This paper is the third of five parts in a series about optimizing simultaneous offset security features. Simultaneous offset is a security printing technology that produces precise registration of offset artwork on opposite sides of a substrate, creating a transmitted light security feature that counterfeiters are often challenged to simulate because it requires specific security press hardware. Part one of this series discussed mechanical aspects of simultaneous offset, such as multiplate icon design and registration requirements in traditional and digital counterfeiting workflows. Part two described inspection ergonomics, icon placement relative to other transmitted light security features, and the use of artwork to create four discrete visual/perceptual effects: image completion, image disappearance, contrast increase and colour change. Expanding on this prior work, this part three paper explores novel colour strategies for simultaneous offset features.
Part two of this series introduced the examples in Figures 1 and 2, which illustrate simultaneous icon designs that feature an increase in saturation and a colour change, respectively. If both the artwork and ink colours are the same between the front and back images then the simultaneous offset icon shows increased saturation in transmitted light as shown in Figure 1, which is a “contrast increase” icon type as described in part two of this series. If the front and back artwork remain identical but have different ink colours then the icon also changes colour in transmitted light, as shown in Figure 2. For purposes of this paper, Figures 1 and 2 will be regarded as templates from which an expanded range of simultaneous offset strategies can be derived (Figures 3 through 11).
Figure 1. Saturation-changing simultaneous offset design in an issued banknote. Both the artwork and ink colors are the same on the front (left) and back (right). In transmitted light (center) the front and back images are viewed simultaneously, darkening the icon. Saturation is increased in transmitted light, but this design does not produce a color (hue) change. Document users could be trained to look for a doubling of the icon image as evidence of counterfeiting, as that would be the result of misregistration.
Figure 2. Color-changing simultaneous offset design in an issued banknote. The artwork is the same on both sides (except inside the little circle) but the ink colors are different. In reflected light (left and right images) the design includes red and green on the front and red and blue on the back, so in transmitted light (center) the color scheme changes to brown/purple. In user training this could be described as a feature that changes color in transmitted light, in addition to users checking for image doubling.
About The Mockups
The mockups in Figures 3 through 11 depict some colour-changing simultaneous offset icons using simple non-security artwork intended to illustrate concepts. Designers will surely identify creative ways to incorporate colour changes and multiple visual effects (image completion, image disappearance and contrast increase) into simultaneous offset artwork of greater complexity and security. Further, the mockup designs in Figures 3 through 11 are based on cyan, magenta, and yellow (CMY) process colour inks. Process colours are not usually associated with security printing but are used here to make the mockups easy to understand. For actual security applications, similar concepts could be utilized with any desired spot colours.
Additionally, colour and saturation in real print depends on ink layer thickness, pigment content, viewing conditions, substrate characteristics, quality control and other factors, but for simplicity in the mockups these real-world variations are not accounted for here. For example, comparing offset artwork and a good inkjet simulation that look alike in reflected light, do both prints also block transmitted light equally? If not, which offset colours/inks are most easily distinguished from inkjet simulations, and how does that impact selection of the best offset inks and ink colours for simultaneous offset features? How does substrate thickness or composition (in polymer banknotes or multilayer cards, for example) affect simultaneous offset feature visibility? Addressing these questions is a complete research endeavor on its own and it is raised here primarily to stimulate thought and recognize limitations in the mockups.
Finally, to better organize large quantities of graphics, Figures 3 through 11 are split into “A” and “B” components. Part “A” shows the individual front and back colour plates in isolation and part “B” shows the complete multiplate front and back art in reflected and transmitted light. In considering Figures 3 through 11 focus on how the plate artwork and colour placement are coordinated between the front and back to produce specific colour transitions when the view changes from reflected to transmitted light. What visual effect is created when the plate images are registered accurately in a genuine document? How is this visual effect derived from the plate art design and ink colour choices? How could the visual effect be described in security feature training materials? If the simultaneous offset images were out of register in a counterfeit, how would document users know to be suspicious?
Solid Colour Mockups
Beginning with some straightforward examples that do not incorporate split fountains, Figure 3A shows a simultaneous offset icon comprised of two front plate images and two back plate images. The front and back have identical artwork but opposite colour placement. Figure 3B illustrates how the front and back each show cyan and magenta in reflected light, but the transmitted light image appears only blue. For training purposes, this icon could be described as a change from cyan/magenta to blue, or as a change from a multi-colour to monochromatic, or both.
