Color encoding-decoding method
BACKGROUND OF THE INVENTION 
     This is a continuation of application Ser. No. 311,229 filed Dec. 1, 1972 now abandoned. 
    
    
     The invention is a method of encoding and decoding graphic material such as writing or a photograph. There is a recognized need for such a method and a number of such methods have been devised. One that has found commercial use is described in the U.S. Pat. No. 2,952,080 of Avakian et al. Avakian et al have dummy bits mix with information bits to form an encoded graphic. This encoded graphic is decoded quite simply by superimposing an appropriate mask and the encoded graphic. A disadvantage of a method utilizing dummy bits is that the original material can never be fully restored during decoding. Another method, described in the U.S. Pat. No. 3,234,663 of Ferris et al, forms an encoded graphic that is composed of a mixture of small positive and negative areas, each positive or negative area being, respectively, a positive or negative image of corresponding portions of the original material. In the method of Ferris, the original material is fully restored, but the decoding process is relatively complicated-involving the exposing and developing of film-making the method unsuitable for all possible uses. The present invention, like Ferris et al, forms an encoded graphic consisting of a mixture of positive and negative portions of the original material, and like Ferris et al the original material is fully reconstructed during decoding. Encoding and decoding are, however, are accomplished by a quite different method with decoding using a masking system similar in some ways to that of Avakian et al. 
     SUMMARY OF THE INVENTION 
     The present invention is a method of using colors for encoding and/or decoding graphic material, e.g., a signature. In the encoding process, an encoded graphic is formed. This encoded graphic is a mixture of corresponding positive and negative portions of the original graphic material. If the pattern of positive and negative portions is well chosen, it will be difficult or impossible for an unauthorized person to &#34;read through&#34; the encoded graphic and learn what the original material consists of. 
     To encode, using colors, the original material must be composed of two colors, neither of which is black or white. A pattern of two transparent colors (usually the same two colors that are in the original material) and the original material are superimposed. Pattern colors mix in a subtractive manner with the colors of the original material they overlie and a multicolored image is formed. The image is recorded on monochromatic film. Because of the way the colors are chosen, where one pattern color overlies the original material, the corresponding area on the film will be a positive image of the original material, and where the other pattern color overlies the original material, the corresponding area on the film will be a negative image of the original material. The film constitutes one form of the encoded graphic. 
     Decoding is similar to encoding. A transparent colored pattern-similar to the one used for encoding-is placed over a suitably colored encoded graphic. Again, none of the colors used are black or white. Colors mix and a multicolored image is formed. This image is a reconstruction of the original material and can be viewed directly or recorded on film. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the accompanying drawing: 
     FIG. 1 is a composite view of an original signature card, a first pattern, and a resulting light and dark photograph with corresponding areas from each of the same shown enlarged and located to the right hand side, 
     FIG. 2 is a composite view of a two color encoded signature card, a second pattern, and a visual image resulting from the combination of the encoded signature card and the second pattern; corresponding areas of each of the same being shown enlarged. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present method of encoding-decoding is a method that might be used by a bank for encoding a customer&#39;s signature in a bank book. The encoded signature would be decoded at the bank and used for identification purposes. The use of the present method will be illustrated in a bank system. 
     A red signature card 1 is signed by a bank customer, the signature at 2 in green opaque ink. This signed signature card is the graphic material to be encoded. A pattern 3 having red and green transparent colors and the signed signature card 1 are superimposed. Here, the pattern 3 colors are arranged on a plastic base material (pattern 3 might, e.g., be a color film transparency), but in other forms of the invention the pattern might be colored inks placed directly on signature card 1. 
     The colors of pattern 3 mix in a subtractive manner with the signature card 1 colors they overlie. In particular, red and green of the pattern mix, respectively, with green and red of the signature card to form dark colors, and red and green of the pattern mix, respectively, with red and green of the signature card to form, respectively, the relatively lighter colors of red and green. 
     A record of the relative lightness and darkness of the colors formed by the superimposition is made with a camera on black and white film 4. Lighting is adjusted so that all superimpositions of like colors (red on red or green on green) record in the same way in corresponding portions on the film and produce the same densities on the developed film. Similarily, all superimpositions of unlike colors (red on green or green on red) record in the same way in corresponding portions on the film and produce the same densities on the developed film. Film 4 in FIG. 1 is shown developed as a positive. The light (L) and dark (D) densities resulting from the superimpositions are indicated. Ideally, film 4 should be a high contrast variety as used in the graphic arts. The colors used here necessitate the film be panchromatic. When high contrast film is used, L and D portions of film 4 would be, respectively, clear and opaque black. 
