Video signal transmission

Video transmission comprising detecting whether the resolution of an input video is in a lower or higher resolution range 712; if the resolution is in a higher range, compressing video colour data of the input video by a constant compression ratio 730; if the resolution is in a lower range, applying no compression to video colour data of the input video 710; transmitting the resultant video frames at the same frame rate as the input video frame rate. The receiver of the transmitted video expands the video frames by a constant expansion ratio to restore the resolution to the original input video resolution when it detects that the video has been transmitted in a compressed format. Preferably the lower resolution range corresponds to a single link DVI or an HDMI with a low pixel clock frequency, and the higher range correspond to a dual link DVI or an HDMI with a high pixel clock frequency. Preferably the compression ratio is one half and compression involves chrominance sub-sampling 730. The transmission system may further comprise a KVM extender. The invention allows DVI or HDMI cable to transmit high definition video over long distances without the need for frame stores at the transmitter or receiver.