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Label Center Checking

Label Center Checking

It is a known fact that using a camera to measure the centeredness of a stick-on label can be difficult. In this case we are referring to product that is typically oblong or has a near flat front surface. Typically bottle position and orientation are not very repeatable as they exit the labeler. Thus as the bottle moves down the line there will be variation in in/out position and the rotational aspect of the bottle, with respect to the camera. Here at Decision Technology, a company specializing in machine vision solutions, we have developed a new algorithm that determines a “Goodness of Center” factor which is proportional to how well a label is centered even thru a reasonable amount of positional ambiguity of the bottle. This typically includes:

  • in/out position (tested up to +/- .05 inches)
  • rotational variation (tested up to +/- 3-degrees)

We believe that the algorithm will work with over a larger degree of variation but have not tested it as of yet. This measure can then be used in conjunction with a set of min/max allowances in regard to a judgment for ejecting the product. Given appropriate lighting, the technique is compatible with both solid and translucent labels and bottles. It is also compatible with a wide range of camera resolutions.

The following test results are provided. It is our opinion that an allowed “Centeredness” value of between +/-15 would work quite well at providing a “Good Judgment” range. Of course the system can also detect vertical rotation of the label, with additional image processing methods.

Resulting measure
of centeredness value
near center large marginal
label offset offset
rotation in/out
0 deg rotation centered 0.214 53.58 4.38
In.05" -0.121 55.65 4.229
Back .05" -0.297 53.48 3.973
CW 1.5deg centered -4.387 49.637 -0.454
In .05" -4.269 49.529 -0.681
Back .05" -4.622 49.559 -0.822
CW 3.0deg centered -10.709 45.103 -5.31
In .05" -10.667 45.146 -5.331
Back .05" -10.825 45.132 -5.495
CCW 1.5deg centered 4.082 59.827 8.696
In .05" 4.077 59.868 8.721
Back .05" 3.943 57.755 8.638
CCW 3.0 deg centered 8.054 64.1 13.694
In .05" 8.129 64.097 13.699
Back .05" 7.965 64.048 13.722