Figure 3A. Mockup simultaneous offset design with four plates and four ink colors, showing no overlap of plate artwork on either the front or the back of the substrate. Individual plate images are shown here. Composite front, back and transmitted light images are shown in Figure 3B.
Figure 3B. Composite images from the individual plates shown in Figure 3A. Both the front and back images contain two colors in reflected light, but the feature becomes monochromatic when the simultaneous offset feature is viewed in transmitted light because the two colors are in opposite placements within identical artwork on the front and back. Consider how deliberate arrangement of colors and artwork on the front and back creates this transition to monochromatic in transmitted light.
Figure 4A is similar to Figure 3A, except that some of the stripes are included in both the cyan and magenta plate art on each side, resulting in same-side image overprinting. Viewed in reflected light in Figure 4B, the front colour scheme appears to be magenta and blue while the back shows cyan, magenta and blue. Transmitted light shows a duotone with darker stripes (three plates: two magenta and one cyan) and a lighter star outline (two plates: one magenta and one cyan). Consider how partitioning of art on individual plates in Figure 4A produces the transmitted light image shown in Figure 4B.
Figure 4A. Mockup simultaneous offset design with four plates and four ink colors. Unlike Figures 3A and 3B, this example shows overlap of plate artwork (in some of the stripes) on the same side of the substrate. Individual plate images are shown here. Composite front, back and transmitted light images are shown in Figure 4B.
Figure 4B. Composite images from the individual plates shown in Figure 4A. This design is different from Figure 3B because it contains some same-side plate art overlap. Artwork from the cyan and magenta plates on either side intersects to create the appearance of blue in reflected light. In transmitted light, just as the front and back artwork in Figure 3B produce a monochromatic effect, this artwork creates a two-color effect with darker stripes and a lighter star design.
Prior work has explored applications of monochromatic security design for disrupting reverse engineering of document artwork1,2,3, and these concepts can be compatible with simultaneous offset. Figure 5A shows two front plates and two back plates containing different images but inked with the same colour. In Figure 5B, the front and back reflected light images each contain two discrete saturations that depend on whether a particular area of the art was printed with one plate or both. In transmitted light, the stripes and circles are designed to collapse to a single saturation while the interior stars become visible, an “image appearance” effect as described in part two of this series. Figure 5B shows only two discrete saturations in transmitted light, but if the reflected light artwork were partitioned differently between the plates up to four saturations could be shown in the transmitted light view.
Figure 5A. Mockup simultaneous offset design with four plates and one ink color, with overlap of some plate artwork on both the front and back. This design is already monochromatic, so where plate images intersect the result is more an increase in saturation than a change in color. Individual plate images are shown here. Composite front, back and transmitted light images are shown in Figure 5B.
Figure 5B. Composite images from the individual plates shown in Figure 5A. Where one ink color is applied from several different plates, overlap of artwork increases saturation instead of changing hue. In this example the transmitted light image shows just two discrete saturations, but a design with more complex art intersections could incorporate up to four discrete saturation levels. This art also shows an “image appearance” effect as the smaller stars become visible from the front only in transmitted light.
While Figures 3A and 4A included four plates and only two colours, Figure 6A contains five plates and adds yellow to complete the CMY subtractive colour gamut. Just as in Figure 3A, the plates in Figure 6A do not show any same-side overlap of artwork, so the front and back reflected light images in Figure 6B only show CMY art. In transmitted light, the stripes appear red due to intersection of magenta and yellow images, the left circle appears green due to intersection of cyan and yellow images, and the right circle appears blue due to intersection of cyan and magenta images. The colour change effect in Figure 6B is essentially a shift from CMY subtractive colour images in reflected light to an RGB (red, green, and blue) design in transmitted light. For user training, this design could be framed in terms of the multiple colour changes, or the appearance of the magenta and yellow stars, or both. Again, this mockup is based on CMY but designers could adapt the model to include whatever spot colours are desired.
Figure 6A. Mockup simultaneous offset design with five plates and three ink colors, with no overlap of plate images on the same side of the substrate (like Figure 3A). This example illustrates how cyan, magenta and yellow subtractive inks can produce the appearance of red, green and blue additive colors in a simultaneous offset feature viewed in transmitted light. Individual plate images are shown here. Composite front, back and transmitted light images are shown in Figure 6B.
