# Image Probe

## Overview

Given a probe, this tool calculates the its centroid coordinates and region statistics such as total number of pixels, total sum of the pixel values (flux) and mean pixel value (mean flux). When the image probe dialog box is open, POW is in the "probe" mode. To go back to the normal mode, user can just simply press the Exit button and return to the normal mode.

## Creating and manipulating probe

A probe basically is a region. Its shape can be selected by clicking the Probe Shape button. The available shapes are Circle, Box, Ellipse, and Polygon. To create a new probe, place the mouse at the desired location in the graph and click-and-drag with the right mouse button down (Command-Click on Mac-OS). For Circle and Ellipses, the initial mouse location is the center of the probe and the final location is its radius or width and/or height. For Boxes, the mouse movements traces out opposite corner of the rectangle. For Polygon, the mouse locations determines its verteces. To add extra segments to the Polygon, let up on the mouse button, press it again without moving, and drag it to the next vertex.

To move a probe, simply put cursor inside the probe, and click-and- drag it to the new position with the left mouse. The left mouse is also used for changing and rotating probe. To change the shape, click- and-drag the "change" handle (a small green box) on the probe. To rotate the probe, click-and-drag the "rotation" handle (a small green triangle). The rotation only applies to the shape of ellipse and box.

For details of creating and manipulating the probe, please refer to the Regions help file.

## Calculating the coordinates of centroid and statistics

Whenever the probe is created, changed, moved or rotated, the coordinates of centroid and statistics are calculated and shown in the Image Probe dialog box.

The coordinates of centroid are presented in two ways, in pixel in the Pixel field, and in the graphical coordinate in the Coordinate field. The format of graphical coordinate is either in decimal or hms, determined by the Coord. Format button.

The statistics of a probe includes total number of pixels ( the N Pixels field), total flux (the Total Flux field) and mean flux (the Mean Flux field). The mean flux is defined as the average flux per pixel inside the probe.

## Saving the coordinates of centroid and statistics

To save the coordinates of centroid and statistics of current probe to a disk log file, click the Record button. For the first recording or after closing the current log file, you have chance to enter the log file name through a opened file dialog box. To close the current log file, press the Close Log button.