Grammatically speaking, you might be best off with,

  Make good-looking pictures spectacular.

Or:

  Turn good-looking pictures into spectacular ones.

I think "good-looking pictures" is an awkward phrase that negatively affects the whole sentence. Personally, I would go with:

  Turn a good image into a spectacular one

or, brevis:

  Make good images spectacular

Or "Turn 'good looking' into 'spectacular'".

There are several other grammatical errors or awkward sentence constructions. Pixelmator team: I think you could benefit greatly from hiring a native English speaker to comb through your website copy and fix these (admittedly small) issues. Please don't take offense at that suggestion; I honestly think it would benefit you and your business to do so.

This sentence is grammatically incorrect, too:

"With the new Layer Styles, a complete set of Liquify Tools, and support for the new OS X Mavericks features — creating advanced and polished compositions — is now so much simpler, faster, and more enjoyable."

I suggest something like:

"Creating advanced and polished compositions is now simpler, faster, and more enjoyable with new Layer Styles, a complete set of Liquify Tools, and support for the new OS X Mavericks features."

Its very clunky, maybe 'into something spectacular' (i'm not sure if thats any better)?

Think different!