Method and apparatus for point-of-sale digital half-toning image verification

Abstract

 Apparatus and method provide a method for providing recognizable halftone images from using printing apparatus which is not, or only marginally capable of intrinsic halftone operation from a transaction card. By increasing the capability to provide halftone images, fraud associated with transaction cards can be reduced.

Description

Field of Invention

[0001] The present invention is in the field of transaction card validation, with the particular emphasis on providing a method for producing an inexpensive means of printing a hard copy digital halftoned image at the point of sale.

Background of the Invention

[0002] Transaction card fraud is a significant problem in the credit industry, and there are various means and methods to attempt to reduce the fraudulent use of transaction cards. One of these methods encodes the digital image of the cardholder (e.g., Lawrence A. Ray and Richard N. Ellson, "Method and Apparatus for Credit Card Verification," U.S. Patent Application Serial No. 019,538, filed February 18, 1993.) Another method is to print the cardholder's image directly onto the card using "digital imprinting." This method offers additional credit card security as it provides the salesperson a quick method for checking the resemblance between the card image and the card presenter. Still another method to approach the problem encodes a likeness of the cardholder in digital form on the card's magnetic stripe or within an internal card microprocessor (as in smart cards). As the image is not visible on the card, the image information must be extracted, decoded and displayed to the salesperson in some form.

[0003] One approach to improve the security in the use of transaction cards is to have images of cardholders contained in an image data base and when a transaction occurs the database retrieves the image and sends it to the appropriate location for visual display (see Luther G. Simjian, "Verification System using Coded Identifying and Storage Means," U.S. Patent No. 3,569,619, issued March 9, 1971). This approach presents two major logistical problems. The first is to retrieve the digital image from a database which has millions of image records within acceptable time constraints. The second obstacle is the transmission over existing communications lines and with standard transmission rates. Since a merchant wishes to complete the transaction as quickly as possible, any time delays are undesirable.

[0004] Many merchants have a digital printer at the point of sale for the purpose of printing receipts. Some merchants encode the logo of their company and print it on their receipts as a means of differentiation. Simple dot-matrix impact printers capable of printing between 100-200 dots/inch are adequate for the task of receipt printing.

[0005] Many systems print or display bi-level output, and methods to produce images which appear to have multiple levels of print density are referred to generically as half-toning. Half-toning of images is done throughout the graphic arts field. In very simplistic terms, the gray levels are implemented by modulating the area of a dot which is printed, more of the dot is filled in for higher density levels. The underlying idea is that the human visual system will integrate the amount of area filled and the perception of multiple density levels is achieved. Since a regular array is used there is a high likelihood that the spatial frequencies of the image to "beat" with the half-toning array to generate an objectionable modulation known as a Moiré pattern. The typical means to reduce the Moiré pattern is to rotate the dot array until the pattern is minimized or becomes unnoticeable.

[0006] Digital printers, such as laser printers, ink-jet, or dot-matrix printers, and display units, such as selected liquid crystal display units, are more constrained than traditional graphic arts methods. Dot area can not be modulated, but instead a full dot is printed or is empty. Also, the angle of the dot array is fixed to a rectilinear grid which is oriented in a simple horizontal-vertical alignment. The process of image creation under these restrictive conditions requires different strategies, which are commonly referred to as digital half-toning. A number of approaches to this problem have been formulated. Common methods are commonly referred to as error diffusion and dithering (see Digital Half-toning, by Ulichney, MIT Press, Cambridge, Mass., pp. 77-79, 127, 239-240) Another method known as blue-noise masking (see Sullivan and Ray, U.S. Patent 5,214,517, May 25, 1993) produces an aggregate of dither patterns to overcome many of the limitations of digital printing. These methods differ in implementation based upon requirements of particular embodiments. In particular, error diffusion is an adaptive method which requires moderately sophisticated data processing. Blue-noise masking is a simple process when implemented, and is well suited to devices with very limited memory and processing capability.

[0007] In cases where information capacity of a card, such as a "smart card" or a high-density magnetic stripe card, is sufficient for the data of a multi-level image it is desirable to output the image using a bi-level display or printing device. In order to accomplish this task it is preferable to use a digital half-toning method.

