Building a parallax barrier light field display is pretty straightforward, and in this section we will show you how to make a portable one using the iPhone/iPod touch.
What you will need:
- An iPhone4(s) or iPod touch 4th generation with Retina display (326PPI).
Since we will cover a plastic on top of the touch screen, you will need to jailbreak the cellphone to enable remote desktop or Bluetooth mouse to control it.
Otherwise, your fingerprints *might* ruin the printed mask, it is up to you!
- Printed pinhole mask. Source file available here “pinhole_mask_x9”. It is a 5050PPI image file with and open it with Windows Image Viewer might cause it to freeze.
You can print it at www.pageworks.com for $90, and it will have 9 masks on a letter size transparency.
- Transparent acrylic sheet as spacer (optional) and screen protector. You probably want to cut it to the same size as the iPhone/iPod touch screen.
- Double side tapes.
We will use the magnification trick that aligns the pinhole mask to the display panel.
- Display the image file ”pinhole pattern” on your iPhone/iPod touch, as shown below.
- Use the spacer and the screen protector to sandwich the mask, as shown below, and place it on top of the screen. (don’t glue it now, you will need some time to practice!)
- Keep your head fixed; gently rotate the mask until the grid pattern is maximized. This can take a while, so be patient.
If your mask is placed like the above configuration, gently rotate clockwise, until the dots are maximized; depending on your distance to the display, you might see 1 or more dots.
otherwise, rotate counterclockwise. Note that the rotation is extremely sensitive as you are close the optimum.
- Once you are comfortable with the setup, you can start to put everything together like the figure below. Optionally, you can also put a transparent diffuser in between the display and mask, this will remove color artifacts, as you will see in the animation at the bottom of this page. For the mask, you can either use tapes or glues(but be careful, it can sometime ruin your pinhole mask!) We use two double-side tape to fix the mask onto the display.
We choose iPhone/iPod touch because it is widely available with high pixel density; more importantly, it has a near integer pixel size. The panel has density of 326 pixel per inch (PPI), the size of each pixel is 77.9 micron (10^-6 m), about 78 micron.
Since the printing machine has maximum resolution of 5050PPI, each printer pixel has size 5 micron; ultimately we want the multiples of the display pixels size to be divisible by the printer pixel size, and the closest number is 5-to-1 trade-off, leading to a 390 micron megapixel.
For the pinhole mask, the criterion is to avoid diffraction, so we choose 75micro as pinhole width; the illustration of the mask is shown below:
Field of View
The design factor for the light field display is the field of view (FOV), which can be determined by the depth of the spacer. The FOV can be approximately calculated by the arc-tangent (width / height), as shown in the above figure.
Note the conversion between the micron and millimeter for the depth “d”. Higher number of depth will cause the FOV to be narrow.
In practice, for a typical usage case, the glass screen on top of the iphone4/ipod touch display should be just good enough, you won’t need additional spacer.
Completion and Testing
Once you finish the alignment and glue the sandwiched mask to the device (using double side tapes around the edge is enough), you can test your light field display with the image file “1-to-5-image“. This give you a horizontal parallax.
And Finally, here are some pre-generated light field image suitable for this particular display that I have tested:
PhD Student, UC Berkeley