What's the Difference between Contrast Detection and Phase Detection AF?

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QUESTIONS: "Why is autofocus different in Liveview vs. TTL? I know Liveview on my D7000 has additional options such as face recognition. Wouldn't the EVF and LCD on my Lumix both use autofocus the same way?" Fred

ANSWER: Most mirrorless cameras use contrast detection autofocus for everything. So you are correct in your assumption that the autofocus system on your Lumix is the same regardless of whether you are using the electronic viewfinder (EVF) or the LCD. 

 Most DSLRs, however, use contrast detection autofocus for Liveview and phase detection autofocus for through the lens (TTL) focusing. The reason for this is that the traditional DSLR phase detection autofocus implementation involves the use of a beam splitter on the reflex mirror. Given that the mirror is raised in Liveview, the autofocus method must change. We are starting to see on-chip phase detection autofocus making it into some cameras, such as the Nikon 1 series and the Canon 70D, so this may all change in the not too distant future.

The main benefit of phase detection autofocus is speed, while the main benefit of contrast detection autofocus is accuracy.  The contrast detection autofocus systems implemented on most recent mirrorless cameras have gotten quite fast, so for many photographers, they're fast enough. However, phase detection autofocus is still far superior for action photography, with the ability to reacquire focus at rates of several frames a second. Contrast detection autofocus just can't keep up with that speed yet.

For a technical overview of autofocus systems you might want to check Wikipedia's post on the subject