Traditionally, making a 3D lenticular print requires taking multiple
pictures of the same scene along a straight line. The pictures are then
interlaced together to create a lenticular print. However, obtaining the
source images this way requires very careful planning ahead of time and
it is not always feasible due to various environmental limitations and
time constraints. Hence, converting a 2D picture into a 3D image easily
has been the interest of the lenticular printing industry for years.
Before Photoshop CS4 Extended, converting a 2D image to a 3D image
required ad hoc software. Since CS4 Extended, 2D to 3D image conversion
became possible within the integrated environment of Photoshop. To the
lenticular printing enthusiast, this is a quantum leap. Nevertheless, it
is still not intuitive enough to the novice. Beginners still need to do
many trial and error runs in order to gain the experience.
In this paper, the author will explain the theory on how to convert a
flat 2D picture into a 3D picture by using only the basic functions of
pre-CS4 Extended Photoshop in a systematic manner. By understanding the
theory behind the conversion you will become confident in creating
successful lenticular prints; whether you are using ad hoc software or
Photoshop CS4 Extended. Users of pre-CS4 Extended and other graphics
editing software such as Gimp or PhotoImpact will also benefit from this
Principle of lenticular printing
Lenticular printing is a technology in which a lenticular sheet is
used to let different images be seen by the left and right eyes so that
the illusion of depth becomes possible on a 2D image. The theory is
simple and it is based on the principle of binocular
disparity. To understand this, one can do a simple
experiment by looking at an object using the left and the right eye
separately. You will find that the relative position of an object seen
from the left and the right eye is slightly different. By emulating this
binocular disparity using a lenticular sheet, one can see an illusive3D
effect come alive.
Principle of 2D to 3D conversion
Figure 1: Spatial
relationship of 3D objects
Figure 1 shows the plane view of three objects in different
locations. Once this view is captured by a 2D camera, all the depth of
field information will be lost and you will notice these three objects
appear to be on the same plane as show in Figure 2.
Figure 2: 2D picture loses depth information
The linchpin of converting a 2D picture to a 3D picture is the
reverse process that converts the image in Figure 2 back to the image in
Figure 3: Binocular shift of objects
In Figure 3, A2, B2,
and C2 are the original positions of
objects A, B, and C
in the 2D picture. In order to create the spatial depth, the left eye
needs to see objects A, B, and C
at position AL, BL,
and CL. Similarly, the right eye should see
them at positions AR, BR,
and CR. When the objects are layered with
Photoshop it is easy to create a left-eye picture and a right-eye
picture as shown in Figure 4.
Figure 4: New positions of objects
The foreground, middle-ground, background, and the focal plane
Conceptually, when choosing a 2D picture for the 3D conversion, the
best picture should have a very obvious foreground, middle-ground, and
background. In Figure 1, one can consider object B to be the foreground,
object A to be the middle-ground, and object C to be the background.
Although this partition might not be obvious in some pictures, it will
be a guideline for choosing a good candidate for the 2D to 3D
conversion. Pictures that deviate too much from this property will
become either too tedious for the time and effort or it is simply
impossible for the conversion.
A focal plane is the plane where there is no parallax, i.e. the left
and the right eyes are seeing the same objects on this plane. One can
actually set the focal plane anywhere along the axis perpendicular to
the picture surface. For example for the three objects in Figure 1 and
Figure 3, if the focal plane is set at the same position as object A,
then object B will seem to pop out of the picture and
object C will seem to be set further into the picture
leaving object A to appear as if it is on the
lenticular print itself.
The Game Plan
You can download the asset files for this exercise from our 2D to 3D Conversion
(34.3 MB) archive.
Figure 5: A 2D picture to be converted
Figure 5 is a picture obtained from Google image by searching the
keyword "US Open." The picture has a very clear foreground (the net),
middle-ground (the tennis player), and the background (everything else).
To enhance the 3D effect a tennis ball is added to the picture as shown
below. The size of the tennis ball is deliberately magnified to
exaggerate the effect that the ball is just right in front of the
viewer's eyes. The position of the ball should be somewhere before the
net and in-line with the player's eye sight.
Figure 6: Adding object to the original 2D picture
For this exercise, let's plan to set the focal plane on the tennis
player, hence the net and the tennis ball will be in the foreground
giving the viewer the "popping out" impression. On the other hand, the
background will recess into the picture.
Now, let's open the picture in Photoshop and set the Resolution to
720 dpi if you intend to use an Epson printer. If you plan to use HP or
Canon printer, set the Resolution to 600 dpi instead. Set the width to
12 inches. We will explain these settings later.
Figure 7 - Setting of image size
How much parallax?
Figure 8 - Schematic for parallax planning
Figure 8 is used to determine the amount of parallax. Please do not
be intimidated by the complexity of the drawing. Once explained, it will
become obvious. We also suggest that you print out this drawing for
reference so you do not have to scroll up and down.
On the drawing point "a" is the original position of the tennis
player and point "b" is the original position of the net and the
background. The net and the background span across the entire picture so
the mid-point of the picture is considered as their positions. Point
"c" is the original position of the tennis ball.
If we are going to use the Micro Lens 40 LPI lenticular sheet, the
specifications suggest the viewing distance to be 3-feet, i.e. 36-in.
The width of the picture is 12-in as we have set.
Since we choose to use the layer of the tennis player as the focal
plane, we can ignore point "a" from now on as it already lies on the
The tennis ball will be moved from point "c" to point "f", 5 inches
in front of the focal plane. Because of this move, the left eye should
see the tennis ball at point "r", and the right eye should see it at
The net will be moved from point "b" to point "e", 2 inches in front
of the focal plane. Again, the left eye should see it at point "o", and
the right eye should see it at point "n".
Similarly, the background will be moved from point "b" to point "d", 4
inches behind the focal plane. To account for this move, the left eye
should see it at point "m", and the right eye should see it at point
The table below summarizes the descriptions above
||New position for left eye
||New position for right eye
Now we need to use our knowledge of geometry and trigonometry to find
out the necessary shifts. Let's work out the details on the tennis
ball. The net and the background are less tedious and can be calculated
by the properties of similar triangles.
Left eye of the tennis ball
The original position of the tennis ball is at point "c". From
Photoshop we know that its x coordinate is 5850.5 pixels from the left,
or 8.126 inch if we divide it by 720 dpi.
Since point "b" is at the center of a 12 inch wide picture therefore
the length of line "bc" should be 8.126 - 6 = 2.126 inch.
Now to find the shift for "cr".
Since ?rfw ~ ?fLt,
||Lt . rw
||(2.126 + 1.25) x 5
||0.545 or 392 pixels
||(36 - 2 3)
Right eye of the tennis ball
Similarly for the right eye we need to find the shift for "cq".
Since ?qfx ~ ?fRt,
||Rt . qx
||(2.126 + 1.25) x 5
||0.141 or 102 pixels
||(36 - 2 3)
The following table summaries all the necessary shifts which include
the shift for the net and also the shift for the background.
||New position for left eye
||New position for right eye
||cg = 102 pixels
||bo = 53 pixels
||bn = -53 pixels
||bm = -90 pixel
||bp = 90 pixels
Using above table as a guide, we can come up with two new pictures;
one for the left eye and one for the right eye as shown below.
Figure 9 - Picture for left eye
Figure 10 - Picture for right eye
If you observe carefully, you will see a slight difference between
the above two pictures.
Test drive the depth
To see how it works out, the simplest way is to make an anaglyph
picture. This can be done relatively easily.
Use Photoshop to open the right picture first then follow by opening
the left picture. Copy and paste the left picture on top of the right
picture. Double click the layer property of the left picture and then
disable the [G] and [B] checkboxes under the [Advanced Blending]
section. Now you can view the result in the following picture (picture
with some red tint) with a pair of red-cyan glasses.
