In printing parlance, the term “registration” is used to describe the alignment of images applied in multiple printing steps. Good alignment of plate images applied in sequential printing steps is an important quality control need for all industrial and consumer printing workflows, but for non-security applications these capabilities are limited to registration of images on the same side of a substrate. In contrast, many security offset presses feature front-to-back capabilities in which registered offset art is printed simultaneously on both sides of the sheet, to be later inspected as a transmitted light security feature. Counterfeiters can find it difficult to achieve front-to-back register with traditional or digital commercial printing equipment that is not designed specifically for security work, allowing counterfeits to be detected in transmitted light when images are not correctly aligned.
This is the first of a five-part series of simultaneous offset papers designed to explore this profoundly underutilized security feature, which is sometimes also called see-through register or front-to-back register. This first paper considers single and multiplate simultaneous offset features, how same-side and opposite-side image registration are approached in traditional and digital counterfeiting workflows, and the relationship between simultaneous offset icon art and external offset artwork. The second paper will analyze soft design-based perceptual and visual effects to include changes in color and contrast, and how inspection ergonomics in simultaneous offset designs are related to design and placement. The third and fourth papers will explore novel implementations for simultaneous offset features in relation to color and contrast. Finally, the fifth paper will cover full-document simultaneous offset designs. The purpose of the series is to outline concepts; not all approaches described will be manufacturable or appropriate for all documents or all issuers.
Icons and Associated Variables
In most security documents, simultaneous offset features are implemented in a single discrete area of limited size that may or may not be joined to other document artwork. This will be referred to as an icon. Icons have many aspects, including hardware/material variables like plate count, ink colors and ink saturation and soft design variables like artwork, placement and size. The scope of this first part will focus primarily on plate count, registration and artwork integration. Figure graphics are displayed in triplicate to illustrate both the front and back images in reflected light as well as the complete feature artwork in transmitted light, following the format demonstrated in Figure 1.
Figure 1. Model showing the figure structure used throughout this paper. The left image shows the front of the document in reflected light, the right image shows the back of the document in reflected light, and the center image shows both together in transmitted light as viewed from the front.
The Simplest Example
To begin, consider the simple simultaneous offset icon shown in Figure 2 in terms of three characteristics. First, it only requires one plate image on either side. All simultaneous offset features require both traditional and digital counterfeiters to register images between opposing sides of the substrate. However, because there is only one plate image on either side of the icon in Figure 2, this icon design does not also force counterfeiters to register multiple plate images on the same side. Second, this icon is not connected to any other nearby offset artwork. One potential advantage of an isolated icon like the one in Figure 2 may be that it is easier for document users to locate and inspect without competing images nearby. However, this isolation may allow counterfeiters to execute certain kinds of icon simulations that are only possible when the icon can be treated as a separate image. Third, the icon is composed of large block artwork. The large shapes are easy for document users to see and inspect but might cause small registration variations to go unnoticed, if the degree of misregistration is small compared to the size of the shapes. This has everything to do with quality control. Issuers confident about their own registration capabilities might take advantage of finer art, or if not, more forgiving large shapes might be preferable, or both types might be integrated together to capture the advantages of each. Despite its simplicity, this example shows how an icon can be assessed across a variety of metrics that affect how it is printed, counterfeited, and interpreted by document users.
Figure 2. Two-plate simultaneous offset design with one plate on the front and one on the back. The icon is not connected to other document artwork, which may make it easier for users to find but could also allow counterfeiters to attack it in isolation. This design only features one plate on each side and does not force traditional counterfeiters to register same-side multiplate artwork. The blocky artwork contains no thin lines, which may make it tolerant of small registration variations.
Multiplate Isolated Icons
More complex simultaneous offset designs with multiple same-side plate images can require both same-side and opposite-side registration, with different consequences for traditional and digital counterfeiting workflows. Traditional offset counterfeiters must align multiple same-side plate impressions in the same way as genuine issuers, and more plate images means more opportunities for registration errors. In contrast, digital counterfeiters can simulate any number of registered conventional spot colors on one side of a substrate with a single CMYK printing step. Therefore, increasing the number of same-side colors in a genuine simultaneous offset icon does not necessarily also introduce same-side registration problems in digital counterfeiting workflows (though one possible solution is presented in Figure 8). Home/office inkjet devices are not designed to register images on opposite sides of a sheet, so front and back inkjet art simulations in counterfeits may be misaligned in transmitted light even though simulated color registration is excellent in reflected light. Just as noted in prior work on microprinting[i],[ii], multiplate simultaneous offset designs that target traditional counterfeiting workflows are not necessarily equally effective against digital counterfeiting workflows, and vice versa.
