Open with command - EPS file confusion.

Question

I recieved a folder of Illustrator vector eps files that seemed to want to open in Photoshop by default. I changed all in Finder to 'open with' Illustrator CS.
Now my Photoshop files try to open in Illustrator too. So I change all to open in Photoshop and am back to square one with vectors opening there by default too.
Is there a way to set Illustrator EPS to open in Illustrator and Photoshop EPS to open in Photoshop? I know I can just drag them onto the relevant icon but if I double click a Photoshop EPS I have to force out of Illustrator to stop it opening.
Who's bright idea it was to give two distinctly different file formats the same extension anyway?

Answer 1

I think the underlying cause of the problem is the change Apple has made in how Launch Services is identifying these files in Tiger.
An Illustrator EPS file has a creator code of 'ART5', a file type of 'EPSF', and a filename extension of ".eps". A Photoshop EPS file has a creator code of '8BIM', a file type of 'EPSF' (same as an Illy EPS), and a filename extension of ".eps" (again, same as an Illy EPS).
Prior to OS X 10.4, Launch Services would consider an Illustrator EPS file to be different from a Photoshop EPS file because of the different creator codes on the file. (While we know that they are "different" based on the type of data they contain (i.e. vector vs. raster), Launch Services doesn't really know anything about the content of the files; it only looks at the file properties to make its decisions). Since they were different, you could choose to have one open in Illustrator and the other open in Photoshop. So, just by default, Photoshop EPS files would open in Photoshop and Illustrator EPS files would open in Illustrator.
In OS X 10.4, Apple changed some things around. Prior to 10.4, a combination of a file's creator code, file type, and filename extension were mapped to a particular application that would open it. In 10.4, the file's creator code, file type, and filename extension aren't mapped directly to an application, but to an intermediary called a "Uniform Type Identifier" (UTI). It's the UTI then that is mapped to an application that will open it. The UTI for an EPS file is the string "com.adobe.encapsulated- postscript". Launch Services doesn't really distinguish between an Illustrator "com.adobe.encapsulated-postscript" file or a Photoshop "com.adobe.encapsulated-postscript" file. So, what happens is that both an Illustrator EPS file (creator code 'ART5', file type 'EPSF', filename extension ".eps") and a Photoshop EPS file (creator code '8BIM', file type 'EPSF', filename extension ".eps") are mapped to the same UTI type, "com.adobe.encapsulated- postscript", which itself can be globally mapped to only one application. In other words, globally either Illustrator or Photoshop, but not both.
While not ideal, files do support a per-file preference setting. So if you have a global setting to open eps files in Illustrator then by default double-clicking on will, well, open them in Illustrator. If you have a Photoshop EPS file and would like to open it in Photoshop, you could use the Get Info window to choose Photoshop instead -- just don't click the Change All button. That file, from then on, should always open in Photoshop when you double click on it. (That "user override" preference is saved in the resource fork of the file so it should stay with it).
The switch to UTIs has helped simplify things quite a bit, such as this example with the different types of PDF files. Prior to OS X 10.4, you'd have to repeat the custom "Open With" preference for each type of PDF, which was confusing for most users.
Technically, both Illustrator EPS files and Photoshop EPS files contain the same type of information: Encapsulated PostScript; the fact that Adobe provides two applications, one to edit image-based EPS files, and a second to edit vector-based EPS files is somewhat beside the point. While you could send feedback to Apple about this, I think it's probably up to Adobe to figure something out. They could quite easily define Illustrator EPS and Photoshop EPS files as subclasses of "com.adobe.encapsulated-postscript". For example, vector-based Illustrator EPS files might be "com.adobe.encapsulated-postscript.vector" that conform to "com.adobe.encapsulated-postscript", while raster-based Photoshop EPS files might be "com.adobe.encapsulated-postscript.raster" that conform to "com.adobe.encapsulated-postscript". Since there'd be two distinct types, they could each be mapped to their own application.
Hope this helps....
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