Figure 11 - Setting for creating an anaglyph
Figure 12 - Anaglyph
Interlacing the pictures
We just created an anaglyph by combining a picture that is for the
left eye and a picture that is for the right eye. Now it is time to
slice these pictures to match them up with the lenticular sheet.
Remember we set the resolution of the picture to 720 dpi (or 600 dpi if
you use HP or Cannon printer)? Now let us explain why.
Since an Epson printer can print 720 dots per inch, we want to map
each dot the printer prints to a single pixel on the image file. This is
why we need to set the image resolution to the resolution of the
printer, i.e. 720 for Epson and 600 for HP and Canon.
Another number we need to know is how many dots will be under each
lenticule. We will continue to use the Micro Lens 40 LPI lenticular
sheet as an example. Since 720 divided by 40 equals 18, there will be 18
dots under each lenticule. There are several ways we can arrange these
dots, all with the purpose of alternating the dots from left and right
picture. For example, we can arrange the first 9 dots from the left
(9L), and the next 9 dots from the right (9R). Alternatively we can have
3L3R3L3R3L3R because this pattern can be repeated and the sum of dots
also equals to 18. 2L2R2L2R2L2R2L2R2L won't work because the pattern
cannot be repeated to the next lenticule although the sum is still 18.
Let's use the simpler pattern 9L9R in the following interlacing
To accomplish this, all we need to do is to create a mask for both
pictures. The mask will contain vertical stripes of 9 pixels wide and 9
pixels apart. For the left picture, the mask will start with a white
stripe and for the right picture, the mask will start with a black
stripe. When we paste the mask to the channel of the mask layers, the
image will be interlaced as we intended.
Let's outline the steps below.
Step 1: Create a mask for both the left and the right layer.
Figure 13 - Create a mask for each layer
Step 2: Create a vertical stripe pattern for the left layer and the
right layer with the same image size as the image.
Figure 14 - Pattern used as mask for interlacing
Step 3: From the [Channel] palette, highlight and make it visible for
the mask layer, paste over the vertical stripe pattern, one for the
left and one for the right.
Figure 15 -
Paste mask pattern to the mask layers on the [Channel] palette
Step 4: Flatten the image, print it at 720 dpi on a photo glossy
Figure 16 - Epson 720 setting
Step 5: Put the lenticular lens over the printout and align them to
obtain the clearest picture.
Step 6: Laminate the lenticular sheet to the printout by using
double-sided adhesive sheet.
If the steps above are too detailed for you to follow, then try to
understand the principle behind the 2D to 3D image conversion. By
understanding the principle, you can draw your own diagram, map out the
necessary shift for each object, and experiment with the effect by using
the anaglyph diagram. The steps described above are part of a tutorial
so that you can try them out yourself. The values in your calculation
can be quite different depending on the objects and the complexity of
the picture you are using.
The main point is that we need to create a picture for the left eye
and a slightly different picture for the right eye in order to create
proper depth amongst all the objects in the picture. If this is our
goal, we can use Photoshop to move the objects left and right to achieve
this goal. With this in mind, here is a high level set of steps for any
2D to 3D image conversion project for lenticular printing.
Choose a 2D picture that can be layered easily
Layer the objects in this 2D picture
Identify the foreground, middle-ground, and the background
Decide which object among the layers will be the focal plane.
Create a diagram to represent the objects and their prospective
Use your knowledge of geometry and trigonometry to find out the
necessary shift for each object
Make a picture for the left eye by adding necessary positional
shift for each object
Repeat step 7 for the right eye. Interlace the pictures for the left eye and the right eye by using
vertical stripes pattern.
The width of the stripe is the function of the
printer resolution and the line density of the lenticular sheet to be
use. Print and laminate.