset group of standard shapes can be used to mask an image for some kitschy designs. The simplest way to do this is to choose a shape via Format > Mask with Shape once the image is selected.

For example, for this image of yours-truly as a five-year-old – and apparently a Mouseketeer – I used the standard diamond shape to mask the photo.

Three views of the same image  standard, with masking tools, with diamond mask applied.

The diamond shape was used to mask the photo of this outstanding, yet sickeningly cheery young feller

Finally, you can also create your own custom masking shape using the Draw tool. This is done as follows:

1. Via Insert > Shape > Draw with Pen, create the shape you want to use as a mask, and drag it over the image you want to mask.

2. Hold down the Shift key and click to select both the shape and the image, and then click the Mask button in the toolbar, or choose Format > Mask with Selected Shape.

A teardrop shape was drawn with the Draw tool and applied as a mask to a photo

A teardrop shape was drawn with the Draw tool and applied to mask my photo to that shape

3. Resize and position the image and the mask as you would for any masked image as previously described.

If you've been following along, you may have noticed that it gets a tad bit confusing when working with image selection handles, mask selection handles, and the edit mask button. As with many things, the more of these you do, the easier it gets.

A Special Case

Aside from masking any photo that you would like to include in a Keynote presentation, you can use the Mask tool to customize existing images for your own particular need.

Let me clarify with an example. I often give presentations about Apple products. To make my talks more meaningful, I always use existing stock product imagery. Sometimes, individual images that I use depict multiple products. However, I want to isolate each product and position them to fit into my Keynote slides without having to edit the actual images.

A single image showing a black iPad mini and a white iPad mini side-by-side

This is a single image showing two iPad minis side-by-side. I want to show them individually in my slide

In this simple illustration, the original image shows both a black and a white iPad mini, standing side-by-side. Without altering the original image, I want to separate each model and place each at opposite corners of the Keynote slide.

A Keynote slide with two copies of the image ready for masking.

The two copies are masked and adjusted in order to visually separate the two iPads without damaging the image

Simple. I import the image, configure the mask so that the black iPad mini is the only one visible, and position it in its corner. I then duplicate the image and adjust – flip – the mask, as described previously, so that the white iPad mini is the only one visible. I then position it to its corner. Done.

A Keynote slide with a black and a white iPad mini appearing in opposite corners.

The finished slide

Masking – it's a powerful, advanced feature for you to exploit in Keynote, Pages and Numbers. Give your presentations and documents that professional flair with this modern tool.

Next week: the Instant Alpha Tool.