Direction Of Light Source Research Articles

Shading with Curve Light Sources1

AbstractA new shading model for curve light sources is presented. It accounts for both diffuse reflection and specular reflection of the illuminated surface. By regarding a linear light source as a directional quadrilateral light source with very small width, a simple formula is derived first for calculating the diffuse reflection component due to the illumination of the linear segment. The diffuse reflection of the surface by direct illumination of a curve light source is then evaluated by approximating the curve light with a series of linear segments. The specular reflection component due to a curve light source is represented by an integration taking Phong's specular model as the kernel and evaluated by summing the contributions from the linear segments. Finally, an efficient shadow detection algorithm for curve light sources is proposed. The images rendered with the shading model are very photo‐realistic.

Tracking Level Sets by Level Sets: A Method for Solving the Shape from Shading Problem

A new algorithm for recovering depth to a Lambertian L 1 smooth object given its gray-level image under uniform illumination from the viewing direction is presented. To recover depth, an almost arbitrarily initialized surface is numerically propagated on a rectangular grid, so that a level set of this surface tracks the height contours of the depth function. The image shading controls the propagation of the surface. When the light direction is tilted with respect to the viewing direction the problem is solved by tracking the projection of equal-height contours defined with respect to the light source direction. This projection approach provides a solution that overcomes ambiguity problems encountered in previous work, while the level set approach of implementing the contour propagation overcomes numerical problems and some of the topology problems of the evolving contours.

Miniaturized Light Source Direction Sensitive Device: DSD

Title: Miniaturized Light Source Direction Sensitive Device: DSD | Keywords: Direction sensitive device (DSD), Target direction detection, Compound eye lens, PSD array, Micro optics | Author: Masanori Idesawa

Photometric stereo under a light source with arbitrary motion

A new photometric-stereo method for estimating the surface normal and the surface reflectance of objects without a priori knowledge of the light-source direction or the light-source intensity is proposed. First, I construct a p × f image data matrix I from p pixel image intensity data through f frames by moving a light source arbitrarily. Under the Lambertian assumption the image data matrix I can be written as the product of two matrices S and L, with S representing the surface normal and the surface reflectance and L representing the light-source direction and the light-source intensity. Using this formulation, I show that the image data matrix I is of rank 3. On the basis of this observation, I use a singular-value decomposition technique and useful constraints to factorize the image data matrix. This method can also be used to treat cast shadows and self-shadows without assumptions. The effectiveness of this method is demonstrated through performance analysis, laboratory experiment, and out-of-laboratory experiment.

Local shape approximation from shading

Shading can be used as an independent cue for exact shape recovery, or it can be used as a supplementary cue for shape interpolation between features whose depths are known from other cues. Exact shape cannot be inferred from a local analysis of shading. However, for shape interpolation a crude local approximation may be sufficient. This paper explores the limits of such local approximations that are easy to compute. In particular, the shape of shading is used to approximate the surface in areas of monotonic change of intensity. This analysis is accompanied by a method for computing the direction of a single-point light source from the shading on occluding contours. A qualitative classification of shape near shading singularities is also discussed.

Multicolour lasers

Traditionally, when one thinks of a laser, one thinks of a powerful, coherent and highly directional light source radiating at a well defined wavelength. This last property, the highly monochromatic nature of laser radiation, results from the presence of discrete energy levels within the atoms or molecules in the laser media, which give rise to transitions with specific frequencies. For some applications, such as cutting or heating, the exact colour of the laser is not important. However, for other applications such as spectroscopy and certain medical uses, a range of laser wavelengths is essential. Some laser media, such as organic dyes and titanium-doped sapphire, afford a degree of tunability due to their broadened energy bands. However, even for the titanium:sapphire laser, tuning is limited to ±20% of the laser frequency (between 700 and 1100 nm).

Object and head orientation effects on symmetry perception defined by shape from shading.

A grey disc which exhibits a vertical gradient of shading usually appears convex if lighter above and concave if lighter below. This phenomenon was investigated by Howard et al (1990) who varied both the shading axis relative to gravity and the orientation of the head. Their results indicated that head-centric or retinocentric coordinates determined the depth effect rather than gravitational axes. However, several possible problems with their study were noted, not the least of which was the possible intrusion of response rather than perceptual factors in the task they used. Here, we attempted to use an indirect measure of the perception of depth from shading; rather than asking subjects whether discs looked convex or concave, we constructed ensembles of shaded discs which, in terms of depth from shading, were or were not bilaterally symmetrical about an horizontal axis. These stimulus displays were briefly flashed to prohibit the intrusion of conscious assumptions about direction of light sources. Subjects were never asked whether any discs looked concave or convex, merely whether the set of discs was or was not depth symmetrical. Results were generally consistent with those of Howard et al and supported the conclusion that depth from shading is largely a low-level and automatic mechanism.

Circatidal variability in the behavioural responses of a sandbeach isopod Eurydice pulchra (Leach) to orientational cues

Spontaneous, phasic changes in the behavioural responses of freshly collected Eurydice pulchra (Leach) (Isopoda;Crustacea) to light and water flow were studied in the laboratory and related to what is known of the behaviour of this isopod when free swimming. During the expected flood tide period, isopods in laboratory experiments generally expressed positive phototaxis, high photokinesis and negative rheotaxis. On the shore at that time they usually move upshore in the surface waters of the surf zone. In the laboratory, a spontaneous change in rheotaxis behaviour was recorded at the time of the expected high tide and the isopods tended to stem water currents, presumably associated with the avoidance of stranding on the shore. During the expected ebb tide period, isopods studied in the laboratory showed negative phototaxis, low photokinesis and a resumption of negative rheotaxis, when on the shore they migrate down in the water column and so downshore in the undertow. When held with sand in a test tank, E. pulchra burrowed before expected low tide, away from a directional light source. If, however, the isopods were not able to reburrow due to the absence of sand in laboratory experiments, a return to photopositive swimming was recorded during the expected ebb, behaviour which on the shore would return the individuals to the water's edge. Rhythmic responsiveness of E. pulchra to directional cues appears to fine-tune the tidal swimming pattern of this isopod, inducing temporal changes in behaviour which control both vertical and horizontal distribution on the shore.

Image synthesis based on the recognition of 3‐D polyhedras

Abstract A methodology of synthesizing images from the point of view of considering the object's recognizability is developed. The viewing parameters determining the synthesized image are decided based on the recognizability of the object. An object is identified through the determination of its position and orientation. In this paper, it is shown that we cannot distinguish topographically similar objects from a single perspective. Thus, the threshold i, determined by a scheme developed here for model i, is used to check whether a candidate model is accepted. The procedures of synthesizing an image also consist of determining the lighting conditions. The direction of light source is so chosen that |i‘•n k1 – i‘ • nk2 | ≥ (1/K), where i’ is the opposite direction of light source, nk 1 and nk 2 are the normals of two visible neighboring surfaces, and K is the number of edges between the visible surfaces of an object. After the direction of the light source is obtained, the intensity of the light source is determined such that the differences between two visible neighboring planes should be greater than a threshold. Finally, all the concepts presented are illustrated through several examples given in this paper. The result may be applied to the icon representation of an object which represents an execution process or a filename in a pictorial information system.

Host tracking and photosensitivity in Chaetogaster limnaei limnaei (Oligochaeta)

Chaetogaster limnaei limnaei were separated from host snails (Physa skinneri) for increasing periods of time. The oligochaetes responded to a snail's slime trail by increased activity and distance moved along the slime trail. These responses increased with increasing periods of separation from the snail. When exposed to a directional light source, C. l. limnaei displayed an initial positive phototactic response. Movement towards light from the same direction decreased significantly in a second 4-h period, but movement towards light from a different direction was equivalent to the initial response, suggesting the response was an initial one to a change in light.

Shape description via shading images

As we perceive a world of three-dimensional objects, one of the most important property is that a smooth opaque object will give rise to a shade image. The shading can provide information for describing or recovering the shape of an object. A process performing this purpose is known as shape description from shading images. In this paper we propose a method called extended photometric stereo using four light sources to solve the shading problem. When the least square estimation method is employed, the shading problem happens if the reflectance map is not known exactly (except for the direction of light sources), and how the object reflects the light falling on it. In dealing with this process we have met the ill-posed problem that there are not sufficient data to describe the shape of the object. Therefore, we develop iterative algorithms in accordance with the concepts of the regularization method and incorporation of the physical constraints to overcome the ill-posed problem. These algorithms can converge very soon and avoid the clumsiness of initial value assignment, and they are robust against noise. Our approach has been applied to both ideal and noisy computer-synthesized images to confirm its correctness and feasibility, and its performance has also been studied with a set of real images.