The example icons in Figures 3 and 4 are akin to the icon in Figure 2 because they are not connected to other document artwork but differ in two ways. First, consider the plate count. Figure 3 incorporates five plates and Figure 4 includes eight plates. Again, traditional counterfeiting workflows become increasingly complicated as more plate images are added, but digital simulation of the front and back reflected light images in either Figure 3 or Figure 4 still require only one printing step per side. Second, the lines in the artwork of Figures 3 and 4 are fine instead of blocky as in Figure 2 and are connected end-to-end in the icon art. Consider how the fine lines in Figures 3 and 4 might appear if one or more plate images were even slightly out of register in either reflected or transmitted light, and why small registration variations might be more apparent in Figures 3 and 4 than the block shapes in Figure 2.
Figure 3. Five-color simultaneous offset design with three colors on the front and two on the back. As in Figure 2, the icon is not connected to other document artwork. In addition to front/back registration, traditional counterfeiters must register same-side images since each offset color is a separate printing step. Because CMYK can simulate multiple same-side spot colors in good register in one printing step, for this icon front/back registration would be the main alignment problem for digital counterfeiters.
Figure 4. Eight-color simultaneous offset icon with four colors each on the front and back (the brown at the upper left on the front is composed of two different colors). The thin lines and end-to-end placement of colors make this isolated icon intolerant of even small variations in same-side registration that might go unnoticed in less subtle art (compare to Figure 2). As in Figure 3, traditional and digital counterfeiters have different challenges when simulating multicolor/multiplate icons like this one.
Integrating Icons with External Artwork
Figures 2 through 4 were examples of isolated simultaneous offset icons, but icons can also be connected or registered to surrounding offset artwork. An advantage of this strategy is that certain methods of counterfeiter simulation are impeded when the simultaneous offset feature ceases to be a standalone graphic and becomes inseparable from other artwork. Depending on the design, connecting the icon to other offset artwork can force counterfeiters to register not just images within the icon itself, but the entire multiplate offset artwork on one or both sides of the substrate. Figures 5 through 8 illustrate some examples where the simultaneous offset icon is joined to external artwork on one or both sides. In each case, the interior of the icon, the icon border (if it has one) and the exterior artwork might each be viewed as an independent element. Consider not just front-to-back registration requirements within the icon and its border, but also what other plate images must be correctly registered to the icon edges or border but are not directly involved in the icon itself.
Consider the simultaneous offset feature shown in Figure 5. The front features only one plate image that is not connected to other offset artwork, so traditional counterfeiters are not confronted with a same-side registration challenge. However, the back of the icon in Figure 5 contains two plate images: the block shapes inside the fish and the thin horizontal pattern of gray lines that also includes the outline of the fish, such that the fish and surrounding art are not independent. In addition to the front/back registration problem both traditional and digital counterfeiters face, traditional counterfeiters must also register the two back plate images or the fish outline will not align with the fish interior. Because both back plate images are spot colors that can be simulated by CMYK in one printing step, digital counterfeiters do not face this registration problem.
Figure 5. Three-color simultaneous offset icon with one color on the front and two colors on the back. The front of the icon contains only one isolated plate image. On the back, the fish interior is one split fountain plate and the gray fish outline is on the same plate as the gray fine line pattern surrounding and adjacent to the outline. That the fish outline on the back is directly joined to the fine line pattern makes it difficult for counterfeiters to treat the outline and the fine line pattern as separate images.
Of course, icons can also be integrated with external artwork on both sides. In the six-plate icon in Figure 6, consider the interior of the icon, its border, and the external artwork as separate elements of the design. On the front of Figure 6, the interior contains red and blue, the border is blue and the exterior art contains red, blue and green. On the back, the interior is green and orange, the border is green and the external art contains green, orange and blue. In transmitted light only the red and blue plates on the front and the green and orange plates on the back are directly engaged in the icon itself, but the green on the front and the blue on the back must also register to the icon border or they will intrude into the white space at the icon edges. In actuality, this icon engages all six offset plates, not just four. Consider how this icon would appear if one plate were out of register in a traditional counterfeit, how the appearance would be different depending on which plate, or if the entire front and back were out of register in a digital counterfeit. Potential effects include disruption of the uniform width of the white space inside the border in the transmitted light image, doubling of the border outline, or separation of the interior elements of the flower. This has implications for both icon design and user training and suggests that simultaneous offset features can influence and are influenced by all offset artwork, even outside a small icon itself. This concept will be expanded upon significantly in later parts of this series.
