Optimize Images

Emerge finds all large images in your app, including ones in asset catalogs, and determines if their size could be reduced by more than 4kb through lossy compression or updating to new image formats.

Image formats and compression

Emerge starts by setting the compression level of each image to 85, and flags any with significant size reductions as optimizable. If the image is not already in HEIC format, and your app targets iOS 12 or later, Emerge will run the same analysis but with the image conversion to HEIC. The larger of these savings will be used to compute your total estimated size reduction, but both are displayed in the details row for an image:

Optimize your images

Once you decide to optimize an image, you can use command line tools such as Imagemin or a GUI like ImageOptim to export a compressed image. To convert an image to HEIC on Mac simply open it in Preview and choose File -> Export then select HEIC from the format dropdown.