There are a few standard algorithms, like Bicubic, trilinear, and others. Photoshop generally lets you choose. Different algorithms work better for different

There are a few standard algorithms, like Bicubic, trilinear, and others. Photoshop generally lets you choose. Different algorithms work better for different types of images, and also depend on whether you're shrinking or enlarging. Photoshop has the most common ones and probably works for 95% of common cases.