changes nonlinear 。how to correct?

the openmv will find one blob, i will check, i push the blob in one direction with 1mm.and i get the cx and cy. push the blob 1mm again ,get another cx and cy .but finally i find the result is not good.
how can i correct that nonlinear。

托瓦外沿到帽子底50mm。未计算实际移动距离–real location.
圆心 圆心 圆心x-deta_x= cx(k)-cx(k-1)
0mm,real location 1292 153
1mm 1270 150 22
2mm 1258 149 12
3mm 1246 148 12
4mm 1234 148 12
5mm 1222 148 12
6mm 1208 147 14
7mm 1195 148 13
8mm 1180 148 15
9mm 1168 148 12
10mm 1154 149 14
9mm 1169 148 15
![image 690x241](upload://hgFMtk0rSCjPVobThovfyPnPnTb.png)

dear friend,
unfortunatelly there isnt only programming in vision applications.
As i can see your program works.
If it is not accurate a lot of things can involve Like optics and lighting.
The resolution of the camera is a main factor too.
Which sensor do you have?
how big is the blob?
Can you post an image from the camera?
What is the resolution of the snapshot?
WHat lights do you use?
As i can see you have arround 12 pixels per mm accurancy…
if you want more accurancy you have to go with more pixels…

openmvH7 plus FHD: 1920x1080, OV5640

Hi, that’s because of the lens distortion. We have a very basic lens correction algorithm onboard. But, I’d just fix that via a remapping algorithm in the x y position. Actually remapping all the pixels is very computationally expensive.

Hi there,
Trying to overcome this little failure you can try to use higher lens with smaller field of view.
Do you need to track the orange circle all over this image?
Regarding calibration there isn’t in this camera any. Just a lens filter …
The smaller the lens the bigger the distortion

thank you .
your post is very important . now the len is 2.8mm normal len. i have order the 2.8mm with small distortion. if it doesn’t work ,i will try the 4mm lens.
thank you again.

thanks friend.
There are more than you can do!
I see in your field of view a lot of shadows that for sure can defect your measurements.
You must go with a light that doesnt affect the inspection and ofcourse use an enclosure to get rid of the enviroment lighting contitions…
and many more…

shank hands。
yes 。the light is very important. i got the ring shape led light .but the back panel has strong reflection。and the yellow reflects and openmv lost that yellow 。 :joy:
there are many thing i should do.

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remember that dome lights have the less to none reflection.
Depending the field of view you have to build or purchase one good led light.


I build my own lights for my projects and the biggest i have used has field of view arround 200mmx170mm:

Your reply has been very enlightening to me。thank u :smiley: