Browsing by Author "Jacobson, Samuel G."

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Open Access
Modeling of high resolution digital retinal imaging
(1991) Cideciyan, Artur V.; Nagel, Joachim H.; Jacobson, Samuel G.
High resolution digital images of the retina can be obtained by photography with a Zeiss fundus camera followed by digitization of the photographic slide with a high resolution scanner. A complete model of this imaging system is developed based on its four components; the eye, the camera, the film and the scanner. The actual and modeled step responses and system noise are compared to validate the model. A simulated retinal reflection is used to demonstrate the extent of information degradation caused by such an imaging system. Preliminary results of linear restoration using a simplified version of the complete model are given. Development of nonlinear restoration incorporating the complete model is in progress.
Open Access
Multi-scale segmentation of retinal images
(1991) Cideciyan, Artur V.; Jacobson, Samuel G.; Nagel, Joachim H.
Tiny bright golden patches can be seen on the dark retinal background of some carriers of X-linked retinitis pigmentosa, an incurable blinding disease. We are interested in analyzing quantitatively these unique "tapetal-like reflex" patches in order to increase our understanding of the cellular mechanisms of the disease. In this paper, we describe the multi-scale thresholding method and its application to the segmentation of the tapetal-like reflex in high resolution digital fundus images. Multi-scale thresholding is a local thresholding method that generates results very similar to that of human intuition. Unlike other local thresholding methods, our method successfuIly ignores small artifacts in dark regions and simultaneously generats high resolution definitions of objects. Other segmentation applications where there are many bright objects on a darker background should profit from the use of multi-scale thresholding.
Open Access
Registration of high resolution images of the retina
(1992) Cideciyan, Artur V.; Jacobson, Samuel G.; Kemp, Colin M.; Knigthon, Robert W.; Nagel, Joachim H.
A method of image registration is presented for the case when the deformation between two images can be well approximated with a combination of translation, rotation and global scaling. The method achieves very high accuracy by combining a global optimization in the 4-dimensional discrete parameter space with a local optimization in the 4-dimensional continuous parameter space. The 4-dimensional global optimization is accomplished with two 2-dimensional optimizations. The Fourier magnitude is used to decouple translation from rotation and scaling, and a log-polar mapping of the Fourier magnitude is used to convert rotation and scaling into shifts. Optimal rotation and scaling parameters are determined with a cross-correlation in the log-polar domain. After compensation for rotation and scaling differences, cross-correlation in the spatial domain yields the translation parameters. The four registration parameters are further refined with a local optimization using the correlation coefficient as a similarity measure in the 4-dimensional continuous parameter space. Results are shown from simulations and from registration of retinal images. For simulated images with a signal-to-noise ratio of -5 dB, the accuracy of the registration method is estimated to be better than 0.07 degrees, 0.1 %, and 0.3 pixels for rotation, scaling, and translation, respectively. In the case of 512x512 pixel images the computation resource requirements are compatible with high end PCs, i.e., approximately 25 minutes on an Intel 80486/33MHz based IBM/PC compatible.