1. Capture the Characteristics of the Object

One of the most important aspects of icon design is to create an icon that is immediately recognizable. Whether it is meant to represent a blue frog or a tin of pencils, what it is trying to portray must be identifiable at a glance or the purpose of the icon is defeated. An icon must, of course, be 'iconic' of the metaphor it represents.

In an icon design tutorial over at Smashing Magazine, master icon designers Vu and Min Tran discuss their process behind the pencil graphic as part of their Bright! Icon Set.

Drawing an icon means to draw the most typical characteristics of an object so that it can capture the icon’s action or represent the concept and nuance. As you might know, there are generally three kinds of pencils to select from:

1. Prism-shaped body with a shiny glaze-coated end.
2. Prism-shaped body with an eraser secured to the pencil body by a bright white metal ring.
3. Cylinder-shaped body without an eraser.

We choose the second kind for the icon design because it has all necessary elements, making it easier for the viewer to recognize the image.

Sometimes it's better to choose the more complicated form of an object because there are fewer other items that share those unique characteristics, making the specific object you're trying to portray easier to identify. There are plenty of cylindrical objects with pointy tips besides pencils (pens, markers, nails) and at smaller sizes they might be indistinguishable, but only a pencil has a prism-shaped body with an eraser attached by a bright white metal ring. It becomes 'iconic'.

2. Keep Icons Simple and Versatile to Fit Into a Range of Projects

For icon creators DryIcons, an key value in their design process is to keep their icons fairly simple and basic style-wise, as opposed to aiming for a definitive style. This helps make the icons much more versatile and useable in a range of projects once sold as a complete pack to software developers. If your icon looks at home in a broader range of settings, its potential market becomes bigger.

Regarding trends, we feel that it’s very important to keep things simple and basic, so they could serve their initial purpose: to fit in one’s project as it would seem like that was the way it should naturally be. That’s the only trend we follow.

3. Use a Consistent Light Source

One particularly useful tip when designing multiple icons for a pack is to provide consistency between them not only in style but also in the details such as the light source. While usually a secondary thought, any mismatch of one icon in the pack could seriously affect the overall quality of the icons.

In this overview of the Windows Vista icons, it is noted how the light source has changed between operating systems, but is consistent with all icons in each set.

Shadows in Vista icon objects are indicative of true, realistic depth just as they exist in any object in the real world. Vista icons do not have the flat lower-right drop shadows that are default for Windows XP icons. The light source is also completely different in Vista icons. All objects now face directly into the light source. From Windows 95 to Windows XP the light source on all icons has always come from the top left and objects are rotated counter-clockwise, away from the light source. The Vista icons placement and lighting will be completely opposite in comparison to Windows XP and older Windows system icons.

4. Create Icons in Vector Format (Argument 1)

Icons often need to be used in a range of sizes, therefore it is a good opportunity to make the most of the scaleable nature of vector graphics to create a great looking design that can be used for multiple purposes.

What’s more, with vector software packages such as Adobe Illustrator, every shape, gradient and stroke that makes up the icon can be tweaked and changed at any point, unlike a pixel based design that needs redrawing when changes are made.

This excellent icon design tutorial here at VECTORUTS goes through the process of how a stunning graphic can be created based on the basic shapes and gradients of Illustrator.

5. DON’T Create Icons in Vector Format (Argument 2)

On the contrary, vector graphics aren’t always the best approach for icon designers. With many icons requiring very small scales vector graphics often don’t manage to reproduce a crisp render when rasterized. In these cases completely redrawing the icon at a number of specified sizes gives the best result.

Web Interface Designers Firewheel Design highlight this approach in their discussion of bitmap vs. vector:

When you take a vector image, originally sized at 24x24 and scale it down to 16x16, the relative proportions do not match. There's no way you can evenly distribute 24 pixels of information into 16 pixels of space (remember, there's no such thing as half a pixel). So the image blurs.
There's also no way you can evenly scale 24 pixels of information upwards into 32 pixels of space. Again, the image blurs.
Furthermore, if you take that same vector image, originally sized at 24x24 and scale it up to 48x48, you're now doubling the proportions. You no longer have crisp 1-pixel lines. You have chunky 2-pixel lines. Scale it up larger (say to 96x96) and those lines become even thicker.