[0008] Point-of-sale terminals with automatic receipt printers typically use a dot-matrix printer. These printers are preferable as they are very inexpensive, and these printers are able to print multiple copies with a single pass. However, the methods of the current invention are suitable for other digital printing methods, such as ink-jet or laser printing. These printers typically have very limited image printing capability and have a small number of dots per inch, on the order of 100 dots per inch. To use printing devices which are inexpensive and with limited resolution there needs to be a printing system which best utilizes the characteristics of the human visual system.

[0009] Image information as stored can be considered simply as data. As such the information can be used in conjunction with a card administration agency to perform a multiple-validation arrangement. Details of this approach are contained in patent application (see Lawrence A. Ray and Richard N. Ellson, "Method and Apparatus for Credit Card Verification," U.S. Patent Application cited above.) This invention explains how to make extremely remote the likelihood a fraudulent image passing the card administration agency validation as well as the visual validation performed at the point of sale.

[0010] A need has been felt for an apparatus and method which can reconstruct an image stored on a transaction card which can more easily be recognized and/or more easily compared with the face of the person with whom the transaction card is identified.

Summary of the Invention

[0011] The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, an image is reconstructed from the data on a transaction card or other device with limited storage capability. The signal set of the reconstructed image is converted to a format which will provide a halftone display on the available printer. Several techniques for achieving a halftone are described in detail. Although the present invention is described in terms of printers, any device which produces a bi-level output signals including dot-matrix printers, laser printers, liquid crystal displays can advantageously use the techniques herein described.

[0012] The availability of the halftone images advantageously permits a recognizable image to be provided at a transaction site with relatively inexpensive apparatus.

[0013] These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings.

Brief Description of the Drawings

[0014] Figure 1 is a block diagram of the apparatus providing a half-tone image from the data strip stored on a transaction card.

[0015] Figure 2 illustrates the process in generating a half-tone image from the data stored on a transaction card.

[0016] Figure 3 is an example of a facial image generated as a result of the data stored on a transaction card with a low density storage medium.

[0017] Figure 4 illustrates a character set and a halftone font set.

Detailed Description of the Invention

[0018] Many merchants have point-of-sale devices for printing credit card receipts on demand instead of imprinting the embossed information on the card onto pre-printed credit-card receipt forms. In addition to the on-demand printing of receipts, the printers are attached to credit-card readers which decode the information contained in the magnetic stripe and automatically contact a financial institution via a telephone modem. The printers, simple dot-matrix impact printers having between 100-200 dots/inch, typically print several copies of the receipt (e.g., one copy for each the customer, merchant and financial institution). Printers which are capable of printing graphics information are commonly known as "all pins addressable" printers and are assumed to be the class of point-of-sale printing device for this invention. Many manufacturers produce point-of-sale printers with this feature.

[0019] The information capacity on a transaction card which conforms to standard ISO 7811 is 456 data bits for Track 1, with other bits used for parity checks, and start and end of data delimiters. While this is a very restrictive space to encode an 8 bit/pixel image, it is still possible by taking advantage of prior information about the image (see Lawrence A. Ray, Richard N. Ellson and Bhavan R. Gandhi, "Method and Apparatus for Image Compression, Storage and Retrieval on Magnetic Transaction Cards," U.S. Patent Application Serial Number            filed on October 29, 1993). It is assumed that the information capacity on the credit card or smart card is sufficient to store image information which has been compressed and can be reconstructed to have acceptable image quality.

[0020] Once the image information is retrieved from the credit card and decompressed, it is to be processed and printed onto a standard receipt. Other information that is contained on the card can also be printed. Examples of such additional information is the cardholder's name, expiration date and perhaps a facsimile of the cardholder's signature.

[0021] Converting the continuous tone image into a digital halftone can be done in a variety of methods, such as center-growing dot, error diffusion, dithering, or "blue-noise" methods. The invention is not limited to a particular method of digital half-toning, as the choice for implementation will be made depending upon processing power of the point-of-sale device, memory restrictions, speed and acceptable image quality. If the output printer has a reasonable degree of dot placement accuracy and the output dot is well behaved then blue-noise methods offer are a good choice for system simplicity and image quality. However, other system combinations make schemes such as simulated center-growing dots more attractive. The purpose of this invention is to describe the use of a receipt printer to output images that are encoded on transaction cards, or transmitted to the transaction site from some central location.

