Rockwell Automation 5370-CVIM2 Module - Manual (Page 51)

Chapter 3
Image Acquisition Parameters
3–12
Light Probe Operation: General
The light probe tool is a small, special–purpose window or “box” that is
positioned during configuration over a user–designated light reference
“patch” somewhere in the top half of the image. Typically, the patch should
be near the top of the image, and always at least eight raster lines above the
highest tool. During inspection operations, the light probe measures the light
intensity reflected from the reference patch on a scale of 0 to 255 (0 is the
darkest light intensity and 255 is the brightest), and the CVIM2 system
calculates the average value of the pixels within the light probe.
The light probe is a pre–inspection tool. Thus, when the light intensity
changes from the original setting, the CVIM2 system uses the light probe’s
calculated value to modify gray scale values from the camera in order to
produce the best match to the original image. When the image is thus
compensated, the threshold and filter values for the inspection tools remain
valid.
Note that the calculated average value reflects the brightness of the reference
patch relative to the minimum and maximum values of 0 and 255. Therefore,
in order to ensure adequate light compensation flexibility, the light reference
patch should be a shade of gray that yields an initial value in the range of 160
to 200. This allows a margin for both an increase and a decrease in light
intensity.
The basic steps for configuring the light probe for use are these:
•
If a suitable background area is not available in the field of view, prepare
a light– or medium–gray reference “patch” and position it within the
image using the
Focus function.
•
Enable the light probe for use by setting the Enabled/Disabled button to
Enabled .
•
Position and “size” the light probe “box” over the reference area or
“patch” using the
(pick and place) button.
•
Store the initial calculated average brightness of the pixels in the light
probe window, using the
Nominal or “learn” function.