1. How a Film With Gaps Sends Different Pictures to Each Eye
Hold your hands open in front of your face and look through the gaps between your fingers at a window. The view through the gap looks slightly different when you use only your left eye compared to only your right eye. The screen of the Nintendo 3DS has a thin film like this stuck in front of the liquid crystal display. This film hides the image meant for the right eye from the left eye, and hides the image meant for the left eye from the right eye [1]. On the screen, the images for the left and right eyes are divided into thin vertical strips and arranged alternately.
Because two slightly different pictures reach your two eyes, your brain creates depth, making objects appear to pop out. The screen itself is not actually popping out. This method has been known for over 100 years. It is said that Frederic Eugene Ives announced a stereoscopic image using left and right images arranged in strips and a grid of transparent and opaque lines in 1901, and received a patent for it in 1903 [2].
2. Whether 3D Displays Without Glasses Appeared in Phones and Cameras
According to a report by ITmedia in 2010, Sharp put a parallax barrier naked-eye 3D display into practical use in 2002, installing it in computers and pachinko machines. However, early versions had problems: the screen was dark, the resolution was not high enough, and ghosting (where two images mix together) was likely to occur [3]. Around the same time, the Sharp mobile phone SH251iS featured a 3D-capable screen that combined a standard liquid crystal with a unique switching liquid crystal. Users could switch between 2D and 3D with a button [5].
The 3D liquid crystal announced by Sharp in 2010 also had a structure where turning the film "on" showed 3D, and turning it "off" showed normal 2D [3]. Because the function of the film's "gaps" can be switched with electricity, you can turn off the 3D display when you are not using it, since it can make text hard to read. The Fujifilm digital camera FinePix REAL 3D W1, released in 2009, allowed naked-eye 3D viewing on its 2.8-inch rear liquid crystal screen. It used a method that separately controlled the light entering the left and right eyes [6].
In a review, it was noted that the angle for seeing 3D was much narrower than on a normal liquid crystal, and the image looked most three-dimensional at about 30 cm from the screen [7]. This 30 cm distance was the reviewer's impression, not a specification number. So, what happens if we change the direction of these "gaps" slightly? Next, we try placing seats to the left and right instead of eyes.
3. What Changes When the Film Separates Seats Instead of Eyes
The distance between car seats is much wider than the distance between eyes. If we change the direction in which the film's "gaps" send light, we should be able to send different pictures to the person on the right and the person on the left. Based on this idea, Sharp developed the dual-view liquid crystal. It uses a barrier to split light left and right, producing different images depending on the viewing angle. Uses listed included car navigation (different displays for driver and passenger), TVs, PC monitors, laptops, and digital signage. A triple-view option, splitting into left, right, and center, was also proposed [4].
According to an article by MONOist, in September 2005, the former Fujitsu Ten (now Denso Ten) released a car navigation system called "ECLIPSE DUAL AVN" with a "dual display function" that allowed different images for the driver and passenger. It was also adopted as a standard navigation system in a special edition of the Toyota Alphard [8]. By simply dividing what was split between "right eye and left eye" in naked-eye 3D into "right seat and left seat," the mechanism of the film remained the same. Yet, for the user, it became a completely different tool.
4. Why Splitting the Screen Between Two Seats Halves the Detail
A screen is made of tiny points called pixels. In the dual display function, pixels for the driver and pixels for the passenger are arranged alternately. Therefore, the number of pixels visible from each seat drops to half [8]. For example, if a screen has 1920 pixels horizontally, the number of horizontal pixels visible from each seat is about 960 (this is a hypothetical number for calculation, not an actual product spec). Maps with fine text become hard to read when the screen becomes coarse.
A veteran Sharp engineer recalled that at the time, "the number of pixels was not sufficient." This function did not become established afterward [8]. Of course, from this material, we cannot say that pixel count was the only reason. The situation is the same for 3D: the horizontal pixels reaching one eye are halved. The viewing position is also limited to specific spots [3]. So, why did this feature, with these weaknesses, appear again about 20 years later?
Note: This material presents recollections and results; it does not conclude that low pixel count was the sole cause.
5. What Japan Display Announced in 2024 Using the Same Mechanism
According to MONOist, on August 2, 2024, Japan Display Inc. (JDI) announced an automotive "2-vision display" that shows different images to the driver and passenger from one display and can distinguish touch operations from the left and right. The point of arranging left and right pixels alternately is the same as in 2005 [9].
There are changes, too. JDI says they use a dedicated ASIC (a circuit for specific purposes) to analyze and correct the situation where two images mix (crosstalk), suppressing it. They also reviewed the process of creating the barrier within a single panel to ensure high definition [9]. JDI explains that combining two screens into one has advantages in terms of cost and design [9]. At the time of the announcement, mass production was planned to begin as early as 2025, with support for OLED targeted for 2026–2027 [9]. Whether mass production actually started is not clear from the materials used here.
6. How to Try the Film's Mechanism With the Gaps Between Your Fingers
The gaps between your fingers can help you feel the mechanism of the film with gaps. Look at a wall clock or picture from a little distance. Then, spread your hands in front of your eyes and look through the gaps between your fingers. Close one eye at a time and compare what you see through the gaps. If the visible parts differ, you can feel the concept of "different pictures reaching each eye" in your body. Try moving your head slightly to see how the visible parts change.
For safety, do this in a place where your hands will not hit anything and there are no objects around. The actual film has gaps so fine they are invisible to the naked eye. Since the size is completely different from finger gaps, this is only a simulation to grasp the feeling of the mechanism. If you want to read more, Nintendo's "How 3D Works" [1], Sharp's introduction to dual-view liquid crystals [4], and articles by MONOist [8] [9] are available in Japanese. Comparing how the 2005 feature was described versus how it is described 20 years later can reveal interesting differences.