[0022] Simulated center-growing dots is a digital analog to traditional halftoning methods from graphic arts. This analog is accomplished by combining pixel locations and the group of pixels becomes a dot. One embodiment is to combine a 4 x 4 region of pixels. This grid acts as a halftone dot and as more of the pixels within the dot are printed the dot becomes progressively dense. The obvious problem with this method is that the spatial resolution is reduced by a factor of four. However, the advantage is printing stability when the system has significant levels of uncontrolled variation, sometimes referred to as noise. For instance, many receipt printers are impact printers and the ink-paper combination permits the dots to spread beyond the pixel boundaries. In some cases a checkerboard pattern appears completely filled from ink-bleeding. For these cases a simulated center growing dot is superior, as the ink-bleeding can be compensated somewhat by the dot growth structure. In the case of the 4 x 4 grid, up to 17 gray-levels can be designed, though in actual practice the number of gray levels is less than the potential.

[0023] For receipt printers other than dot-matrix impact printers other digital halftoning methods are preferable. In particular, if the receipt is to be printed with an ink-jet system, or potentially a laser printer, then blue-noise or error diffusion is preferable. The blue-noise methods use a small data base of patterns, one for each level of gray which are optimized to minimize the visual artifacts that occur because of the restrictive imaging conditions previously discussed. A pattern is a two-dimensional array which implicitly determines whether a dot is to be written or left blank. An example of such a pattern is an (n x m)-array, e.g., 32 x 32, where elements of the array are in one of two states, print or leave blank. The patterns are accessed by a simple indexing method. For a pixel in an image at pixel location (i,j), where i and j indicate the row and column respectively, the pixel has an image intensity value of between 0-255, this value is used to index the associated pattern in the data base. The element of the pattern which is (i mod n, j mod m) is extracted. If the state of the entry was print, then a dot is printed. Similarly, if it is blank then a dot is not printed.

[0024] There are several embodiments of "blue-noise" and the differences largely are the method by which the data base of dithering patterns are derived. While it is important to determine patterns for individual gray levels, it is also essential for the patterns to be sufficiently correlated in order that transitions across patterns do not destroy the advantages attained for regions of constant gray. The method to accomplish these correlations is to build what is sometimes referred to as a threshold table. Elements of the threshold table are values between 0-255 for an 8-bit/pixel gray-scale image. A threshold table is a special case of the pattern data base. All patterns can be simply recovered from the threshold table by the following rule for a pixel at pixel location (i,j):

a) Extract the element (i mod n, j mod m) of the threshold table;

b) If the value of the table element is at or above the pixel intensity value, then print a dot;

c) If the value of the table element is below the pixel intensity value, then leave the dot blank.

[0025] This table naturally implements the desired correlation across gray-levels. Moreover the memory required to store the data base is quite small, e.g., a 32 x 32 pattern data base the memory requirement is 1,024 bytes of computer memory. The algorithm to access and use the data base is extremely simple and can be done without resorting to storing and processing of the incoming pixel values. This method is preferred for devices such as point-of-sale terminals.

[0026] Other approaches are the use of one of many variations of error diffusion. This method results is images of good image quality, but with the requirement of having a more sophisticated processor at the point-of-sale. The underlying idea of error diffusion is that as a dot is printed there is some error introduced, either the image is too dark or is too light and since the error cannot be corrected at the current pixel because of the limited printing options, the error can be carried forward and included in the determination of whether succeeding pixels should be printed. Major differences in this class of algorithms are largely determined to the strategy selected in processing the error. The more sophisticated algorithms spread the error in both the line and row directions, and other take into account where boundaries of objects occur and do not forward the error across these boundaries. This results in an improved image, but clearly more image processing has occurred prior to the error diffusion process.

[0027] Many printers work with a predefined character font, such as a reduced ASCII character font. Many inexpensive printers use this method as little processing is required and multiple buffers are easily determined. When the halftone dot patterns are the same size as the character cells, then a halftoning font can be constructed for the simulated center growing dot. An embodiment is for a character cell to be an 8 x 8 grid. Four simulated center growing dots could be developed within the character cell. As each center growing dot takes one of four gray-levels, then a 256 character font could be used to perform digital halftoning. Other similar schemes could also be devised. Such a font could be included as an alternative character set included within the firmware of the printer, or could be downloaded from an external device. A printer which does not have an "all pins addressable" capability may store a halftone font as a character set.

