Transparency, Opacity, and Darkening Images in Illustrator

In this post we will create a mock-up poster for an art school and in doing so, set up visual hierarchy and accessibility using only solid colors and adjusting opacity settings. This is a quick and easy way to darken images and backgrounds to bring additional focus to other elements in a composition. We will work with some basic shapes, like rectangles and ellipses, add a pixel image as background, and learn how to blend them together using transparencies. This is a step-by-step essentials tutorial, so relax, fire up your laptops, have fun, and read on!

This post is based on my Illustrator Essentials course, make sure to sign up at Bring Your Own Laptop! When you become a BYOL member, you gain access to this course as well as my 30+ additional courses on Photoshop, Lightroom, InDesign, Figma, and more. As a BYOL member you will also enjoy personalized support, earn certificates, and tackle exciting community challenges. Head here to sign-up!

Let’s dive into an amazing and translucid world of color!

Adjusting Opacity Settings in Illustrator

Alright, let’s begin by drawing a basic shape, using the Ellipse tool. We can choose the tool from the left toolbar or use the shortcut key ‘L’ on both Mac and PC. If you can’t see the Ellipse tool in the toolbar, right-click the Rectangle tool button to expand the shapes group in which Ellipse is included. Once the Ellipse tool is active, we click and hold the left mouse button and drag our mouse cursor to create a new shape. If we hold the Shift key as we do this, the dimensions are kept proportional, and we draw a perfect circle.

Let’s add a second circle to our artboard. There are some different ways to do it:

1.      Copy and paste. Select the first circle, tap the shortcut keys Command + C on a Mac or Control + C on a PC to copy the shape. Next, hit Command + V (Mac) or Control + V (PC) to place the duplicate shape on the artboard.

2.      Duplicate. With the Selection tool active (shortcut key ‘V’ on both Mac and PC), bring the cursor to the first shape we’ve drawn. Hold Option (Mac) or Alt (PC). The mouse cursor will change to a double arrow icon. Click, hold, and drag the mouse cursor to create an exact duplicate and release the mouse button to place it in the artboard.

3.      Draw a second shape. Using the Ellipse tool, click the artboard once, and Illustrator will open a new Ellipse options panel. Notice the panel displays the dimensions of the previous ellipse we’ve created, so click OK and that’s it!

Next, let’s give our second shape a new color. Click the Fill color swatch from the Appearance panel to the right of our workspace. I’ll pick one of the available swatches, of course, you can explore any other color you prefer.. Click anywhere outside this panel to close it.

To have a better understanding of how Opacity can influence a shape in Illustrator, partially overlap both circles, making something like a Venn diagram. Setting our shapes this way allows us to see how the orange shape will interact with both the white background and the color of the green circle below. In the following image, we can see path lines for both ellipses, but we will be selecting only the orange one.

When we adjust Opacity settings, we are defining how much a shape allows for the visibility of underlying objects. Imagine a tinted glass window. 100% opacity means that no light goes through the glass, making it impossible to see what’s on the other side. As we lower opacity (in other words, increase transparency), anything behind the glass becomes more visible.

It’s the same in the vector world: less opacity means more visibility or interaction with objects, colors, textures, or images below. Fun!

There is more than one place where we can adjust a shape’s opacity. Let’s begin with the Opacity slider in the Appearance panel. Clicking the arrow next to the percentage value, we open the slider. Then, we click and hold the left mouse button and drag right or left to increase or reduce the Opacity level.

 Did you see what happened to the selected shape’s color? By increasing its transparency, the orange fill blends with the background’s white color and becomes lighter. But there’s more! Remember the overlapping area? There’s a color blending effect happening there, too! The green and brighter orange are mixed to form a new color tone! Cool, huh?

There is an alternative to the slider we’ve just tried. We can manually type a number into the Opacity value field. This allows for higher precision or customization.

Adjusting Opacity to Darken an Image Background in Illustrator

Let’s start by placing an image on our artboards. I’ll use an AI photo I’ve generated in Adobe Firefly, you can choose any image you like. There is a quick shortcut for the Place command: Shift + Command + P (Mac) or Shift + Control + P (PC). We can also go to File in the top menu bar and select Place… from the flyout menu. Next, we browse our folders, select the image we need, and click the Place button to finish the search.