Non-predatory ingestive behaviors of the praying mantids Tenodera aridifolia sinensis (Sauss.) and Sphodromantis lineola (Burr.).

Praying mantids are thought to be so strictly predacious that, historically, carnivorousness has been used as a defining characteristics of the taxon Mantodea, and no data exist on other ingestive behaviors. We observed food- and water-deprived male and female Tenodera aridifolia sinensis (Sauss.) and Sphodromantis lineola (Burr.) in various situations and found that their ingestive behaviors are more variable than generally recognized. Both species regularly drink water in response to deprivation, the amount imbibed being correlated with the total (but not daily) percent of initial body weight lost. When presented with stimuli consisting of plastic beads of different reflective quality (shiny clear, opaque frosted, or matte black), lighted by a single direct light source, the shiny stimuli consistently elicited the most drinking-like behavior by the mantids. The preference was consistent, whether stimuli were presented together or singly. This suggests that visual cues can be used to identify water and are alone capable of maintaining drinking-like behavior. When S. lineola were presented with various stimuli, including diced apple and diced banana, in a five-way or a three-way choice test, mantids that chose a stimulus within the allotted time consistently ate the diced banana. When presented one of two stimuli differing only in odor (30 x 20 x 15 mm cloth bags filled with either plastic beads or banana), S. lineola did not attempt to eat the former, but 50% attempted to eat the bag of banana. Eating bouts were always preceded by antennae drumming in the direction of, or over the stimulus.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of neuronal pathways mediating phototactic modulation of head-waving in Aplysia californica

The marine mollusc Aplysia californica exhibits a complex, rhythmic motor response, head-waving, in a variety of naturally occurring behavioral contexts. A cellular analysis of this behavior would be greatly facilitated by achieving stimulus control over the response. We have found that such stimulus control can be readily achieved by exposing a head-waving animal to a directional light source, which rapidly elicits a positive phototactic response: the animal either swings its head to face the light or biases its head waving toward the light source. Moreover, we have found that the neural pathways from the principal photoreceptive organs of Aplysia, the eyes and rhinophores, must be intact for the normal execution of this phototactic response: animals with chronic transection of the optic and rhinophore nerves show no phototactic behavior, whereas sham-operated animals continue to exhibit normal phototaxis.

Determining reflectance properties of an object using range and brightness images

The authors discuss a method of recovering reflectance properties of a surface from a range image given by a range finder and a brightness image given by a standard TV camera. The Torrance-Sparrow model is used for the reflectance model. The model consists of the Lambertian and specular components: its reflectance properties consist of the relative strength between the Lambertian and specular components and specular sharpness as well as light source direction. An iterative least square fitting method is used to obtain these parameters based on the range and brightness images. An input image is segmented into four different parts using the parameters: Lambertian reflection, specular reflection, interreflection, and shadow part. The authors also reconstruct ideal images that consist of only Lambertian or specular reflection. >

Photometric stereo under illumination from unknown zenith angles

AbstractAs a photometric stereo method, this paper proposes a new algorithm for reconstructing a surface shape under the condition that the information of zenith angles of three light source directions is unknown.The object has a uniform Lambertian surface which has whole gradients. An illuminating equation consisting of the parameters of light source directions is derived from the information of three shading images. The simultaneous equations can be held at multiple surface elements and be solved by the method of least squares. This method makes it possible to extract the information of zenith angles of three lighting directions and optimized surface gradient distribution of the object.When the method of least squares is applied, a method to set the initial values for three zenith angles of lighting directions is described, and a method to select surface elements which construct the objective function is proposed. The effectiveness and the validity are confirmed by computer experiments.While the conventional photometric stereo treats the information of zenith angles and azimuth angles of three lighting directions as known constants, this algorithm can make it possible to reconstruct the surface shape from the information of only the azimuth angles of lighting directions.

Learning a near-optimal estimator for surface shape from shading

The problem of determining surface shape from shading is formulated in terms of Bayesian estimation. The goal is to select an estimate of surface shape that best fits some criterion on the posterior probability of the surface conditional on the image data. This conditional probability is a function of the imaging function and the prior probability of the surface. A gradient descent technique is used to compute the best linear estimator of the mean of the conditional distribution from a set of random fractal surfaces and their images. Simulations show that the derived estimator works well for a wide range of surfaces, including non-fractals. Once learned, the estimator could be used to implement a fast, non-iterative parallel device for estimating shape from shading with arbitrary light source directions. The estimator has similar perceptual deficits to human observers. In particular, it exhibits a loss of coarse-scale surface shape, while accurately reconstructing fine-scale details.

