Abstract: The invention provides an image output device coupled to a first and second signal source and a method thereof. The image output device includes memories configured to store frame image data respectively, a source selection circuit coupled to the first and second signal sources and the memories and configured to choose to store a first frame image data transmitted by the first or second signal source in one of the memories according to a working state of the first signal source, and an image output circuit coupled to the memories and the source selection circuit and configured to output the first frame image data stored in one of the memories. The image output device may rapidly switch to a backup signal source when the signal source is unstable to achieve fast switching and perfect connection.