Thanks for your interest in the Pendant drop plugin. Let me try to answer your questions.
It seems though that the exact pixel size in my case is
somewhere between the values I can enter: it should be e.g. 0.0123 but
the program doesn’t allow the last decimal and will round it so that I
never arrive at the exact value. E.g. water will be 66 or 75mN/m.
Hum, I’ll have to check but only the display is rounded: you should be able to enter a more precise value and have it taken into account. I quickly checked and it seems to work (take test picture, clear the scale, draw ROI & call plugin, then enter 0.017 (micron/pix) as pixel size, change other parameters to make contour visible and adjust; then change pixel size to 0.018 and repeat fit; note both surface tensions (about 67 and 72 mN/m); now enter more precise value 0.01748; the result is now in between, around 70.9 mN/m, although the pixel size shown is rounded. That being said I will increase the number of significant digits shown to make it less annoying.
In your model file (water dsc1884.tif) I saw that the pixel size has
been entered in the file AND has the extra decimal, giving an almost
If you use ImageJ’s standard tools (line selection, Analyze->Set scale) to set the pixel scale before calling the plugin, then not only will the plugin take it into account, but the scale will also be saved along with the image.
Btw is the pixel size the only
parameter I can reasonably change assuming the density difference for my
materials is typically appr. the same, leading to the ‘density contrast
times g’ of around 9.8?
Yes, once the scale is known the capillary length is well determined. The surface tension is then just a square and a multiplication with the density contrast and the gravitational acceleration away.
Another question would be how to get physical values from the moment the
plugin window is opened instead of having to adjust the numbers in
pixels before running the fit but this apparently would be solved as
soon as pixel size is directly included in the image file (as in your
It would indeed be convenient if the contour parameters were changed with every pixel size modification to yield the same (red) overlay drawing. Thanks for pointing this out, I’ll modify this in the next version.
Good luck with making this work!
If you do not mind, I would like to make this exchange public in a thread on the Pendant Drop Plugin which I will create on http://forum.image.sc/
so that others can benefit from the discussion and add their questions.
I can anonymize it of course. Is that ok with you ?