Measuring perceived gloss of rough surfaces

This thesis is concerned with the visual perception of glossy rough surfaces, specifically those characterised by 1/fB noise. Computer graphics were used to model these natural looking surfaces, which were generated and animated to provide realistic stimuli for observers. Different methods were employed to investigate the effects of varying surface roughness and reflection model parameters on perceived gloss. We first investigated how the perceived gloss of a matte Lambertian surface varies with RMS roughness. Then we estimated the perceived gloss of moderate RMS height surfaces rendered using a gloss reflection model. We found that adjusting parameters of the gloss reflection model on the moderate RMS height surfaces produces similar levels of gloss to the high RMS height Lambertian surfaces. More realistic stimuli were modelled using improvements in the reflection model, rendering technique, illumination and viewing conditions. In contrast with previous research, a non-monotonic relationship was found between perceived gloss and mesoscale roughness when microscale parameters were held constant. Finally, the joint effect of variations in mesoscale roughness (surface geometry) and microscale roughness (reflection model) on perceived gloss was investigated and tested against conjoint measurement models. It was concluded that perceived gloss of rough surfaces is significantly affected by surface roughness in both mesoscale and microscale and can be described by a full conjoint measurement model

Band-Sifting Decomposition for Image-Based Material Editing

Photographers often "prep" their subjects to achieve various effects; for example, toning down overly shiny skin, covering blotches, etc. Making such adjustments digitally after a shoot is possible, but difficult without good tools and good skills. Making such adjustments to video footage is harder still. We describe and study a set of 2D image operations, based on multiscale image analysis, that are easy and straightforward and that can consistently modify perceived material properties. These operators first build a subband decomposition of the image and then selectively modify the coefficients within the subbands. We call this selection process band sifting. We show that different siftings of the coefficients can be used to modify the appearance of properties such as gloss, smoothness, pigmentation, or weathering. The band-sifting operators have particularly striking effects when applied to faces; they can provide "knobs" to make a face look wetter or drier, younger or older, and with heavy or light variation in pigmentation. Through user studies, we identify a set of operators that yield consistent subjective effects for a variety of materials and scenes. We demonstrate that these operators are also useful for processing video sequences

Gloss Dynamics of Inkjet Printers

Inkjet printing is a popular non-impact technology with widespread use in home and office applications. The basic principle involves propelling ink drops of different colors on a substrate. High quality images, near photographic quality, are now possible. The gloss of the printed substrate is an important quality attribute. Printed gloss depends on a number of characteristics of the media and the ink, but a good fundamental understanding is not available in the literature. The dependence of the gloss on the media and ink characteristics is reported in this work. The experimental results are compared with values predicted by a mathematical model. The dynamic post-printing gloss was studied with a specially constructed apparatus, which measured the laser reflectance of the printed surface within 40 ms after drop impact. Both pigmented and dye-based inks are used with rapidly absorbing porous media and swelling polymer-coated media. Various properties of the media such as surface roughness, ink absorption rates, pore size distribution, oil absorption capacity, wettability, and gloss were characterized along with ink properties like surface tension, viscosity, and filtercake resistance or the filtercake forming ability of the pigmented inks. The model and experimental results show that the gloss of dye-based inks on porous media depends on the media roughness. Gloss on swellable media depends on the roughness of the wet swollen polymer coating. The gloss of pigmented inks on porous media is determined by the ink pigment size and the dry media gloss. The gloss on swellable media is determined by ink pigment size and the wet roughness. The model predictions compare well to experiments for a wide range of parameters

High precision dynamic multi-interface profilometry with optical coherence tomography

Optical coherence tomography (OCT) has mostly been used for high speed volume imaging but its profilometry potentials have not been fully exploited. This paper demonstrates high precision (as good as ~50nm) multi-interface profilometry using a Fourier domain OCT system without special anti-vibration devices. The precision is up to two orders of magnitudes better than the depth resolution of the OCT. Detailed analysis of the precision achieved for different surfaces is presented. The multi-interface profiles are obtained as a by-product of the tomography data. OCT has advantage in speed and sensitivity at detecting rough and internal interfaces compared to conventional optical profilometry. An application of the technique to the dynamic monitoring of varnish drying on paint-like substrates is demonstrated, which provides a better understanding of the formation of surface roughness. The technique has potential benefits in the field of art conservation, coatings technology and soft matter physics

Gloss Management for Consistent Reproduction of Real and Virtual Objects

A good match of material appearance between real-world objects and their digital on-screen representations is critical for many applications such as fabrication, design, and e-commerce. However, faithful appearance reproduction is challenging, especially for complex phenomena, such as gloss. In most cases, the view-dependent nature of gloss and the range of luminance values required for reproducing glossy materials exceeds the current capabilities of display devices. As a result, appearance reproduction poses significant problems even with accurately rendered images. This paper studies the gap between the gloss perceived from real-world objects and their digital counterparts. Based on our psychophysical experiments on a wide range of 3D printed samples and their corresponding photographs, we derive insights on the influence of geometry, illumination, and the display’s brightness and measure the change in gloss appearance due to the display limitations. Our evaluation experiments demonstrate that using the prediction to correct material parameters in a rendering system improves the match of gloss appearance between real objects and their visualization on a display device

Development of extinction imagers for the determination of atmospheric optical extinction: final report

The primary goals of this project for JTO and ONR (Grant N00014-07-1-1060) were to further develop Extinction Imagers for use in the ocean environment, and to extend the capabilities into the Short Wave IR (SWIR). Extinction Imaging is a method for determining the effective extinction coefficient over an extended path using a sensor at one end of the path. It uses calibrated imagers to acquire the relative radiance of a dark target near the other the end of the path and the horizon sky in the direction of the dark target. It is completely passive and thus covert, and the hardware is robust and relatively inexpensive. It uses rigorous equations, which determine the extinction coefficient from the measured apparent contrast of the radiance of the dark target with respect to the horizon sky. The project was very successful. We found that the ocean surface could readily be used as a dark target in red and SWIR wavelengths. Both the red and the SWIR measurement results were excellent for daytime. Comparisons with standard instruments, as well as uncertainty analysis, indicated that extinction imagers provide better measurements of the atmospheric extinction losses over extended paths than other methods of which we are aware. Our secondary goals were to address the night regime, and to address slanted paths above the horizontal. Regarding night, we found that the visible sensor acquired excellent data, but the ocean surface was not a good dark target in our wavelengths. Recommendations on the handling of night are given in the report. Regarding the lines of sight above the horizon, we developed a slant path algorithm that determines beam transmittance. It performed very well. Recommendations are made regarding integration of these techniques for military applications.Joint Technology Office via Office of Naval ResearchGrant N00014-07-1-106

Perceptual Modeling and Reproduction of Gloss

The reproduction of gloss on displays is generally not based on perception and as a consequence does not guarantee the best visualization of a real material. The reproduction is composed of four different steps: measurement, modeling, rendering, and display. The minimum number of measurements required to approximate a real material is unknown. The error metrics used to approximate measurements with analytical BRDF models are not based on perception, and the best visual approximation is not always obtained. Finally, the gloss perception difference between real objects and objects seen on displays has not sufficiently been studied and might be influencing the observer judgement. This thesis proposes a systematic, scalable, and perceptually based workflow to represent real materials on displays. First, the gloss perception difference between real objects and objects seen on displays was studied. Second, the perceptual performance of the error metrics currently in use was evaluated. Third, a projection into a perceptual gloss space was defined, enabling the computation of a perceptual gloss distance measure. Fourth, the uniformity of the gloss space was improved by defining a new gloss difference equation. Finally, a systematic, scalable, and perceptually based workflow was defined using cost-effective instruments

Measurement, modeling and perception of painted surfaces : A Multi-scale analysis of the touch-up problem

Real-world surfaces typically have geometric features at a range of spatial scales. At the microscale, opaque surfaces are often characterized by bidirectional reflectance distribution functions (BRDF), which describes how a surface scatters incident light. At the mesoscale, surfaces often exhibit visible texture - stochastic or patterned arrangements of geometric features that provide visual information about surface properties such as roughness, smoothness, softness, etc. These textures also affect how light is scattered by the surface, but the effects are at a different spatial scale than those captured by the BRDF. Through this research, we investigate how microscale and mesoscale surface properties interact to contribute to overall surface appearance. This behavior is also the cause of the well-known touch-up problem in the paint industry, where two regions coated with exactly the same paint, look different in color, gloss and/or texture because of differences in application methods. At first, samples were created by applying latex paint to standard wallboard surfaces. Two application methods- spraying and rolling were used. The BRDF and texture properties of the samples were measured, which revealed differences at both the microscale and mesoscale. This data was then used as input for a physically-based image synthesis algorithm, to generate realistic images of the surfaces under different viewing conditions. In order to understand the factors that govern touch-up visibility, psychophysical tests were conducted using calibrated, digital photographs of the samples as stimuli. Images were presented in pairs and a two alternative forced choice design was used for the experiments. These judgments were then used as data for a Thurstonian scaling analysis to produce psychophysical scales of visibility, which helped determine the effect of paint formulation, application methods, and viewing and illumination conditions on the touch-up problem. The results can be used as base data towards development of a psychophysical model that relates physical differences in paint formulation and application methods to visual differences in surface appearance

Gloss Development of Spray-coated Systems

A spray-coated system involves any substrate on which a liquid coating is applied in a drop-wise fashion. Inkjet printing is the controlled application of drops to print a surface and is the focus of this work. The gloss of the printed substrate is an important attribute of print quality. Print gloss depends on a number of factors, such as ink and media properties. Non-uniform gloss in different regions of a printed image can cause a decrease in quality of a printed sample. However, a good understanding of the gloss development of spray-coated systems is not available in the literature. Several combinations of inkjet inks and media were characterized in terms of physical properties. Both pigmented and dye-based inks were used with absorbing microporous coated media. These ink/media combinations were printed with an inkjet printer and the final gloss measured. A laser system was used to measure the gloss every millisecond right after printing, around 20 ms after drop impact. Some media were modified with chemicals or other treatments to modify physical and chemical properties. Fiber swelling in paper-based media was found to lower gloss in those media which contain fibers that can contact water. This reduction in gloss occurred one second after printing. Media with protected paper fibers do not exhibit this gloss reduction. Plastic-based media with porous coatings obtained the final gloss at 0.1 seconds. Inks can be destabilized by ions on the media surface that leads to low gloss. Some inks were not sensitive to ions on the media. Light color inks were found to have high gloss values at 50% fill compared to 100% fill while most other inks have the opposite behavior. This phenomenon is likely due to the secondary reflection at the ink/media interface; light is able to transmit through the ink layer and reflect at the media surface