How to make a good 3D lenticular print?

How to make a good 3D lenticular print?

I travel a lot and every time when I go to a souvenir store and find some lenticular prints, my brain will automatically kick off an assessment process; good or bad, mediocre or outstanding. Also working for a lenticular printer gives me the chance to see so many projects. When I look at a lenticular print I can usually pinpoint few imperfections that are really bummers. I always told myself that had the designer discussed with me then those letdowns could have been avoided. So let me take this opportunity to say something on how to make a good lenticular print.

Number of stereo pairs

To create a pleasant and smooth 3D viewing experience using lenticular printing, 4 to 6 stereo pairs of an image are ideal. In theory, we need only one “stereo pair” to create binocular disparity and hence a 3D picture. However, in practice, use of only one stereo pair for lenticular printing confines the viewing angle to a very small range; in other words, there will be an abrupt, uncomfortable and unrealistic change of image when the viewing angle is changed. Therefore, the more stereo pairs used to create the 3D image, the higher the binocular resolution, and the better the final result for a smooth 3D viewing experience.
The best way to create natural stereo pairs is to use a motorized camera slider which has a shutter-synchronization feature.

Artwork Resolutions

For the sake of discussion let’s say we have three stereo pairs (or six pictures) under each lenticule. The resolution of the picture will be divided by six. If we start with a 300 dpi picture, then each eye will be seeing the picture at only 50 dpi, or at 100 dpi for both eyes combined. If you have done any printing project, lenticular or plain old printing, you know 100 dpi is not a very high resolution. The lower acceptable limit should be around 200 dpi. So in order to attain 200 visual dpi our original artwork should have 600 dpi. As the number of stereo pair increases, we should expect the source artwork resolution should increase as well. Hence in general

200 x (number of stereo pairs)

is the requirement for the source file. On the other hand we are limited by the hardware printing resolution. For example, the true maximum resolution for most Epson printers is 1440. When this is divided by 200 we can see that using inkjet printers the number of stereo pairs should be 7 or less. Experience tells us that 4 to 6 is the optimum value and the artwork resolutions should be around 800 to 1200 dpi.

Artwork Design

Simplicity is the key. Good 3D artwork has a single focal point which is the life and soul of the 3D print. Simple artwork gives good visual effect and won’t make the viewer feel dizzy or uncomfortable. Artwork that is too complicated confounds the main object and also creates visual noise.

Always choose a main object that is vigorous and has some sort of depth. For example, with a human subject as the focal point, it is better for the person to be posed at a 10-15 degree angle with arms relaxed, casual or in a slight gesture. For non-human objects and scenery, the focused object should be self-interspersed and have distinct layers.

Scene Construction

On top of the main object mentioned above, a good 3D print should have some supporting objects to enhance the 3D effect. The supporting objects can be made as foreground and background. The foreground objects should loosely float out of the picture and should not be too big and too solid to compete for attention with the main object. The foreground should also help create a perspective such that the main object can be seen through the void area of the foreground. Among the foreground, main object, and background there should also be some objects to maintain the continuity to avoid the three layers being too isolated. Color contrast among the layers is also an important criterion for a good 3D print.

Choose the Right Lenticular Spec

There are many types of lenticular specs and some of them are actually designed for flip or any other animatic effects. Such specs will not be suitable for 3D printing. Please be sure to check with your lenticular printer on the lens they are going to use. If you are working on a DIY project then make sure to buy the spec that is designed for 3D printing. Your lens manufacture should give you such information and if they don’t make sure to find that out from their specifications sheet. Using the wrong spec will result in poor 3D effect.

Passion

In essence, a good lenticular print is a piece of art. If a good painting requires inspiration and passion so does a 3D lenticular print. Many lenticular printers see a project just as another chore and fail to advise their clients about the points we have mentioned above. If you have a 3D lenticular project please contact us first whether you intend to hire us or not. I really hate to see a potentially perfect 3D lenticular project ends up tainted with imperfection. To me nothing can be more thrilled than seeing an outstanding 3D artwork finally gets realized.

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Lenticular Pitch Test Using Photoshop

Introduction

If you have been following the tutorials we have published (such as 3D Lenticular Printing Interlacing Algorithm Illustrated Using Photoshop and Converting a 2D picture to a 3D Lenticular Print) you must have encountered a term called “Pitch Test”.

