NI Vision Calibration with an Edmund Industrial Optics grid

[kat_TBG]

I'm developing an application to perform vision inspection and need to include some form of image calibration to correct for any distortion and to allow measurement of objects in mm rather than pixels. Although I'm experienced with LabVIEW I'm new to vision so have never done this before.

The NI page http://digital.ni.com/public.nsf/allkb/7EC6E64CF5A0F2C7862569F3005EF29D recommends the Edmund Industrial Optics grid target which I have got. However I can't see how this can be used in conjunction with the NI Vision Calibration VI's. All the Vision Calibration examples use a large grid of identically sized and spaced dots which fill the image. The EIO target is small so only takes up a small area of my image and includes 3 sections of differently sized and spaced dots (see picture at http://www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productid=1948).

I've attached an image of my calibration grid and an example of an image I want to calibrate (converted to jpgs to be small enough to upload here).

How do the Vision Calibration VI's work with this type of grid?

[Jeremy_T]

Hi Kat

I think that the grid that you have there should be sufficient for the standard calibration procedure as described in the Vision Concepts Manual.

Have you tested out that template with one of the calibration examples to see what result you get?

In terms of the size of the template, which size do you have? I've noticed that there are two sizes available on the Edmund Optics website.

Kind Regards

[kat_TBG]

Thanks for your response.

The grid of dots is 2" x 2", whereas the images we're taking are approx 10" x 10" (see attached images from my previous post).

I've tried adapting the NI examples to use these images but the resulting image still shows the same distortion in the buttons - all should be the same size but the image shows some stretched out and some squashed up. I can't see how this sort of distortion can be corrected when the dots cover such a small area of the image? The calibration VI's also require you to specify the grid spacing but the grid contains 3 different sizes of dots with 3 different lengths of spacing so how can I tell which ones the VI's will use?

[Ashish_Naik_NIUK]

Hi Kat,

I hope you are well. It is generally used that the calibration grid that is used, is of the size, if not larger than the image itself.

Is it possible to use the Calibration grid that ships with NI Vision. This is located generally in C:\Program Files\National Instruments\Vision\Documentation and is called CalibrationGrid.pdf

If you could please give this a go and let us know how you get on.