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SmartSearch can yield sub-pixel resolution position up to 1/64 of a pixel. The actual accuracy depends on various conditions, such as lighting, consistency of the objects you are searching for, quality of the camera, lens, and frame grabber, etc. The following benchmark illustrates that 1/64 pixel accuracy is easily achievable.
A poster was tape on a wall in a typical office, and a ruler is taped below it so that the poster can be moved accurately horizontally to within 0.2 to 0.5 mm of any desired position. A camera is set up a fairly long distance away from the poster, so that 0.5 mm will appear as approximately 1/64 pixels in the image. By training SmartSearch with the actual appearance of the poster in one of the images and manually moving the poster to different positions, a set of measured (on the ruler) and computed positions can be tabulated. The difference between corresponding readings is the sub-pixel accuracy.
Equipment used in the benchmark:
Following is a representative data set:
| Position on Ruler (mm) |
Pixel Position Reported by SmartSearch |
| 0 | 290.0 |
| 50 | 293.281 |
| 100 | 296.625 |
| 250 | 306.594 |
Scale = (306.594 - 290)/250 = 0.066376 pixel/mm
1/64 pixel = 0.015626 pixel = 0.015625/0.066376 = 0.24 mm
1/32 pixel = 0.03125 pixel = 0.47 mm
With such a scale, the accuracy of the location of the poster as measured on the ruler should be adequate to evaluate whether SmartSearch is indeed capable of locating the search target to between 1/32 and 1/64 pixel resolution.
Using the computed scale,
the expected pixel position corresponding to the poster at 50 mm is:
50 x 0.066376 = 3.3188
Error = 3.3188 - (293.281 - 290) = 0.0378
The error is slightly more than 1/32 pixel.
Similarly, for 100 mm:
100 x 0.066376 = 6.6376
Error = 6.6376 - (296.625 - 290) = 0.0126
This error is less than 1/64 pixel!
Even with this simple setup, SmartSearch is capable of delivering 1/32 to 1/64 sub-pixel resolution. With better quality cameras, lenses, and more controlled lighting, SmartSearch should deliver even more reliable results.