Display Color Filter Array
In digital image display devices, data are typically presented via a spatial subsampling procedure implemented as a color filter array, a physical construction whereby each light emitting element controls the intensity level of only a single color. In this work, we examine the problem of color filter array design with respect to spatial resolution and human vision; in doing so we quantify the fundamental limitations of existing designs by explicitly considering the spectral wavelength rep...Read more
Optimal Color Filter Array
In digital imaging applications, data are typically obtained via a spatial subsampling procedure implemented as a color filter array—a physical construction whereby only a single color value is measured at each pixel location. We consider here the problem of color filter array design and its implications for spatial reconstruction quality. We pose this problem formally as one of simultaneously maximizing the spectral radii of luminance and chrominance channels subject to perfect reconst...Read more
Image Quality Assessment
We developed a foundation for assessing visual quality with “corrupted reference” (CR-QA)—a new quality assessment (QA) paradigm for reasoning about human vision and image restoration problems jointly. In most image restoration problems, the notion of an ideal reference that exist only in theory and not in practice. CR-QA assesses the visual quality of a restored image signal relative to this ideal reference image (not provided) with the help of observed image (i.e. corrupted refere...Read more
Noise Parameter Estimation
Noise is present in all images captured by image sensors. Due to photon emission and photoelectric effects that are the foundations of the ways in which quantum mechanics enable image sensors, in fact, random noise is a “necessary evil” of image sensors that will continue to require our attention. The goal of this work is to provide a comprehensive characterization of random noise in ways that enhance post-image-capture signal processing steps. We derive the Poisson approximation to model...Read more
Optimal Exposure Bracketing
A common technique used to acquire high dynamic range image data is that of exposure bracketing—short exposure times are required to capture bright regions of the image without saturation, whereas long exposure times are needed to capture darker image regions effectively. This work investigates how to take into account the statistics of the photon arrival process to derive optimal exposure control for maximizing signal recoverability in high dynamic range imaging. Source Code [code] ...Read more
This work describes a series of new results outlining equivalences between certain “rewirings” of filterbank system block diagrams, and the corresponding actions of convolution, modulation, and downsampling operators. This gives rise to a general framework of reverse-order and convolution subband structures in filterbank transforms, which we show to be well suited to the analysis of filterbank coefficients arising from subsampled or multiplexed signals. These results thus provide a means ...Read more
3D Display Crosstalk
In this work, we analyze the reproduction of light fields on multiview 3D displays. A three-way interaction between the input light field signal (which is often aliased), the joint spatioangular sampling grids of multiview 3D displays, and the interview light leakage in modern multiview 3D displays is characterized in the joint spatioangular frequency domain. Reconstruction of light fields by all physical 3D displays is prone to light leakage, which reduces sharpness of the images shown i...Read more
Single Shot HDR
A combination of photographic filter placed over the lens and the color filter array on image sensor induces differences in red, green, and blue channel sensitivities. Spectrally selective single-shot HDR (S4HDR) imaging treats this as an exposure bracketing. Optimally exposed regions of low dynamic range red/green/blue color components are merged in a principled manner to yield a single HDR color image. Though not expected to yield results superior to the traditional time multiplexing co...Read more
Denoising + Demosaicking
We propose new approaches to demosaicing of spatially sampled image data observed through a color filter array, in which the correlation of color components are exploited in order to reconstruct a subsampled image. Two frameworks for applying existing image denoising algorithms to color filter array data are developed---one for wavelet domain processing, and the other for pixel domain processing. Source Code [wavelet code][pixel code] Publications K. Hirakawa, X.-L. Meng, P.J. Wolfe...Read more
Object Motion From Blur
There are three types of blur in images: defocus, camera shake, and object motion. While defocus and camera shake have received considerable attention, object motion is by far the most difficult feature to detect due to its nonstationarity. Object motion blur, however, is potentially useful for scene analysis because it provides temporal cues from a single image. We developed a technique to infer object motion by detecting spatially varying motion blur from a single image. We are able to...Read more
Multispectral Sensor Design
Color filter arrays (CFA) have enjoyed immense popularity in single sensor imaging, including consumer, professional and scientific imaging. Owing in part to the technical breakthroughs that led to exceedingly high sensor resolution and high quality CFA interpolation algorithms, color image sensors now deliver high quality images. In this work, we investigate the plausibility of extending CFA sampling to enable multispectral imaging capabilities. In contrast to the prior work in this area tha...Read more
The color of a scene recorded by a trichromatic sensor varies with the spectral distribution of the illuminant. For recognition and many other applications, we seek a color representation that is unaffected by illumination changes. Achieving such color constancy is an ill-posed problem because both the spectral distribution of the illuminant and the scene reflectance are unknown. Most methods have approached this problem by leveraging the statistics of individual pixel measurements, indep...Read more
We introduce a new universal demosaicking method that can recover a full color image from an arbitrary array patterns. We recast the data-dependence of Bayer demosaicking as a parsimonious reconstruction of the underlying image signal that is inherently sparse in some representation. Using properties of filterbanks, we generalize this principle to yield a nonlinear recovery method that is consistent with the state-of-the-art Bayer demosaicking methods.Read more
Binning Artifact Removal
Pixel binning refers to the concept of combining the electrical charges of neighboring pixels together to form a superpixel. The main benefit of this technique is that the combined charges would overcome the read noise at the sacrifice of spatial resolution. Binning in color image sensors results in superpixel Bayer pattern data, and subsequent demosaicking yields the final, lower resolution, less noisy image. It is common knowledge among the practitioners and camera manufacturers, howe...Read more
ISSL awarded second NSF grant from CCF on integrating imaging detectors.
ISSL welcomes two new members, Christina Karam and Jiachao Zhang.
PI Hirakawa elected to IEEE IVMSP Technical Committee. (2014-2016 term)
ISSL awarded NSF grant from ECCS on multispectral sensor design.
PI Hirakawa is a summer faculty fellow at the Wright Patterson Air Force Base.