FilmCurve · CLI

Finds zone number for a given film density value (or vice versa).
EARLY EXPERIMENTAL

Installation · Linux

Just clone the repo and symlink it into your bin/ directory. Make sure to have Python 2.7, matplotlib and numpy on your system.

$ git clone https://github.com/filmtools/filmcurve
$ ln -s ~/path/to/filmcurve/bin/filmcurve ~/bin/filmcurve

Homebrew Installation · MacOS

The curvefit executable can be installed by a Homebrew formula, which itself is part of the filmtools/homebrew-filmtools tap.

# Variant 1: Install tap first, formula second
$ brew tap filmtools/filmtools
$ brew install filmcurve

As “tapping” first is not neccessarily needed, you can install the formula directly:

# Variant 2: Install directly
$ brew install filmtools/filmtools/filmcurve

Usage · Command-line API

$ filmcurve -z Z [Z ...] -d D [D ...]
            [--density logD | --zone Zone]
            [-p P]
            [--plot file]
            [-h] 
           
# Print help text
$ filmcurve
$ filmcurve -h
$ filmcurve --help           

Required Arguments

Option	Argument	Description
-z	list of float	Zone numbers (space separated), usually from 0.00 to 10.00 in 0.33 steps (1/3 f-stops)
-d	list of float	Density values (space separated), usually measured densities 'above fog'

Mutually exclusive options

If neither density option nor zone option are passed, the script prints the polynomial coefficients and residuals.

Option	Argument	Description
--density	Density value float	Calculate zone number value for given density
--zone	Zone number float	Calculate density value for given zone number

Other options

Option	Argument	Description
-h --help		Display help
-p --precision	integer	Goal seek precision. 3=fast/fuzzy, 16=too slow and overdone. An appropriate value is 12 (default).
--plot	filename.png	Plot graph and save PNG to filename

Examples

Calculate density value for given zone

$ filmcurve -z 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 \
            -d 0.02 0.10 0.21 0.38 0.53 0.74 0.97 1.20 1.40 1.55 1.66 \
            --zone 2.00

# Calculated density is roughly
0.215413...

Calculate zone number for given density:

$ filmcurve -z 0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00 10.00 \
            -d 0.02 0.10 0.21 0.38 0.53 0.74 0.97 1.20 1.40 1.55 1.66 \
            --density 0.38

# Calculated zone is roughly
3.119267

Display polynomial model:

$ filmcurve \
-z -0.67 -0.33 0.00 0.33 0.67 1.00 1.33 2.33 3.33 4.33 5.33 6.33 7.33 8.33 9.33 \
-d  0.00  0.01 0.02 0.03 0.02 0.10 0.12 0.28 0.49 0.73 0.99 1.22 1.43 1.62 1.75

# Output:

Coefficients:
[ 0.00002172 -0.0004268  -0.00021636  0.03797541  0.03311455  0.011047  ]
Residuals:
[ 0.00157251]

Testing

Go to project directory and run pytest.

$ pytest -v

Output should look like this:

=============================== test session starts ================================
platform darwin -- Python 2.7.14, pytest-3.3.1, py-1.5.2, pluggy-0.6.0 -- /usr/local/opt/python/bin/python2.7
cachedir: .cache
rootdir: /path/to/filmcurve, inifile:
collected 3 items

tests/test_filmcurve.py::TestFilmCurve::test_findOffset[8-1.29--1.63] PASSED [ 33%]
tests/test_filmcurve.py::TestFilmCurve::test_FindZone[1.29-9.63] PASSED      [ 66%]
tests/test_filmcurve.py::TestFilmCurve::test_findDensity[4.0-0.44] PASSED    [100%]

============================= 3 passed in 0.18 seconds =============================

Requirements

This application requires Python's matplotlib and numpy library.

Issues + Development

Being a Python beginner, I assume the script structure can (and surely should) be improved. Any help with this will be appreciated. Feel free to PR or open an issue – head over to the issues page.

$ git clone https://github.com/filmtools/filmcurve