Horizontal And Vertical Flipping / Mirroring

In graphics applications there is often a feature that allows one to flip or mirror objects like images or shapes around the horizontal or vertical axis.

In an application I use the action will be labled and work like this:

• Flip horizontal: Flip around the vertical axis.
• Flip vertical: Flip around the horizontal axis.

So my question is, why is this inverted? I think I can remember that I saw it the other way round at least once. But I am not sure if there was additional information that they were referring to the axes.

Is it obvious what is going to happen when the user chooses either of the options (without an additional icon or text)?