1. Field of the Invention
This invention relates to an optical projection apparatus, and, more particularly, to an optical image projecting apparatus in which an operator of the apparatus who observes the image projected on the screen can generate an output carrying information concerning a part of the image by pointing to part of the image with light spot using a light pen or the like.
2. Description of the Prior Art
An optical image projecting apparatus to which this invention pertains is an apparatus in which an optical image is projected on a projection screen incorporated therein from a recording medium such as a film sheet bearing a number of micro images. The image recorded on the medium is enlarged and projected on the screen and a part of the image projected on the screen is converted into an electric signal when the operator of the apparatus points at the image with a light spot using a light pen or the like. The body of the optical image projecting apparatus can be a microreader, a slide projector or another kind of image projector. This invention, however, is most effectively applied to a microreader which is used as an interface of an image man-machine system. This invention will be hereinafter described with particular reference to an embodiment thereof applied to the microreader used as the interface.
The term "light pen" referred to in this specification in connection with this invention is not the conventional light pen which is used in association with a CRT display of a computer to put a signal in a computer. The light pen used in connection with this invention contains a built-in lamp to project a light spot on the screen and does not contain a photoreceptor to detect the light on the screen, while the conventional light pen used in a computer system is provided with a photoreceptor to detect the light of the raster on the CRT.
It is well known in the electronic computer art to use a CRT graphic display device as an interface in a man-machine system, in which the operator of the computer generates an output by pointing at the information displayed on the CRT with a light pen. This kind of CRT graphic display device is disadvantageous in that all of the images to be displayed must be stored in the memory of the computer and accordingly the expense of the entire system is considerable. In addition complicated images having various gradations cannot be clearly and sharply reproduced on the faceplate of the cathode ray tube. Comparing the cost of the system, the storage cost for the magnetic drum, magnetic disc and magnetic tape and the like used as a memory of a computer is about 4 cents to about $4,000 per image, while that for microfilm is about 12 to about 20 cents including the cost of the retrieval device, in case of memorizing an image having various gradations recorded on an A4-size medium (210 .times. 297 cm). The microfilm projecting or viewing device which is more economical than the CRT graphic display device as shown above, however, is disadvantageous in that it is impossible to put an input directly into an information treating system such as a computer from the projection screen thereof. When using a microfilm projector, the operator of the computer must use an unput keyboard to put information into the computer viewing the image projected on the screen of the projector.
In view of the above described disposition of the conventional apparatus, an apparatus must be provided which projects an optical image from a recording medium of low cost and enables the operator of the computer to put information directly into the computer from the image projected on a screen.
Therefore, a primary object of the present invention is to provide an optical image projecting apparatus which projects an optical image sharply on a projection screen from economical microfilm and in which the information projected on the screen can be converted into an electric signal and put into an information processing system by pointing at the screen with a light spot so that the information on the screen can be put directly into the information processing system such as a computer.
Another object of the present invention is to provide an optical image projecting apparatus which is used as an interface in a man-machine system and requires a very small amount of memory in the information processing system.