     Film 4 is a mixture of positive and negative areas of corresponding portions of signature card 1 and film 4 is an encoded form of signature card 1. In particular, in areas of film 4 corresponding to red of pattern 3, red and green of signature card 1 have been represented on the developed film 4, respectively, as light and dark. On the other hand, in areas of film 4 corresponding to green of pattern 3, red and green of signature card 1 have been represented on film 4, respectively, as dark and light. Thus, areas of film 4 corresponding to red and green of pattern 3 have recorded corresponding portions of signature card 1, respectively, as positive (say) and negative images. 
     To decode, generally speaking, the encoding process is repeated. Film 4 is used to form the encoded signature 5 to be placed, e.g., within an opening in the customer&#39;s bank book. Here, encoded card 5 is composed of transparent red and green colors on a plastic base. Opaque colors can also work. Encoded card 5 can be prepared from film 4 by any of several known printing processes. It is possible that encoded card 5 could be film 4 if, e.g., opaque colors are utilized and a green dye or ink is introduced to the emulsion of high contrast film 4, and green colored film 4 is mounted on a red back ground in the bank book. It is also possible to use a film 4 consisting of light and dark portions in the bank book, but the entire original signature card 1 is not reconstructed during decoding. 
     For decoding encoded card 5, a second pattern at 6 is provided the bank, said second pattern having transparent red and green areas identically arranged to the first pattern 3. Again, the colors are located on a transparent plastic base. The second pattern is superimposed by suitable registration means over signature card 5 with the superimposed pair being placed over illumination means 7. Superimposed colors will mix subtractively and the original signature, as typified by the initial R will appear as a dark image with the dark areas resulting from a mismatching of red and green colors on pattern 6 and the encoded signature card 5. The other or background areas of the image resulting from a superimposition of matching colors. Accordingly, the original signature of card 1 is reconstructed with dark areas of the image corresponding to green of signature card 1, and lighter red and green areas of the image corresponding to red of signature card 1. During superimposition of pattern 6 and encoded card 5, red and green of pattern 5 coincide with, respectively, positive and negative areas of encoded card 5. It can be said that red of pattern 6 leaves the positive areas positive in the resulting image, while green of pattern 6 changes negative portions of encoded card 5 to positive in the resulting image. 
     Since decoding is done visually after superimposing pattern 6 and card 5, since it may not be necessary to record the resultant image on film, and since the eye can discriminate hue as well as brightness, a wider range of colors can be used for decoding than for encoding. It is sometimes possible to decode an encoded graphic by optically superimposing a pattern and having overlying colors mix additively. Also, crossed and uncrossed polarizing means similar to matched and mismatched colors, both for encoding and decoding. For purposes of this specification and claims, where applicable, the word &#34;color&#34; as defined broadly enough to apply to the polarization of light. 
     To encode continuous tone photographs, a black and white photograph must first be transformed into an appropriately colored version. If black is changed to green and white to red, then shades of gray would have to be appropriate additive mixtures of red and green. The film used for encoding would be continuous tone. 
     By proper choice of pattern 3, signature 2 will not be discernable by viewing encoded card 5. The nature of the material to be encoded may determine the nature of the pattern used for encoding. Photographs, e.g., may be better encoded by one type of pattern, signatures by another. If a random collection of red and green squares, as in pattern 3, is used to encode a signature, it may be deemed desirable-at some point in the encoding process-to digitalize the signature or an encoded form of the signature into square units so that the final encoded signature consists of only red and green square areas. That is, there would be no broken squares as in encoded signature card 5. Whatever pattern is used, a red and green pattern like card 5 is more difficult to &#34;see through&#34; than its light and dark counterpart, film 4, because there is less contrast between red and green than between light and dark. If the squares of pattern 3 are made small enough, during decoding, the red and green squares of the viewed image will blend together visually to form a single color. 
     While I have shown but a few embodiments of the invention, it will be apparent to those skilled in the art that the invention may be embodied still otherwise without departing from the spirit and scope of the invention.