Kappa - curvature analysis

I have the question about the values obtained from kappa plugin. Is the curvature value related to the 1/R? Moreover, I checked multiple setting but I’m not sure about some features of this plugin. Is there any manual which describes in detail all settings and analysis results?
I measured two samples, I’d like to estimate the curvature of the upper edge of sample:

The results of average curvature are quite small and the difference between samples is also negligible. If the curvature given by the analyzer is described as 1/R then the curvature radius is 16 and 111 mm respectively. Am I correct?
I set the scale to 40 um/pixel in accordance with the measurement made in Fiji. Samples were photographed on plotting paper with 1 mm mesh

Perhaps @hadim can help you address this issue with Kappa outputs …



First of all please use the latest version of the software: https://github.com/hadim/kappa#installation

Curvature is defined as 1/R and for each curve you can get average curvature or the curvature defined at each point of the curve.

The difference you see are small because of your scale and the fact that kappa uses um.

Your calculations are correct and the curvature radius seems to be ~16 and 111 mm. Looking at the data and the plotting paper those values seem correct to me.

PS: if you have more questions please don’t forget to upload the original image file you are using.

1 Like

Hi @hadim,

Thanks for an explanation. Well, if the curvature is given as 1/R it is fine.
Additional questions:

  1. Why is the average curvature always positive?
  2. Is it possible to increase the ‘analysis step’? Right now despite the points marked on the curve, the fitted curve is always split for 1000 points at which the point curvature can be checked. In my case, I need to estimate the overall curvature of the sample but with the positive or negative sign.
    Please find the exemplary photos attached below. I always mark the shape of the upper edge of the samples from left to right.
    Negative curvature:

Positive curvature

The chart displayed in Kappa always shows absolute values. If you want negative values, please use the export button located in the top right part of the window.

Any Pull Request is welcome to fix this weird behaviour in the software of course!

About the analysis step, it’s not possible to modify it but have a look at the exported data, it might fit your needs.

As I said, if you want to modify the software to fit more your needs, I would be more than happy to review pull requests on github: https://github.com/hadim/kappa

OK, I process my stuff and then notify issues or suggestion. Nevertheless, the app is outstanding and you made a very good job! Thank you!

1 Like

Hello, can anybody help me with using kappa? I want to measure some curves of leaves but did not get kappa work. I got the following messages in the console when opening an image in kappa (1.6.11). The selection tool is gray and can not be selected as well as all other tools.
thanks in advance!
Best, lennox


Hello @Lennart_W,

For next time I would suggest you to create a new post since your question is likely a bug and not directly related to this thread.

I am the developer of Kappa and from the traceback it looks like your image is greater than 2,000x2,000 pixels. Am I correct?

The plugin has been originally developed for ImageJ1 and have some old code that explain this kind of limitation.

Could you reduce your image size or crop it before opening it in Kappa?

I have opened an issue about it and will try to fix it: https://github.com/brouhardlab/Kappa/issues/14