1. Field of the Invention
The present invention is directed generally to the field signal processing and, more particularly, to the field of video signal processing.
2. Description of the Background
It is known in the art to use color as a basis for merging pixel by pixel, two video signals. Chroma-keying, as the process is known, uses color information to control a switching process. A person, for example a weatherperson, stands in front of a blue screen while a first video signal is made. A second video signal is provided which is to be combined with just the weatherperson from the first video signal. The first video signal is analyzed pixel by pixel for the key, i.e., the blue of the background screen. For each blue pixel, the corresponding pixel from the second video signal is selected for the final image. Each non-blue pixel from the first video signal is selected for the final image. Through that simple process, the weatherperson is extracted from the background screen and superimposed on top of the images in the second video signal. The chroma-key process is simple enough to be performed in real time. However, the extracted image is always considered to be in front of the images from the second video signal. That may or may not result in a realistic looking final product. Furthermore, because the extracted image is always in front of the images from the second video signal, there is no physical or geometrical interaction allowed between the extracted image and the images of the second video signal.
Other methods for combining video signals are disclosed in U.S. Pat. No. 5,400,080 entitled Apparatus And Method For Combining Video Signals Representing Images Having Different Depths, U.S. Pat. No. 5,353,068 entitled Video Signal Combining Apparatus And Method, and U.S. Pat. No. 5,280,337 entitled Depth-Based Video Combining. Each of those patents discloses a method which uses depth information for combining one or more video signals. However, the patents do not disclose how to obtain the needed depth information, which is a non-trivial problem if pixel by pixel depth information is to be provided in real time for standard video signals having a frame rate of thirty frames per second. Moreover, there is no recognition in the aforementioned patents of how images from the combined video signals might interact, e.g. one image might cast a shadow on an image which is behind it in the combined video. Thus, the need exists for a method of using depth as the key for merging two video signals in real time in a way which enables the images from the combined video to interact with one another.