[0028] Some receipt printers attain the all-pins-addressable capability. An example of such a device is the PcOS Receipt Printer from Ithaca Peripherals Inc. This printer emulates an IBM Proprinter through a printer driver. In imaging applications, especially when the subject matter is portraits, the printers need to maintain the horizontal and vertical aspect ratio. Printer drivers, such as that for the IBM Proprinter changes the aspect ratio which has the effect that squares become rectangles. In order to recover the aspect ratio the reciprocal simulated center growing dot pattern can be output. In the case of the IBM Proprinter emulation, the printer aspect ratio is 6:5. Clearly a cell printed as 6 x 5 cell would recover the proper aspect ratio. However, since it may be desirable to keep the simulated dot size small another option is for the dot to be a 4 x 5 cell. In addition to the maintenance of small dots, many receipts have a limited width and smaller simulated dots allow for more dot cells to be printed.

[0029] The output from the digital halftone algorithm is a stream a bits which are used to determine whether a pin will print a dot. This type of printing is different than the printing of a character set. A bitstream is processed. In order for printers to determine whether the data is character or image information is often done by sending control signals to the printer controller indicating whether the data is character data or graphics data. In the case of the digital halftones a signal must be sent which indicates the information is for an image and to switch to the "graphics mode." At this point it is necessary for the printer to have a feature known as all pins addressable.

[0030] While the preferred method is for the image information to be solely on the card, there are other methods which have the image information reside in a central data base which is queried by the point-of-sale terminal using information extracted from the card, or a hybrid method where some of the image information is on the card and the remainder is in a central data base. The advantage of these methods is that the storage capacity of the card no longer is a major obstacle. However, the system is not as responsive and some of the security features of the method are reduced in effectiveness.

[0031] Referring to Fig. 1, the apparatus used for providing a halftone image from data stored on a transaction card is shown. The transaction card 10, having data stored in the form of a pattern of physical variations (for example, fluctuations in the orientation of magnetic domains on a strip of magnetic material), is applied to a card reader 11. Card reader 11 converts the patterns of physical properties on the transaction card to digital signals. The signals are then applied to processing unit 12. In processing unit 12, the digital signals are used to reconstruct (and decompress) the image that was compressed and stored in the limited space available on the transaction card. In the preferred embodiment, a matrix (pixel) image, having a standard configuration, is divided into sections and each section has a library of preestablished images. Each preestablished image is associated with a number. Each section of the matrix image is compared with an associated set of library images, and the number of the library image closest to the matrix image is selected. All of the section numbers selected in this manner are stored, a predetermined order, as a physical pattern on the transaction card. Thus, the data required to represent an image by this encoding or compression technique is reduced. When the card is 'read' by the card reader 11, the image numbers along with the order in which the numbers are stored on the transaction card, is used to reconstruct the original matrix image using the library images associated with each number. As will be clear, the restored image is only an approximation of the original image. This data compression/decompression technique is described in more detail in the U.S. Patent Application Serial No.           , entitled "Method and Apparatus for Image Compression Storage and Retrieval on Magnetic Transaction Cards", invented by L. A. Ray, U. Teigman, and R. N. Ellson and filed October 29, 1993; and U.S. Patent Application Serial No.           , entitled "Method and Apparatus for Customer Identification at Automated Teller Machines", invented by L. A. Ray and R. N. Ellson and filed October 29, 1993, both Applications being assigned to the assignee of the present application and incorporated by reference herein. The reconstruction of the image is performed by the processing unit 12 in response to the signals from the card reader 11. After reconstruction of the image by the processing unit 12, signals are applied to printer/display unit 13. The printer/display unit 13 includes the driver circuits to provide a display, either in hardcopy or on a display device, of the reconstructed halftone image 15.

[0032] Referring to Fig. 2, the process implemented by the apparatus of Fig. 1 is illustrated. In step 1, the data on the storage portion of the transaction card is converted from a pattern of physical properties to digital logic signals. The digital signals from the card reader are converted (i.e., decompressed) to provide a matrix image display in step 202. As indicated above, in the preferred embodiment, the digital signals from the transaction card are numbers which designate a selected image portion from a set of image portions. In step 203, the signal set describing the reconstructed image is transformed into activation signals for signals for displaying the reconstructed image either on a display screen and/or in a hardcopy format. The transformation of the signals is specific to the printer/display unit and is performed using any of the techniques for providing a halftone image.

