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Before approaching icon design, there are some guidelines and principles that are worth studying. If you want to create effective icon designs, then you should take a holistic approach to issues such as audience, size, simplicity, lighting, perspective, and style. This article gives you a good starting place for creating icons that work well together and fit seamlessly within your designs.
1. Approach Icon Design Holistically
Icons fit within graphic systems. Whether they are designed for desktop applications or Web sites, an icon is one of many graphic elements that need to work together harmoniously. Carry this logic across icon sets as well. Icons can be appreciated for their aesthetic solutions individually, but they don't function alone. Evaluate your icon designs relative to the graphic system you're using them in. Make sure that each icon differs from surrounding icons, while still working together as a whole.
In the article Designing an iconic language over at Turbo Milk the author Yegor Gilyov states, "If you need to draw several icons, you need to think over images for the whole set of icons before proceeding with illustrating activities." This is one of two major points made in this article on icon design. He goes on to explain how failing to plan how the whole set of icons will work together from the beginning will ensure a huge waste of time, as redesign will be inevitable.
2. Consider Your Audience
You will have different considerations if you're designing an intranet for a small company, rather than for a product that may be sold internationally. When creating icons, cultural considerations are important. Symbols may differ for common elements you may use for your designs.
Turbo Milk has another great article called 10 Mistakes in Icon Design. In it, they point out some clear examples of where many icon designs go wrong. They discuss national and social characteristics in point seven of the article. "It is always necessary to take into account the conditions in which your icon is going to be used. An important aspect here is national characteristics. Cultural traditions, surroundings and gestures can differ radically from country to country." They go on to give an example of how mailboxes differ greatly between countries. Apple uses the same example in its Human Interface Guidelines.
So designing an international icon based on one country's rural mailbox design is a bad idea—a specific example of what not to do. They point out how Apple's Mail icon is more recognizable as stamps have more cultural universality.
3. Design for the Size the Icon will be Used At
If you go vector and make your icon in Illustrator, there is an inherent temptation to scale the design, and try to use it at any size. This doesn't work with icons. What looks good at 512px looks like a blurry smear at 16px. Icons should have a base design that is used as a starting point, but each output size needs to have its own optimized design.
Icon design is not a one design equals scalable solution medium though. This is one reason that Photoshop is just as good a solution as other programs. For designers that make icons in Illustrator, they are still going to clean them up in Photoshop, or jump through some hoops to get their icons to look good at small sizes when being output directly from Illustrator. So, don't buy into the myth that icon design is a purely vector-based medium. We are outputting pixels here, after all.
There are also vector tools in Photoshop and masks that you can take advantage of that equal the scalable playing field between the programs. If you're equally versed with Illustrator and Photoshop, you may find a workflow that goes well between the two programs. Consider using Smart Objects. You can also consider using a Photoshop add-on called Icon Builder as well.
The approach taken for small icons and large icon design is immensely different. Firewheel has a good article that covers the scaling subject called Icon Design: Bitmap vs Vector. Also, review this article on Icon Design Sizing over at Mezzoblue. It covers some inherent issues with designing icons for small sizes.
4. Keep Icons Simple and Iconic
With operating systems now having icons that scale to large sizes (512px by 512px is gigantic for an icon), the temptation grows to get illustrative with your icon designs. While a level of realism can add interest to an icon design, it should not supersede its ability to function simply and effectively.
Smashing Magazine has a great summary of the Apple Human Interface guidelines on Icon Design. The section on Realism in Aqua makes some good points about the limitations of realism in icon design and points out when symbolism is necessary. This section discusses the issues at odds between realism and simplicity in icon design.
Try not to overcomplicate icon designs. Be wary of placing too many items into an icon design, or overly illustrating an icon. I'm sure everyone is familiar with the common symbol for RSS icons. View the example below from Smashing Magazine. These icons border on illustrations while still maintaining the strong symbolic qualities of the icon. Overly illustrating and dressing up icons results in lower recognition though, especially at small sizes. So, be careful with putting to much into an icon design.
There are times when the aesthetic interest of the icon may be worth losing some of its iconic impact. it's always a judgment call, and needs will vary with each design. Compare one of the icon sets below to a simpler RSS icon design, like the one here on Psdtuts+. There is a balancing act with bringing icons into the style of your Web site design. You want to add interest and compliment the design, but not loose the iconic impact of the icon.
The icons below look really cool. It requires a judgment, though, as to whether the loss of some of the quick recognition of the symbol is worth the added design around the symbol. At a large size it works just fine, as they function similar to illustrations. At smaller sizes though, a less-dressed solution may be preferable.
