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"""
Formulas for density calculation.
"""
from math import log10
from colormath.density_standards import ANSI_STATUS_T_BLUE, ANSI_STATUS_T_GREEN, \
ANSI_STATUS_T_RED, VISUAL_DENSITY_THRESH, ISO_VISUAL
def ansi_density(color, density_standard):
"""
Calculates density for the given SpectralColor using the spectral weighting
function provided. For example, ANSI_STATUS_T_RED. These may be found in
:py:mod:`colormath.density_standards`.
:param SpectralColor color: The SpectralColor object to calculate
density for.
:param numpy.ndarray std_array: NumPy array of filter of choice
from :py:mod:`colormath.density_standards`.
:rtype: float
:returns: The density value for the given color and density standard.
"""
# Load the spec_XXXnm attributes into a Numpy array.
sample = color.get_numpy_array()
# Matrix multiplication
intermediate = sample * density_standard
# Sum the products.
numerator = intermediate.sum()
# This is the denominator in the density equation.
sum_of_standard_wavelengths = density_standard.sum()
# This is the top level of the density formula.
return -1.0 * log10(numerator / sum_of_standard_wavelengths)
def auto_density(color):
"""
Given a SpectralColor, automatically choose the correct ANSI T filter.
Returns a tuple with a string representation of the filter the
calculated density.
:param SpectralColor color: The SpectralColor object to calculate
density for.
:rtype: float
:returns: The density value, with the filter selected automatically.
"""
blue_density = ansi_density(color, ANSI_STATUS_T_BLUE)
green_density = ansi_density(color, ANSI_STATUS_T_GREEN)
red_density = ansi_density(color, ANSI_STATUS_T_RED)
densities = [blue_density, green_density, red_density]
min_density = min(densities)
max_density = max(densities)
density_range = max_density - min_density
# See comments in density_standards.py for VISUAL_DENSITY_THRESH to
# understand what this is doing.
if density_range <= VISUAL_DENSITY_THRESH:
return ansi_density(color, ISO_VISUAL)
elif blue_density > green_density and blue_density > red_density:
return blue_density
elif green_density > blue_density and green_density > red_density:
return green_density
else:
return red_density
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