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Glossary
[G]
Gray scale check using the normalization correlation method
Even when the IV-C35M is looking at the same object as the object used for the reference image,
the new target image and the previously stored reference image may not match completely, due to
variations in the illumination conditions and the ambient light.
In order to check the resemblance between the two sets of image data, the normalization correlation
method can be used.
In order to check whether or not the levels match using the normalization correlation method, the
system slides the reference image one pixel at a time in the measurement objective range (mea-
surement window), and calculates correlation value between the reference image and the target
image. The position where the maximum correlation value can be obtained is treated as the position
where the target image might exist, and the IV-C35M calculates resemblance level at this position.
The normalization correlation method also can be applied to binary images. However, gray scale
images (images with shades of light) contain large volumes of information, compared with binary
images (images with 256 levels of gray have 256 times the volume of information than in binary
images). Therefore, gray-scale images offer more precision and more reliable results.
However, the larger the information volume, the larger the number of calculations that must be
made for correlation values. This means that high speed processing hardware and software are
required to use the normalization correlation method on the gray scale images.
Gray scale processing (gray image processing)
This is a process used to handle the unmodified captured image data, obtained from the CCD
camera. In other words, the image data is not converted to binary values.
- This process produces more precise results than binary image processing (one pixel = one bit) by
using 8 bits (one pixel = 256 gray levels) to represent each pixel in a gray scale image.
[Advantage]
[Disadvantage]
Gray scale search (corrected gray scale search)
G
The "gray scale search" function is a system for detecting a point where the input image and the
reference image match, after calculating the matching levels in the input image and the reference
image.
[Procedures]
Store the reference image as a gray scale image with 256 levels of gray.
Capture the workpiece image to be measured.
Move the captured image of the object so that the upper left corner of the captured image is right
on top of the upper left edge of the reference image. Calculates the level of matching between
the two images, based on the stored gray scale image data.
Slide the reference image over one pixel width and then measure the level of matching at that
position.
Repeat step
(Output)
Maximum matching level value
The center coordinates where the highest
level of matching is obtained
Reference image
Search range in the image
Theoretically, better precision and reliability can be offered because the
image more information about the brightness of each pixel in the image.
More processing time is required because this approach must handle a large
amount of data.
above for the whole workpiece image until a good match is found.
G-6
(Application)
Shape inspection
Positional deviation measurement
Detected image
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