5. Cast Consistent Lighting, Reflections, and Shadows
It's important that the realism you add to your designs all function coherently. If you use a light source coming from one direction then stick with it. Or you risk losing the integrated design of your icons. Also consider the light source of the design your icons will be placed in. If the light source of the icons is at odds with the Web site or application design you're using them in, then the design will appear amateurish.
In the Windows Vista User Experience Guide there is a section on icon lighting and shading. The guidebook gives really specific rules for the Vista Icon set. This gives more exacting standards for icon designers and ensures a unified icon system. Following is a specific rule to see an example, "Use shadows to lift objects visually from the background, and to make 3D objects appear grounded, rather than awkwardly floating in space." There are many more rules in this guide.
6. Utilize a Limited Perspective
The range of perspective within your icon design set should work together. If you have icons being looked at from straight ahead then stick with that. If you place one at a specific angle, then make sure all the icons function that way. Imagine a camera being placed from a specific vantage point and looking at all the objects from the same perspective. This helps to maintain consistency in your icon designs.
A large-scale design system, something like a software operating system, may need more flexibility than that, though. Apple covers Icon Perspective in its Human Interface Guidelines. They have a more flexible use of perspective. "The various perspectives are achieved by changing the position of an imaginary camera capturing the icon." The image below shows the difference in perspective between an Application Icon (Top) and a Toolbar Icon (Bottom).
7. Create Consistent Icon Set Styles
Lighting and Perspective certainly contribute to the style of an icon, though there are many other factors that can contribute to the style as well. If you're trying to fit your icon into a grunge-style Web site design, you'll likely be adding texture to the style of the icon's design.
Icon sets have unique features that make them stand out. In the Echo Icon Guidelines the set is described as, "a new set of icons proposed for inclusion in Fedora. Designed with a dynamic perspective, Echo icons aim to appear more realistic while still maintaining a clean and simple design by utilizing high contrast and spots of vibrant colors." Another way that this set stands out is through the consistent use of outlines. See the image below for an example.
Get Started with Icon Design
Designing icons for Web sites is a good way to get started with icon design. Often there are only a few icons needed for a site design. Start simple with a small Web site design project where you are required to design only a handful of icons or less. This is a good way to gain some experience with icon design.
Start the icon design process with research. Consider the common symbolic metaphor used to describe the icon you're looking to make. Sketch as much as necessary to lock down the concept. Compliment the style of the icon designs with the Web site design you'll be using them on. Consider the color, perspective, and graphic look of the site.
Hicks design has a quick SlideShare presentation on Icon Design. One section of the presentation covers his design process. It gives some great visual examples. Below is an example of the sketching step.
Inspirational Professional Icon Sets
Once you've created a one-off or small set of icons for Web sites, you might consider creating application icons. Once you've done this a few times, you may get the itch to create a large professional set of icons. Selling icons can be a profitable endeavor for a designer. If you create a unique and professional set, you can then sell it. Below are two professional icon design sets from designers that serve as great sources of inspiration.
The Classic Pack Icon Set From Icon Drawer
This icon set has a combination of professionalism, great choice of symbols, cartoony realism, and fun design. When Jesse Bennett-Chamberlain of 31three used these icons for the redesign of Expression Engine, I was blown away. It's a great site design, and the icons fit really well with the style.
The Chalkwork Family from Mezzoblue
"Chalkwork is a visually unified set of carefully designed royalty-free icons. Built to cover some of the most common icon needs of Web and software designers, the entire Chalkwork family offers hundreds of computer and internet-related metaphors in a visually consistent style at 3 different sizes in up to 6 file formats." This is a well-designed set of icons from Dave Shea.
Psdtuts+ Icon Tutorials
Jump headfirst into icon design. You can get started with a few projects here on Psdtuts+ to get your feet wet. Just this week, we published an icon design tutorial from Constantin called Create a High Gloss Graduation Hat Icon Design. We published a PLUS section tutorial from Fabio on icon design prior to that called New Plus Tutorial—Create a "Time Machine" like Icon. Fabio also published a tutorial a while ago called Handy Web 2.0 Icons In Photoshop.
Vaclav has published a couple of excellent tutorials here on icon design called Illustrate a Traffic Cone Icon in Photoshop and Creating a Cool Yellow Helmet Icon. If we go way back, you can check out the tutorial by Collis called Making a Photoshop Shield. These are all great places to get started or practice icon design.
Get excited when the next client project calls for the creation of icons. Or practice making icons through the tutorials here. Once you've mastered these techniques, try making a small set of icons. Or go big and create a full set for resale. Let us know of additional icon resources in the comments below.
If you're interested in getting some help with your app icon design, Envato Studio has a great collection of app icon designers that you might like to explore. You could also take a look at icons on Envato Market.