Figure 6. Six-color offset design, of which four colors are incorporated in a simultaneous offset icon and its border. The interior and outline of the icon front only contain red and blue, but the green plate outside the blue outline must also register to the blue outline. The interior and outline of the icon back only contain orange and green, but blue plate outside the green outline must also register to the green outline. The icon interior cannot be counterfeited in isolation from surrounding artwork on either side.
Another multiplate example is shown in Figure 7, which incorporates as many as seven plates and at least two split fountains. In examining Figure 7, the interior text, rectangular border, and external artwork can again be regarded as distinct elements. Consider the consequences of counterfeiting this icon by both traditional and digital workflows. Evaluate which plates both within and external to the icon must register to others and where, what the icon would look like if one or more specific plates (or the full front and back) were out of register, why that could make it easier or harder for document users to inspect the icon and how that impacts potential icon design strategies to address traditional and digital counterfeiting attacks.
Figure 7. Seven-color offset design, of which four colors are incorporated in a simultaneous offset icon. On the front, the text is a split fountain between two blue inks with a purple border. On the back, the text is dark blue with a split fountain border from light blue to purple. The text only includes one plate each on the front and back, but the rectangular border must also register front to back and other plates register to the border, making counterfeiting registration challenges bigger than just the icon interior.
Digital Counterfeiting and Registration
The examples presented thus far may seem to suggest that multiplate simultaneous offset features are disadvantaged against digital counterfeiting workflows as compared to traditional counterfeiting workflows, since digital simulations of reflected light art permit any number of same-side spot colors to be simulated by CMYK in one printing step without risk of misregistration. This is an oversimplification, but assume the critique is legitimate and should be addressed. If so, one way to limit this advantage is to incorporate metallic specular reflection, spot colors that are simulated poorly by CMYK, or other special reflected light ink effects, into simultaneous offset features. If the simultaneous offset icon contains one or more ink effects that cannot be simulated by CMYK, counterfeiters must incorporate a different non-CMYK printing process/step capable of applying the special ink and register that process to the CMYK artwork. Essentially, this changes the same-side digital counterfeiting workflow from one step to two steps and forces same-side registration work that is not necessary for CMYK simulation of reflected light icon images that only contain spot colors.
For example, Figure 8 shows a silver metallic ink in a three-plate simultaneous offset design. Metallic specular reflection cannot be simulated by CMYK inkjet. An inkjet counterfeiter attacking the icon in Figure 8 must choose between two options. One option is forgoing the specular reflection, simulating the silver metallic by CMYK (as gray), and accepting a counterfeit of reduced quality with greater risk of detection. The alternative is abandonment of an all-CMYK workflow, addition of a separate analog or digital printing process/step capable of simulating the metallic specular reflection (entailing costs and labor) and accepting the risk of misregistration between the two printing steps. Similar simultaneous offset icon designs could be enhanced by inclusion of multiple metallics, light-blocking iridescents, glossy spot colors or other specialty inks, microprinting, split fountains and so forth. Special inks are mentioned here primarily in the context of registration but are also foundational for design concepts that will be explored in more depth later in this series in the context of color and contrast.
Figure 8. Three-color simultaneous offset icon with two colors on the front and one color on the back. On the front, the interior contains a tan ink and the circle is a metallic silver ink. On the front the icon itself only involves two plates, but the pink lines outside the circle must also be registered to the circle. Mimicking the specular reflection of the metallic ink forces digital counterfeiters to introduce a non-CMYK simulation process, and register that process to the CMYK art.
The examples given in this paper have illustrated three key points related to registration in simultaneous offset features. First, increasing the number of same-side spot color plates in an icon has different functionality in combating traditional and digital counterfeiting workflows. Second, all offset artwork on both sides can register either within an icon or to the edges of an icon, even if the icon art itself does not include all plates. Third, icons that incorporate inks with properties not amenable to simulation by CMYK (for example, metallics) can force digital counterfeiters to use multistep simulation workflows, which introduces registration problems. However, it is also important to consider the value simultaneous offset offers regarding perceptual effects like image appearance, image disappearance, image movement and color or contrast changes. Accordingly, Part 2 of this series will explore how icons support these visual effects, facilitate ergonomic inspection and integrate with other security features.
Disclaimer: This document represents the opinions of its authors and not necessarily the opinions of the U.S. government. The technologies and strategies described may not be available, appropriate or manufacturable for all document issuers. The examples shown do not imply anything about the quality of a document, its designer, its manufacturer, or the issuing authority. For informational purposes only.