Hans Brettel

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We propose an algorithm that transforms a digitized color image so as to simulate for normal observers the appearance of the image for people who have dichromatic forms of color blindness. The dichromat's color confusions are deduced from colorimetry, and the residual hues in the transformed image are derived from the reports of unilateral dichromats(More)
In this article we describe the experimental setup of a multispectral image acquisition system consisting of a professional monochrome CCD camera and a tunable filter in which the spectral transmittance can be controlled electronically. We have performed a spectral characterisation of the acquisition system taking into account the acquisition noise. To(More)
In two experiments we have determined the discriminability between two sinusoidal gratings as a function of orientation and spatial frequency differences. Twelve orientation (15 degrees steps) and four spatial frequencies (2, 4, 8, 12 c/deg) were considered and corresponding discrimination thresholds were determined. Results indicated that: (a) spatial(More)
In order to properly calibrate an electronic camera for a variety of illuminants it is necessary to estimate the spectral sensitivity of the camera. This spectral characterisation is obtained by measuring a set of samples of known spectral reeectances and by inverting the resulting system of linear equations. In the presence of noise, this system inversion(More)
Cell membrane damage by ultrasound was studied in human nucleated cells in vitro at various concentrations. Suspensions of human blood cells, cells of a human leukemic cell line (Reh) and mixtures of nucleated cells with erythrocytes were exposed to continuous ultrasound of 782 kHz at a SPTA intensity of 15 W/cm2. The surviving nucleated cells without(More)
Suspended cells of a human lymphoblastic cell line were exposed to pulsed ultrasound of 775 kHz. The pulse lengths were varied between 16 and 1000 microseconds. The mark/space ratio was always kept at 1:1. Two ultrasound intensity levels were used: 3.6 and 6.4 W/cm2 spatial peak and temporal peak. After an exposure time of 5 min, cell membrane damage was(More)
In this paper we consider the complementary properties of image amplitude and phase components and their role in normal and amblyopic vision. Specific two-dimensional filtered images are included to demonstrate the possible perceptual distortions due to both amplitude and phase disturbances. Finally, the relationships between amplitude and phase filters are(More)