[0033] Referring to Fig. 3, an image 32 compressed and stored on a transaction card 10 and reconstructed in the manner described above is shown. The image 32 is part of a receipt 30, the receipt 30 also including printed matter 31.

[0034] Referring to Fig. 4, an example of a character set and a center-growing grayscale font set is illustrated.

[0035] It will be now appreciated that there has been presented a technique for providing a recognizable image from a transaction card with a relatively minor investment in apparatus. The apparatus can provide a hard copy record of the transaction for dispute resolution. The ISO standards can be maintained while increasing the ability of the system to minimize fraud with respect to the transaction card.

[0036] Operation of the present invention is believed to be apparent from the foregoing description and drawings, but a few words will be added for emphasis. The use of the halftone process increases the ability to recognize facial images. Because of the limited storage space on a typical transaction card, any increase in the ability to recognize an image can be used to reduce significantly transaction fraud. In addition, the ability to provide halftone images with an apparatus which is relatively inexpensive can permit more widespread use of relevant anti-fraud procedures.

[0037] While the invention has been described with reference to transaction card with magnetic storage strips thereon, it is apparent that the invention is easily adapted to other devices that have different storage media associated therewith or storage media with increased capacity. By way of specific example, the transaction card can have the data stored thereon in an optical storage medium. Similarly, the invention has been described with particular reference to printers. However, the techniques disclosed herein are also applicable to halftone displays such as liquid crystal displays.

[0038] While the invention has been described with particular reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements of the preferred embodiment without departing from invention. In addition, many modifications may be made to adapt a particular situation and material to a teaching of the invention without departing from the essential teachings of the present invention.

[0039] As is evident from the foregoing description, certain aspects of the invention are not limited to the particular details of the examples illustrated, and it is therefore contemplated that other modifications and applications will occur to those skilled in the art. It is accordingly intended that the claims shall cover all such modifications and applications as do not depart from the true spirit and scope of the invention.

Parts List

[0040] 

10

transaction card

11

card reader

12

processing unit

13

printer/display unit

15

halftone image

30

receipt

31

material printed on the receipt

32

image reconstructed from data on a transaction card.

Claims

1. Apparatus for providing a halftone image from data stored on a transaction card, the apparatus comprising:
   a reader unit converting a pattern of a physical property on said transaction card to set of object signals;
   a processing unit coupled to said reader unit, said processing unit converting said object signals to a set of image signals, said processing unit transforming said image signals into activation signals; and
   a printer/display unit coupled to said processing unit and responsive to said activation signals for providing a visual image, wherein said activation signals are selected to provide a halftone image on said printer/display unit.

2. The apparatus of claim 1 wherein said processing unit uses a blue-noise method to provide a activation signals which result in said halftone image being generated for said printer/display unit.

3. The apparatus of claim 1 wherein said processing unit uses a simulated center growing dot technique to provide activation signals which result in said halftone image being generated by said printer/display device.

4. The apparatus of claim 1 wherein said processing unit uses an error diffusion method to provide activation signals which result in said halftone image being generated by said printer/display unit.

5. The apparatus of claim 1 wherein said processing unit uses a dithering method to provide activation signals which result in said halftone image being generated by said printer/display unit.

6. The apparatus of claim 1 wherein said object signals are converted to said set of image signals by associating an object signal number with one of a library of images.

7. The apparatus of claim 1 wherein said data stored on said transaction card is consistent with the ISO 7811 standard.

8. The apparatus of claim 1 wherein said processing unit uses a character set to provide activation signals which result in said halftone images being generated by said printer/display unit.

9. A method of providing a visual image from data stored on a transaction card, said data being stored in a readable format, said method comprising the steps of:
   in a reader unit, generating object signals from said transaction card;
   in a processing unit, converting said object signals to image signals;
   in said processing unit, converting said image signals to activation signals,; and
   generating a visual display on a printer/display unit with said activation signals, said activation signals providing a halftone display using said printer/display unit.

10. Apparatus for reconstructing a visual image stored on a transaction card as a pattern of at least one physical property, said apparatus comprising:
   a reader unit, said reader unit interacting with said pattern to provide a first signal set;
   a processing unit responsive to said first signal set for generating an image signal set derived from said first signal set, said processing unit converting said image signal set to an activation signal set; and
   a printer display unit responsive to said activation signal set for providing an image display of said image signal set, wherein said activation signal set causes said printer/display unit to provide a halftone image display.

Drawing