Does Scorpion Vision do sub-pixel measurement?

The clue about sub-pixel measurement is removing lens distortion. The Calibrator tool is the key for for this.  More information is found in the Scorpion Online Help.

All Scorpion tools work with reference and process image with subpixel accuracy the reference chain contains a Calibrator. This  gives the user the advantage of sub-pixel measurement without any special effort. Sub-pixel measurement is an extremely important feature in 2D and 3D machine vision system. With Scorpion you can increase the accuracy from 10 – 30 times taking advantage of the Calibrator tool.

The image below is a Image from a patented system from Tordivel Solar. The shadowline is located with 1 micrometer accuarcy with a camera pixel resolution of 40 micrometer.

High Precision Line Location

High Precision Line Location

The following rule of thumb can be used to indicate the tolerance of a width measurement : The accuarcy is equal to 1 pixel – the measurement standard deviation is 1/10 pixel or better. This means that with a field of view of 100 x 100 mm and a Sony XCD-700 camera measurements has a accuracy of 0.1 mm and a resolution better than 0.01 mm.

The image below is captured with 4.8 mm wide-angle lens. The grid has the following properties:

  • 15 rows and 22 columns
  • Dot spacing of 50 mm
  • Pixel resolution is 1,01 mm

The following corrections are performed with lens calibration:

  • The RMS position deviation is 0,3 mm or pixels
  • The maximum deviation is 0,8 mm
  • The edge points are moved 58,7 mm

The effect of using the calibrator is that the optical precision is 0,3 mm. Before correction the maximum error 2 * 58 mm = 116 mm. The maximum error is thus reduced with a factor close to 300.

Using the ImageResampler tool the following perfect image can be created:

See also the Calibrated Measurement example.

2 Responses

  1. […] ambition is to use this as an active communication channel with our users. The updated Q&A for sub-pixel measurement show how we link the Q&A to the Scorpion Online Help which contains sample profiles for tools […]

  2. […] Does Scorpion support sub-pixel measurement? November 2009 1 comment 4 […]

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