Aptina's patent application US20130134295 "Imaging systems with selectable column power control" by Hai Yan and Ashirwad Bahukhandi proposes a circuit to independently power down each column readout circuit, in case the column is not used in one of the partial-scan modes:
"In some situations, however, only a portion of the image pixels a pixel array may used to capture image data at any given time. For example, in some situations a sub-array of image pixels may be used to capture image data when it is desired to capture image frames having a reduced size at an increased frame rate. In a conventional image sensor, power that could otherwise be used to operate other portions of the imaging system or that could otherwise be stored and used for later imaging operations can therefore be used to unnecessarily power column readout circuits that are coupled to unused image pixels. It can be particularly useful to conserve this type of power in portable imaging systems that use batteries to provide power to the device or in power-saving modes in larger electronic devices with imaging systems."
One of the possible implementations of the power down latch circuit is below: