Department of Intelligent Media, ISIR, Osaka Univ.


Measurement and analysis of reflectance and scattering property

Hemispherical Confocal Imaging using Turtleback Reflector

We propose a new imaging method called hemispherical con-focal imaging to clearly visualize a particular depth in a 3-D scene. The key optical component is a turtleback reflector which is a specially designed polyhedral mirror. By combining the turtleback reflector with a coaxial pair of a camera and a projector, many virtual cameras and projectors are produced on a hemisphere with uniform density to synthesize a hemispherical aperture. In such an optical device, high-frequency illumination can be focused at a particular depth in the scene to visualize only the depth with descattering. Then, the observed views are factorized into masking, attenuation, and texture terms to enhance visualization when obstacles are present. Experiments using a prototype system show that only the particular depth is effectively illuminated and hazes by scattering and attenuation can be recovered even when obstacles exist.

  1. Y.Mukaigawa, S.Tagawa, J.Kim, R.Raskar, Y.Matsushita, and Y.Yagi, “Hemispherical Confocal Imaging using Turtleback Reflector”, Proc. ACCV2010, pp.331-344, Nov. 2010.[PDF][Presentation]

Analysis of Light Transport in Scattering Media

We propose a new method to analyze light transport in homogeneous scattering media. The incident light undergoes multiple bounces in translucent objects and produces a complex light field. Our method analyzes light transport in two steps. First, single and multiple scattering are separated by projecting high-frequency stripe patterns. Then, multiple scattering is decomposed into each bounce component based on the light transport equation. The light field for each bounce is recursively estimated. Experimental results show that light transport in scattering media can be decomposed and visualized for each bounce..

  1. Y.Mukaigawa, Y.Yagi, R.Raskar, “Analysis of Light Transport in Scattering Media”, In Proc. CVPR2010, June, 2010.

Statistical Analysis of Refection and Scattering Characteristics on Human Skin

The characteristic of human skin depends on the age and gender. In this paper, we statistically analyze skin characteristics based on the large-scale database of about 1000 people in a wide age range to find the differences of skin characteristics in personality. Since skin is translucent, the incident ray on the skin surface is divided into reflection and scattering. That is, some rays reflect on the surface while the other rays scatter into the media. In our method, we first acquire the reflection component and scattering component from facial images. The translucency of skin is analyzed by calculating the proportion of both components. Then, the reflection component is divided into diffuse reflection and specular reflection. We analyze how oily the skin is by calculating the specular strength. Facial images among people of overall ages were taken with a measurement system including three projectors and two cameras. The characteristic of the facial image is calculated and the skin characteristic which depends on age and gender is statistically analyzed.

  1. T. Mashita, Y. Mukaigawa, Y. Yagi, “Measuring and Modeling of Multi-layered Subsurface Scattering for Human Skin”, HCI International 2011, Organized Session, July 2011.

Analysis of Subsurface Scattering based on Dipole Approximation

We present a new method of analyzing subsurface scattering occurring in a translucent object from a single image taken under generic illumination. In our method, diffuse subsurface reflectance in the subsurface scattering model can be linearly solved by quantizing the distances between each pair of surface points. Then, the dipole approximation is fit to the diffuse subsurface reflectance. By applying our method to real images, we confirm that the parameters of subsurface scattering can be computed for different materials.

  1. Y.Mukaigawa, K.Suzuki, Y.Yagi, “Analysis of Subsurface Scattering based on Dipole Approximation”, IPSJ Transactions on Computer Vision and Applications, vol.1, pp.128-138, Sep., 2009.
  2. Y.Mukaigawa, K.Suzuki, Y.Yagi, “Analysis of Subsurface Scattering under Generic Illumination”, In Proc. 12th Sanken International Symposium, Feb., 2009.
  3. Yasuhiro Mukaigawa, Kazuya Suzuki, Yasushi Yagi, “Analysis of Subsurface Scattering under Generic Illumination”, In Proc. of the 19th Int. Conf. on Pattern Recognition, Tampa, Florida USA, Dec., 2008.
  4. Y.Mukaigawa, K.Suzuki, Y.Yagi, “Analysis of Subsurface Scattering under Generic Illumination”, In Proc. MIRU International Workshop on Computer Vision 2008, July, 2008.

Rapid BRDF Measurement using an Ellipsoidal Mirror and a Projector

Measuring BRDF (Bi-directional Reflectance Distribution Function) requires huge amounts of time because a target object must be illuminated from all incident angles and the reflected lights must be measured from all reflected angles. In this paper, we present a high-speed method to measure BRDFs using an ellipsoidal mirror and a projector. Our method makes it possible to change incident angles without a mechanical drive. Moreover, the omnidirectional reflected lights from the object can be measured by one static camera at once. Our prototype requires only fifty minutes to measure anisotropic BRDFs, even if the lighting interval is one degree.

  1. Y.Mukaigawa, K.Sumino, Y.Yagi, “Rapid BRDF Measurement using an Ellipsoidal Mirror and a Projector”, IPSJ Transactions on Computer Vision and Applications, vol.1, pp.21-32, Jan., 2009.
  2. Y.Mukaigawa, K.Sumino, Y.Yagi, “BRDF Measuring System using an Ellipsoidal Mirror and a Projector”, In Proc. 11th Sanken International Symposium, Feb., 2008.
  3. Y.Mukaigawa, K.Sumino, Y.Yagi, “High-Speed Measurement of BRDF using an Ellipsoidal Mirror and a Projector”, In Proc. IEEE International Workshop on Projector-Camera Systems (PROCAMS2007), June, 2007.
  4. Y.Mukaigawa, K.Sumino, Y.Yagi, “Multiplexed Illumination for Measuring BRDF using an Ellipsoidal Mirror and a Projector”, In Proc. 8th Asian Conference on Computer Vision, pp.246–257, Tokyo, Japan, Nov. 18-22, 2007.

Spectral Reflectance Estimation of Outdoor Scene Considering Daylight Changes

Recently, studies on spectral image processing have gained more attention for more precise object modeling and object recognition. We propose a method of spectral reflectance estimation of outdoor scenes considering daylight changes. First, we assume that outdoor illumination is represented as a weighted linear combination of sunlight as direct light and skylight as ambient light, and we learn the relation between them using a pair of sunny and shady points of an object. Next, we extract a pair of sunny and shady points of another object based on the learned relation and estimate illumination and spectral reflectance at each point.