1. Field of the Invention
The present invention relates to an apparatus for extracting a feature from images using a first image and a second image of an object.
More specifically the invention uses a first signal of the first image which is in relatively sharp focus and a second signal of the second image which is in relatively soft focus in order to extract a feature from the images.
2. Background Information
A feature extracting apparatus is commonly used with a system which stores data of an input image from a TV camera, and then extracts a feature of an object from the stored data using a two dimensional filtering processing. The two dimensional filtering process uses spatial filtering with Fourier transforms.
However, the foregoing two dimensional processing requires a lot of processing time. Faster processing can only be achieved using much larger memory capacity and faster, more expensive hardware.
An apparatus described in Japanese Non-examined Patent Publication No. 58-208875, takes an image of the object with two TV cameras, and stores data of the image. One image is in exact sharp focus, and the other image is out of focus. The apparatus then extracts edge information of the object using a differential operation of the image data taken by the two TV cameras.
However, if the view of one of the pair of video cameras is obstructed ("occluded"), it is impossible to extract edge or profile information of the object with the differential operation which relies on parallax to produce two images. Moreover, using two cameras introduce other inaccuracies in that the two cameras have slightly different characteristics both in their optics and electronics and in downstream processing circuits.
In the foregoing, if one camera is used to get two images of the object, the problem of parallax and possible image obstruction as well as different characteristics between the cameras is solved. But there are still problems in precise extracting of feature information because of changing a position of the principal point and varying the magnification with changing focal position.