can't perform an effective grid calibration

[ericmateovisan]

Hi everyone

I have a system that have a camera in a distance of about 60cm from object, and the FOV is a rectangle with about 50cm*60cm dimensions. because of this big FOV I had to use a lens with 5mm focal length. with this lens I have about 7% of error in the corners of the image because of the lens distortion. and when I use the Distortion Model(Grid) calibration step in Vision Assistant , the 7% error exists again.

please let me know if there is a tip in setting or anything else that would help.. 

this is my main picture:

and this is the corrected image after calibration process:

thank you in advance

best regards, Eric

[BruceAmmons]

You need one continuous grid.  It can't figure out the spacing when there are multiple grids side by side with space between them..

You could print grids right up to the edge of the paper and align them so they make one continuous grid if necessary.  I would do a little overlap and tape them carefully.

Bruce

[ericmateovisan]

---

@BruceAmmons wrote:

You need one continuous grid.  It can't figure out the spacing when there are multiple grids side by side with space between them..

You could print grids right up to the edge of the paper and align them so they make one continuous grid if necessary.  I would do a little overlap and tape them carefully.

Bruce

---

Thank you Bruce for your reply..🌷

I will try to print a grid sheet on A2 paper or make it by six A4 papers as you said. Is it the main reason It did not work correctly or I have missed another thing as well?

[BruceAmmons]

I assume that is the only problem, but it is hard to be sure.  When there is a big problem it is hard to see the small problems.

I do vaguely remember NI having a utility that allows you to use multiple images of grids and combine them into a single calibration.  It seems like it could be used with a smaller grid that you move around.  I don't know much about the tool, though.

Bruce

[SamiF]

Printing a grid in A2 format should be ok, trying to make a continuous grid with small ones might be quite difficult.

Another option I think would be to use multiple images : the vision assistant calibration tool allows you to use multiple images, each of them having the grid in a different position.

Sami

[ericmateovisan]

thank you guys for your help. I've done the grid calibration process and the result was satisfactional in comparison to last one. but now I have focus problem.. my focus quality is not equal all over the field of view.. is there anything in camera attributes would help this? or anything physical? I have set the focus ring on the camera and tried some change in settings like exposure or contrast but have not got the ideal focus.. as you see here the focus in the edges of the grid sheet is not as clear as in the middle ... 

by the way, please let me know if I should move this focus subject to another post🙂

best regards

Eric

[SamiF]

As the blur effect is the same on both sides and adjusting the focus ring did help, it may be that your system is lens limited : basically your lens quality is not good enough to give you a good resolution on the whole sensor. I would recommend you check with your lens supplier.

If we consider the calibration process this might not be a big issue, but the lack of light uniformity on your image could be.

Sami

[BruceAmmons]

If you close the aperture some and make the exposure longer, you should have a deeper range of focus.

On the other hand, I would recommend better lighting.  There is a lot of glare and the light is uneven.

Bruce

[ericmateovisan]

---

@SamiF wrote:

As the blur effect is the same on both sides and adjusting the focus ring did help, it may be that your system is lens limited : basically your lens quality is not good enough to give you a good resolution on the whole sensor. I would recommend you check with your lens supplier.

If we consider the calibration process this might not be a big issue, but the lack of light uniformity on your image could be.

Sami

---

Thank you Sami for your reply, I use Computar lens with 5mm focal length.. I will check the compatibility of The lens and the camera👍🌷

[ericmateovisan]

---

@BruceAmmons wrote:

If you close the aperture some and make the exposure longer, you should have a deeper range of focus.

On the other hand, I would recommend better lighting.  There is a lot of glare and the light is uneven.

Bruce

---

Thank you Bruce for your reply, I will try the aperture setting and try to minimize the light unevenness .. 😊🌷