A display system includes a source device that outputs image-data and a sink device that performs a displaying operation based on the image-data. The sink device changes a frame-rate of a panel driving frame as the source device changes a frame-rate of an image frame. The sink device sets a first clock cycle starting point at which a first clock cycle of an emission on-off clock starts as a scan starting point of the panel driving frame when the first clock cycle starting point is consistent with an input starting point of image frame data. The sink device moves the input starting point to a second clock cycle starting point, at which a second clock cycle following the first clock cycle starts, and sets the second clock cycle starting point as the scan starting point when the first clock cycle starting point is inconsistent with the input starting point.