Let's discuss purely technical aspects of icon creation
1. Lines, angles
One of the vital parts of the image is the outline of the object, i.e. rough linear marking, which separates the object from the background. When designing large-scale graphics, the designer occasionally cares about highlighting of objects with additional outlines. This is not needed because of the size: even low contrast objects do not mix into a single whole. Icon graphics is different. Two solutions are possible: either foreground and background colors must be from opposite sides of the color chart, or the object must be separated from the background by contrast outlines and shadows. I would like to dwell on lines in more detail.
If we return again to the large scale graphics, we see that in order to define contours, we can use any (even the most complex) angles, Bezier splines and borders. In any case, the line will look perfect due to anti-aliasing. When decreasing the image scale to the size of an icon, situation changes greatly. When every particular pixel is equally important and can ruin the overall look of the icon, anti-aliasing is simply not applicable. It comes that you have to think about the possible line slopes.
The slope you choose for the line, specifies the step for this line. Because every line consists of primary elements, the combination of which defines its accuracy and esthetics.
For instance, a 18-degree angle contains many small 3-pixel lines connected using a 1-pixel downshift:
This is how nearly each line looks like. Primary element with joining followed by another basic element. Unfortunately, not every slope creates lines that look look attractive and not annoying.
For example, look at 25 and 20-degree angles:
It can be easily seen which line is more appealing. The 25-degree angle makes a line consisting of equal 2-pixel basic elements. The 20-degree slope has a primary element containing of three lines: 3-pixel, 3-pixel and 2-pixel. The slope is more complex, thus, when not combined by other visual effects, it brings a feeling of messiness: the basic elements have contrast which is too obvious to hide from the human eye.
Now we can see the first conclusion. The most "appropriate" angles have to make as simple primary elements as possible. therefore, the ideal angles are 0 and 90 degrees. In them, 1-pixel primary elements are joined without any shift and form even lines. Less ideal are slopes which form primary elements of 1, 2, 3 pixel with 1-pixel downshift. Surely, the lines will not be even, but the human brain will process the image and provide to the viewer what you intended to show to him. Also, the mentioned slopes can be considered acceptable (but at a stretch): angles with basic elements made of unequal lines shifted by more than 1 pixel.
It is the time to discuss another issue. In the last paragraph, I purposely defined slopes with primary elements of 1, 2 and 3 pixels as correct. Such tiny lines, especially when a great amount of them is joined, look like solid. But what do we see if we change the basic elements to 10 or 20 pixels?
Here is an example:
It can be clearly noticed that the line loses its integrity. It is not a single line anymore; it is a set of several lines, located near one another. Rarely any designer wants its composition to look that way. Thus, we have the second rule: if you use small angles, which make long primary elements, it must be justified and employed with great caution.
And, finally, the third aspect I wanted to tell about lines. I did write that the basic element has to be as plain as possible.
For instance, a 25-degree angle can be drawn in the two (of course more of them are possible) following ways:
In the first picture the basic element is a 2-pixel line. In the second picture, it consists of three elements: 3-pixel, 2-pixel and 1-pixel. The same angle but the image is different. The complicated primary element produced the line messy.
Such examples can be made for about any slope, so in your projects, try to simplify as much as possible.
It can be stated without an exaggeration that the color is the main element of your work; improper or badly matched colors can ruin even the most creative idea. What can we say about the color in icon graphics?
First, there is a clear rule: if the image looks poor when converted to monochrome, it means the colors that were used are wrong. This rule is valid not exclusively for icons but for the entire graphic design.
Second, you will be unable to apply safe RGB. Sure, you can use GIF colors only, but this limits you greatly. Gradients, shadows, dithering and many other effects will not be available to you.
Third, try to increase the portion of "flat" color. The more evenly colored areas without diffusion and jumps your composition has, the more neat it appears. Pictograms are too tiny and the excess usage of special filters makes the picture look messy.
Fourth, gradients. This is a great tool which can change the appearance of any composition. Other than visuals, gradients are a perfect solution to get rid of the "broken line" look (lines with too long basic elements). But be attentive when using them because too much gradients can ruin the flat color, and be unable to fit into the gif palette.
Fifth, shadows and highlights. All aspects of using shadows and highlights in icon making are totally identical to the rules of the general graphic design. The only thing I would like to note: create everything yourself. Don't apply effects, make all shadows and highlights in a different layer and then edit its transparency. If using filters, you almost never can predict what the result will be. It is unfavorable when you don't control the making of a composition. It is awful if you can't control it when drawing icons.
And, finally, sixth. Tinting is the main aspect of icon design, which largely results the esthetic appearance of the project. When the blue human eye in the picture is sized 1 pixel, increase the color saturation. For instance, instead of 0, 131, 159 make 71, 195, 242. It is indifferent that the human eye can't have such color; in the first case it will appear like a gray dot, but in the second case it will really be a green eye.
Thoroughly control the image, do not let the visual tricks to spoil your work. It is acceptable if objects is not perfect technically, but the entire image must be perfect.
As an example, I pictured the pack of juice located before me. The image has plain color, gradients with broken lines, shadows and highlights and tints.
If I wrote about something bigger than miniature design, this part wouldn't fit into an entire book, but the resolution of pictures restricts fonts too.
The size of letters is the leading issue as opposed to their beauty. Nearly in all cases, unless the letters are the primary part of the project, the font size must be reduced to the greatest extent possible.
In general, virtually any graphic studio has its unique font with little characters. Such a font can be created in several hours. You can search the web and make your own collection of very nice fonts. Primarily, I advice you to download the DS Pixel and Seventen 7Vedi website and the whole set of fonts from the Lakmus Lab website.
If you don't want a new font, tiny sizes of Arial and Verdana may work. As a last resort, you can create the necessary letters yourself.
There are not many rules there. First, letters cannot be less than 5 pixels high or less than 3 pixels wide.
Second, letters cannot use anti-aliasing. It transforms the text into an unrecognizable mixture of pixels.
However, there are no rules without exceptions and the 5-point Arial looks perfectly understandable.