Using Opacity Masks in Illustrator CS
Opacity masks can be used in Illustrator "blend to transparent" which is generally accomplished very easily in Photoshop. However, Photoshop isn't always the correct tool for a project. So in this brief tutorial I'll show you how to create, apply and adjust opacity masks in Adobe Illustrator for a reflection effect.
We're going to use this art as a base object:
You'll notice all the artwork is on one layer. This makes it easier but it's not required.
If your art is on multiple layers you'll want to select all, copy, then paste onto a new layer and then group (command/control-g) to make this process easier. In addition, there are other steps in this tutorial that may be slightly different if your artwork is set up in this manner.
If your artwork is all on one layer, like mine, then just select all and group it.
Now, pick the Reflect tool. It's hiding underneath the rotate tool in the tool bar. Click and hold on the rotate tool and you should see it pop up.
Hold down the Option/Alt key and click near the base of the art. This will be the point of reflection.
Check the Horizontal option because we want the object to reflect along a horizontal axis. This way it will "flip" downward. You can check the "preview" option if you like and you should see your artwork flipped downward.
Now simply click the copy button. This is important because it creates a duplicate of the original art in the new position. We need the original object and a copy of it to be the reflection. If you are working on multiple layers and you've already duplicated the art to a new layer, then click the okay button rather than the copy button.
You should now see both objects and the reflected art should be selected:
If your art is on one layer send this reflection backwards by choosing Object > Arrange > Send to back from the menu or hold down Command/Control and the shift key and type a [ (left bracket) to send the artwork to the back of everything else. If your art is on multiple layers simply click and drag your reflected object layer below all other layers in the layer palette.
Step 2: The Mask
Now the fun stuff....
Select the rectangle tool and draw a rectangle that covers your reflected object. Don't be concerned if it inadvertently also appears to cover the original art a little. It simply need to cover the "reflection".
Fill this rectangle with a black to white gradient. Set the gradient to "Linear" and enter -90 in the angle field. This should result in a white to black vertical gradient, white being on top.
With Opacity masks, white means to show the object and black means to cover the object. Therefore anything 100% will completely hide the object it's masking.
Now, select the gradient and the reflected object underneath it.
Move to the transparency palette. if it's not visible choose Window > Transparency from the menu. Click the flyout menu on the transparency palette and choose "Make Opacity Mask"
You should see immediate results in your art. The reflection will appear to have "luminosity" gradient overlaying making some areas lighter than others. Also note the transparency palette. There's now a small thumbnail of the object used for the opacity mask (the gradient) linked with a thumbnail of the art it's applied to. This is similar to Photoshop mask linking.
Step 3: Refining
This is okay.. but we want a little better gradient. This one doesn't drop off well enough. So, in the transparency palette click directly on the thumbnail for the gradient. This selects the mask object. You should see it highlight in the artwork. It will simply appear as a rectangle.
This sets the mask object as the object being edited. Since I want a sharper drop off for the opacity I'm going to adjust the gradient. In the gradient palette simply drag the gradient slider, that little diamond in he middle of the gradient bar, to the left to adjust where the drop off point is within the gradient. Moving the slider to the left increases the amount of black in the gradient. Therefore it increases the point at which my art becomes transparent. You can see in the image below that there is now a definite area where the artwork vanishes.
This looks like a good gradient to me. So now that I'm done adjusting the mask object I want to return to my art to refine that a little. To do this click directly on the thumbnail in the transparency palette that displays the artwork.
You should see the art highlight. If you fail to select the artwork thumbnail, things can get a little confusing since it will appear that you can't select or edit anything other than the mask object. Clicking the artwork thumbnail ensures you can edit the artwork itself and the mask will remain in tact.
Step 4: Final Notes
That pretty much covers it. I did use the direct selection tool to select and delete the areas of shadow in the reflected art (shadows rarely reflect).
Opacity masks can be used for all sorts of different effects. In this case I was just taking art to a transparency for a drop off effect. However you can place art on top of other things and apply masks to them as well.
Here I\ve applied a simple background behind everything to add a bit more depth to the image.
I hoped this has helped explain opacity masks in Adobe Illustrator.Have a question?