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I've been given a solid black design that I have to print in a manner which is view-able through 3D red-blue stereoscopic glasses (Old school 50's cinema type)

When I offset the design into Red-only and GreenBlue-only channels, it gives the required effect. However, when I then convert colour space mode in Photoshop to CMYK for printing the colors become massively desaturated, the blue more than the red.

RGB & CMYK stereoscopy

The CMYK version is spot on to how a physical print looks. However, the color is so different it completely kills the effect while wearing glasses. I was expecting to have to do some color space wrangling but I have no idea how I could alleviate this issue as it's not usable. Is it possible to print a cyan as saturated as in the RGB image? Is this a colour space issue or an inking issue?

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    Hi Al, thanks for your question. I took the liberty to try and clarify the title even further. If this mangled your intention beyond recognition, feel free to reverse my edit!
    – Vincent
    Dec 20, 2019 at 9:58
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    There is way more information here than I can digest to give an answer, but there are many types of 3D 'red/blue' glasses, all suitable for different purposes, from screen to paper - en.wikipedia.org/wiki/Anaglyph_3D Maybe you need to investigate using another colour set that can work more easily with standard CMYK printing
    – Tetsujin
    Dec 20, 2019 at 13:43
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    It look like you just applied an horizontal offset to a 2d drawing. This will in no way produce a 3D stereoscopic. For true 3D stereoscopy, you need two different drawings whose 3D→2D projection is offset with a slight angle difference. The closer to the point of view, the larger the horizontal offset so at infinity both drawing are same. The other issue with your drawing is that the 3D is isometric, so there is no possible stereoscopic that can trick our brain to reconstruct a 3D.
    – Léa Gris
    Dec 21, 2019 at 17:47

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Sadly, these very saturated colors can't be reproduced in CMYK.

You could try to make the image in CMYK mode, where you make sure that the red is CMYK(0, 100, 100, 0) and the cyan is CMYK(100, 0, 0, 0). Don't make it in RGB and convert to CMYK as it might pollute the clean inks.

I believe that it's important to only use solid colors (all CMYK values 0% or 100%). Halftone screening might fool the human eye, but I'm not sure if they will fool colored glass. The glass might not be able to filter the resulting color, but only the individual inks.

Even using two inks for the red might be problematic if your artwork has 8-bit transparency as there will be halftone dots of magenta and yellow along the lines which might not be filtered fully by the glasses.

Your best option might be to look into printing your work with two spot colors. You need to get your hands on a physical color book with samples, so you can test which colors will work with the glasses.

The most used system of spot colors is Pantone, but you should ask your print house about what they recommend. There are Pantone colors which are way more vivid than achievable with CMYK, but there is no Pantone cyan quite like RGB cyan. I don't think it's physically possible to achieve that color on paper.

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    This would be more accurate if you said to print with two spot colors, rather than two Pantone colors.
    – barbecue
    Dec 21, 2019 at 23:19
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    @barbecue true. Pantone is just a brand. My point here is that it must be a solid color and it must be a color you have a physical sample of, so you can test it with the glasses.
    – Wolff
    Dec 22, 2019 at 9:37
  • @barbecue I edited my answer to be more clear about spot colors.
    – Wolff
    Dec 22, 2019 at 17:20
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If you MUST use Cyan and you want something around RGB saturation then you need to work with paper. There are some that reacts very well to certain paints and give them extra boost. They are also usually custom ordered so much pricey than regular print.

Which make sense to eaither print with Pantone (as per Wolff answer) or ask your printhouse for a custom mix. So the they mix 100C, 15M, 15Y and use it as one plate. Most printhouses carry their own colorbooks so you can just put on your 3D glasses and see what mix is best filtered out.

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The pictures from your sample are not stereoscopic. You used the exact same picture for the left and right eye.

You can not recreate a stereoscopic view from a single picture.

Both pictures need a different perspective with preferably lines converging at the focus distance.

Engineering drawings like the illustration uses isometric, so every line curve can be measured at scale regardless of distance from observer.