Finally, we simply click anywhere on the artboard to bring in the image in its original size. We can also click and hold the left mouse button and drag the cursor to set a custom size. There’s so much creative freedom in Illustrator!

Pro tip: we can resize and/or crop the placed image to match the artboard, allowing you to fully control your composition and balance all the elements on your artwork. With the image selected, click Object in the top menu bar and then select Crop Image from the flyout menu. Click and drag the corner and side handles to adjust what gets cut off from the initial image. This does not affect the original file you have stored in your computed or Cloud folders. Hit the Enter key or click the Apply button up in the Tool Options bar to finish cropping. If you can’t find the Tool options bar, click on Window and select Control from the menu that pops up.

Now let’s jump to an easy way to darken this cute photograph, setting a stage for additional elements like text and shapes. Oh, and we won’t change any of its settings! Remember what we’ve seen about overlapping elements and how opacity changes can hide or reveal content or blend colors? Let’s try those skills now!

Imagine we are going to place a filter or a piece of stained glass over our photo to remove some of its light and color intensity. We know we can do this in Illustrator in just a few steps! Let’s begin by picking the Rectangle tool from the left toolbar.  

Click and hold the left mouse button and drag to draw a rectangle that matches our artboard’s dimensions. Any color fill will work for now, we will change it in the next step.

Once the shape is set, let’s open the Fill options panel, select the color Mixer tab from the four options on top (it’s the one with a painter’s palette icon), and click the options icon on the top-right corner to open the additional settings menu. Select HSB to adjust our initial orange color’s Hue, Saturation, and Brightness levels.

I won’t adjust Hue (position of the color in the color wheel), because there are some strong orange accents in the photo, so I want to set up a black color with just a hint of orange, something like burnt amber.

I’ll bring down Saturation (color intensity, from rich and vivid to washed out or grey) somewhere below 50% to make the orange less strong.

As for Brightness (how close to white or black a color is), and because I’m aiming for an almost black look, I’ll reduce it to a low value, around 10%.

These settings should give our rectangle the look we need to darken the photo behind it! You may end up working with different values, depending on the color you begin with and how dark you want your shape to be.

Let 's push on!

Time to play around with Opacity levels and reveal a shadowy version of the vivid image we have hidden below our dark rectangle. Let’s drag the Opacity value slider to set an opacity level of around 75%.

Pro Tip: One other way to manipulate opacity in Illustrator is clicking the Opacity link between the swatch and value field. Once inside the panel that pops up, we can type an Opacity percentage value or use the slider tool to set a new transparency level. But there’s a bonus: Blending Modes! In just a few words, Blending Modes determine how overlapping objects (or layers) interact visually, combining colors and tones, mixing them up, blending everything together to create unique and beautiful effects. We won’t explore these in this tutorial, but you can read this awesome BYOL blog post on this subject and master these skills in no time!

Now let’s add some text elements to our artwork and see if our darkened background does its job! Let’s begin by picking the Type tool from the left toolbar. There’s a shortcut key for the Type tool: ‘T’ on both Mac and PC.

Next, we add any text we like. I’ll write a slogan for an art school, you can set your imagination free and come up with a cool title, a description, anything you prefer and that you feel your users will relate with and be attracted to.

To wrap things up, let’s bring out those transparent and opaque shapes from the beginning of this post and decorate our composition to make it more dynamic and fun! I’ll take this opportunity to show you the last way we can adjust a shape’s opacity level in Illustrator: the Appearance panel. We can open it by clicking Window on the top menu bar and selecting Appearance from the menu, use the shortcut keys Shift + F6 on Mac and PC, or clicking the three dots icon on the bottom of the Appearance panel to the right of the workspace.

From here, we can set each object’s Stroke or Fill color, Opacity settings, and even add additional effects, like Drop Shadow, Gaussian Blur, etc.

Cool, huh?

And There We Have It!

Brilliant! Let’s have a look at the finished design! Keep in mind that we have basically used only basic shapes, one photo, a couple of text lines, and did all this incredible magic using opacity and transparency settings, no complex advanced effects or pro-level skills. How great is that? If you are taking your first steps in Illustrator and vector design, it is ok to feel excited and ready to start your learning journey!

What 's Next?

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See you in class! – Dan