14
4. X-Ray Tube Focal Spot Measurements
Slit Measurement Using Digital Image
RTI Slit Camera User’s Manual
1.0B
4.4.1.2.
Calibrate the pixel values
In ImageJ the calibration is performed by “setting scale”.
This is done from the menu
Analyze/Set Scale…
.
In this case the number of pixels was 3600 for a known
distance of 290 mm.
4.4.1.3.
Invert the image
The original image is inverted. This is done from the menu
Edit/Invert
, (or Ctrl+Shift+I).
4.4.1.4.
Rotate the image
If the image of the slit is horizontal the image has to be
rotated 90 deg before measure with ImageJ. This is
done from the menu
Image/Transform/Rotate 90
Degrees Right.
4.4.1.5.
Measure the distances, X
1
and X
2
In the image the distance, X
2
, between the front
edge and the edge of the open part of the slit
holder is measured.
In ImageJ this distance can be measured by
using either the rectangular or the line tool. In
the image to the right the rectangular tool is
used and the width is read to be 82.17 mm.
One can also read the x-values by moving the
pointer over the image. In this case the x-value
for the left edge was 117.61, and the right edge
was 199.78. That gives the width.
X
2