Keep in mind, Photoshop is a raster program, which means icons won’t be scalable unless you convert them to vectors. You can open and edit them in Adobe Photoshop. EPS files can save vector, bitmap, and text data. PNGs should only be used if the icon doesn’t need to be scaled up. For example, a setting icon formatted in PNG might look fine on mobile screens but look pixelated on a desktop device. PNGs are raster-based graphic files, which means they are an area of pixel information and are not scalable. Scalable Vector Graphics, or SVGs, are one of the preferred file formats for icons because they aren't resolution-dependent.

When you’re downloading or creating icon sets, it’s important to understand the common file formats used for icons. There is never one design answer that's perfect for every purpose, as seen in these Instagram logo redesigns. They should all be the same size, have the same amount of detail, and have the same amount of color saturation. No icon should look more important or interesting than another in a set. They should only have enough detail to be recognized, otherwise they look cluttered and hard to see at small sizes. Icons aren’t supposed to be full illustrations. Good contrast occurs when you can differentiate between the design elements easily and nothing blends together. Contrast is the visual difference between design elements. You can also do the same thing by squinting your eyes. The best test to check for good space is to just zoom out and see if you can still make out the icon at a small size. If the positive space (the icon) isn’t properly balanced with the negative space (the blank area surrounding the icon), the design will coalesce at small sizes and become a blob. Icons need to be easy to see at small sizes. If they aren’t, they’ll look sloppy in use. This means they're based on perfect shapes like squares and circles. Lines should all be the same weight, the edge style (rounded, fileted, or square) should match on every icon, and the color scheme must be the same throughout. The feeling of unity is intuitive, but if you’re unsure, there are a few specifics you can check off. All the icons should look like they go together. The most important thing to look for in an icon set is unity.

Here are the main tenets and requirements of a quality icon set: If you want to ensure you’re using or purchasing a good icon library, you need to understand the fundamentals of icon set design. Using a poorly designed icon set diminishes the overall usability and aesthetic of your project. Not all icon sets are of the same quality.

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