Recovering three-dimensional shape from a single image of curved objects

An algorithm to recover three-dimensional shape, i.e., surface orientation and relative depth from a single segmented image is presented. It is assumed that the scene is composed of opaque regular solid objects bounded by piecewise smooth surfaces with no markings or textures. It is also assumed that the reflectance map R(n) is known. For the canonical case of Lambertian surfaces illuminated by a point light source, this implies knowing the light-source direction. A variational formulation of line drawing and shading constraints in a common framework is developed. The global constraints are partitioned into constraint sets corresponding to the faces, edges and vertices in the scene. For a face, the constraints are given by Horn's image irradiance equation. A variational formulation of the constraints at an edge both from the known direction of the image curve corresponding to the edge and shading is developed. At a vertex, the constraints are modeled by a system of nonlinear equations. An algorithm is presented to solve this system of constraints.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Extended photometric stereo for an object with unknown reflectance property

AbstractConventional Photometric Stereo can obtain the surface gradients of an object when its reflectance property is known. This paper proposes a new method of accurately obtaining the surface gradients with three light source directions under the assumption that the reflectance property of the surface is unknown. Assuming that the reflectance property is uniform over the entire surface, surface gradients can be obtained by the following two steps: (1) reflectance property parameters and the gradients of the suitable surface elements that characterize the reflectance property by solving the nonlinear simultaneous equations for them, so that a pseudo‐reflectance map is obtained; and (2) the gradient of each surface element is determined by using parameters obtained by (1). The reliability for the values of the reflectance property parameters (i. e., those for the pseudo‐reflectance map) can be improved by applying the method of selecting the surface elements that are sensitive to the reflectance property; this is called the characterized surface elements selection method. In computer experiment with 8‐bits shading resolution using three parallel light sources, the values of the reflectance property parameters can be obtained in optimum, and the accurate surface gradients for a glossy object can be determined.A mean square error in a depth measurement becomes an order of 10−2, confirming the usefulness of the proposed method.

Photoreceptor evoked potentials and phototactic behaviour in Cercaria caribbea LXXI cable

1. 1. Transient potential changes evoked in response to light stimuli, and presumably arising from rhabdomeric eye-spots in the cercarial body, were recorded for the first time, to our knowledge, in helminth parasites. 2. 2. Pigmented Cercaria caribbea LXXI gave a very slowly adapting response to maintained light stimulus, while a non-pigmented variety appeared to emit a stronger, rapidly adapting response to light onset. 3. 3. Swimming towards a directional light source is disrupted by several neuropharmacological agents, which presumably disturb synaptic transmission in the nerve/muscle system. 4. 4. The light evoked potentials were unaffected by these same agents and therefore, appeared to be directly recorded receptor potentials.

Behavioral responses of a sand-beach amphipod to light and pressure

Light-oriented responses of the sand-beach amphipod Synchelidium micropleon (Barnard) in an optical arrangement that simulated the natural underwater angular light distribution were compared with previous measurements upon stimulation with a highly directional light source. Since positive and negative phototaxis occurred in both situations, phototaxis is not a laboratory artifact and will occur in nature. During rising tide amphipods move up the beach at the leading edge of the wave uprush zone. Maintenance of this position during the day results from an interaction of behavioral responses to light and hydrostatic pressure. The sequence of events is that a wave passing over the buried amphipods causes an increase in pressure, which evokes a negative geotaxis, and the animals exit from the sand. The increase in light intensity upon leaving the sand evokes an initial ascent into the wave due to positive phototaxis. This response reverses to negative within a few seconds, and the animals reenter the sand before they are swept back down the beach. The magnitudes of the increases in light intensity and pressure regulate the time until the reversal. This phototactic sequence can reoccur if upon entering the sand the animals are exposed to light levels below the lower threshold for phototaxis for at least 1 s. Reburrowing in the sand to a depth of about 7 mm will reset responsiveness. In this state, the animals are ready to ride the next wave up the beach and remain at the leading edge of the wave uprush.