Particle Density and Color

classic Classic list List threaded Threaded
5 messages Options
Tobi Tobi
Reply | Threaded
Open this post in threaded view
|

Particle Density and Color

Hello everybody,

After seeing all these pictures in the recent publications, I was wondering if the particle color matters to the toolbox - either white particles before black background or black before white background?
Also, is there a recommendation of how many particles should be in the image? I had some good results with a very thick particle solution - although I'm not sure if the program now rather analyses the gaps between the particles than the other way around. I guess this could be misleading if there is inhomogeneous movement, right?

Thanks for the help,
Tobi
William William
Reply | Threaded
Open this post in threaded view
|

Re: Particle Density and Color

Hi Tobi,
PIV assumes that black is the background with no movement and white are the image parts that actually move.
If you look at figure 2.14 in the PIV chapter
http://dissertations.ub.rug.nl/FILES/faculties/science/2014/w.thielicke/Chapter2.pdf
then you'll see that there should be about 5-20 particles per interrogation window (this applies for particles with the "optimal diameter" =3 pixels). I think generally the more texture available, the better will be the analysis.

Please consider donating for the PIVlab project:
http://paypal.me/pools/c/81Y8wBVi4y

The developer needs to update to a recent Matlab release in order to keep the project running.

Tobi Tobi
Reply | Threaded
Open this post in threaded view
|

Re: Particle Density and Color

Thanks! I guess with texture you mean background...?!

I hope I'm not stretching this too far - What about shading in the background? Would it interfere? Like in this recording:


or after your last comment rather:


Tobi
William William
Reply | Threaded
Open this post in threaded view
|

Re: Particle Density and Color

The lower picture should work better. The seeding is very low however. A non-uniform background illumination will be almost removed when CLAHE is enabled.
With "texture" I mean: best solution might be when the particles cover as much area as the background. That would result in the max texture.

Please consider donating for the PIVlab project:
http://paypal.me/pools/c/81Y8wBVi4y

The developer needs to update to a recent Matlab release in order to keep the project running.

Tobi Tobi
Reply | Threaded
Open this post in threaded view
|

Re: Particle Density and Color

Thank you, William. That helps a lot !