Pitch test is a very important step and one must not skip. Simply put, the need for pitch test is to avoid miss-alignment between the lenticules on the lenticular sheet and the interlaced image that is ready for printing.   In other words we need to ensure a 40LPI (Lenticule Per Inch) lenticular sheet really has exactly 40 lenticules per inch as stated by lenticular sheet maker’s technical specification.  Likewise the technical data published by the maker of the printer you are using must be accurate also.

Environmental factors such as temperature and humidity might also affect the result of a pitch test.

For example, a lenticular sheet with a published specification of 40 LPI may in fact be 40.1 LPI.  The extra 0.1 LPI will be a catastrophe if it is not accounted for.   A printer printing at the published 720 DPI (Dot per Inch) may also deviate from the specification and prints at a slightly higher or lower resolution.  The purpose of pitch test to identify such deviations so that miss-alignment can be avoided.

Many integrated lenticular printing software such as PhotoProjector, Imagiam, PhotoIllustion,and SuperFlip have built-in pitch test function.  But if you have followed our tutorials and prefer to just use the bare bone Photoshop to accomplish a 3d printing project then you will need to create a  pitch test pattern by yourself.  This is the purpose of this article.

The Theory of Lenticular Pitch Test

As usual we are going to review a little bit of  math first. Let us use a 40 LPI lentuclar sheet as an example.  Since there are 40 lenticules per inch, therefore

Width of each lenticule = 1 ÷ 40 = 0.025 inch

Now depends on whether you are going to print your pitch test pattern using Epson (Artisan 50 for example) at 720 DPI or HP/Canon at 600 DPI, the number of pixels to represent 0.025 inch will be different.  In this tutorial we will use Epson 720 DPI printer as an example.  You can easily deduct the numbers if you are using HP or Canon or any other 600 DPI printers.

At 720 DPI, there will be 18 pixels in 0.025 inch because 720 x 0.025 = 18 as shown in the picture below.

width of a lenticule

Width of a lentucule

Our plan is to create a pattern where half of a lenticule will have a black stripe and the other half to have a white stripe as seen in the above picture (width of a lenticule).  So there will be 9 pixels of black stripe and 9 pixels of white stripe in an alternating pattern.  In this pattern a perfect 40 LPI sheet will show a flipping effect where viewers will see either a solid black pattern or a solid white pattern by a side-to-side viewing orientation.

Pitch Test Pattern Around the Ideal Neighborhood

By the same deduction we can conclude that when the LPI  is 40.1, the width of each lenticule will be 1 ÷ 40.1 = 0.02494 inch.  Again at 720 DPI the number of pixels should be 17.955 pixels. Since pixel is the smallest unit we can use, i.e. we cannot create a 0.955 pixel dot, we will need to use this new set of numbers to create a new black and white pattern.

From the numbers we have derived above, i.e. 0.025 inch @ 40 LPI and 0.02494 inch @ 40.1 LPI, we can see that we need to re-size the stripes.  This is where we can use Photoshop’s re-size feature to accomplish this!

Re-sizing from 0.025-in to 0.02494-in is equivalent to reducing the artwork (002494 ÷ 0.024) x 100%, or

1/40.1 ÷ 1/40 = 40 ÷ 40.1 = 0.997506 = 99.7506 %

From Photoshop go to [Image] > [Image Size…] we can bring up the re-size dialog as shown

Resizing using Photoshop

Photoshop Image > Image Size…

Uncheck the [Constrain Proportions] checkbox so the height can be kept at the original, then change the way you want to re-size from [Pixels] to [Percent] as shown below.

For the other LPIs, we can use a spreadsheet to calculate the re-sizing percentage as shown below. The formulae for cell B2, for example, will be = 40 / A2.  You can then copy and paste cell B2 to the other cells and format the column to display in percentage.

Calculate the resizing percentage using a spreadsheet

Calculate the resizing percentage using a spreadsheet

Lenticular Printing Pitch Test Pattern

Lenticular Printing Pitch Test Pattern

Once re-sized, we can copy and paste to a letter size canvas as shown on the left and print it out on your target printer at the desire resolutions, 720 DPI on any Epson inkjet printer for example.

Vertical lines should also be printed along the edges to guide the alignment.

When we put a lenticular sheet over the pitch test pattern, we can determine the optimum setting by choosing the one that shows either solid black or solid white when we look at them with a side-to-side viewing orientation.

As shown in the picture below, the accurate LPI is proven to be 40 LPI. This is the 40 LPI, 8 x 10 inch lenticular sheet with adhesive backing we purchased from Microlens. We have tested lens sold by Microlens to be precise but that does not give us the reason to skip the pitch test.  To be more accurate, we can even create a test pattern up to two decimal points with the same principles.

You can download the completed Photoshop pitch test pattern for 40 LPI from the link below.

40 lpi pitch test ( a 71.1 MB file)

final-pitch-test-pattern

 

Conclusion

We can’t emphasize more on the importance of conducting a pitch test for any lenticular printing project.  Without pitch test your are under the mercy of the published data sheet.  Even if that is the case, your printer may not be printing at the exact resolutions you want.  It is a misnomer that a lenticular sheet has been calibrated at certain LPI because pitch test is for testing the combination of lenticular sheet and printer (and also the type of paper sometimes), and not just the lenticular sheet alone.

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Difference in choosing lenticular lens for 3D and Flip

lenticular lensWhen choosing lenticular lens for lenticular printing one needs to know that there is a big difference between lens used for 3D and flip.  In general lens for 3D should have the thickness 3 to 4 times of the lenticule width, and lens for flip should have the thickness of 1.5 to 2 times of its lenticule width.

Your lens suppliers should offer two specifications for you on each line density.  For example 40 LPI 3D, and 30 LPI flip.  You can just feel the thickness to know which lens is meant for 3D and which lens should be used for flip.  Using the wrong lens can be disappointing, if not a complete disaster.

What if you only have the thin flip lens but you want to create 3D effect?  Yes, that is still possible but you cannot set too deep a depth.  If you set the depth too deep, the result will look more like a flip than 3D.

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The optimum lateral displacement for stereo photography

The optimum lateral displacement for stereo photography

By
Isaac Cheung
Co-founder of vicgi.com

Introduction

When taking the stereo pairs for 3D photography or lenticular printing the normal procedure is to take the first picture to simulate the image to be seen by the left eye, and then move the camera side way to the right to take another picture for the right eye.  The amount of lateral displacement, i.e. how much the camera moves to the right, is an independent variable that one can control.  The final depth in a stereo image will be the function of this displacement.  The more the camera moves to the right, the deeper the depth, and vice versa.  In this paper we try to define the maximum displacement, also called maximum parallax or the maximum stereo base, for a 3D image that is pleasant to be viewed.

Comfort reading distance

reading distance

Figure 1. Most Comfortable Reading Distance

When a person reads, the most comfortable reading distance is about 30cm (11.8″).  At this distance the ciliary muscles of the eyes are at their most relaxed state.  Since the distance between two eyes is about 6.5cm (2.6″), from Figure 2 below we can deduct that the angle of view α will be

α = 2.tan-1(65÷2/300) = 12.37o ≅ 12o

optimum parallax

Figure 2 Optimum Parallax

The Optimum Parallax

Since stereo photography has been around for some time, many empirical formulas have been proposed; the Golden Rules of Stereo Photography, for example. Free software such as StereoBase can also be used to calculate camera shift.

But based on the 12o deduction we had above and our experience, the maximum parallax should not create an angle of view greater than 12o.

When we view a far object the viewing angle will be small and the 3D effect will be less. For example we know that the sun and the moon are spheres but they look like a disc to us instead because the viewing angle is practically zero.  On the other hand, when we view closer objects the viewing angle will be big and the 3D effect will be strong.  But when the viewing distance is less then 30cm we will need to cross our eyes and that will create dizziness when we focus too long.

Based on this fact, the optimum parallax or stereo base should always create a viewing angle between 0o and 12o. When shooting far away objects such as a mountain the stereo base can be as big as few meters.  When shooting close-up objects such as an inset then the stereo base can just be as little as few millimeters.

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How to obtain stereo pairs or sequential pictures for 3D lenticular printing?

We have explained in few occasions that lenticular printing is based on the principle of binocular disparity. Theoretically we only need a stereo pair or two pictures, one for the left eye and one for the right eye, to create the disparity for 3D perception.  But in reality high quality 3D lenticular prints will require more than just two pictures for creating a realistic 3D perception and a smoother 3D viewing experience.  In this article we will present different ways to obtain source pictures for excellent lenticular 3D printing .

  1. By 3D modeling
    Programs such as 3dsMax, Bryce, LightWave 3D, Maya etc can create 3D images by modeling.  Once 3D objects are modeled by these programs, you can use the virtual camera function in these programs to take a series of pictures for these 3D objects as if these images were taken by a real camera which was mounted on a slider.  Sequential pictures taken this way will have the same effect as if pictures are taken from real objects put on a real stage.

    3D modeling

    3D Modeling

    This type of simulation is the most economical way to build a rich 3D objects library for any artwork composition.  For example it will be very difficult and expensive to take a series of  pictures of a live sea turtle swimming in the ocean.

  2. By taking actual pictures
    This is the traditional way of getting stereo pictures.  Series of pictures can be taken by single camera  which is set up to slide along a slider bar or multiple cameras can be mounted along a straight line or a curve. The challenge with single camera setup is that the objects need to be 100% still when the camera  moves along the slider.  For multiple camera setup the cameras’ shutters need  to be synchronized.

    camera on slider bar

    Single camera for stereo photography

  3. By converting single 2D image for 3D lenticular printing
    As an alternative, images required for 3D lenticular printing  can be obtained by layering 2D pictures in Photoshop and move the objects left or right to crate the necessary binocular disparity.  People find this approach more practical because 2D pictures are more accessible.  With this approach the distance between layers can be easily manipulated.  Objects on a specific layer can also be 3D’ed with either depth map or equal-distance slicing.  Photoshop has its depth map functions to enhance the 3D depth in its layers.For example,  a depth map can be created for a 2D tennis ball to have the sphere look.  On a gray scale depth map the lighter color represents points that are closer to the viewer, and dark color represents points farther away from the viewer.

    depth map

    depth map for 3D

    The equal-distance slicing method is similar to the isobars on a weather map.  For example, the yam in the following picture is sliced into pieces and the perimeter of each slice represents the locus of points with equal distance to an imaginary plane parallel to the face of the slice.

    Both depth map and isobar approaches are used in some ad hoc lenticular printing software.  They both provide very intuitive concept to add depth to objects. But in terms of convenience the isobar approach is easier. Creating a workable depth map can be tedious and requires a great deal of experience.

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Relationship between perceived depth and viewing distance for 3D lenticular printing

Wonder if you have the experience that when you look at a 3D lenticular mural the 3D effect will change depending how far you are away from the mural.  When you walk closer to the mural the depth will become more shallow.  On the contrary when you walk away from the mural the depth will become deeper.

The reason is very simple and can be explained by high school geometry.  In our article titled The Relationship between perceived depth and viewing distance for 3D lenticular printing we derived the formulas and concluded that the perceived depth is always proportional to the viewing distance.

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3d printing vs lenticular printing

3d printing and lenticular printing are two terms used mistakenly by the laymen and even professionals for the visual effect of three dimension presented on a flat surface.  But technically they are not the same thing. In a more subtle way, 3d printing refers to additive manufacturing to create a physical prototype from a digital blue print such as AutoCAD file.  3d lenticular printing, on the other hand, is a way to create 3d illusion by utilizing the concept of selective light redirection to create a fake binocular disparity so as to fool the human minds that something is three dimensional.

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On Ghosting Shadows…

The definition of Ghosting on lenticular printing is:

An undesirable result of lenticular printing which happens when more than one image is visible at certain viewing angle. Possible causes are:

  1. Images on the same lenticule (lens) have too much color contrast
  2. Poor registration
  3. Mismatched pitch, or
  4. Too many frames.

Since we received many questions on how to minimize ghosting shadows, we decided to write up an article to explain the causes, the way to detect and minimize ghosting shadows.

If you are interested in reading this write up, please click on following article:

How to Prevent Ghosting in Lenticular Printing

Your questions, suggestions, and comments will be most welcome!

Best and cheers!

-cg-

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The Quantitative Analysis of Stereoscopic Effect

When taking pictures for lenticular printing or making anaglyph images it is very important to grasp the concept of foreground, mid-ground, and background. Properly arrange the scene will give rise to optimal stereoscopic effect or otherwise the viewer will become dizzy to look at the picture. Although there is no universal formula, we do came up with a very good one based on our experience.

For those who are interested in the theoretical aspect of this subject please take a look at our article titled: The Quantitative Analysis of Stereoscopic Effect. If you information is too intimidating or too hard to digest, don’t worry, just skip almost everything and just jump to the last paragraph and take it as it is. Feel free to contact us if that’s still not good enough.  Students may find this article a good subject for a nice term paper too.

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L’impression lenticulaire

Bonjour tout le monde,

Ce message est pour nos clients en France et au Canada. Si vous avez besoin de l’impression lenticulaire, nous pouvons vous garantir que nous sommes la meilleure compagnie avec la meilleure qualité et prix les plus compétitifs. Bien que je peux pas parler très bien le français, je vais essayer de mon mieux pour vous aider. Je suis impatient de vous servir.

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