Research Projects

Abstract: Synthetic aperture radar is a well-known technique for improving resolution in radio imaging. Extending these synthetic aperture techniques to the visible light domain is not straightforward as optical receivers cannot measure phase information. In this work, we propose to use macroscopic Fourier ptychography (FP) as a practical means of creating a synthetic aperture for visible imaging to achieve sub-diffraction limited resolution. We demonstrate the first working prototype for macroscopic FP in a reflection imaging geometry that is able to image optically rough objects. In addition, a novel image space denoising regularization is introduced to reduce the effects of speckle and improve perceptual quality of the recovered high resolution image. Our approach is validated experimentally where the resolution of various diffuse objects is improved six fold.

Paper Links:

This work has been appears in the open access journal Science Advances. Please download the official copy of the paper directly from the website (free!).

Citation (APA):

Holloway, J., Wu, Y., Sharma, M. K., Cossairt, O., & Veeraraghavan, A. (2017). SAVI: Synthetic Apertures for Long-Range, Sub-Diffraction Limited Visible Imaging Using Fourier Ptychography. Science Advances, 3(4) doi:10.1126/sciadv.1602564

[+] BibTex Citation

@article{holloway2017SAVI,
author = {Jason Holloway and Yicheng Wu and Manoj Kumar Sharma and Oliver Cossairt and Ashok Veeraraghavan}
journal={Science Advances},
title={SAVI: Synthetic Apertures for Long-Range, Sub-Diffraction Limited Visible Imaging Using Fourier Ptychography},
year={2017},
volume={3},
number={4},
publisher={American Association for the Advancement of Science},
doi={10.1126/sciadv.1602564},
URL={http://advances.sciencemag.org/content/3/4/e1602564},
eprint={http://advances.sciencemag.org/content/3/4/e1602564.full.pdf},
}

Comparison before and after SAVI:

Drag the sliders to see the comparison between a single low-resolution image captured with a normal camera (left) and the high-resolution image recovered using SAVI (right). You may also click anywhere on the image to make the slider jump to that position.

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USAF target

Interactive SAVI sampling demo

To illustrate the effect of speckle and diffraction blur on image resolution a simple demonstration on synthetic data is provided.

Demonstration: Impact of speckle and diffraciton blur on image resolution
The target is a optically rough object that modulates both the magnitude and phase of the incident light. The image on the left is the magnitude of the true high-resolution image. The phase is a sampled from a random uniform distribution in the interval [-π,π]. The background of the center image represents the full extent of the Fourier transform at the aperture plane of the lens and the red circle delineates the extent of the camera aperture. The magnitude of the Fourier transform is shown here. On the right is the observed intensity image for a given camera position; each image is independently scaled to the range [0-255] for display.
To use, click and (slowly) drag the aperture around the Fourier plane. As the aperture translates, the observed intensity image changes.
Disclaimer: The intensity image is not being calculated for each aperture position, instead an image is being loaded based on the center position of the red circle. The displayed image may not change if the displacement of the circle is less than ~10% of the image size.

Image comparison code implemented using the Cocoen script available under an MIT license.