Isometric 3D is intrinsically incompatible with stereoscopic display because of its fixed perspective whose goal is to represent accurate scales rather than projection at an angle.

To see what change from one eye to the other on stereoscopic images:

  1. Place your right hand pointing up and perpendicular to your right eye so that you see only your forefinger's edge and the tip of your middle finger's edge.
  2. Close your left eye, you see only the edge of your fingers.
  3. Open your left eye and close your right eye: You now see your fingers at a different angle.

Repeat with placing your hand centered to your nose. Now each eye see a different side of your hand.

The closer is your hand to your eyes, the more extreme are the differences between the left and right images.

At a distance, the perspective difference are less extreme because the distance between your eyes is much less than the distance from your eyes to the object.

The gears from your illustration with their isometric proportions, is more like a telephoto shoot. A telephoto shoot renders poorly as stereoscopic because at long distance, both images are nearly the same.

When left and right images are the same, then render a single image, because having two, brings nothing to the perception of 3D but the inconvenience of colored glasses to recover that single image.

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    This does not answer the question, and it makes assumptions which are not supported by the original question. The original post never claimed that a single picture was used to produce the examples. Also, the original post states that the stereoscopic effect DOES work with the RGB version, and it's only the conversion to CMYK has problems.
    – barbecue
    Dec 22, 2019 at 18:00
  • @barbecue I actually checked the poster's illustration and verified that indeed the Graph is isometric and offset red and blue are the exact same picture. I answer the poster's explicit intent to produce stereoscopic print-out, witch is is impossible. The RGB->CMYK issue witch received good answers already, becomes secondary with the impossible isometric→stereoscopic upstream.
    – Léa Gris
    Dec 22, 2019 at 18:29
  • You are technically correct that you cannot create an accurate 3D representation from a single image, but that's not relevant for two reasons: 1. the original question never mentions that this is the goal. OP said "I have to print in a manner which is view-able through 3D red-blue stereoscopic glasses" 2. It is definitely possible to produce a pseudo-3D effect which is visible through stereoscopic glasses with a single image. OP said "When I offset the design into Red-only and GreenBlue-only channels, it gives the required effect." That suggests that the effect works as is.
    – barbecue
    Dec 22, 2019 at 21:58
  • @LéaGris Even if this doesn't answer the question, I understand your point. Except because we only require a background, in-between and a foreground layer for these "flat" designs as pictured, we are able to cheat with these simple varied horizontal displacements quite effectively on screen
    – Al Longley
    Dec 24, 2019 at 1:37
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The other answers are right: converting from RGB to CMYK after preparing your artwork is a recipe for dull colours. While CMYK cyan is duller than RGB cyan, it shouldn’t be nearly as dull as what you’ve shown here. You should work directly in CMYK and make sure your art is only on the correct channels.

Having said that, the artwork preparation will depend a lot on the printer and paper you’re using, plus the specific coloured filters in the glasses you’re using. You should do test prints in the colours you’re using to make sure the colours you print are opaque through one filter and effectively invisible in the other.

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You can't print what you want with process CMYK inks, but if you really MUST print with CMYK then you certainly can make an image that works with the glasses.

What you need to to is turn down the brightness in the image until all the colors become printable. This will make your background grey, but through the red lens it will look just like the red ink, and through the blue lens it will look just like the blue ink.

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It is simply the wrong filter. You are using blue red glasses optimized for monitor colors. You should simply use different set of glasses optimized for cyan and magenta works fine you just need a different filtering material that's all.

Can you find a spot color that may work with your glasses. Sure, but its probably cheaper to change the filter to match that of your process print. After all the print shop has the correct pigment, just ask them to print it on a transparent film.

Probably the glasses also work OK if you print in 100% cyan and 100% magenta instead of converting the colors. So why do you need to use cyan and magenta. Simply because these are the only clean colors in a process color print. All other colors include other colors thus ruining your shot.

Note: You can not appraise the results from screen. So you can only appraise the result on a printed medium. Since again the simulated monitor colors aren't pure.

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