By Franklin J. Garner, III

NOTE: Due to the limitations of electronic document transmission, the high-resolution details of actual printed specimens cannot be accurately depicted. Please contact the author for hard-copy examples of the technologies discussed herein.

Pixels and Paper
The building block of digital imaging is the pixel. Pixels are those tiny points of light that you see on your computer display when you examine it with a magnifying glass. On color displays, carefully focused pixels are arranged in red, green, and blue clusters to simulate various hues that are modulated in brightness to approximate color intensities. Laser printers apply a charge to a magnetic recording surface with a sweeping beam that flashes at the center points of pixels. Scanning machines reverse the action of the pixel to "read" an image through a moving array of sensors. Pixels are the smallest addressable element under the control of the device. The spacing of these pixels is referred to as the resolution of the display, scanner or printer.

Within the printing industry, device pixels are truly microscopic. Imagesetting machines that make printing plates create pixels that are approximately 1/2500 of an inch (or smaller) in size. Compared to a standard computer display, these machines have as much as 30 times more pixel resolution. Although computer displays cannot accommodate images at these resolutions, regular printing plates and paper handle them well. Hundreds of pixels are typically illuminated together to create a halftone dot. For instance, a single halftone dot used in standard 133-line commercial printing is constructed from 366 (or more) individual pixels. Based of the virtues of offset halftone printing, a new technique has been developed that exploits paper’s exceptional resolution-holding potential. Now, a halftone dot itself is being used to store microscopic images. And once printed on paper, these images cannot be accurately copied.

Conventional Halftone Technology
Halftone screening dots have been in use for years to enable the printing of continuous tone images. To print various tones of color on paper with printing presses and ink or toner, the area of color must be converted to halftone dots (or lines) of an appropriate radius or thickness, with the (normally white) base paper (or other substrate) color showing through. Close examination of almost any commercially printed document will reveal these halftone dots. The inventors of halftone screening have strived to develop methods to generate halftone dots that are free from artifacts, and that render printed images which are as faithful as possible to the original continuous tone (unscreened) original. Typically, conventional halftone dots are shaped as solid squares, filled circles or ellipses, filled diamond shapes, and/or solid lines, and they are used to print everything from newspapers and magazines to elaborate security documents such as checks and certificates.

Halftone dots are successful in visually representing tones and images on a printed object because the human eye merges the dots into a perceived continuous tone. This occurs because the dots are typically very small, and only obvious if the printed document or object is enlarged or magnified.

Round Dot
Square Dot
Ellipse Dot
Diamond Dot
Horizontal Line Screen
Diagonal Line Screen
Figure 1: Examples of conventional halftone dots.

LogoDot Technology
Called LogoDot, this patent-pending invention describes a method to capture any image such as a corporate logo, a photograph, or a key word or phrase, and to convert that image into a microscopic halftone dot. The dot can also include tonal variation features. The technology allows for the use of custom dots as a substitute for the conventional square, round, elliptical, diamond and/or other shaped dots typically used in normal commercial printing. Through this invention, all or selected areas of a printed image can be rendered in LogoDots that can be verified with a magnifying device. The ability to include one's corporate logo or self-portrait as a repetitive microscopic image within a printed document or object has the appeal of extreme personalization as well as providing original document validation.

Capture Any Image
The dot designer can capture a "seed" image to use as the LogoDot. The image can be scanned from a hard copy of the image or obtained via a digital camera or other means. The image then is reduced to a rectangular bit-map with an overall pixel count not to exceed 255 x 255 pixels. Using standard desktop publishing pixel-editing software, the bit-map is edited to indicate the preference for progressive illumination of the pixels from white to black, by making the most prominent pixels black, the least prominent pixels white, and the order of tonal variation across the dark to light spectrum in various shades of gray. The resultant seed image is saved from the pixel editor program then processed into a LogoDot consisting of illumination ranking instructions.

Shape Dot
Photo Dot
Symbol Dot
Phrase Dot
Figure 2: Examples of custom halftone dots.

These coded instructions are then stored in a dot library and can be utilized with postscript imaging devices to create printing plates, negatives, and/or films that contain the LogoDots. Like conventional halftone dots, LogoDots automatically adjust their tonal density from white to black, and all variations of gray level between black and white, dynamically according to the attributes of the graphical element or the wishes of the graphical designer. The microscopic images are inserted during the document’s or printed object’s creation and/or composition. Because all other aspects of the document’s production are unaffected, LogoDots provide an economical means to create and print highly personalized documents. LogoDots can be used in combination with conventional halftone dots for rendering any graphical object, e.g.. photographs, raster images, logos, symbols, text and typefaces, rules and lines, circles, arcs, splines, colored areas, borders, pantographs, patterns, and any other graphical element found or used in a commercially printed document.

Figure 3: Preview the line dot image as the density progresses from 0% to 60% .

The Ideal Graphical Security Feature
One of the first applications of LogoDots is for the manufacture of printed security documents. Desktop publishing systems with low-cost scanners and color printers have made it easy for criminals to counterfeit all but the most secure documents. In addition, photocopying equipment has improved, especially in the case of color copiers, and the many "void" pantographs are no longer reliable. New color copiers compensate for subtle tonal variations with remarkable results, producing near perfect copies that cannot easily be identified as copies.

Documents that contain LogoDots have a magnifying glass symbol that shows an enlarged image of the custom halftone dot utilized within the document. Since the LogoDot does not photocopy, a quick check with a magnifier will reveal if the document is an original. Not only does the LogoDot fail to photocopy, it tends to degrade and spoil the appearance of the document.

The ideal graphical security document feature is something that is commercially simple to print yet difficult to copy, and usable as a non-intrusive background image on an original that subsequently interferes with the document’s legibility on the copy. The perfect security document is easily verified and provides a high level of confidence in its authenticity. The LogoDot technology has the potential to offer these benefits.

Good Original – Bad Copy

Figure 4: Pocket Eye™ handheld reader

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