Is a Photoshop EPS file a vector format?

If I save my file from Photoshop as a Photoshop EPS is that going to be okay as a vector across the board (ie will it be resizeable in whatever it's opened in)? I know if you open a .psd in Photoshop and resize the image, it holds it's quality, so that's fine, but when people need an EPS file because they might want to print it on the side of a building one day (or whatever) is a Photoshop EPS going to be okay? Or is there something else I need to be doing?

All my designs are always vectors within Photoshop, so text/shapes/designs done with the pen tool - I just need to know that they'll still be a vector for people who don't have Photoshop and can't open it in there to resize it.

Answer

To a degree.....

With the exception of Live Type, Photoshop creates vector containers with raster fills. What this means is the edges of shape layers will remain crisp and clear when resized because the shape/vector layer edge is saved as a vector and it is recalculated when resized.

However, what is inside the shape layer is not vector. For example, if you create a shape/vector layer and then apply a pattern overlay, an inner glow, and a drop shadow, all those layer styles are not vector and will not scale infinitely. Layer styles are always raster and are bound by raster limitations.

Live type is vector and will remain vector and scalable when used in a Photoshop file and saved as an EPS. However, at times live type can be converted to outlines in eps files to maintain appearance. When converted to outlines, the type loses it's hinting properties and although it is vector, it may not look ideal at smaller sizes. Type is generally not a problem for anything above 12-14 points though.

As DA01 pointed out, eps is merely a file wrapper. Simply saving as an eps does not mean something is vector. EPS can contain 100% raster content or 100% vector content or a mix of the two. When using Photoshop, you always get a mix of the two if you have type and/or shape/vector layers. It is not possible to create a true vector file with any version Photoshop regardless of what you do.

See Also: How to create vector graphics In Photoshop?