wassname/scikit-image
1
0
Fork 0
mirror of https://github.com/wassname/scikit-image.git synced 2026-08-12 12:30:16 +08:00
Code Issues Packages Projects Releases Wiki Activity

better cmc implementation

Browse Source
This commit is contained in:
Matt Terry
2013-07-22 09:35:25 -07:00
parent c50c926eae
commit a821ad518c
1 changed files with 32 additions and 19 deletions
Download Patch File Download Diff File Expand all files Collapse all files
skimage/color/delta_e.py
+32 -19
View File
@@ -234,13 +234,17 @@ def deltaE_ciede2000(lab1, lab2, kL=1, kC=1, kH=1):
return np.sqrt(dE2)
def deltaE_cmc(lab1, lab2):
def deltaE_cmc(lab1, lab2, kL=1, kC=1):
"""Color difference from the CMC l:c standard.
This color difference developed by the Colour Measurement Committee of the
Socieity of Dyes and Colourists of Great Britian (CMC). It is intended for
use in the textile industry. Color differences less than 1.0 are
officially indistiguisable, but 2.0 is the usual threshold.
use in the textile industry.
The scale factors kL, kC set the weight given to differences in lightness
and chroma relative to differences in hue. The usual values are kL=2, kC=1
for "acceptability" and kL=1, kC=1 for "imperceptability". Colors with
dE > 1 are "different" for the given scale factors.
Parameters
----------
@@ -260,24 +264,33 @@ def deltaE_cmc(lab1, lab2):
in terms of the first color. Consequently
deltaE_cmc(lab1, lab2) != deltaE_cmc(lab2, lab1)
"""
l1, c1, h1 = _unpack_last(lab2lch(lab1))
l2, c2, h2 = _unpack_last(lab2lch(lab2))
l1, a1, b1 = _unpack_last(lab1)
l2, a2, b2 = _unpack_last(lab2)
sl = np.where(l1 < 16, 0.511, 0.040975*l1 / (1 + 0.01765*l1))
sc = 0.638 + 0.0638*c1 / (1 + 0.0131*c1)
c1 = np.sqrt(a1**2 + b1**2)
c2 = np.sqrt(a2**2 + b2**2)
dC = c1 - c2
c1_4 = c1**4
f = np.sqrt(c1_4 / (c1_4 + 1900))
t = np.where(np.logical_and(h1 >= 2.862, h1 <= 6.021),
0.56 * 0.2 * np.abs(np.cos(h1 + 2.93)),
0.36 + 0.4 * np.abs(np.cos(h1 + 0.611))
da = a1 - a2
db = b1 - b2
dH = np.sqrt(da**2 + db**2 - dC**2)
dL = l1 - l2
h1 = _arctan2pi(b1, a1)
T = np.where(np.logical_and(h1 >= 164*DEG, h1 <= 345*DEG),
0.56 + 0.2 * np.abs(np.cos(h1 + 168*DEG)),
0.36 + 0.4 * np.abs(np.cos(h1 + 35*DEG))
)
sh = sc * (f*t + 1-f)
c1_4 = c1**4
F = np.sqrt(c1_4 / (c1_4 + 1900))
l, c = 1, 1
ans = ((l2 - l1)/(l * sl))**2
ans += ((c2 - c1)/(c * sc))**2
deg = np.pi/180.
ans += ((h2 - h1)*deg/sh)**2 # metric defines h in terms of degrees
SL = np.where(l1 < 16, 0.511, 0.040975*l1 / (1. + 0.01765*l1))
SC = 0.638 + 0.0638 * c1 / (1. + 0.0131*c1)
SH = SC * (F*T + 1 - F)
return np.sqrt(ans)
dE2 = (dL / (kL*SL))**2
dE2 += (dC/(kC*SC))**2
dE2 += (dH/SH)**2
return np.sqrt(dE2)