OSX Equivalent to Greenshot?

[Wardenski]

Hi.

Has anyone come across any free screen capture software for OSX that can capture a specific region of a screen and be able to repeatedly take a screen shot from the previously defined region without having to define the capture region each time.

Greenshot can do this very easily in Windows but it outputs compressed images with alternative greyscale which is not good for what I want.

Cheers