6. Beware of Cultural Differences

Similar to point number one, where it was mentioned that it’s crucial to capture the 'iconic' characteristics of an object, it’s also important to remember that there may be huge cultural differences in the recognition of everyday items.

Turbomilk discuss this in their useful roundup of 10 Mistakes in Icon Design with the example of a mailbox. What might be the recognized shape and color of a mailbox in one country, might be totally wrong for another.

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.

Use universal imagery that people will easily recognize. Avoid focusing on a secondary aspect of an element. For example, for a mail icon, a rural mailbox would be less recognizable than a postage stamp.

Note: pay particular attention to this rule when designing icons based on warning and traffic signs, which differ on a country by country basis.

7. Use Out of the Ordinary Color Combinations

If an icon is created as a bland graphic presented in a circular shape it is likely to be overlooked. Using strong colors and an interesting shape that reinforces the object will help the icon to stand out. Remember that icons are rarely going to be displayed on a mono-colored background -- in most cases there will be a lot going on behind them, so they'll need to stand out. Consider also using gloss and shading to create a more dynamic final effect.

Jasper Hauser, the designer behind the Camino icon, touches on this in an interview discussing 'What makes good icon design?'

Basically there are two aspects that are the base of a good icon: 1) shape, and 2) use of color. If you look at the Appzapper icon you will see that it 1) has a original shape, and 2) uses irregular colors and an irregular color combination. Doing a blue circle will not stand out.

8. Design Icons to Work at Large Formats as well as Small Scales

It has already been mentioned that icon designers need to accommodate small scales into their icon creations. However, with the forward development of technology designers should also be taking into consideration the use of icons at a much larger scale than the standard. An example of this occurs in Windows Vista, where the icons can be scaled up to 256px tall!

In an interview with Brian Brasher, an artist at Firewheel Design, he was asked:

John Marstall: What's your opinion on the shift to larger icons and resolution independence?

Brian: Larger icons mean more detail, which means a richer GUI experience as well as removing a lot of restrictions an icon maker has placed upon him to make an image legible. Unfortunately, throwing out those restrictions means that a lot of icons that look quite spiffy at full size will be muddy, cruddy horrors at 32x32 and below. A two-edged sword. There will be casualties.

9. Carefully Plan Out Your Design Process

Sketching is a common process in any aspect of design and it continues into icon design. Fleshing out a range of ideas on paper really helps develop a concise product that fits the requirements of its purpose. Because an icon design must conform to a defined set of proportions and dimensions while still being 'iconic' and immediately recognizable, forward planning is incredibly important.

Michael Matas, a graphic designer who has created icons for the Mac OS X platform shares his own working practices:

I always start on my white board. I try to come up with good and clear metaphors for the icon. I sketch out different ideas and usually end up covering the entire white board. When I do come up with a good metaphor, I then start sketching the layout of the icon and what angle I am going to draw it from. I go on Google image search and Watson's picture search and try to find good pictures for the object I'm drawing. I download anything that looks decent and open them all up in Photoshop. I create a new Photoshop file to draw the icon in and surround that window with the images I downloaded from the Web. I use the Web images to help me get an idea for what the texture and shape looks like. But if I can, I always try to look at real objects to get inspiration.

10. Generate an Interesting yet Clear Metaphor for the Icon

The job of an icon is to represent an action or idea in the form of a graphical symbol. Therefore metaphors play a crucial role in translating that action or idea instantly to the user. When commissioning a set of fresh icon designs for Macinstruct, the team contemplated a range of metaphors to represent the difficulty of their online tutorials:

Perhaps the most difficult icons to decide upon were our tutorial gauges. We needed a way to rank the difficulty of our tutorials, and we wanted a really creative, effective way to show this. After a couple days of brainstorming, we came up with the following ideas:

• Thermometers: Easy tutorials are cold, medium tutorials are medium, and hard tutorials are hot.
• Traffic Lights: Green for easy, orange for medium, and red for hard.
• Karate Belts: White, orange and black belts, ala karate skill levels.
• Puzzles: A puzzle with 1 piece off to the side. Smaller pieces equate to harder.
• Aviation themes: Goggles for easy, old leather helmet and goggles for medium, and fighter pilot's helmet and air mask for hard.
• Engineering Images: A manual and a circuit board, a circuit board and some tools, and oscilloscope.

In the end, we nixed all of these ideas for one volunteered by our own Ric Getter. Everyone agreed that using pocket protectors to indicate difficulty was a great idea!