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Spot Tool

 
  •   -> S Wdow - Add spot tools.
  • Clear - Clear graphics (spots or rings)
  • Show... - Show array, spots, bv lines, spot deviations, camera constant
  • Pop... Brings spot or ring window to the front.
  • Measure... Measure basis vectors, set cam constant, D values
  • S Rad... Set spot radius.
  • Delta xf... Set scale factor for arrows showing spot deviations. (magnifies arrow length).
  • Parameters... Shows parameter list - similar in concept to mlx_parameters list.

To Use...




For a diffraction spot example, load the rutile spots.tiff image in the Demo_images/EDIF folder with the MLx->Image Files->TIFF->read menu.

Invoke the ->S Window button.
This is analogous to the -> R Window button. The image of the diffraction spots is converted to a window with the spot measuring tools.

Move (and zoom?) the window so that all of it visible.

The window will appear black except for a few white spots. This digression was left into this demonstration because many diffraction images are just of this nature, where they must be scaled appropriately to visualize the diffraction spots. I.e., the contrast and brightness must be adjusted to see the spots. The image is a 16 bit TIFF image, but the diffraction spots intensities (less than 2500) are small compared to the few bright pixels (65530) in the image that are noise. The contrast and brightness must be adjusted to see the spots. The range of brightness of the spots is so large, that the contrast and brightness must be adjusted in any case to position the spots tool accurately. (As initially displayed, zero in the image is black, and 65530 is white. Since the intensities of the spots are less than 4% of the intensity of the few bright pixels, they will be shown as black.)

To see the diffraction pattern, scale the image by clipping .5% of the outliers. The few very bright pixels make up a small percentage (much less than 5%) of the image area. Excluding them from the calculation of what intensity to show as white will render the diffraction spots visible.


Initialize Button | top
Places an initialized pattern of spots in the center of the image.
After the scale->clip button is used and the init Spots menu is invoked, the image appears this way:
The spot pattern tool is placed arbitrarily on the image. Most of the spots are now visible, but the brighter ones are clipped too much to measure their positions acccurately.
Show Spots | top
Redisplays the spots (as adjusted). This is analogous to the Show Ring menu.

Matching the pattern to the image

The spots at the edge of the pattern of circles are what are used to determine the basis vectors. It is best to inspect ALL of them. Some spots that look good may not be located correctly because of noise in the image and should be ommitted. Don't worry - the next closest spot to the pattern center will be used. The spots can be clicked on rapidly, going around the edge of the pattern - the blow up is displayed immediately in the small 'spot' window.

BV Average | top
Once the circles are adjusted, this measures the spot locations from the image, and calculates the basis vector lengths and the angle between them. The following figure shows a suitable selection of circles for the Rutile spots.tiff, and the spots circled in green that are used to calculate the length (and direction) of the basis vector shown in red.

The vectors between the green circles are calculated from the measured spot positions from the image. All the green vectors are then averaged together for a good determination of the basis vector shown in red. The same is done for the other basis vector (shown in black).

The printout should look something like this:
Basis vectors: 49.26 pixels, 53.23 pixels, 56.91 deg.