Image Acquisitionand Proces

24 Image Acquisition Processing with LabVIEW
using a series of LabVIEW state machines. Four state machines were used to handle
the major control processes:
1. Cold start procedure: initial log-on and vacuum system conditioning
2. Warm start procedure: repeat log-ons and NHVG preparation
3. Scan procedure: conveyor automation, x-ray generation and image data
collection
4. Fault/reset procedure: fault handling and system reset
The automatic state machines control approximately 200 I/O points. A maintenance
mode will bypass the automatic state machines and allow maintenance personnel
to control any I/O point individually. This was very useful during system
development and troubleshooting.
A system administrator screen allows the system administrator to provide names,
passwords and access levels to users. User names are included in the header of each
archived image and passwords prevent regular users from going into the maintenance
and administrator modes.
2.1.3.4 Imaging Software
The imaging software handles display and manipulation of x-ray image data. The
imaging functions run on separate screens and take advantage of the multi-threaded
parallel loop capabilities that are built into LabVIEW. There are three screens
dedicated to image manipulation; each screen has an x-ray image, a thumbnail copy
of the x-ray image and a control palette for controlling image functions (Figure 2.11).
When image data is acquired, the data is Þrst processed and then buffered in 16 bit
integer format. A fourth x-ray detector is used to normalize the data while it is being
collected. Because the x-ray detectors pick up cosmic rays from outer space, a
software routine is used to eliminate them before display. By double-buffering the
data while it is being collected, the Transmission 1 image is updated 20 scans at a
time while the images are being acquired. Transmission 2 and Backscatter images
are updated after the scan is complete. The 16 bit data is converted to Unsigned 8
bit integer format before it is displayed on the screen as 256 grayscale.
Data for the x-rays has much higher resolution than can be seen with 256
grayscale. A process called window and level is used to “see into” the x-ray data.
The window and level routine allows the operator to set the upper and lower depths
of x-ray penetration that is displayed for each image. This has the affect of being
able to see through materials of different densities.
IMAQ Vision is used to display and manipulate the image data. These functions
include zoom, pan, reverse video, edge enhance and 3-D position, which is used to
Þnd the vertical height of an object after the operator makes a selection on each of
the two stereoscopic transmission images. A thumbnail of each image displays the
entire image in a 250 ¥ 250 pixel area. If the image is zoomed beyond 1¥, the
operator can simply click on the portion of interest in the thumbnail image and the
zoomed image will pan to this portion of the image.