PTV Matlab program

This T-SAIL WiKi page details the capabilities and the working procedures of a PTV program (Matlab) originally built by Dan. The current version of the program (.zip) can be downloaded here, use liberzon@technion.ac.il for questions.

The program is Matlab routine available here for download. After downloading the archive extract its contents into a folder of choice, an additional folder will be created named VXXX (XXX being the current software version number).

This PTV routine/program allows you to process series of consecutive images taken at time intervals of dt (frame rate 1/dt) to obtain paths and velocities of particles. The program operates using a GUI (call Main-GUI) and requires the data (series of images) to be prepared in a specific way. See explanations below.

All images must be saved in .jpeg format, file names may include only letters, numbers and _. Each image file must be numbered in sequential order, numbers appearing after _, for example:

ImageL_0123.jpeg
ImageL_0124.jpeg
ImageL_0125.jpeg
ImageL_0126.jpeg

Make sure enough digits are used and the preceding digits are zeros for numbers of smaller size, e.g. if series contain 1052 images the numbers should be of 4 digits (_0001 or _0123 or _1010). First image number is 1, not 0!

Images should contain dark background and bright particles, see example below.

Try to avoid blinks, unwanted features and sharp gradients in background/particles illumination. Particles detection is based on brightness threshold. Before running the program perform a detailed examination of the images to ne the following features, they will be useful in setting the PTV processing parameters: Spatial resolution of the images [pix/cm]. Typical diameter of particles [pix]. Brightness value of the bright particles. The images will be converted by the program into 256 shades of gray images. Total number of particles in each frame and the typical displacement of particles between images. The combinatorics algorithm calculating each particle displacement between each pair of consecutive images has it's limitations. You will have to practice to achieve acceptable seeding parameters for the specific velocities range, but generally 30-50 particles being displaced by 20-40 diameters between each pair of images is the limit.

Direct Matlab to work in the folder containing the PTV program (i.e. VXXX) and execute/run the main function

Main_GUI;

The program GUI will appear,

Then follow the routine:

1. Set the Skip # Images parameter (min 1) first.
2. Use the Load Files button to load images to be processed.
3. Use the Select ROI button to select the desired ROI (a Region Of Interest) if only part of the image area is of interest.
4. Set all the required parameters to detect all particles.
5. Use the Preview button to examine the results. If ROI was selected only the relevant part of the image will be displayed in the main plot area.
6. Set additional parameters and perform the calculations.
7. Use the Calculate Tracks button to calculate the detected particles tracks.
8. Use the Calculate Velocities button to calculate horizontal and vertical velocities.
9. All resulted/calculated paths and velocities will be stored in .mat and text files in the folder containing the data images. See Results for details.
   1. Alternatively you can choose previously calculated tracks to recalculate velocities. Choose previously obtained tracks file using the the Browse button to choose the file and use the the Calculate Velocities button again.
10. Use the Show Velocities button to plot the obtained velocities as vectors. You can browse between images using the « and » buttons below the main plot area.
11. Finally you can use the Save Current Image button to save an screen image of the whole GUI at it's current stage, including the presented results.

A list of parameters required to perform the PTV processing of the images:

The results of PTV processing will be saved in several files and images in the same folder with the original image files. All results containing files and images will have a specific _NNNN ending to their respective names, the NNNN being the unique name given to the current PTV calculation session. The full list of files is given below.

Two images are also stored, one depicting the calculated tracks of all particles

Second of velocities vectors (if relevant option is selected)