Albert J. Ahumada

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ABSTRACT t q A model is developed to approximate visibility thresholds for discrete cosine transform (DCT) coefficien uantization error based on the peak-to-peak luminance of the error image. Experimentally measured visibility thresholds for , , and DCT basis functions can be predicted by a simple luminance-based detection R G B model. This model allows DCT(More)
Nonlinear contributions to pattern classification by humans are analyzed by using previously obtained data on discrimination between aligned lines and offset lines. We show that the optimal linear model (which had been identified by correlating the noise added to the presented patterns with the observerÕs response) can be rejected even when the parameters(More)
In this research we addressed the problem of obstacle detection for low altitude rotorcraft flight. In particular, the problem of detecting thin wires in the presence of image clutter and noise was studied. Wires present a serious hazard to rotorcrafts. Since they are very thin, their detection early enough so that the pilot has enough time to take evasive(More)
A semiautomated computer analysis was developed to estimate fluid volumes in each hemicranium from computed tomography scans. The method was used to estimate total ventricular and sulcal fluid in 123 normal subjects aged 23-88 years. A wide range of normal values was found. The trend was for the estimated ventricular and sulcal fluid volumes to remain(More)
Changes on computed cranial tomography related to aging were studied in 123 normal subjects aged 23 to 88 years. The attenuation value of the white matter in the centrum semiovale decreased with age. When the effect of age was excluded, ventricular and sulcal size did not have an independent effect on the attenuation value. This finding suggests that there(More)
The aim of the ColorFest is to extend the original ModelFest (http://vision.arc.nasa.gov/modelfest/) experiments to build a spatio-chromatic standard observer for the detection of static coloured images. The two major issues that need to be addressed are (1) the contrast sensitivity functions for the three chromatic mechanisms and (2) how the output of(More)