Figure 6B. Composite images from the individual plates shown in Figure 6A. In reflected light, the front and back images contain no plate overlap and show only cyan, magenta and yellow art. In transmitted light, intersection of cyan and magenta art produces blue, cyan and yellow makes green, and yellow plus magenta creates red. Like Figure 5B, the small center star “image appearance” effect only becomes visible when the icon is viewed from the front in transmitted light.
Figure 7A shows an extension of the CMY/RGB concept presented in Figures 6A and 6B, with three differences. First, the back artwork includes a cyan plate. Second, in reflected light the back image includes overprinting of cyan and magenta to produce blue stripes, overprinting of cyan and yellow to produce green stripes, and overprinting of magenta and yellow to produce red stars in the reflected light back image shown in Figure 7B. The front reflected light image in Figure 7B contains no overprinted artwork, so it still shows only CMY. Third, every stripe was designed to intersect one cyan plate, one magenta plate, and one yellow plate such that the entire stripe pattern turns black when all three colours combine in transmitted light. For training, this icon could be described in many ways – the stars appear, the circles change from one colour to two, and/or the pattern of stripes turns black.
Figure 7A. Mockup simultaneous offset design with six plates and three ink colors, with no overlap of plate images on the same side of the substrate. This example is like Figures 6A and 6B, except that it incorporates same-side overlap of plate artwork to produce the appearance of additive colors on the back in reflected light, and the appearance of black in transmitted light. Individual plate images are shown here. Composite front, back and transmitted light images are shown in Figure 7B.
Figure 7B. Composite images from the individual plates shown in Figure 7A. Unlike Figure 6B, the back design contains several areas of same-side plate art overlap, so the back appears to contain not only magenta and yellow, but also red, green, and blue. In transmitted light, the intersection of identical artwork in all three subtractive colors – cyan, magenta, and yellow – turns the entire pattern of stripes black, since the stripes on either side incorporate complementary colors for this specific purpose.
Figures 5A and 5B illustrated a monochromatic icon concept where a single ink was applied from four plates to create a design showing multiple saturations. Expanding on this concept to incorporate both multiple saturations and multiple colours, Figure 8A includes four cyan plates and four magenta plates, all with different artwork. In comparing Figure 8A to Figure 8B, examine how the high plate count and overlapping of artwork produces many complex multi-colour effects in both reflected and transmitted light. For training, the stripe colours are complex but could be described as a variation on the multi-colour-to-monochromatic transition presented in Figure 3B. Additionally, consider the appearance of the stars, how the saturation of the circles increases, and how the saturation of the stars and circles are different in transmitted light.
Figure 8A. Mockup simultaneous offset design with just two ink colors spread over eight plates, incorporating substantial same-side overlap of plate artwork on both the front and back. This example shows how many overlapping plate images can create a variety of color and saturation effects, even with (and especially with) a restricted gamut of ink colors. Individual plate images are shown here. Composite front, back and transmitted light images are shown in Figure 8B.
Figure 8B. Composite images from the individual plates shown in Figure 8A. Depending on which ink colors are overlapped on either side in reflected light or between both sides in transmitted light, in some areas the effect is a change of saturation and in other areas a change of color. In this example, it is the large number of plates that allows for the wide gamut of both colors and saturations that can be seen in both the reflected and transmitted light images.
Split Fountain Mockups
Prior work presented applications of split fountain printing in monochromatic security artwork design4,5,6,7,8 and microprinting, and part two of this series illustrated some ways that split fountains (and other offset printing capabilities) are currently integrated with simultaneous offset icons. Figures 9 through 11 present some novel combinations of split fountains and simultaneous offset with a focus on colour effects. As before, these simple mockups are intended only to illustrate concepts. Designers will undoubtedly conceive of more elegant and secure artwork through which to combine these features.
To begin, the three plates in Figure 9A are all split fountains. The two front plates each contain cyan and magenta inks, but in opposite placements at the edges and centers. This can also be seen in the composite reflected light front image shown in Figure 9B, in which the split fountain colours seem to flow in opposite directions simultaneously. The transmitted light view in Figure 9B shows two effects. First, the circles and some of the stripes produce a blue flat tone because of the opposite colour placement between the front and back in those areas. Essentially, this is a change from a split fountain transition to a solid colour. Second, the saturation of the split fountain effect in the top and bottom stripes is enhanced because the direction of the split fountain transition is consistent between the front and back. Training materials could describe these as two different features because the visual effects are totally distinct from one another.
