cielab-gamut-tools 0.4.0

Calculate and visualize CIELab colour gamuts of displays

cielab-gamut-tools

Calculate and visualize CIELab colour gamuts of displays.

Implements the gamut volume algorithm from the gamut-volume-m MATLAB library. Results are normative under IDMS v1.3, IEC 62977-3-5, and IEC 62906-6-1.

Installation

Requires Python 3.10 or later.

pip install cielab-gamut-tools

On Ubuntu 24.04+ / Debian 12+ you may need a virtual environment or pipx due to PEP 668:

# virtual environment
python3 -m venv gamut_env && source gamut_env/bin/activate
pip install cielab-gamut-tools

# or pipx (CLI only)
pipx install cielab-gamut-tools

Install from source

git clone https://github.com/CIELab-gamut-tools/cielab-gamut-tools-py.git
cd cielab-gamut-tools-py
pip install -e .

Updating

pipx upgrade cielab-gamut-tools   # if installed with pipx
pip install --upgrade cielab-gamut-tools  # if installed with pip

If --version still shows the old version after upgrading, force-reinstall:

pipx install cielab-gamut-tools --force
pip install --force-reinstall cielab-gamut-tools

cielab-tools about will tell you if a newer version is available.

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Command-line usage

After installation, three equivalent commands are available:

cielab-gamut-tools   # canonical name used in standards citations
cielab-tools         # short alias
cgt                  # shortest alias for everyday use

Standards and citation information

cgt about

Calculate gamut volume

# From a CGATS measurement file
cgt calculate volume display.txt

# Named reference gamut
cgt calculate volume srgb

# Multiple gamuts — tabulated output
cgt calculate volume display1.txt display2.txt srgb bt.2020

# Machine-readable output
cgt calculate volume display.txt -f json
cgt calculate volume display.txt -f csv

# Standards-traceable output (appends algorithm metadata)
cgt calculate volume display.txt -s IDMS -f json

# Value only, for scripting
cgt calculate volume srgb -q

Named gamuts: srgb, bt.2020, dci-p3, display-p3, adobe-rgb.

Calculate gamut coverage

# Coverage against a single reference
cgt calculate coverage display.txt -r srgb

# Multiple references in one pass
cgt calculate coverage display.txt -r srgb,bt.2020,dci-p3

# CSV for spreadsheet import
cgt calculate coverage display.txt -r srgb,bt.2020 -f csv

Compare multiple gamuts

# Volume comparison — delta vs first gamut
cgt calculate compare display1.txt display2.txt display3.txt

# Coverage of each against a single reference
cgt calculate compare display1.txt display2.txt -r srgb

# Full pairwise intersection matrix (entry (i,j) = % of gamut j covered by gamut i)
cgt calculate compare srgb bt.2020 dci-p3 display-p3 -m
cgt calculate compare srgb bt.2020 dci-p3 -m -f csv

Visualise gamut diagrams

Rings diagram	3D surface
sRGB ∩ BT.2020	sRGB solid + BT.2020 wireframe

# 2D ring diagram (a*-b* plane, L* encoded as ring radii)
cgt plot rings display.txt
cgt plot rings display.txt -r srgb          # with reference overlay
cgt plot rings display.txt -r srgb -i       # intersection view
cgt plot rings display.txt -r srgb -o rings.png --dpi 200

# 3D surface in CIELab space
cgt plot surface display.txt
cgt plot surface srgb bt.2020 --alpha 0.4   # overlay, see-through
cgt plot surface srgb bt.2020 --style ",wireframe+grey+lw:0.5"  # mixed solid/wireframe
cgt plot surface display.txt srgb -o comparison.png

Both commands have many more options — see the detailed references: Rings diagram options · Surface plot options

Generate reference files

# RGB test signal list for measurement (normative 602-point set, m=11)
cgt generate rgb-signals                     # CGATS to stdout
cgt generate rgb-signals -o signals.txt
cgt generate rgb-signals -g 9 -b 10         # reduced grid, 10-bit

# Synthetic reference gamut as CGATS file
cgt generate synthetic srgb -o srgb_envelope.txt
cgt generate synthetic bt.2020 -m measurement -o bt2020_meas.txt

# Custom primaries
cgt generate synthetic \
    --primaries 0.64,0.33,0.21,0.71,0.15,0.06 \
    --white 0.3127,0.3290 --gamma 2.2 -o custom.txt

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Numerical precision

All three computation paths give the same volume result:

Path	sRGB example
calculate volume srgb	830,807
CGATS measurement file	830,807
CGATS envelope file	830,807

The MATLAB reference value for sRGB is 830,766 (~0.005% difference). The standards specify a tolerance of ±1%.

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Using as a Python library

The CLI covers most workflows. If you need to integrate gamut calculations into a Python script or pipeline:

from cielab_gamut_tools import Gamut, SyntheticGamut

# Load measured display gamut
display = Gamut.from_cgats("measurements.txt")

# Reference gamuts
srgb   = SyntheticGamut.srgb()
bt2020 = SyntheticGamut.bt2020()

# Volume and coverage
print(f"Display volume: {display.volume():.0f}")
intersection = display.intersect(srgb)
print(f"sRGB coverage: {intersection.volume() / srgb.volume() * 100:.1f}%")

# Visualize (returns a matplotlib Figure)
fig = display.plot_rings(reference=srgb)
fig.savefig("rings.png", dpi=150)

Available reference gamuts: srgb(), bt2020(), dci_p3(), display_p3(), adobe_rgb(), or construct a custom gamut from CIE xy primaries and white point:

custom = SyntheticGamut(
    primaries_xy=[[0.68, 0.32], [0.265, 0.69], [0.15, 0.06]],
    white_xy=[0.3127, 0.329],
    gamma=2.2,
)

Test signal generation and CGATS export are also available via the API — see the module docstrings for details.

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Troubleshooting

"error: externally-managed-environment" (Ubuntu 24.04+, Debian 12+)
Use a virtual environment or pipx — see Installation above.

CLI command not found after installation
The Scripts (Windows) or bin (macOS/Linux) directory may not be on your PATH. Either add it, or run via python -m cielab_gamut_tools.

File not found errors
Pass an absolute path to your measurement file. On Windows you can Shift+right-click the file and choose "Copy as path"; on macOS hold Option when right-clicking and choose "Copy … as Pathname".

Plot window doesn't appear when using the Python API
Call import matplotlib.pyplot as plt; plt.show() after plotting, or use --output via the CLI to save directly to a file.

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Development

git clone https://github.com/CIELab-gamut-tools/cielab-gamut-tools-py.git
cd cielab-gamut-tools-py
pip install -e ".[dev]"
pytest

Citation

If you use this software in academic work, please cite:

Smith, E., et al. (2020). "Gamut volume calculation for display color characterization."
Journal of the Society for Information Display.

License

MIT — see LICENSE for details.