Adobe Illustrator is a designer’s best friend. It differs from Photoshop in one primary function.
Illustrator is for vector art. Photoshop is primarily for raster.
Or put another way, Illustrator handles companies’ logos, text and illustrations where Photoshop handles photos. Now, over the past few versions, these lines have progressively blurred. Photoshop effectively works with vector designs, and Illustrator works well incorporating photos into projects.
For example: When creating a logo that incorporates a photo, I will edit and output the photo in Photoshop, then import it into Illustrator to merge with the vector elements and then save to web.


