Red, Green, Blue. Colors of the light spectrum. When you mix them they make white light. They create the page white behind the text you’re reading right now! If you add a drop of water to your screen you’ll see them crystal clear. But, what if you look through RGB to see printed colors, which are in a whole different color mode altogether? We did just that, looking through RBG to “decode” an image in CMYK (Cyan, Magenta, Yellow, and Black, the color mode used for printing). To achieve this required several hours over several days to solve a surprisingly COMPLEX situation we did not anticipate!
ArtBox Singapore asked Paper Truly to create decoder lenses (just the lenses at first) for an activity at their “Eden” event. We’ve worked with red lens decoders before with our Decode the Date suite, which work so great! Our initial thought was, “There’s no way we can supply just lenses without the coded cards and it work without lots of testing to get the colors right for the hidden image to be visible.” We would need to carefully engineer all pieces for the illusion to work at all. We accepted the challenge, one that involved more science than any project we’ve done before.
How Decoder Illusions Work:
There are three elements involved in decoder illusions: A lens, a pattern, and a secret image. They seem basic enough but they are not! The pattern and the lens need to closely match in color, to give the illusion that the pattern “disappears” when you look through the lens, allowing the secret image to be visible. Not only is it important to select just the right color for the lens, pattern, and secret image, but pattern style, detailing for the secret image, layer ordering, and humidity were important considerations for this project as well.
Looking through a green lens swatch to see which CMYK swatch disappears most without being too light or too dark.
Lens Colors:
We figured it best to stay fairly basic for lens colors, not selecting shades that had too much of another color mixed in. We wanted a lens to view only it’s correlating color pattern card. (Red views red, but red can’t view green or blue, so we couldn’t use a greenish blue lens for blue, because it might also reveal the green pattern card). Red and blue were easier to select than green was. Something about how our eyes perceive the wavelength of green made it so tricky! Possibly because green is a secondary color while red and blue are primary. Maybe?
Pattern Color:
To get started of course we selected colors on screen as we would with any other project, and checked the visibility of the image through the pattern and lens colors on screen. Unfortunately this was fairly useless. We had to see those colors printed. Screen colors (RGB) are different than printed colors (CMYK). CMYK colors were initially selected by checking which printed swatches seemed to disappear most through the lens swatch, shown looking through the green lens in the photo above. The pattern can’t be too dark because it wouldn’t disappear enough through the lens. It can’t be too light because it wouldn’t hide the secret image (it would force the secret image to be too light and therefore not visible).
Test, trial, error, take notes.
Pattern Style:
Our first pattern (pictured above in a wavy design) was busy enough to cover the space and allow some white space in between. At first we didn’t realize how important the design of the pattern was. Later we discovered how the white space and the design affected the illusion. We changed the wavy pattern to dots. At first we tried colored dots on a white background, which worked for red and blue but not for green! Then we tried making those dots larger to decrease the white space, which still didn’t work for green. Finally we inverted, using white dots on a solid colored background, reducing the white space dramatically. It turns out that using less white space tricks the naked eye, almost making the color vs white “vibrate”, making it harder to see the secret image through the pattern, which is exactly what we wanted, forcing you to use the lens to see the image.
Layer Ordering:
Once we had the white dots working, we used the solid color fill farthest in the background, next the white dots layer, then the secret image with Multiply applied as the top layer, it worked! Relatively…
Secret Image Color, Stroke & Detailing:
We knew light blue worked with the red pattern since we aced that illusion with our Decode the Date design. But what color under green and blue patterns? We tried several shades and colors, nothing worked great until we considered visually mixing colors between the image and the lens, like using your eyes instead of a paintbrush to mix paint. Red lens / light blue image make a grayish purple which is dark enough to be visible and work quite well. Green lens / orange image did not work because orange contains yellow and so does green – too close in hue to work. We then went as bright and opposite green as possible with magenta (very light magenta). Bingo! Blue lens / red image did not work because we couldn’t use the right shade of red to be visible through the lens but invisible to the naked eye. However, considering visual color mixing, when blue lens and yellow image mix, it creates a darker green which is visible through the lens, but not to the naked eye, since yellow on white paper is hard to see.
Humidity:
As if all the color and light science wasn’t enough for us (it was very exhausting), we also had to consider humidity! When selecting the pattern and image colors, all selections needed a test print and slight adjustment, because how ink lays and dries on the paper is affected by the humidity level in the print shop on any given day. This is a factor we are always aware of when printing, but for this project it was especially important. Once we got all colors noted that worked best with the effect, the entire run (a rather large order) had to be printed in the same sitting with relatively the same level of humidity.
Top row: Colored dots on white background. Bottom row: White dots over solid background.
Great! Light blue under red, light magenta under green, and light yellow under blue. But at first the teacup and paintbrush images weren’t disappearing to the naked eye as much as we’d like. So we considered changing the image itself to make it harder to discern without the lens. What worked about the cupid? It used a slightly heavier stroke (line) thickness, which we applied to the others. Narrower strokes made the image too sharp and too easy to see without the lens, while some wider strokes made the amount of color too much and too easy to see without the lens. The right balance for stroke weight was meticulously adjusted for all 3 images. The cupid outlines also have a more complicated shape which works well, so we added a scallop detail to the tea cup. Angling the cup helped too, so the lines on the lip of the cup and on the plate were not parallel to rows of dots in the pattern, which drew the eye to that location, giving too easy a starting point to see without the lens. The paintbrush image just needed more detail, because that long brush shape stood out too easily. We added a paint palette for more detailing which did the trick!
Check out the final product!
Here’s a look between the white dots/solid background (top) working better than colored dots/white background (bottom) for the green. So interesting!
We should also note something ELSE interesting! In taking the photos above, we discovered that the camera lens (my Nikon DSLR) can see the hidden image without a colored lens better than the naked eye can, what!? We actually had to doctor some of the photos a bit to make it look how it really looks to the naked eye, because the camera lens parsed the hidden image too clearly! This feels like science on top of science here with optical illusions.
We are relieved to have solved this big riddle, which originally seemed like such a simple project! It looks like a simple project to experience the pieces in person, but with optical illusions, looks certainly are deceiving. Exhausting, yes, but knowledge is gained through challenge, and we are really excited to play with more decoder style designs. We hope the guests at the Eden exhibit had fun being deceived by our decoders!