116 research outputs found
Visual quality of printed surfaces: Study of homogeneity
International audienceThis paper introduces a homogeneity assessment method for the printed versions of uniform color images. This parameter has been specifically selected as one of the relevant attributes of printing quality. The method relies on image processing algorithms from a scanned image of the printed surface, especially the computation of gray level cooccurrence matrices and of objective homogeneity attribute inspired of Haralick's parameters. The viewing distance is also taken into account when computing the homogeneity index. Resizing and filtering of the scanned image are performed in order to keep the level of details visible by a standard human observer at short and long distances. The combination of the obtained homogeneity scores on both high and low resolution images provides a homogeneity index, which can be computed for any printed version of a uniform digital image. We tested the method on several hardcopies of a same image, and compared the scores to the empirical evaluations carried out by non-expert observers who were asked to sort the samples and to place them on a metric scale. Our experiments show a good matching between the sorting by the observers and the score computed by our algorith
Dust Settling in Magnetorotationally-Driven Turbulent Discs I: Numerical Methods and Evidence for a Vigorous Streaming Instability
(Abridged) In this paper we have used the RIEMANN code for computational
astrophysics to study the interaction of a realistic distribution of dust
grains with gas in a vertically stratified protostellar accretion disc. The
disc was modeled to have the density and temperature of a minimum mass solar
nebula, and was driven to a fully-developed turbulence via the
magnetorotational instability (MRI). We find that the inclusion of standard
dust to gas ratios does not have any significant effect on the MRI even when
the dust sediments to the midplane of the accretion disc. The density
distribution of the dust reaches a Gaussian profile, and the scale heights for
the dust that we derive are shown to be proportional to the reciprocal of the
square root of the dust radius. The largest dust shows a strong tendency to
settle to the midplane of the accretion disc, and tends to organize itself into
elongated clumps of high density. The dynamics of these clumps is shown to be
consistent with a streaming instability. The streaming instability is seen to
be very vigorous and persistent once it forms. Each stream of high density dust
displays a reduced RMS velocity dispersion, and the densest clumpings of large
dust are shown to form where the streams intersect. We have also shown that the
mean free path and collision time for the dust that participates in the
streaming instability is reduced by almost two orders of magnitude relative to
the average mean free paths and collision times. We show that some of the large
dust in our 10 au simulations should have a propensity for grain coalescence.Comment: 44 pages, 12 figures, submitted to MNRA
Psychometrics of Disembodiment and Its Differential Modulation by Visuomotor and Visuotactile Mismatches
Altered states of embodiment are fundamental to the scientific understanding of bodily self consciousness. The feeling of disembodiment during everyday activities is common to clinical conditions; however, the direct study of disembodiment in experimental setups is rare compared to the extensive investigation of illusory embodiment of an external object. Using mixed reality to modulate embodiment through temporally mismatching sensory signals from the own body, we assessed how such mismatches affect phenomenal and physiological aspects of embodiment and measured perceptual thresholds for these across multimodal signals. The results of a principal component analysis suggest that multimodal mismatches generally induce disembodiment by increasing the sense of disownership and deafference and decreasing embodiment; however, this was not generally reflected in physiological changes. Although visual delay decreased embodiment both during active movement and passive touch, the effect was stronger for the former. We discuss the relevance of these findings for understanding bodily self plasticity
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