Creating a sticker pack is really easy, and to make the best sticker packs, you should make sure that you properly optimize your image assets. Stickers can be displayed to the user in three sizes: small, medium, and large. To change the size of stickers in your sticker pack, simply click the Sticker Pack folder and open the attributes inspector. You can pick the sticker size there.

You should optimize the size of the stickers you provide according to the display size you choose. The following is a list of sticker sizes and their recommended asset sizes:

• Small: 100x100 @3x
• Medium: 136x136 @3x
• Large: 206x206 @3x

Note that all sizes have an @3x annotation. This means that the exported dimension of your images should be three times larger than the size listed to accommodate screens with a 3x resolution, such as the plus-sized iPhones. So, a small sticker should be exported at 300x300 pixels. Unlike other image assets on iOS, you only supply a single image for each sticker, the 3x image. Normally you supply a 1x, 2x, and 3x version of each asset you include in your app.

Sticker packs can contain PNG images, animated PNG images, GIFs, and JPEGs. All images you use must be smaller than 500 kb. It's recommended that you provide all of your assets as either PNG or animated PNG because this image format has superior image quality and supports transparency. Transparent stickers are recommended because they look a lot better when placed on top of other stickers or messages.

Now that you're familiar with sticker packs and testing them in the simulator, let's see how we make our sticker pack a bit more special by customizing the sticker-picking interface a bit.