I am no expert on image sensors, but from my basic understanding, pixels are read out line by line and in sequential order. A VSYNC pulse shall initiate a frame transfer, while HREF pulses initiate a pixel line transfer, which will begin a transfer of pixel data from the first pixel in a row to the last pixel in a row. Please see the following webpagethis webpage for more details. Hope that helps.. http://www.cs.utah.edu/~gavin/3710/camera_extension_II.htm