caliper calibration not working

[niccarroll]

Hi,

I am using the IMAQ caliper tool to find edges and measure the distance between the jaws of a real caliper. My problem is as follows:

When I set the real caliper to a measurement of 1 mm and use the caliper vi to measure the distance between the jaws I get a pixel measurement of 45.59 pixels. I then configured the vi to divide the distance output of the caliper vi (in pixels) by the 45.59 to achieve 1 mm. However, when I then move the real caliper to a measurement of 10 mm my caliper vi measurement reads 3.9mm. This may be a painfully obvious answer, but I am new to machine vision and am confused by this. Can someone please point out where I am going wrong with my calibration?

Best Regards,

Nicholas Carroll

[MoviJOHN]

You need:

Telecentric Lens

Diffuse Backlight Illumination, preferably collimated

16 Bit Greyscale Camera

A distortion-corrected image

[Klemen]

Hello,

what you are describing is not a proper calibration. You have radial and perspective distortion in your measurements (which you clearly do, based on what I can understand from your problem). Did you use the planar calibration grid? Take a look for example at the "Perspective Calibration" in the NI Example Finder.

Best regards,

K

[niccarroll]

Thank you very much. I am using a 12 bit greyscale camera. Is that not sufficient? I only ask because you mention a 16-bit camera. I definitely need to get the lighting and telemetric lens though.

[niccarroll]

I did not use the planar calibration grid. I was unaware of its existence. Thank you for bringing it to my attention!

[MoviJOHN]

12 bit is fine.  I suppose it all depends on the level of accuracy that you need.

[Brzhou]

Hi Sir,

Have you fixed your issue ?

I am also new, and would like to learn something of vision, such as capture the contour, calculate the distance.

Are you still there ?

Thanks.