Image processing techniques for printing identification cards and documents
View Patent ↗The invention relates to identification documents, and in particular to pre-printing processing covert images, such as UV or IR images, provided on such identification documents. In one implementation, the invention includes a method of processing a digital image that is to be printed on a surface of an identification document as a fluorescing-capable image to improve the quality of the image. Edges or boundaries are detected within the image, the detected edges or boundaries forming an intermediate image. The edges or boundaries within the image are emphasized, and the emphasized image is used for printing the covert image. In some implementations of the invention, a digital watermark is embedded in the covert image.
1. A computerized method to reduce at least one of image washout and blurring caused by the fluorescence of a covert image that is to be transferred to an identification document for printing, said method comprising, prior to the transfer of the covert image:
providing a computer system, the computer system running executable software, the executable software running one or more edge detection algorithms, at least one digital image to be processed by the computer system using the executable software, the digital image being stored in association with the computer system and comprising image pixels of varying degrees of dark and light;
the computer system accessing and retrieving the digital image that is to be used as a model to generate a covert image that is to be printed using the computer system on the identification document using a fluorescing medium;
the executable software increasing contrast in the digital image, the step of increasing contrast including making dark pixels relatively darker and light pixels relatively lighter;
the executable software identifying one or more contour(s) of the image pixels of the digital image where luminosity of the increased-contrast digital image changes more sharply than at adjoining regions in the image using the computer system;
the executable software, in the step of identifying contours of image pixels of the digital image further comprising the steps of generating a horizontal edge image comprising horizontal edge components, generating a vertical edge image comprising vertical edge components and summing the vertical and horizontal edge images to form a composite image;
the executable software emphasizing said contour(s) by iteratively adding copies of the composite image onto itself wherein each added copy is offset with respect to the previous copy; and
the computer system forming a master for guiding printing of the covert image.
2. The method of claim 1 , wherein the offset comprises a range of 2-5 pixels.
3. The method of claim 1 , wherein the step of emphasizing comprises growing at least one of contour(s) by a predetermined thickness.
4. The method of claim 1 , further comprising the step of converting the emphasized contour(s) to a bitonal image comprising pixels, wherein each pixel is assigned either a first or second value, but no other value, and inverting the bitonal image.
5. The method of claim 4 , further comprising the step of the computer system causing printing of the inverted bitonal image on the identification document with at least one covert medium.
6. The method of claim 1 , wherein said covert image comprises steganographic encoding.
7. The method of claim 1 , wherein the steganographic encoding comprises a digital watermark.
8. The method of claim 1 that further comprises the step of the computer system causing printing of the emphasized image with a thermachromic material, the material changing in appearance with changes in temperature.
9. The method of claim 1 that further comprises the step of the computer system causing printing of the emphasized image with a ferrofluid material, the material changing in appearance with changing in applied magnetic field.
10. The method of claim 1 that further comprises the step of the computer system causing printing of the emphasized image with an ink which is not visible to humans under ordinary illumination, the material becoming visible when illuminated with infrared illumination.
11. The method of claim 1 that further includes the step of the computer system causing printing of the image, including the emphasized contour(s) but excluding other features of the input digital image, as an element of an identification document.
12. The method of processing of claim 1 wherein the step of identifying one or more contour(s) of image pixels comprises the step of the executable software processing the image pixels using a Sobel edge detection algorithm.