Untitled Document

Ring Tool

->R Window
Makes the image into a window with the ring diameter and circle averaging tools. Analogous to the -> S Window button.

An image needs to be loaded before this menu can be used. As an example, load the Au rings.tiff image
in the Demo_images / EDIF folder.

Then, invoke the ->R Window button. The image will be put into a special 'ring' window, and displayed:

The window title has 'Rings-' appended to the end (figure is out of date) to indicate that this is a 'ring' image, that is and image with the ring tools available in it. Later on, spots will be loaded into a 'spot image', which will have the spot tools, but will NOT have the ring tools. Images as displayed normally do not have either tool set.

Draws a new spot pattern in the center of the image. Adjustments are lost if window is already a ring window and you choose 'yes' in the warning dialog.

In this example, the image will look like this:

Due to the nature of this ring tool, it is not 'redrawn' with the window, in other words, if the window is covered and uncovered for any reason (such as temporarily switching to Netscape to read these instructions), the parts of the ring that were convered will not be redrawn. Sometimes the ring tool can disappear altogether. Use the Show tool to make it visible again.

Show | top
Redraws the ring pattern. If the ring image window is covered, and then uncovered, or if the lower right corner (the grow square) is clicked, for instance, the ring pattern will disappear. This menu redraws the pattern. If any part of the ring pattern is lost, it is best to erase the whole pattern by clicking on the Grow Box, and then inviking the Show Ring menu.

Adjusting the Ring pattern.
Adjust the ring pattern by moving the three small circles with the mouse. The central circle moves the whole pattern around the image: this circle should be placed as closely as possible to the beam center in the image. Usually the beam is obscured (as by the beam stop in the image above), but the pattern can be centered nicely by adjusting the ring diameter with either of the other two circles to almost match any of the rings in the image, and then moving the 'Ring Center' circle so that the movable ring lies just inside or just outside of the ring in the image.

The "Gap" circles are for adjusting the gap in the ring to correspond with the beam stop. The "Gap Position" circle will move the gap around the ring - the "Gap Angle" circle will follow along so that the size of the gap is not changed. When the "Gap angle" circle is moved, the "Position" circle stays fixed, so that the size of the gap can be changed. The image below shows the ring adjusted to measure the diameter of one of the outer rings:

It is sometimes difficult to tell if the 'match' is good, when the ring lies on top of the ring in the image. To check the match, just change the radius of the ring slightly so that the ring tool lies just beside (and concentric with) the ring in the image. Readjust the radius before any diameter measurements are made.

Note

Here is a circular average , for this diffraction pattern. that is a plot of averaged intensity going around a circle vs. diameter of that circle. In the electron diffraction ring image, for example, if the ring tool is adjusted to match any of the rings in the pattern, the circle average will plot will have a distinct sharp peak for each ring. At this point in the example, with the ring tool centered on the image pattern, the circle average can be done. Note that the circle average does not use any information about the ring tool other than the center location - the position of the gap, and the radius of the ring are ignored.

The left of this plot is the center of the ring pattern. Clicking on this plot window causes the radius in pixels, A and average intensity (pixel values), B to be shown. Only the horizontal position of the mouse is used for this. The values A and B are for the peak position,C, which was found by holding the mouse down and sliding it along the plot, watching the values at B for a maximum. If the center of the ring tool is not exactly on the center of the diffraction pattern, the peaks in the above plot will broaden. The radius for peak E, to be measured more accurately with the ring diameter menu item, is 96 from this plot. The gap in the plot at D is caused by the printouts for A and B. The plot can be redrawn, filling in this gap, by clicking on the grow box. This will cause the blue numbers A,B to disappear. The plot can be resized by moving the grow box. Ring Diameter | top
For diffraction camera calibration. This tool will measure the radii, then the diameters every degree, plot them, and print the average diameter in pixels.

For the example, as in the steps above, place the circle tool squarely on top of a diffraction ring, and adjust the gap to include the blank space caused by the beam stop.

To check on the ring tool placement, click on the ring in any position. A line segment will be drawn across the ring, and a plot of intensity along the segment will be shown in a small window above the diffraction image. (You will have to click three times on the ring to get the first plot.)

The plot in the 'Untitled' window is for line segment D. The other three segments are left over from three previous plots. The plot has corners, because there are not very many pixels along the line segment.

Then, this menu item will do the plots above for one degree intervals, plot the results, and print the averaged diameter. The maximum from each of the 'Untitled' plots is used as the 'center' of the ring at that location, and is used to calculate the radius for that angle. When the plot has two adjacent and equal maxima, the position between the two is used to determine the radius.

As the average diameter is being calculated, the short line segments will be drawn around the circle, and the 'Untitled' plot will rapidly show the plots for each. When it is finished, the windows look like this:

where the plot is for the last short line segment (B). The red lines illustrate how the diameters are calculated - the radius is known for each angle. The diameters are sums of radii that are 180 degrees apart. Since no radii are known for the gap over the beam stop, the radii measurements at the complementary angles are ommitted. The radii for each angle (actual value, and expanded) and the diameters are shown below:

This window was expanded slightly using the grow box at the bottom right. Note that the radius values show a periodicity that is probably caused by the center of the ring tool not being exactly at the center of the pattern in the image. Since the diameter measurements do not depend directly on the exact center position of the tool, they will be immune to small offsets of the ring tool. The average diameter is 194.07, giving an averaged radius of 97.03, to compare with the measurement taken from the Circle Average plot above.