Figure 9A. Mockup simultaneous offset design with three plates and two ink colors incorporated into split fountains, with no overlap of plate artwork between the two front plates. The two front plates incorporate the same ink colors, but in opposite placements within the split fountains. Individual plate images are shown here. Composite front, back and transmitted light images are shown in Figure 9B.
Figure 9B. Composite images from the individual plates shown in Figure 9A. In the top and bottom stripes the color placement within the front and back split fountains is the same, causing the saturation of each color to increase in transmitted light without change to the hue. In contrast, the circles around the stars change from split fountains in reflected light to a flat tone when viewed in transmitted light because the front and back splits show opposing color placements in that artwork.
The mockup shown in Figures 10A and 10B is similar to the previous example but differs in two ways. First, Figure 10A shows four plates instead of three. Second, the back image in Figure 10B shows overlap of split fountains with opposite colour placement, so the back image shows a blue flat tone that can be seen in reflected light. The transmitted light image in Figure 10B contains three different effects: the stars change from a split fountain to a flat tone, the saturation of the split fountains in the circles increases, and the split fountain in the stripes darkens where the front split fountain image combines with the flat tone on the back. Again, these could all be regarded as distinct security features for training purposes.
Figure 10A. Mockup simultaneous offset design with four plates and two ink colors incorporated into split fountains, with some overlap of plate artwork only on the back. Every plate contains the same two ink colors, but in opposite positions within the split fountains on each side. Individual plate images are shown here. Composite front, back and transmitted light images are shown in Figure 10B.
Figure 10B. Composite images from the individual plates shown in Figure 10A. In contrast to Figure 9B that produces a flat tone in transmitted light, overlap of split fountains with opposite color placement creates a flat tone on the back in reflected light. In transmitted light, the split on the front can still be seen but is darkened, the small stars change from split fountains to a flat tone, and the circles around the stars retain their split fountain appearance but with saturation increased.
Figures 11A and 11B show an extension of the concept in Figures 7A and 7B, in which parts of the transmitted light image appear black. In Figure 11A each side contains three plates, and each plate contains two process colours. The artwork has been partitioned across plates and colours in such a way that every colour in the composite front art shown in Figure 11B is mirrored by its complementary colour on the back. Accordingly, all colours are eliminated from the transmitted light image shown in Figure 11B and the design appears entirely black. Such a colour-to-black transition is bold and dramatic and would be both easy to explain in user training materials and straightforward to inspect.
Figure 11A. Mockup simultaneous offset design with six plates and three ink colors incorporated into split fountains, with substantial overlap of plate artwork on both sides. The colors on all six plates have been deliberately placed and paired to produce a monochromatic black image when the simultaneous offset feature is viewed in transmitted light. Individual plate images are shown here. Composite front, back and transmitted light images are shown in Figure 11B.
Figure 11B. Composite images from the individual plates shown in Figure 11A. Just as in Figure 7B, overlap of identical front and back artwork where opposite sides feature complementary colors can produce black when viewed in transmitted light. The appearance of black in transmitted light was done without split fountains in Figure 7B, but this example shows how color placement within split fountains could be arranged to achieve a transmitted light image that appears to be entirely black.
Like many security features, simultaneous offset offers substantial design flexibility that is not often fully utilized in contemporary security documents. The mockups in Figures 3 through 11 have illustrated many simultaneous offset strategies relating to colour and saturation changes, partitioning of art between plates, split fountains and more. If each of these distinct colour and image effects were regarded as a unique security feature and a new opportunity for user training, inventive designers might incorporate several simultaneous offset colour transition effects within a single document or even within a single icon. But novel simultaneous offset concepts are not limited to the colour strategies described in this paper, which do not fully address the gamut limitations of CMYK digital counterfeiting. Next, part four of this series will explore contrast and simultaneous offset, with a new look at monochromatic design and ideas for using specialty inks like metallic, clear and white inks.
Disclaimer: This document represents the opinions of its authors and not necessarily the opinions of the US 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.