caber — capillary-breakup video analysis

A pip-installable, Pyodide-compatible library for analyzing capillary-breakup (CaBER) extensional rheometry videos: video in → filament neck radius vs time → thinning analysis.

import caber

# headless: video -> neck size vs time
df = caber.measure_video("filament.mp4", polarity="dark", axis="horizontal", fps=100)

# Newtonian thinning analysis (Papageorgiou similarity solution)
summary = caber.thinning_summary(df, mm_per_px=0.0263,
                                 surface_tension_mN_per_m=30.0)
print(summary["fit"])            # slope, t_c, R^2 ...
print(summary["viscosity_Pa_s"]) # from the thinning slope

Interactive ROI definition in a notebook (works in JupyterLite/Pyodide):

%pip install -q opencv-python pillow ipywidgets
from caber.widgets import CaberVideo
viewer = CaberVideo("filament.mp4")  # tune ROI, then "Run Full Analysis"
viewer.result  # DataFrame: frame, time_s, neck_px

Or from the shell:

caber analyze filament.mp4 --polarity dark --axis horizontal --fps 100 \
    --mm-per-px 0.0263 --surface-tension 30 -o neck.csv

The method

Each frame is cropped to a region of interest, thresholded to a binary mask of the filament, and the filament's minimum extent is measured — row widths for a vertical filament, column heights for a horizontal one. A fully empty line inside the filament span means breakup (neck = 0).

Close to breakup a Newtonian filament thins linearly (R(t) = 0.0709·(σ/η)·(t_c − t), Papageorgiou 1995), so the thinning slope gives the viscosity once the surface tension is known.

Test clip

A short Newtonian test clip is available via caber.data.test_clip_path() (downloaded once from the repo's public URL, then cached — not shipped in the wheel): a 6000 cP viscosity-standard oil filament thinning to breakup, 100 fps (rate taken from the camera overlay timestamps — the container metadata is wrong on the source file).

License

MIT