Extraction of diffuse objects from images by means of watershed and region merging: example of solar images.

This paper presents a new method for extraction of diffuse objects from images, which was developed for segmentation of solar images obtained from extreme-UV imaging telescope (EIT) experiments of the satellite SOHO mission. As a particular type of objects to be extracted coronal holes in EIT images have been chosen. The method described is based on the use of a watershed algorithm. The result of the watershed segmentation is a partition of the whole domain of the image into a large number of small regions. These regions are then combined in a region merging process. The proposed region merging algorithm iteratively adds the darkest regions and maximizes the average contrast between a current mask and a set of its neighboring regions. We show that the maximization of the average contrast gives segmentation results that are visually acceptable. Furthermore, this approach allows us to conduct the segmentation of EIT images independently of any explicit fine-tuning parameters. The proposed method was extensively tested on EIT images obtained at various times and various levels of solar activity, and we will show that it can be used independently of the local brightness level and the extent of coronal holes.     

Testing the randomness of shares in color visual cryptography

Pattern Analysis and Applications - The concept of black-and-white visual cryptography with two truly random shares, previously applied to color images, was improved by mixing the contents of the...     

Mathematical Modeling of a Digital Current Control Loop for Electrical Drives

Analysis of a digitally controlled current loop in a drive system is performed by a newly developed z-transform method that serves both the discontinuous and continuous case, and is verified by an interactive computer program based on system modeling. The assumption made is that the drive system has a sufficiently high mechanical inertia so that the current loop responds before the speed has changed. It is shown that under such conditions the transient response in discontinuous conduction can be approximated by a series of rectangular pulses, the heights of which are calculated by assuming that the current-time areas for the actual current increment and the equivalent pulse are equal. The results of the z-transform method agree well with those obtained from ditigal modeling.     

Digital Simulation of an SCR-Driven DC Motor

The digital computer program simulating the SCR-driven dc motor is described. The program is particularly well suited to the investigation of the motor dynamics when both continuous and discontinuous conduction occur. The input signals to the system are a sequence of gate pulses and the instantaneous load torque, and the output signals are the instantaneous armature current and speed. The flowchart of the program, which is based on numerical integration, and an example of the calculated response to a change in the firing angle are given.