3DHologram

This project implements a 3D holographic projector. The 3D Computer Generated Hologram (CGH) we compute allows per-pixel focal length control. Our code described below computes a CGH from an input intensity image and the corresponding input depth map image.

Results

We only show a finite range of depths for demonstration. Per-pixel focal control is possible by using an input image where each pixel is at a different depth.

Results (simulated and captured) for a multi-depth hologram

The depth range of the hologram is [0.020m, 0.021m].

The video demo.mp4 shows a live video recording of the displayed hologram at varying focusing depths.

We can see that from depth 1 to depth 5, different parts of the face are focused and de-focused. It is apparent that the ears and the face center are at different depths. When the face center is focused, the ears go out of focused, and vice versa.

Results (captured) for a 2-depth hologram

The depth range of the hologram is [0.080m, 0.085m].

We can see that from left to right, the letter E and H get focused and de-focused interchangeably. It is apparent that the two depth planes are reconstructed.

During the experiments, we found a bright DC term in the propagated hologram. Theoretically, we can apply a linear phase ramp to the hologram and thus shift it away from the DC term and use an aperture to crop the DC term out. However, by applying a linear phase ramp, we are also skewing the shape of our 3D hologram volume. Therefore, instead of applying a linear phase ramp, we opted to capture the first order diffraction, which were not impacted as much by the strong DC output of the laser.

Program

Run Simulation

All codes are run in MATLAB.

To replicate my simulation results, cd src and run simulateHologram.m. This is the main file that calls either propagateMultiDepths, propagate2Depths, or propagate2DepthsIter.

The input images to the pipeline are in the data/scenes/ folder. The input used for the multi-depth hologram above is:

where the depth map values is discretized into 13 depth value bins.

The generated outputs are:

• a Computed Generated Hologram (CGH), essentially a phase pattern to be displayed on the SLM. Scaled to the resolution of the SLM. Saved to the data/CGH/ folder.
• simulated reconstructed views of the propagated hologram at different depths. Saved to the data/reconstructions/ folder.

Files

Functions

• simulateHologram.m: main program where physical parameters and input images are defined
• propagate2Depths.m: propagation function for an image of 2 depths, depth z1 for the left half, depth z2 for the right half
• propagate2DepthsIter.m: iterative propagation function for an image of 2 depths; backward + forward count as one iteration of propagation
• propagateMultiDepths.m: propagation function allowing per-pixel focal control; takes as input the file names of the intensity image and depth map image as well as the number of depths numdepths to discretize the depth map to
• genHolo1Depth.m: forward propagation function to generate hologram H
• reconHoloAt1Depth.m: backward propagation function to simulate a reconstructed hologram view
• encodeAmplitude.m: encode a complex-valued hologram into a phase-only hologram using one of the two modes: the double phase method mode dpe and direct amplitude removal mode amprm

Data Files

The data folder has subfolders:

• CGH: computed generated 3D holograms
• experimentalresults: the captured results using our optics setup
• reconstructions: the simulated results
• scenes: input images

Methods

As explained in our Final_Project_Report.pdf: