One glance at its cover and you snap the book up for a closer look. You see good-looking people caught mid-action within some exotic setting. The title jumps at you in its dynamic font. Your eyes widen. Your heart quickens. You feel you could almost step into the frame of the design and tumble into the book's world, as you anticipate the wild ride the book could take you on. You may not realize that your emotional reaction was partly inspired by one or more blur effects. Blurs stand behind other design elements, so their contribution is often overlooked. They provide dimension and keep a design from looking flat. If you'd like to use blurs to give your self-designed book covers more impact, I'll relate in this post how I created a blurring effect with Adobe Illustrator's Transparency Mask feature.
The first image I'll show you is a design idea I created in Photoshop. This whole concept was mocked up as one in a series of ideas for my novel, The Name I Chose. At this point, I was ready to finish the concept in Illustrator with the blur and text. The next image shows the pink glow I created behind the idea's female figure
I achieved this effect in Illustrator by creating a transparent gradient mask. This "recipe" combines ingredients such as the line path tool, the color gradient tool, and the Gaussian blur filter.
I drew a shape roughly conforming to the outline of the woman and the curves of the design's gold scroll frame, using the pen and arrow tools. Then I filled the shape with this solid pink lemonade color.
Ok, I can't remember but ...I either created a circle over the drawn shape or ... I copied this shape and pasted the copy directly on top of the original. Either way, I filled the top shape with Illustrator's pre-loaded black and white radial gradient.
The gradient at the top affects how much of the bottom shape's color is going to show. The more black you have in the gradient, the less color you'll see in the underlying shape. It's like the dark part of the gradient acts like an eraser -- however, it's not really going to erase color, only block the eyes' ability to see the color.
To make the resulting blur so soft, like you're looking through organza, I applied the Gaussian blur filter to the gradient-filled shape. This filter is found through the blur filter offered under Illustrator's Filter tab. I played with the degrees of Gaussian blurring until I was satisfied, then I selected the top shape and cut it by pressing the X key while holding down the Ctrl key on my PC.
I selected the pink shape and chose "Make Opacity Mask from the drop-down menu that appears when you click the arrow to the right of the Gradient tab in the color palette. The resulting mask is depicted in an icon, connected to the pink shape's icon in the Transparency palette.
I selected that mask icon and pressed Ctrl and V keys simultaneously to paste the gradient-filled shape back into the picture. That applied the mask.
This makes the bottom shape's pink appear or not appear, depending on how the top shape's gradient applies black and shades of gray. You can adjust the gradient as shown in pink, by adjusting the actual gradient in the top shape. Keep in mind that the pink is not actually a gradient at all -- solid pink is masked to gradual degrees by the gradient in the shape above it. I also made minute adjustments to the pink shape's outline so the pink blur flows directly to the outlines of the frame and figure in the cover idea.
The finished design idea, shown here, demonstrates how the "white" parts of the pink gradient shown in the previous graphic are actually transparent. Remember, that shape is solid pink. The gradient above it is masking that pink, allowing the design's underlying pattern to show. The degree to which the underlying pattern shows through depends on the percentage of gray in the transparency mask's radial gradient. The softness of the pink is due to the Gaussian blurring of the gradient. This customized blur adds depth to the design, as well as softness.
The soft pink glow helps give this cover an air of femininity and magic. This design idea would work for a romance novel or a gaslamp fantasy!
Before creating this affect, I brushed up on the technique by watching Design Made Simple's YouTube tutorial. I think you'll find it as helpful as I did.
You may find features in different places than I described if your Illustrator is a later version than mine. You can subscribe to an ongoing Illustrator license through Adobe's Creative Cloud.